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Saturday, December 6, 2025

Transgenerational epigenetic inheritance

From Wikipedia, the free encyclopedia
"Intergenerational" vs "transgenerational" inheritance

Transgenerational epigenetic inheritance is the proposed transmission of epigenetic markers and modifications from one generation to multiple subsequent generations without altering the primary structure of DNA. Thus, the regulation of genes via epigenetic mechanisms can be heritable; the amount of transcripts and proteins produced can be altered by inherited epigenetic changes. In order for epigenetic marks to be heritable, however, they must occur in the gametes in animals, but since plants lack a definitive germline and can propagate, epigenetic marks in any tissue can be heritable.

The inheritance of epigenetic marks in the immediate generation is referred to as intergenerational inheritance. In male mice, the epigenetic signal is maintained through the F1 generation. In female mice, the epigenetic signal is maintained through the F2 generation as a result of the exposure of the germline in the womb. Many epigenetic signals are lost beyond the F2/F3 generation and are no longer inherited, because the subsequent generations were not exposed to the same environment as the parental generations. The signals that are maintained beyond the F2/F3 generation are referred to as transgenerational epigenetic inheritance (TEI), because initial environmental stimuli resulted in inheritance of epigenetic modifications. There are several mechanisms of TEI that have shown to affect germline reprogramming, such as transgenerational increases in susceptibility to diseases, mutations, and stress inheritance. During germline reprogramming and early embryogenesis in mice, methylation marks are removed to allow for development to commence, but the methylation mark is converted into hydroxymethyl-cytosine so that it is recognized and methylated once that area of the genome is no longer being used, which serves as a memory for that TEI mark. Therefore, under lab conditions, inherited methyl marks are removed and restored to ensure TEI still occurs. However, observing TEI in wild populations is still in its infancy, as laboratory studies allow for more tractable systems.

Environmental factors can induce the epigenetic marks (epigenetic tags) for some epigenetically influenced traits. These can include, but are not limited to, changes in temperature, resources availability, exposure to pollutants, chemicals, and endocrine disruptors. The dosage and exposure levels can affect the extent of the environmental factors' influence over the epigenome and its effect on later generations. The epigenetic marks can result in a wide range of effects, including minor phenotypic changes to complex diseases and disorders. The complex cell signaling pathways of multicellular organisms such as plants and humans can make understanding the mechanisms of this inherited process very difficult.

Epigenetic categories

There are mechanisms by which environmental exposures induce epigenetic changes by affecting regulation and gene expression. Four general categories of epigenetic modification are known.

  1. self-sustaining metabolic loops, in which an mRNA or protein product of a gene stimulates transcription of the gene; e.g. Wor1 gene in Candida albicans;
  2. Structural templating: structures are replicated using a template or scaffold structure of the parent. This can include, but is not limited to, the orientation and architecture of cytoskeletal structures, cilia and flagella. Ciliates provide a good example of this type of modification. In an experiment Beisson and Sonneborn in 1985, it was demonstrated in Paramecium that if a section of cilia was removed and inverted, then the progeny of that Paramecium would also display the modified cilia structure for several generations. Another example is seen in prions, special proteins that are capable of changing the structure of normal proteins to match their own. The prions use themselves as a template and then edit the folding of normal proteins to match their own folding pattern. The changes in the protein folding results in an alteration in the normal protein's function. This transmission of programming can also alter the chromatin and histone of the DNA and can be passed through the cytosol from parent to offspring during meiosis.
  3. Histone modifications in which the structure of chromatin and its transcriptional state is regulated. DNA is wrapped into a DNA–protein complex called chromatin in the nucleus of eukaryotic cells. Chromatin consists of DNA and nucleosomes that comes together to form a histone octamer. The N- and C- terminal of the histone proteins are post-translationally modified by the removal or addition of acetyl (acetylation), phosphate (phosphorylation), methyl (methylation), ubiquitin (ubiquitination), and ubiquitin-like modifier (SUMOylating) groups. Histone modifications can be transgenerational epigenetic signals. For example, histone H3K4 trimethylation (H34me3) and a network of lipid metabolic genes interact to increase the transcription response to TEI obesogenic effects. TEI can also be observed in Drosophila embryos through the exposure of heat stress over generations. The induced heat stress resulted in the phosphorylation of ATF-2 (dATF-2) which is required for heterochromatin assembly. This epigenetic event was maintained over multiple generations, but over time dATF-2 returned back to its normal state.
  4. Non-coding and coding RNAs in which various classes of RNA is implicated in TEI through maternal stores of mRNA, translation of mRNA (miRNA), and small RNA strands interfering with transcription (piRNAs and siRNAs) via RNA interference pathways (RNAi). There has been an increase in studies reporting noncoding RNA contributions to TEI. For example, altered miRNA in early trauma mice. Early trauma mice with unpredictable maternal separation and maternal stress (MSUS) were used as a model to identify the effects of altered miRNA in sperm. In MSUS mice, behavior responses were affected, insulin levels, and blood glucose levels were decreased. Notably, these effects were more severe across the F2 and F3 generation. The expression of miRNA in MSUS mice was down regulated in the brain, serum, and sperm of the F1 generation. However, the miRNA was not altered in the sperm of the F2 generation, and the miRNAs were normal in the F3 generation. This provides supportive evidence that the initial alterations in miRNAs in sperm are transferred to epigenetic marks to maintain transmission. In C.elegans, starvation is induced in which survival is dependent on the mechanisms of the RNAi pathway, repression of microRNAs, and regulation of small RNAs. Thus, memorization of dietary history is inherited across generations.

Inheritance of epigenetic marks

Although there are various forms of inheriting epigenetic markers, inheritance of epigenetic markers can be summarized as the dissemination of epigenetic information by means of the germline. Furthermore, epigenetic variation typically takes one of four general forms, though there are other forms that have yet to be elucidated. Currently, self-sustaining feedback loops, spatial templating, chromatin marking, and RNA-mediated pathways modify epigenes of individual cells. Epigenetic variation within multicellular organisms is either endogenous or exogenous. Endogenous is generated by cell–cell signaling (e.g. during cell differentiation early in development), while exogenous is a cellular response to environmental cues.

Removal vs. retention

In sexually reproducing organisms, much of the epigenetic modification within cells is reset during meiosis (e.g. marks at the FLC locus controlling plant vernalization), though some epigenetic responses have been shown to be conserved (e.g. transposon methylation in plants). Differential inheritance of epigenetic marks due to underlying maternal or paternal biases in removal or retention mechanisms may lead to the assignment of epigenetic causation to some parent of origin effects in animals and plants.

Reprogramming

In mammals, epigenetic marks are erased during two phases of the life cycle. Firstly just after fertilization and secondly, in the developing primordial germ cells, the precursors to future gametes. During fertilization the male and female gametes join in different cell cycle states and with different configuration of the genome. The epigenetic marks of the male are rapidly diluted. First, the protamines associated with male DNA are replaced with histones from the female's cytoplasm, most of which are acetylated due to either higher abundance of acetylated histones in the female's cytoplasm or through preferential binding of the male DNA to acetylated histones. Second, male DNA is systematically demethylated in many organisms, possibly through 5-hydroxymethylcytosine. However, some epigenetic marks, particularly maternal DNA methylation, can escape this reprogramming; leading to parental imprinting.

In the primordial germ cells (PGC) there is a more extensive erasure of epigenetic information. However, some rare sites can also evade erasure of DNA methylation. If epigenetic marks evade erasure during both zygotic and PGC reprogramming events, this could enable transgenerational epigenetic inheritance.

Recognition of the importance of epigenetic programming to the establishment and fixation of cell line identity during early embryogenesis has recently stimulated interest in artificial removal of epigenetic programming. Epigenetic manipulations may allow for restoration of totipotency in stem cells or cells more generally, thus generalizing regenerative medicine.

Retention

Cellular mechanisms may allow for co-transmission of some epigenetic marks. During replication, DNA polymerases working on the leading and lagging strands are coupled by the DNA processivity factor proliferating cell nuclear antigen (PCNA), which has also been implicated in patterning and strand crosstalk that allows for copy fidelity of epigenetic marks. Work on histone modification copy fidelity has remained in the model phase, but early efforts suggest that modifications of new histones are patterned on those of the old histones and that new and old histones randomly assort between the two daughter DNA strands. With respect to transfer to the next generation, many marks are removed as described above. Emerging studies are finding patterns of epigenetic conservation across generations. For instance, centromeric satellites resist demethylation. The mechanism responsible for this conservation is not known, though some evidence suggests that methylation of histones may contribute. Dysregulation of the promoter methylation timing associated with gene expression dysregulation in the embryo was also identified.

Decay

Whereas the mutation rate in a given 100-base gene may be 10−7 per generation, epigenes may "mutate" several times per generation or may be fixed for many generations. This raises the question: do changes in epigene frequencies constitute evolution? Rapidly decaying epigenetic effects on phenotypes (i.e. lasting less than three generations) may explain some of the residual variation in phenotypes after genotype and environment are accounted for. However, distinguishing these short-term effects from the effects of the maternal environment on early ontogeny remains a challenge.

Examples of TEI

The relative importance of genetic and epigenetic inheritance is subject to debate. Though hundreds of examples of epigenetic modification of phenotypes have been published, few studies have been conducted outside of the laboratory setting. Therefore, the interactions of genes with the environment cannot be inferred despite the central role of environment in natural selection. Multiple epigenetic factors can influence the state of genes and alter the epigenetic state. Due to the multivariate nature of environmental factors, it is difficult for researchers to pinpoint the exact cause of epigenetic changes outside of a laboratory setting.

In Plants

Studies concerning transgenerational epigenetic inheritance in plants have been reported as early as the 1950s. One of the earliest and best characterized examples of this is b1 paramutation in maize. The b1 gene encodes a basic helix-loop-helix transcription factor that is involved in the anthocyanin production pathway. When the b1 gene is expressed, the plant accumulates anthocyanin within its tissues, leading to a purple coloration of those tissues. The B-I allele (for B-Intense) has high expression of b1 resulting in the dark pigmentation of the sheath and husk tissues while the B' (pronounced B-prime) allele has low expression of b1 resulting in low pigmentation in those tissues. When homozygous B-I parents are crossed to homozygous B', the resultant F1 offspring all display low pigmentation which is due to gene silencing of b1. Unexpectedly, when F1 plants are self-crossed, the resultant F2 generation all display low pigmentation and have low levels of b1 expression. Furthermore, when any F2 plant (including those that are genetically homozygous for B-I) are crossed to homozygous B-I, the offspring will all display low pigmentation and expression of b1. The lack of darkly pigmented individuals in the F2 progeny is an example of non-Mendelian inheritance and further research has suggested that the B-I allele is converted to B' via epigenetic mechanisms. The B' and B-I alleles are considered to be epialleles because they are identical at the DNA sequence level but differ in the level of DNA methylation, siRNA production, and chromosomal interactions within the nucleus. Additionally, plants defective in components of the RNA-directed DNA-methylation pathway show an increased expression of b1 in B' individuals similar to that of B-I, however, once these components are restored, the plant reverts to the low expression state. Although spontaneous conversion from B-I to B' has been observed, a reversion from B' to B-I (green to purple) has never been observed over 50 years and thousands of plants in both greenhouse and field experiments.

Examples of environmentally induced transgenerational epigenetic inheritance in plants has also been reported. In one case, rice plants that were exposed to drought-simulation treatments displayed increased tolerance to drought after 11 generations of exposure and propagation by single-seed descent as compared to non-drought treated plants. Differences in drought tolerance was linked to directional changes in DNA-methylation levels throughout the genome, suggesting that stress-induced heritable changes in DNA-methylation patterns may be important in adaptation to recurring stresses. In another study, plants that were exposed to moderate caterpillar herbivory over multiple generations displayed increased resistance to herbivory in subsequent generations (as measured by caterpillar dry mass) compared to plants lacking herbivore pressure. This increase in herbivore resistance persisted after a generation of growth without any herbivore exposure suggesting that the response was transmitted across generations. The report concluded that components of the RNA-directed DNA-methylation pathway are involved in the increased resistance across generations. Transgenerational epigenetic inheritance has also been observed in polyploid plants. Genetically identical reciprocal F1 hybrid triploids have been shown to display transgenerational epigenetic effects on viable F2 seed development.

It has been demonstrated in wild radish plants (Raphanus raphanistrum) that TEI can be induced when the plants are exposed to predators such as Pieris rapae, the cabbage white caterpillar. The radish plants will increase production of bristly leaf hairs and toxic mustard oil in response to caterpillar predation. The increased levels will also be seen in the next generation. Decreased levels of predation also results in decreased leaf hairs and toxins produced in the current and subsequent generations.

In Animals

It is difficult to trace TEI in animals due to the reprogramming of genes during meiosis and embryogenesis, especially in wild populations that are not reared in a lab setting. Further studies must be conducted to strengthen the documentation of TEI in animals. However, a few examples do exist.

Induced transgenerational epigenetic inheritance has been demonstrated in animals, such as Daphnia cucullata. These tiny crustaceans will develop protective helmets as juveniles if exposed to kairomones, a type of hormone, secreted by predators while they are in utero. The helmet acts as a method of defense by decreasing the ability of predators to capture the Daphnia, thus induction of helmet presence will lower mortality rates. D. cucullata will develop a small helmet if no kairomones are present. However, depending upon the level of predator kairomones, the length of the helmet will almost double. The next generation of Daphnia will display a similar helmet size. If the kairomone levels decrease or disappear, then the third generation will revert to the original helmet size. These organisms display adaptive phenotypes that will affect the phenotype in the subsequent generations.

Genetic analysis of coral reef fish, Acanthochromis polyacanthus, has proposed TEI in response to climate change. As climate change occurs, the ocean water temperature increases. When A. polyacanthus is exposed to higher water temperatures of up to +3 °C from normal ocean temperatures, the fish express increased DNA methylation levels on 193 genes, resulting in phenotypic changes in the function of oxygen consumption, metabolism, insulin response, energy production, and angiogenesis. The increase in DNA methylation and its phenotypic affects were carried over to multiple subsequent generations.

Possible TEI has been studied in guinea pigs (Cavia aperea) by exposing males to increased ambient temperature for two months. In the lab, the males were allowed to mate with the same female before and after the heat exposure to determine if the high temperatures affected the offspring. Since it serves as a thermoregulatory organ, samples of the liver were studied in the father guinea pigs (F0 generation) and liver and testes of the male offspring (F1 generation). The F0 males experienced an immediate epigenetic response to the increase in temperature; the levels of hormones in the liver responsible for thermoregulation increased. The F1 generation also displayed the different methylated epigenetic response in their liver and testes, indicating that they could potentially pass on the epigenetic marks to the F2 generation.

In humans

Although genetic inheritance is important when describing phenotypic outcomes, it cannot entirely explain why offspring resemble their parents. Aside from genes, offspring come to inherit similar environmental conditions established by previous generations. One environment that human offspring commonly share with their maternal parent for nine months is the womb. Considering the duration of the fetal stages of development, the environment of the mother's womb can have long lasting effects on the health of offspring.

An example of how the environment within the womb can affect the health of an offspring is the Dutch hunger winter of 1944–45 and its causal effect on induced transgenerational epigenetic inherited diseases. During the Dutch hunger winter, the offspring exposed to famine conditions during the third trimester of development were smaller than those born the year before the famine. Moreover, the offspring born during the famine and their subsequent offspring were found to have an increased risk of metabolic diseases, cardiovascular diseases, glucose intolerance, diabetes, and obesity in adulthood. The effects of this famine on development lasted up to two generations. The increased risk factors to the health of F1 and F2 generations during the Dutch hunger winter is a known phenomenon called "fetal programming", which is caused by exposure to harmful environmental factors in utero.

The loss of genetic expression which results in Prader–Willi syndrome or Angelman syndrome has in some cases been found to be caused by epigenetic changes (or "epimutations") on both the alleles, rather than involving any genetic mutation. In all 19 informative cases, the epimutations that, together with physiological imprinting and therefore silencing of the other allele, were causing these syndromes were localized on a chromosome with a specific parental and grandparental origin. Specifically, the paternally derived chromosome carried an abnormal maternal mark at the SNURF-SNRPN, and this abnormal mark was inherited from the paternal grandmother.

Several cancers have been found to be influenced by transgenerational epigenetics. Epimutations on the MLH1 gene has been found in two individuals with a phenotype of hereditary nonpolyposis colorectal cancer, and without any frank MLH1 mutation which otherwise causes the disease. The same epimutations were also found on the spermatozoa of one of the individuals, indicating the potential to be transmitted to offspring. In addition to epimutations to the MLH1 gene, it has been determined that certain cancers, such as breast cancer, can originate during the fetal stages within the uterus. Furthermore, evidence collected in various studies utilizing model systems (i.e. animals) have found that exposure during parental generations can result in multigenerational and transgenerational inheritance of breast cancer. More recently, studies have discovered a connection between the adaptation of male germinal cells via pre-conception paternal diets and the regulation of breast cancer in developing offspring. More specifically, studies have begun to uncover new data that underscores a relationship between transgenerational epigenetic inheritance of breast cancer and ancestral alimentary components or associated markers, such as birth weight. By utilizing model systems, such as mice, studies have shown that stimulated paternal obesity at the time of conception can epigenetically alter the paternal germ-line. The paternal germ-line is responsible for regulating their daughters' weight at birth and the potential for their daughter to develop breast cancer. Furthermore, it was found that modifications to the miRNA expression profile of the male germline is coupled with elevated body weight. Additionally, paternal obesity resulted in an increase in the percentage of female offspring developing carcinogen-induced mammary tumors, which is caused by changes to mammary miRNA expression.

Aside from cancer related afflictions associated with the effects of transgenerational epigenetic inheritance, transgenerational epigenetic inheritance has recently been implicated in the progression of pulmonary arterial hypertension (PAH). Recent studies have found that transgenerational epigenetic inheritance is likely to be involved in the progression of PAH because current therapies for PAH do not repair the irregular phenotypes associated with this disease. Current treatments for PAH have attempted to correct symptoms of PAH with vasodilators and antithrombotic protectors, but neither has effectively alleviated the complications related to the impaired phenotypes associated with PAH. The inability of vasodilators and antithrombotic protectants to correct PAH suggests that the progression of PAH is dependent upon multiple variables, which is likely to be consequent of transgenerational epigenetic inheritance. Specifically, it is thought that transgenerational epigenetics is linked to the phenotypic changes associated with vascular remodeling. For example, hypoxia during gestation may induce transgenerational epigenetic alterations that could prove to be detrimental during the early phases of fetal development and increase the possibility of developing PAH as an adult. Though hypoxic states could induce the transgenerational epigenetic variance associated with PAH, there is strong evidence to support that a variety of maternal risk factors are linked to the eventual progression of PAH. Such maternal risk factors linked to late-onset PAH includes placental dysfunction, hypertension, obesity, and preeclampsia. These maternal risk factors and environmental stressors coupled with transgenerational epigenetic changes can result in prolonged insult to the signaling pathways associated with the vascular development during fetal stages, thus increasing the likelihood of having PAH.

One study has shown childhood abuse, which is defined as "sexual contact, severe physical abuse and/or severe neglect", leads to epigenetic modifications of glucocorticoid receptor expression. Glucocorticoid receptor expression plays a vital role in hypothalamic-pituitary-adrenal (HPA) activity. Additionally, animal experiments have shown that epigenetic changes can depend on mother–infant interactions after birth. Furthermore, a recent study investigating the correlations between maternal stress in pregnancy and methylation in teenagers/their mothers has found that children of women who were abused during pregnancy were more likely to have methylated glucocorticoid-receptor genes. Thus, children with methylated glucocorticoid-receptor genes experience an altered response to stress, ultimately leading to a higher susceptibility of experiencing anxiety.

Additional studies examining the effects of diethylstilbestrol (DES), which is an endocrine disruptor, have found that the grandchildren (third-generation) of women exposed to DES significantly increased the probability of their grandchildren developing attention-deficit/hyperactivity disorder (ADHD). This is because women exposed to endocrine disruptors, such as DES, during gestation may be linked to multigenerational neurodevelopmental deficits. Furthermore, animal studies indicate that endocrine disruptors have a profound impact on germline cells and neurodevelopment. The cause of DES's multigenerational impact is postulated to be the result of biological processes associated with epigenetic reprogramming of the germline, though this has yet to be determined.

Effects on fitness

Epigenetic inheritance may only affect fitness if it predictably alters a trait under selection. Evidence has been forwarded that environmental stimuli are important agents in the alteration of epigenes. Ironically, Darwinian evolution may act on these neo-Lamarckian acquired characteristics as well as the cellular mechanisms producing them (e.g. methyltransferase genes). Epigenetic inheritance may confer a fitness benefit to organisms that deal with environmental changes at intermediate timescales. Short-cycling changes are likely to have DNA-encoded regulatory processes, as the probability of the offspring needing to respond to changes multiple times during their lifespans is high. On the other end, natural selection will act on populations experiencing changes on longer-cycling environmental changes. In these cases, if epigenetic priming of the next generation is deleterious to fitness over most of the interval (e.g. misinformation about the environment), these genotypes and epigenotypes will be lost. For intermediate time cycles, the probability of the offspring encountering a similar environment is sufficiently high without substantial selective pressure on individuals lacking a genetic architecture capable of responding to the environment. Naturally, the absolute lengths of short, intermediate, and long environmental cycles will depend on the trait, the length of epigenetic memory, and the generation time of the organism. Much of the interpretation of epigenetic fitness effects centers on the hypothesis that epigenes are important contributors to phenotypes, which remains to be resolved.

Deleterious effects

Inherited epigenetic marks may be important for regulating important components of fitness. In plants, for instance, the Lcyc gene in Linaria vulgaris controls the symmetry of the flower. Linnaeus first described radially symmetric mutants, which arise when Lcyc is heavily methylated. Given the importance of floral shape to pollinators, methylation of Lcyc homologues (e.g. CYCLOIDEA) may have deleterious effects on plant fitness. In animals, numerous studies have shown that inherited epigenetic marks can increase susceptibility to disease. Transgenerational epigenetic influences are also suggested to contribute to disease, especially cancer, in humans. Tumor methylation patterns in gene promoters have been shown to correlate positively with familial history of cancer. Furthermore, methylation of the MSH2 gene is correlated with early-onset colorectal and endometrial cancers.

Putatively adaptive effects

Experimentally demethylated seeds of the model organism Arabidopsis thaliana have significantly higher mortality, stunted growth, delayed flowering, and lower fruit set, indicating that epigenes may increase fitness. Furthermore, environmentally induced epigenetic responses to stress have been shown to be inherited and positively correlated with fitness. In animals, communal nesting changes mouse behavior increasing parental care regimes and social abilities that are hypothesized to increase offspring survival and access to resources (such as food and mates), respectively.

Inheritance of Immunity

Epigenetics play a crucial role in regulation and development of the immune system. In 2021, evidence of inheritance of trained immunity across generations to progeny of mice with a systemic infection of Candida albicans was provided. The progeny of mice survived the Candida albicans infection via functional, transcriptional, and epigenetic changes linked to the immune gene loci. The responsiveness of myeloid cells to the Candida albicans infection increased in inflammatory pathways, and resistance was increased to infections in the next generations. Immunity in vertebrates can also be transferred from maternal through the passing of hormones, nutrients and antibodies. In mammals, the maternal factors can be transferred via lactation or the placenta. The transgenerational transmission of immune-related traits are also described in plants and invertebrates. Plants have a defense priming system which enables them to have an alternate defense response that can be accelerated upon exposure to stress actions or pathogens. After the event of priming, priming stress clue information is stored, and the memory may be inherited in the offspring (intergenerational or transgenerational). In studies, the progeny of Pseudomonas syringae infected Arabidopsis were primed during the expression of systemic acquired resistance (SAR). The progeny showed to have resistance against (hemi)-biotrophic pathogens which is associated with salicylic dependent genes and the defense regulatory gene, non expressor of PR genes (NPR1). Transgenerational SAR in the progeny was associated with increased acetylation of histone 3 at lysine 9, hypomethylation of genes, and chromatin marks on promoter regions of salicylic dependent genes. Similarly in insects, the red flour beetle Tribolium castaneum is primed through the exposure of the pathogen Bacillus thuringiensis. Double-mating experiments with the red flour beetle demonstrated that paternal transgenerational immune priming is mediated by sperm or seminal fluid which enhances survival upon exposure to pathogens and contribute to epigenetic changes.

Feedback loops and TEI

Positive and negative feedback loops are commonly observed in molecular mechanisms and regulation of homeostatic processes. There is evidence that feedback loops interact to maintain epigenetic modifications within one generation, as well as contributing to TEI in various organisms, and these feedback loops can showcase putative adaptations to environmental perturbances. Feedback loops are truly a repercussion of any epigenetic modification, since it results in changes in expression. Even more so, the feedback loops seen across multiple generations because of TEI showcases a spatio-temporal dynamic that is associated with TEI alone. For example, elevated temperatures during embryogenesis and PIWI RNA (piRNA) establishment are directly proportional, providing a heritable outcome for repressing transposable elements via piRNA clusters. Furthermore, subsequent generations retain an active locus to continue establishing piRNA, which its formation was previously enigmatic. In another case, it was suggested that endocrine disruption had a feedback loop interaction with methylation of varying genomic sites in Menidia beryllina, which may have been a function of TEI. When exposure was removed, and M. beryllina F2 offspring still retained these methylation marks, which caused a negative feedback loop on expression of various genes. In another example, hybridization of eels can lead to feedback loops contributing to transposon demethylation and transposable element activation. Because TE's are typically silenced in the genome, their presence and potential expression creates a feedback loop to prevent hybrids from reproducing with other hybrids or non-hybrid species, which eliminates the proliferation of TE expression and prevents TEI in this context. This phenomenon is known as a form of post-zygotic reproductive isolation.

Macroevolutionary patterns

Inherited epigenetic effects on phenotypes have been well documented in bacteria, protists, fungi, plants, nematodes, and fruit flies. Though no systematic study of epigenetic inheritance has been conducted (most focus on model organisms), there is preliminary evidence that this mode of inheritance is more important in plants than in animals. The early differentiation of animal germlines is likely to preclude epigenetic marking occurring later in development, while in plants and fungi somatic cells may be incorporated into the germ line.

It is thought that transgenerational epigenetic inheritance can enable certain populations to readily adapt to variable environments. Though there are well documented cases of transgenerational epigenetic inheritance in certain populations, there are questions to whether this same form of adaptability is applicable to mammals. More specifically, it is questioned if it applies to humans. As of late, most of the experimental models utilizing mice and limited observations in humans have only found epigenetically inherited traits that are detrimental to the health of both organisms. These harmful traits range from increased risk of disease, such as cardiovascular disease, to premature death. However, this may be based on the premise of limited reporting bias because it is easier to detect negative experimental effects, opposed to positive experimental effects. Furthermore, considerable epigenetic reprogramming necessary for the evolutionary success of germlines and the initial phases of embryogenesis in mammals may be the potential cause limiting transgenerational inheritance of chromatin marks in mammals.  

Life history patterns may also contribute to the occurrence of epigenetic inheritance. Sessile organisms, those with low dispersal capability, and those with simple behavior may benefit most from conveying information to their offspring via epigenetic pathways. Geographic patterns may also emerge, where highly variable and highly conserved environments might host fewer species with important epigenetic inheritance.

History and Controversy

Humans have long recognized that traits of the parents are often seen in offspring. This insight led to the practical application of selective breeding of plants and animals, but did not address the central question of inheritance: how are these traits conserved between generations, and what causes variation? Several positions have been held in the history of evolutionary thought.

Blending vs. particulate inheritance

Blending inheritance leads to the averaging out of every characteristic, which as the engineer Fleeming Jenkin pointed out, makes evolution by natural selection impossible.

Addressing these related questions, scientists during the time of the Enlightenment largely argued for the blending hypothesis, in which parental traits were homogenized in the offspring much like buckets of different colored paint being mixed together. Critics of Charles Darwin's On the Origin of Species, pointed out that under this scheme of inheritance, variation would quickly be swamped by the majority phenotype. In the paint bucket analogy, this would be seen by mixing two colors together and then mixing the resulting color with only one of the parent colors 20 times; the rare variant color would quickly fade.

Unknown to most of the European scientific community, the monk Gregor Mendel had resolved the question of how traits are conserved between generations through breeding experiments with pea plants by 1856. Charles Darwin thus did not know of Mendel's proposed "particulate inheritance" in which traits were not blended but passed to offspring in discrete units that we now call genes. Darwin came to reject the blending hypothesis even though his ideas and Mendel's were not unified until the 1930s, a period referred to as the modern synthesis.

Inheritance of innate vs. acquired characteristics

In his 1809 book, Philosophie ZoologiqueJean-Baptiste Lamarck recognized that each species experiences a unique set of challenges due to its form and environment. Thus, he proposed that the characters used most often would accumulate a "nervous fluid". Such acquired accumulations would then be transmitted to the individual's offspring. In modern terms, a nervous fluid transmitted to offspring would be a form of epigenetic inheritance.

Lamarckism, as this body of thought became known, was the standard explanation for change in species over time when Charles Darwin and Alfred Russel Wallace co-proposed a theory of evolution by natural selection in 1859. Responding to Darwin and Wallace's theory, a revised neo-Lamarckism attracted a small following of biologists, though the Lamarckian zeal was quenched in large part due to Weismann's famous experiment in which he cut off the tails of mice over several successive generations without having any effect on tail length. Thus the emergent consensus that acquired characteristics could not be inherited became canon.

Revision of evolutionary theory

Non-genetic variation and inheritance, however, proved to be quite common. Concurrent with the 20th-century development of the modern evolutionary synthesis (unifying Mendelian genetics and natural selection), C. H. Waddington (1905–1975) was working to unify developmental biology and genetics. In so doing, he adopted the word "epigenetic" to represent the ordered differentiation of embryonic cells into functionally distinct cell types despite having identical primary structure of their DNA. Researchers discussed Waddington's epigenetics sporadically - it became more of a catch-all for puzzling non-genetic heritable characters rather than a concept advancing the body of inquiry. Consequently, the definition of Waddington's word has itself evolved, broadening beyond the subset of developmentally signaled, inherited cell specialization.

Some scientists have questioned whether epigenetic inheritance compromises the foundation of the modern synthesis. Outlining the central dogma of molecular biology, Francis Crick succinctly stated, "DNA is held in a configuration by histone[s] so that it can act as a passive template for the simultaneous synthesis of RNA and protein[s]. None of the detailed 'information' is in the histone." However, he closes the article stating, "this scheme explains the majority of the present experimental results!" Indeed, the emergence of epigenetic inheritance (in addition to advances in the study of evolutionary-development, phenotypic plasticity, evolvability, and systems biology) has strained the current framework of the modern evolutionary synthesis, and prompted the re-examination of previously dismissed evolutionary mechanisms.

Furthermore, patterns in epigenetic inheritance and the evolutionary implications of the epigenetic codes in living organisms are connected to both Lamarck's and Darwin's theories of evolution. For example, Lamarck postulated that environmental factors were responsible for modifying phenotypes hereditarily, which supports the constructs that exposure to environmental factors during critical stages of development can result in epimutations in germlines, thus augmenting phenotypic variance. In contrast, Darwin's theory claimed that natural selection strengthened a populations ability to survive and remain reproductively fit by favoring populations that are able to readily adapt. This theory is consistent with intergenerational plasticity and phenotypic variance resulting from heritable adaptivity.

In addition, some epigenetic variability may provide beneficial plasticity, so that certain organisms can adapt to fluctuating environmental conditions. However, the exchange of epigenetic information between generations can result in epigenetic aberrations, which are epigenetic traits that deviate from the norm. Therefore, the offspring of the parental generations may be predisposed to specific diseases and reduced plasticity due to epigenetic aberrations. Though the ability to readily adapt when faced with a new environment may be beneficial to certain populations of species that can quickly reproduce, species with long generational gaps may not benefit from such an ability. If a species with a longer generational gap does not appropriately adapt to the anticipated environment, then the reproductive fitness of the offspring of that species will be diminished.

There has been critical discussion of mainstream evolutionary theory by Edward J Steele, Robyn A Lindley and colleagues, Fred Hoyle and N. Chandra Wickramasinghe, Yongsheng Liu Denis Noble, John Mattick and others that the logical inconsistencies as well as Lamarckian Inheritance effects involving direct DNA modifications, as well as the just described indirect, viz. epigenetic, ransmissions, challenge conventional thinking in evolutionary biology and adjacent fields.

Evolutionary neuroscience is the scientific study of the evolution of nervous systems. Evolutionary neuroscientists investigate the evolution and natural history of nervous system structure, functions and emergent properties. The field draws on concepts and findings from both neuroscience and evolutionary biology. Historically, most empirical work has been in the area of comparative neuroanatomy, and modern studies often make use of phylogenetic comparative methods. Selective breeding and experimental evolution approaches are also being used more frequently.

Conceptually and theoretically, the field is related to fields as diverse as cognitive genomics, neurogenetics, developmental neuroscience, neuroethology, comparative psychology, evo-devo, behavioral neuroscience, cognitive neuroscience, behavioral ecology, biological anthropology and sociobiology.

Evolutionary neuroscientists examine changes in genes, anatomy, physiology, and behavior to study the evolution of changes in the brain. They study a multitude of processes including the evolution of vocal, visual, auditory, taste, and learning systems as well as language evolution and development. In addition, evolutionary neuroscientists study the evolution of specific areas or structures in the brain such as the amygdala, forebrain and cerebellum as well as the motor or visual cortex.

History

Studies of the brain began during ancient Egyptian times but studies in the field of evolutionary neuroscience began after the publication of Darwin's On the Origin of Species in 1859. At that time, brain evolution was largely viewed at the time in relation to the incorrect scala naturae. Phylogeny and the evolution of the brain were still viewed as linear. During the early 20th century, there were several prevailing theories about evolution. Darwinism was based on the principles of natural selection and variation, Lamarckism was based on the passing down of acquired traits, Orthogenesis was based on the assumption that tendency towards perfection steers evolution, and Saltationism argued that discontinuous variation creates new species. Darwin's became the most accepted and allowed for people to starting thinking about the way animals and their brains evolve.

The 1936 book The Comparative Anatomy of the Nervous System of Vertebrates Including Man by the Dutch neurologist C.U. Ariëns Kappers (first published in German in 1921) was a landmark publication in the field. Following the Evolutionary Synthesis, the study of comparative neuroanatomy was conducted with an evolutionary view, and modern studies incorporate developmental genetics. It is now accepted that phylogenetic changes occur independently between species over time and can not be linear. It is also believed that an increase with brain size correlates with an increase in neural centers and behavior complexity.

Major arguments

Over time, there are several arguments that would come to define the history of evolutionary neuroscience. The first is the argument between E.G. St. Hilaire and G. Cuvier over the topic of "common plan versus diversity". St. Hilaire argued that all animals are built based on a single plan or archetype and he stressed the importance of homologies between organisms, while Cuvier believed that the structure of organs was determined by their function and that knowledge of the function of one organ could help discover the functions of other organs. He argued that there were at least four different archetypes. After Darwin, the idea of evolution was more accepted and St. Hilaire's idea of homologous structures was more accepted. The second major argument is that of Aristotle's scala naturae (scale of nature) and the great chain of being versus the phylogenetic bush. The scala naturae, later also called the phylogenetic scale, was based on the premise that phylogenies are linear or like a scale while the phylogenetic bush argument was based on the idea that phylogenies were not linear, and more resembled a bush – the currently accepted view. A third major argument dealt with the size of the brain and whether relative size or absolute size was more relevant in determining function. In the late 18th century, it was determined that brain to body ratio reduces as body size increases. However more recently, there is more focus on absolute brain size as this scales with internal structures and functions, with the degree of structural complexity, and with the amount of white matter in the brain, all suggesting that absolute size is much better predictor of brain function. Finally, a fourth argument is that of natural selection (Darwinism) versus developmental constraints (concerted evolution). It is now accepted that the evolution of development is what causes adult species to show differences and evolutionary neuroscientists maintain that many aspects of brain function and structure are conserved across species.

Techniques

Throughout history, we see how evolutionary neuroscience has been dependent on developments in biological theory and techniques. The field of evolutionary neuroscience has been shaped by the development of new techniques that allow for the discovery and examination of parts of the nervous system. In 1873, C. Golgi devised the silver nitrate method which allowed for the description of the brain at the cellular level as opposed to simply the gross level. Santiago and Pedro Ramon used this method to analyze numerous parts of brains, broadening the field of comparative neuroanatomy. In the second half of the 19th century, new techniques allowed scientists to identify neuronal cell groups and fiber bundles in brains. In 1885, Vittorio Marchi discovered a staining technique that let scientists see induced axonal degeneration in myelinated axons, in 1950, the "original nauta procedure" allowed for more accurate identification of degenerating fibers, and in the 1970s, there were several discoveries of multiple molecular tracers which would be used for experiments even today. In the last 20 years, cladistics has also become a useful tool for looking at variation in the brain.

Evolution of brains

Many of Earth's early years were filled with brainless creatures, and among them was the amphioxus, which can be traced as far back as 550 million years ago. Amphioxi had a significantly simpler way of life, which made it not necessary for them to have a brain. To replace its absence of a brain, the prehistoric amphioxi had a limited nervous system, which was composed of only a bunch of cells. These cells optimized their uses because many of the cells for sensing intertwined with the cells used for its very simple system for moving, which allowed it to propel itself through bodies of water and react without much processing while the cells remaining were used for the detection of light to account to the fact that it had no eyes. It also did not need a sense of hearing. Even though the amphioxi had limited senses, they did not need them to survive efficiently, as their life was mainly dedicated to sitting on the seafloor to eat. Although the amphioxus' "brain" might seem severely underdeveloped compared to their human counterparts, it was set well for its respective environment, which has allowed it to prosper for millions of years.

Although many scientists once assumed that the brain evolved to achieve an ability to think, such a view is today considered a great misconception. 500 million years ago, the Earth entered into the Cambrian period, where hunting became a new concern for survival in an animal's environment. At this point, animals became sensitive to the presence of another, which could serve as food. Although hunting did not inherently require a brain, it was one of the main steps that pushed the development of one, as organisms progressed to develop advanced sensory systems.

In response to progressively complicated surroundings, where competition between animals with brains started to arise for survival, animals had to learn to manage their energy. As creatures acquired a variety of senses for perception, animals progressed to develop allostasis, which played the role of an early brain by forcing the body to gather past experiences to improve prediction. Since prediction beat reaction, organisms who planned their manoeuvres were more likely to survive than those who did not. This came with equally managing energy adequately, which nature favoured. Animals that had not developed allostasis would be at a disadvantage for their purpose of exploration, foraging and reproduction, as death was a higher risk factor.

As allostasis continued to develop in animals, their bodies equally continuously evolved in size and complexity. They progressively started to develop cardiovascular systems, respiratory systems and immune systems to survive in their environments, which required bodies to have something more complex than the limited quality of cells to regulate themselves. This encouraged the nervous systems of many creatures to develop into a brain, which was sizeable and strikingly similar to how most animal brains look today.

Evolution of the human brain

Darwin, in The Descent of Man, stipulated that the mind evolved simultaneously with the body. According to his theory, all humans have a barbaric core that they learn to deal with. Darwin's theory allowed people to start thinking about the way animals and their brains evolve.

Reptile brain

Plato's insight on the evolution of the human brain contemplated the idea that all humans were once lizards, with similar survival needs such as feeding, fighting and mating. In the classical era Plato first described this concept as the "lizard mind" – the deepest layer and one of three parts of his conception of a three-part human mind. In the 20th century P. MacLean developed a similar, modern triune brain theory.

Recent research in molecular genetics has demonstrated evidence that there is no difference in the neurons that reptiles and nonhuman mammals have when compared to humans. Instead, new research speculates that all mammals, and potentially reptiles, birds and some species of fish, evolve from a common order pattern. This research reinforces the idea that human brains are structurally no t any different from many other organisms.

The cerebral cortex of reptiles resembles that of mammals, although simplified. Although the evolution and function of the human cerebral cortex is still shrouded in mystery, we know that it is the most dramatically changed part of the brain during recent evolution. The reptilian brain, 300 million years ago, was made for all our basic urges and instincts like fighting, reproducing, and mating. The reptile brain evolved 100 million years later and gave us the ability to feel emotion. Eventually, it was able to develop a rational part that controls our inner animal.

Visual perception

Vision allows humans to process the world surrounding them to a certain extent. Through the wavelengths of light, the human brain can associate them to a specific event. Although the brain obviously perceives its surroundings at a specific moment, the brain equally predicts the upcoming changes in the environment. Once it has noticed them, the brain begins to prepare itself to encounter the new scenario by attempting to develop an adequate response. This is accomplished by using the data the brain has at its access, which can be to use past experiences and memories to form a proper response. However, sometimes the brain fails to predict accurately which means that the mind perceives a false illustration. Such an incorrect image occurs when the brain uses an inadequate memory to respond to what it is facing, which means that the memory does not correlate with the real scenario.

The rabbit–duck illusion is a famous ambiguous image in which a rabbit or a duck can be seen. The earliest known version is an unattributed drawing from the 23 October 1892 issue of Blätter magazine.

Research about how visual perception has developed in evolution is today best understood through studying present-day primates since the organization of the brain cannot be ascertained only by analyzing fossilized skulls.

The brain interprets visual information in the occipital lobe, a region in the back of the brain. The occipital lobe contains the visual cortex and the thalamus, which are the two main actors in processing visual information. The process of interpreting information has proven to be more complex than "what you see is what you get". Misinterpreting visual information is more common than previously believed.

As knowledge of the human brain has evolved, researchers discover that our visual perception is much closer to a construction of the brain than a direct "photograph" of what is in front of us. This can lead to misperceiving certain situations or elements in the brain's attempt to keep us safe. For example, an on-edge soldier believes a young child with a stick is a grown man with a gun, as the brain's sympathetic system, or fight-or-flight mode, is activated.

An example of this phenomenon can be observed in the rabbit–duck illusion. Depending on how the image is looked at, the brain can interpret the image of a rabbit, or a duck. There is no right or wrong answer, but it is proof that what is seen may not be the reality of the situation.

Auditory perception

The organization of the human auditory cortex is divided into core, belt, and parabelt. This closely resembles that of present-day primates.

The concept of auditory perception resembles visual perception very similarly. Our brain is wired to act on what it expects to experience. The sense of hearing helps situate an individual, but it also gives them hints about what else is around them. If something moves, they know approximately where it is and by the tone of it, the brain can predict what moved. If someone were to hear leaves rustling in a forest, the brain might interpret that sound as being an animal which could be a dangerous factor, but it would simply be another person walking. The brain can predict many things based on what it is interpreting, however, those predictions may not all be true.

Language development

Evidence of a rich cognitive life in primate relatives of humans is extensive, and a wide range of specific behaviours in line with Darwinian theory is well documented. However, until recently, research has disregarded nonhuman primates in the context of evolutionary linguistics, primarily because unlike vocal learning birds, our closest relatives seem to lack imitative abilities. Evolutionary speaking, there is great evidence suggesting a genetic groundwork for the concept of languages has been in place for millions of years, as with many other capabilities and behaviours observed today.

While evolutionary linguists agree on the fact that volitional control over vocalizing and expressing language is a quite recent leap in the history of the human race, that is not to say auditory perception is a recent development as well. Research has shown substantial evidence of well-defined neural pathways linking cortices to organize auditory perception in the brain. Thus, the issue lies in our abilities to imitate sounds.

Beyond the fact that primates may be poorly equipped to learn sounds, studies have shown them to learn and use gestures far better. Visual cues and motoric pathways developed millions of years earlier in our evolution, which seems to be one reason for our earlier ability to understand and use gestures.

Cognitive specializations

Evolution shows how certain environments and surroundings will favor the development of specific cognitive functions of the brain to aid an animal or in this case human to successfully live in that environment.

Cognitive specialization in a theory in which cognitive functions, such as the ability to communicate socially, can be passed down genetically through offspring. This would benefit species in the process of natural selection. As for studying this in relation to the human brain, it has been theorized that very specific social skills apart from language, such as trust, vulnerability, navigation, and self-awareness can also be passed by offspring.

International Military Tribunal
Judges' bench at the Palace of Justice, Nuremberg
IndictmentConspiracy, crimes against peace, war crimes, crimes against humanity, mass murder, unethical human experimentation, false imprisonment, hate crimes
Started20 November 1945
Decided1 October 1946
Defendants24 (see list)
Witnesses37 prosecution, 83 defense
Transcripts
Case history
Related actions
Court membership
Judges sitting

The Nuremberg trials were international criminal trials held by France, the Soviet Union, the United Kingdom, and the United States against leaders of the defeated Nazi Germany for plotting and carrying out invasions of several countries across Europe and committing atrocities against their citizens in the Second World War.

Between 1939 and 1945, Nazi Germany invaded many countries across Europe, inflicting 27 million deaths in the Soviet Union alone. Proposals for how to punish the defeated Nazi leaders ranged from a show trial (the Soviet Union) to summary executions (the United Kingdom). In mid-1945, France, the Soviet Union, the United Kingdom, and the United States agreed to convene a joint tribunal in Nuremberg, occupied Germany, with the Nuremberg Charter as its legal instrument. Between 20 November 1945 and 1 October 1946, the International Military Tribunal (IMT) tried 22 of the most important surviving leaders of Nazi Germany in the political, military, and economic spheres, as well as six German organizations. The purpose of the trial was not only to try the defendants but also to assemble irrefutable evidence of Nazi war crimes, offer a history lesson to the defeated Germans, and delegitimize the traditional German elite.

The IMT verdict followed the prosecution in declaring the crime of plotting and waging aggressive war "the supreme international crime" because "it contains within itself the accumulated evil of the whole". Most defendants were also charged with war crimes and crimes against humanity, the Holocaust significantly contributing to the trials. Twelve further trials were conducted by the United States against lower-level perpetrators and focused more on the Holocaust. Controversial at the time for their retroactive criminalization of aggression, the trials' innovation of holding individuals responsible for violations of international law is considered "the true beginning of international criminal law".

Origin

Jews arriving at Auschwitz concentration camp, 1944. According to legal historian Kirsten Sellars, the extermination camps "formed the moral core of the Allies' case against the Nazi leaders".

Between 1939 and 1945, Nazi Germany invaded many European countries, including Poland, Denmark, Norway, the Netherlands, Belgium, Luxembourg, France, Yugoslavia, Greece, and the Soviet Union. German aggression was accompanied by immense brutality in occupied areas; war losses in the Soviet Union alone included 27 million dead, mostly civilians, which was one seventh of the prewar population. The legal reckoning was premised on the extraordinary nature of Nazi criminality, particularly the perceived singularity of the systematic murder of millions of Jews.

In early 1942, representatives of nine governments-in-exile from German-occupied Europe issued a declaration to demand an international court to try the German crimes committed in occupied countries. The United States and United Kingdom refused to endorse this proposal, citing the failure of war crimes prosecutions following World War I. The London-based United Nations War Crimes Commission—without Soviet participation—first met in October 1943 and became bogged down in the scope of its mandate, with Belgian jurist Marcel de Baer and Czech legal scholar Bohuslav Ečer arguing for a broader definition of war crimes that would include "the crime of war". On 1 November 1943, the Soviet Union, United Kingdom, and United States issued the Moscow Declaration, warning Nazi leadership of the signatories' intent to "pursue them to the uttermost ends of the earth ... in order that justice may be done". The declaration stated high-ranking Nazis who had committed crimes in several countries would be dealt with jointly, while others would be tried where they had committed their crimes.

Soviet jurist Aron Trainin developed the concept of crimes against peace (waging aggressive war) which would later be central to the proceedings at Nuremberg. Trainin's ideas were reprinted in the West and widely adopted. Of all the Allies, the Soviet Union lobbied most intensely for trying the defeated German leaders for aggression in addition to war crimes. The Soviet Union wanted to hold a trial with a predetermined outcome similar to the 1930s Moscow trials, in order to demonstrate the Nazi leaders' guilt and build a case for war reparations to rebuild the Soviet economy, which had been devastated by the war. The United States insisted on a trial that would be seen as legitimate as a means of reforming Germany and demonstrating the superiority of the Western system. The United States Department of War was drawing up plans for an international tribunal in late 1944 and early 1945. The British government still preferred the summary execution of Nazi leaders, citing the failure of trials following World War I and qualms about retroactive criminality. The form that retribution would take was left unresolved at the Yalta Conference in February 1945.[22] On 2 May, at the San Francisco Conference, United States president Harry S. Truman announced the formation of an international military tribunal. On 8 May, Germany surrendered unconditionally, bringing an end to the war in Europe.

Establishment

Nuremberg charter

Aron Trainin (center, with moustache) speaks at the London Conference.
Aerial view of the Palace of Justice in 1945, with the prison attached behind it
Ruins of Nuremberg, c. 1945

At the London Conference, held from 26 June to 2 August 1945, representatives of France, the Soviet Union, the United Kingdom, and the United States negotiated the form that the trial would take. Until the end of the negotiations, it was not clear that any trial would be held at all.

The offences that would be prosecuted were crimes against peace, crimes against humanity, and war crimes. At the conference, it was debated whether wars of aggression were prohibited in existing customary international law; regardless, before the charter was adopted there was no law providing for criminal responsibility for aggression. Despite misgivings from other Allies, American negotiator and Supreme Court justice Robert H. Jackson threatened the United States' withdrawal if aggression was not prosecuted because it had been the rationale for American entry into World War II. However, Jackson conceded on defining crimes against peace; the other three Allies were opposed because it would undermine the freedom of action of the United Nations Security Council.

War crimes already existed in international law as criminal violations of the laws and customs of war, but these did not apply to a government's treatment of its own citizens. Legal experts sought a way to try crimes against German citizens, such as the German Jews. A Soviet proposal for a charge of "crimes against civilians" was renamed "crimes against humanity" at Jackson's suggestion after previous uses of the term in the post-World War I Commission of Responsibilities and in failed efforts to prosecute the perpetrators of the Armenian genocide. The British proposal to define crimes against humanity was largely accepted, with the final wording being "murder, extermination, enslavement, deportation, and other inhumane acts committed against any civilian population". The final version of the charter limited the tribunal's jurisdiction over crimes against humanity to those committed as part of a war of aggression. Both the United States (concerned that its Jim Crow system of racial segregation not be labeled a crime against humanity) and the Soviet Union wanted to avoid giving an international court jurisdiction over a government's treatment of its own citizens.

The charter upended the traditional view of international law by holding individuals, rather than states, responsible for breaches. The other three Allies' proposal to limit the definition of the crimes to acts committed by the defeated Axis was rejected by Jackson. Instead, the charter limited the jurisdiction of the court to Germany's actions. Article 7 prevented the defendants from claiming sovereign immunity, and Article 8 meant that the plea of acting under superior orders was not a valid defence, although it might be treated in mitigation. The trial was held under modified common law. The negotiators decided that the tribunal's permanent seat would be in Berlin, while the trial would be held at the Palace of Justice in Nuremberg. Located in the American occupation zone, Nuremberg was a symbolic location as the site of Nazi rallies. The Palace of Justice was relatively intact but needed to be renovated for the trial due to bomb damage; it had an attached prison where the defendants could be held. On 8 August, the Nuremberg Charter was signed in London.

Judges and prosecutors

In early 1946, there were a thousand employees from the four countries' delegations in Nuremberg, of which about two thirds were from the United States. Besides legal professionals, there were many social-science researchers, psychologists, translators, interpreters, and graphic designers, the last to make the many charts used during the trial. Each state appointed a prosecution team and two judges, one being a deputy without voting rights.

Jackson (whom historian Kim Christian Priemel described as "a versatile politician and a remarkable orator, if not a great legal thinker") was appointed the United States' chief prosecutor. The United States prosecution believed Nazism was the product of a German deviation from the West (the Sonderweg thesis) and sought to correct this deviation with a trial that would serve both retributive and educational purposes. As the largest delegation, it would take on the bulk of the prosecutorial effort. At Jackson's recommendation, the United States appointed judges Francis Biddle and John Parker. The British chief prosecutor was Hartley Shawcross, Attorney General for England and Wales, assisted by his predecessor David Maxwell Fyfe. Although the chief British judge, Sir Geoffrey Lawrence (Lord Justice of Appeal), was the nominal president of the tribunal, in practice Biddle exercised more authority.

The French prosecutor, François de Menthon, had just overseen trials of the leaders of Vichy France; he resigned in January 1946 and was replaced by Auguste Champetier de Ribes. The French judges were Henri Donnedieu de Vabres, a professor of criminal law, and deputy Robert Falco, a judge of the Cour de Cassation who had represented France at the London Conference. The French government tried to appoint staff untainted by collaboration with the Vichy regime; some appointments, including Champetier de Ribes, were of those who had been in the French resistance. Expecting a show trial, the Soviet Union initially appointed as chief prosecutor Iona Nikitchenko, who had presided over the Moscow trials, but he was made a judge and replaced by Roman Rudenko, a show trial prosecutor chosen for his skill as an orator. The Soviet judges and prosecutors were not permitted to make any major decisions without consulting a commission in Moscow led by Soviet politician Andrei Vyshinsky; the resulting delays hampered the Soviet effort to set the agenda. The influence of the Soviet delegation was also constrained by limited English proficiency, lack of interpreters, and unfamiliarity with diplomacy and international institutions.

Requests by Chaim Weizmann, the president of the World Zionist Organization, as well as the Provisional Government of National Unity in Poland, for an active role in the trial justified by their representation of victims of Nazi crimes were rejected. The Soviet Union invited prosecutors from its allies, including Poland, Czechoslovakia, and Yugoslavia; Denmark and Norway also sent a delegation. Although the Polish delegation was not empowered to intervene in the proceedings, it submitted evidence and an indictment, succeeding at drawing some attention to crimes committed against Polish Jews and non-Jews.

Indictment

Handing over the indictment to the tribunal, 18 October 1945

The work of drafting the indictment was divided up by the national delegations. The British worked on aggressive war; the other delegations were assigned the task of covering crimes against humanity and war crimes committed on the Western Front (France) and the Eastern Front (the Soviet Union). The United States delegation outlined the overall Nazi conspiracy and criminality of Nazi organizations. The British and American delegations decided to work jointly in drafting the charges of conspiracy to wage aggressive war. On 17 September, the various delegations met to discuss the indictment.

The charge of conspiracy, absent from the charter, held together the wide array of charges and defendants and was used to charge the top Nazi leaders, as well as bureaucrats who had never killed anyone or perhaps even directly ordered killing. It was also an end run on the charter's limits on charging crimes committed before the beginning of World War II. Conspiracy charges were central to the cases against propagandists and industrialists: the former were charged with providing the ideological justification for war and other crimes, while the latter were accused of enabling Germany's war effort. The charge, a brainchild of War Department lawyer Murray C. Bernays, and perhaps inspired by his previous work prosecuting securities fraud, was spearheaded by the United States and less popular with the other delegations, particularly France.

The problem of translating the indictment and evidence into the three official languages of the tribunal—English, French, and Russian—as well as German was severe due to the scale of the task and difficulty of recruiting interpreters, especially in the Soviet Union. Vyshinsky demanded extensive corrections to the charges of crimes against peace, especially regarding the role of the German–Soviet pact in starting World War II. Jackson also separated out an overall conspiracy charge from the other three charges, aiming that the American prosecution would cover the overall Nazi conspiracy while the other delegations would flesh out the details of Nazi crimes. The division of labor, and the haste with which the indictment was prepared, resulted in duplication, imprecise language, and lack of attribution of specific charges to individual defendants.

Defendants

The defendants in the dock

Some of the most prominent Nazis—Adolf Hitler, Heinrich Himmler, and Joseph Goebbels—had died by suicide and therefore could not be tried. The prosecutors aimed to prosecute key leaders in German politics, business, and the military. Most of the defendants had surrendered to the United States or United Kingdom.

The defendants, who were largely unrepentant, included former cabinet ministers: Franz von Papen (who had brought Hitler to power), Joachim von Ribbentrop (foreign minister), Konstantin von Neurath (foreign minister), Wilhelm Frick (interior minister), and Alfred Rosenberg, minister for the occupied eastern territories. Also prosecuted were leaders of the German economy, such as Gustav Krupp of the Krupp AG conglomerate, former Reichsbank president Hjalmar Schacht, and economic planners Albert Speer and Walther Funk, along with Speer's subordinate and head of the forced labor program, Fritz Sauckel. While the British were skeptical of prosecuting economic leaders, the French had a strong interest in highlighting German economic imperialism. The military leaders were Hermann Göring—the most infamous surviving Nazi and the main target of the trial—Wilhelm Keitel, Alfred Jodl, Erich Raeder, and Karl Dönitz. Also on trial were propagandists Julius Streicher and Hans Fritzsche; Rudolf Hess, Hitler's deputy who had flown to Britain in 1941; Hans Frank, governor-general of the General Governorate of Poland; Hitler Youth leader Baldur von Schirach; Arthur Seyss-Inquart, Reich Commissioner for the Netherlands; and Ernst Kaltenbrunner, leader of Himmler's Reich Security Main Office. Observers of the trial found the defendants mediocre and contemptible.

Although the list of defendants was finalized on 29 August, as late as October, Jackson demanded the addition of new names, but was denied. Of the 24 men indicted, Martin Bormann was tried in absentia, as the Allies were unaware of his death; Krupp was too ill to stand trial; and Robert Ley had died by suicide before the start of the trial. Former Nazis were allowed to serve as counsel and by mid-November all defendants had lawyers. The defendants' lawyers jointly appealed to the court, claiming it did not have jurisdiction against the accused, but this motion was rejected. Defense lawyers saw themselves as acting on behalf of their clients and the German nation.

Initially, the Americans had planned to try fourteen organizations and their leaders, but this was narrowed to six: the Reich Cabinet, the Leadership Corps of the Nazi Party, the Gestapo, the SA, the SS and the SD, and the General Staff and High Command of the German military (Wehrmacht). The aim was to have these organizations declared criminal, so that their members could be tried expeditiously for membership in a criminal organization. Senior American officials believed that convicting organizations was a good way of showing that not just the top German leaders were responsible for crimes, without condemning the entire German people.

Evidence

United States Army clerks with evidence

Over the summer, all of the national delegations struggled to gather evidence for the upcoming trial. The American and British prosecutors focused on documentary evidence and affidavits rather than testimony from survivors. This strategy increased the credibility of their case, since survivor testimony was considered less reliable and more vulnerable to accusations of bias, but reduced public interest in the proceedings. The American prosecution drew on reports of the Office of Strategic Services, an American intelligence agency, and information provided by the YIVO Institute for Jewish Research and the American Jewish Committee, while the French prosecution presented many documents that it had obtained from the Center of Contemporary Jewish DocumentationThe prosecution called 37 witnesses compared to the defense's 83, not including 19 defendants who testified on their own behalf. The prosecution examined 110,000 captured German documents and entered 4,600 into evidence, along with 30 kilometres (19 mi) of film and 25,000 photographs.

The charter allowed the admissibility of any evidence deemed to have probative value, including depositions. Because of the loose evidentiary rules, photographs, charts, maps, and films played an important role in making incredible crimes believable. After the American prosecution submitted many documents at the beginning of the trial, the judges insisted that all of the evidence be read into the record, which slowed the trial. The structure of the charges also caused delays as the same evidence ended up being read out multiple times, when it was relevant to both conspiracy and the other charges.

Course of the trial

The International Military Tribunal began trial on 20 November 1945, after postponement requests from the Soviet prosecution, who wanted more time to prepare its case, were rejected. All defendants pleaded not guilty. Jackson made clear that the trial's purpose extended beyond convicting the defendants. Prosecutors wanted to assemble irrefutable evidence of Nazi crimes, establish individual responsibility and the crime of aggression in international law, provide a history lesson to the defeated Germans, delegitimize the traditional German elite, and allow the Allies to distance themselves from appeasement. Jackson maintained that while the United States did "not seek to convict the whole German people of crime", neither did the trial "serve to absolve the whole German people except 21 men in the dock". Nevertheless, defense lawyers (although not most of the defendants) often argued that the prosecution was trying to promote German collective guilt and forcefully countered this strawman. According to Priemel, the conspiracy charge "invited apologetic interpretations: narratives of absolute, totalitarian dictatorship, run by society's lunatic fringe, of which the Germans had been the first victims rather than agents, collaborators, and fellow travellers". In contrast, the evidence presented on the Holocaust convinced some observers that Germans must have been aware of this crime while it was ongoing.

American and British prosecution

Nazi Concentration and Prison Camps (1945)
Presenting information on German aggression, 4 December

On 21 November, Jackson gave the opening speech for the prosecution. He described the fact that the defeated Nazis received a trial as "one of the most significant tributes that Power has ever paid to Reason". Focusing on aggressive war, which he described as the root of the other crimes, Jackson promoted an intentionalist view of the Nazi state and its overall criminal conspiracy. The speech was favorably received by the prosecution, the tribunal, the audience, historians, and even the defendants.

Much of the American case focused on the development of the Nazi conspiracy before the outbreak of war. The American prosecution became derailed during attempts to provide evidence on the first act of aggression, against Austria. On 29 November, the prosecution was unprepared to continue presenting on the invasion of Czechoslovakia, and instead screened Nazi Concentration and Prison Camps. The film, compiled from footage of the liberation of Nazi concentration camps, shocked both the defendants and the judges, who adjourned the trial. Indiscriminate selection and disorganized presentation of documentary evidence without tying it to specific defendants hampered the American prosecutors' work on the conspiracy to commit crimes against humanity. The Americans summoned Einsatzgruppen commander Otto Ohlendorf, who testified about the murder of 80,000 people by those under his command, and SS general Erich von dem Bach-Zelewski, who admitted that German anti-partisan warfare was little more than a cover for the mass murder of Jews.

Evidence about Ernst Kaltenbrunner's crimes is presented, 2 January 1946.

The British prosecution covered the charge of crimes against peace, which was largely redundant to the American conspiracy case. On 4 December, Shawcross gave the opening speech, much of which had been written by Cambridge professor Hersch Lauterpacht. Unlike Jackson, Shawcross attempted to minimize the novelty of the aggression charges, elaborating its precursors in the conventions of Hague and Geneva, the League of Nations Covenant, the Locarno Treaty, and the Kellogg–Briand Pact. The British took four days to make their case, with Maxwell Fyfe detailing treaties broken by Germany. In mid-December the Americans switched to presenting the case against the indicted organizations, while in January both the British and Americans presented evidence against individual defendants. Besides the organizations mentioned in the indictment, American, and British prosecutors also mentioned the complicity of the German Foreign Office, army, and navy.[141]

French prosecution

From 17 January to 7 February 1946, France presented its charges and supporting evidence. In contrast to the other prosecution teams, the French prosecution delved into Germany's development in the nineteenth century, arguing that it had diverged from the West due to pan-Germanism and imperialism. They argued that Nazi ideology, which derived from these earlier ideas, was the mens rea—criminal intent—of the crimes on trial. The French prosecutors, more than their British or American counterparts, emphasized the complicity of many Germans; they barely mentioned the charge of aggressive war and instead focused on forced labor, economic plunder, and massacres. Prosecutor Edgar Faure grouped together various German policies, such as the annexation of Alsace–Lorraine, under the label of Germanization, which he argued was a crime against humanity. Unlike the British and American prosecution strategies, which focused on using German documents, French prosecutors took the perspective of the victims, submitting postwar police reports. Eleven witnesses, including victims of Nazi persecution, were called; resistance fighter and Auschwitz survivor Marie Claude Vaillant-Couturier testified about crimes she had witnessed. The French charges of war crimes were accepted by the tribunal, except for the execution of hostages. Due to the narrow definition of crimes against humanity in the charter, the only part of the Germanization charges accepted by the judges was the deportation of Jews from France and other parts of Western Europe.

Soviet prosecution

Roman Rudenko opens the Soviet case.

On 8 February, the Soviet prosecution opened its case with a speech by Rudenko that covered all four prosecution charges, highlighting a wide variety of crimes committed by the German occupiers as part of their destructive and unprovoked invasion. Rudenko tried to emphasize common ground with the other Allies while rejecting any similarity between Nazi and Soviet rule. The next week, the Soviet prosecution produced Friedrich Paulus—a German field marshal captured after the Battle of Stalingrad—as a witness and questioned him about the preparations for the invasion of the Soviet Union. Paulus incriminated his former associates, pointing to Keitel, Jodl, and Göring as the defendants most responsible for the war.

More so than other delegations, Soviet prosecutors showed the gruesome details of German atrocities, especially the death by starvation of 3 million Soviet prisoners of war and several hundred thousand residents of Leningrad. Although Soviet prosecutors dealt most extensively with the systematic murder of Jews in eastern Europe, at times they blurred the fate of Jews with that of other Soviet nationalities. Although these aspects had already been covered by the American prosecution, Soviet prosecutors introduced new evidence from Extraordinary State Commission reports and interrogations of senior enemy officers. Lev Smirnov presented evidence on the Lidice massacre in Czechoslovakia, adding that German invaders had destroyed thousands of villages and murdered their inhabitants throughout eastern Europe. The Soviet prosecution emphasized the racist aspect of policies such as the deportation of millions of civilians to Germany for forced labor, the murder of children, systematic looting of occupied territories, and theft or destruction of cultural heritage. The Soviet prosecution also attempted to fabricate German responsibility for the Katyn massacre, which had in fact been committed by the NKVD. Although Western prosecutors never publicly rejected the Katyn charge for fear of casting doubt on the entire proceedings, they were skeptical. The defense presented evidence of Soviet responsibility, and Katyn was not mentioned in the verdict.

Inspired by the films shown by the American prosecution, the Soviet Union commissioned three films for the trial: The German Fascist Destruction of the Cultural Treasures of the Peoples of the USSR, Atrocities Committed by the German Fascist Invaders in the USSR, and The German Fascist Destruction of Soviet Cities, using footage from Soviet filmmakers as well as shots from German newsreels. The second included footage of the liberations of Majdanek and Auschwitz and was considered even more disturbing than the American concentration camp film. Soviet witnesses included several survivors of German crimes, including two civilians who lived through the siege of Leningrad, a peasant whose village was destroyed in anti-partisan warfare, a Red Army doctor who endured several prisoner-of-war camps and two Holocaust survivors—Samuel Rajzman, a survivor of Treblinka extermination camp, and poet Abraham Sutzkever, who described the murder of tens of thousands of Jews from Vilna. The Soviet prosecution case was generally well received and presented compelling evidence for the suffering of the Soviet people and the Soviet contributions to victory.

Defense

Hermann Göring under cross-examination
A member of the Soviet delegation addresses the tribunal.

From March to July 1946, the defense presented its counterarguments. Before the prosecution finished, it was clear that their general case was proven, but it remained to determine the individual guilt of each defendant. None of the defendants tried to assert that the Nazis' crimes had not occurred. Some defendants denied involvement in certain crimes or implausibly claimed ignorance of them, especially the Holocaust. A few defense lawyers inverted the arguments of the prosecution to assert that the Germans' authoritarian mindset and obedience to the state exonerated them from any personal guilt. Most rejected that Germany had deviated from Western civilization, arguing that few Germans could have supported Hitler because Germany was a civilized country.

The defendants tried to blame their crimes on Hitler, who was mentioned 12,000 times during the trial—more than the top five defendants combined. Other absent and dead men, including Himmler, Reinhard Heydrich, Adolf Eichmann, and Bormann, were also blamed. To counter claims that conservative defendants had enabled the Nazi rise to power, defense lawyers blamed the Social Democratic Party of Germany, trade unions, and other countries that maintained diplomatic relations with Germany. In contrast, most defendants avoided incriminating each other. Most defendants argued their own insignificance within the Nazi system, though Göring took the opposite approach, expecting to be executed but vindicated in the eyes of the German people.

The charter did not recognize a tu quoque defense—asking for exoneration on the grounds that the Allies had committed the same crimes with which the defendants were charged. Although defense lawyers repeatedly equated the Nuremberg Laws to legislation found in other countries, Nazi concentration camps to Allied detention facilities, and the deportation of Jews to the expulsion of Germans, the judges rejected their arguments. Alfred Seidl [de] repeatedly tried to disclose the secret protocols of the German–Soviet pact; although he was eventually successful, it was legally irrelevant and the judges rejected his attempt to bring up the Treaty of Versailles. Six defendants were charged with the German invasion of Norway, and their lawyers argued that this invasion was undertaken to prevent a British invasion of that country; a cover-up prevented the defense from capitalizing on this argument. Fleet admiral Chester Nimitz testified that the United States Navy had also used unrestricted submarine warfare against Japan in the Pacific; Dönitz's counsel successfully argued that this meant that it could not be a crime. The judges barred most evidence on Allied misdeeds from being heard in court.

Many defense lawyers complained about various aspects of the trial procedure and attempted to discredit the entire proceedings. In order to appease them, the defendants were allowed a free hand with their witnesses and a great deal of irrelevant testimony was heard. The defendants' witnesses sometimes managed to exculpate them, but other witnesses—including Rudolf Höss, the former commandant of Auschwitz, and Hans Bernd Gisevius, a member of the German resistance—bolstered the prosecution's case. In the context of the brewing Cold War—for example, in early March 1946, Winston Churchill delivered the Iron Curtain speech—the trial became a means of condemning not only Germany but also the Soviet Union.

Closing

On 31 August, closing arguments were presented. Over the course of the trial, crimes against humanity and especially against Jews (who were mentioned as victims of Nazi atrocities far more than any other group) came to upstage the aggressive war charge. In contrast to the opening prosecution statements, all eight closing statements highlighted the Holocaust. The French and British prosecutors made this the main charge, as opposed to that of aggression. All prosecutors except the Americans mentioned the concept of genocide, which had been recently invented by the Polish-Jewish jurist Raphael Lemkin. British prosecutor Shawcross quoted from witness testimony about a murdered Jewish family from Dubno, Ukraine. During the closing statements, most defendants disappointed the judges with lies and denials. Speer managed to give the impression of apologizing without assuming personal guilt or naming any victims other than the German people. On 2 September, the court recessed, and the judges retreated into seclusion to decide the verdict and sentences, which had been under discussion since June. The verdict was drafted by British deputy judge Norman Birkett. All eight judges participated in the deliberations, but the deputies could not vote.

Verdict

The International Military Tribunal agreed with the prosecution that aggression was the gravest charge, stating in its judgment that because "war is essentially an evil thing", "to initiate a war of aggression, therefore, is not only an international crime; it is the supreme international crime differing only from other war crimes in that it contains within itself the accumulated evil of the whole". The work of the judges was made more difficult due to the broadness of the crimes listed in the Nuremberg Charter. The judges did not attempt to define the crime of aggression and did not mention the retroactivity of the charges in the verdict. Despite the lingering doubts of some of the judges, the official interpretation of the IMT held that all of the charges had a solid basis in customary international law and that the trial was procedurally fair. The judges were aware that both the Allies and the Axis had planned or committed acts of aggression, writing the verdict carefully to avoid discrediting either the Allied governments or the tribunal.

The judges ruled that there had been a premeditated conspiracy to commit crimes against peace, whose goals were "the disruption of the European order" and "the creation of a Greater Germany beyond the frontiers of 1914". Contrary to Jackson's argument that the conspiracy began with the founding of the Nazi Party in 1920, the verdict dated the planning of aggression to the 1937 Hossbach Memorandum. The conspiracy charge caused significant dissent on the bench; Donnedieu de Vabres wanted to scrap it. Through a compromise proposed by the British judges, the charge of conspiracy was narrowed to a conspiracy to wage aggressive war. Only eight defendants were convicted on that charge, all of whom were also found guilty of crimes against peace. All 22 defendants were charged with crimes against peace, and 12 were convicted. The war crimes and crimes against humanity charges held up the best, with only two defendants charged on those grounds being acquitted. The judges determined that crimes against humanity concerning German Jews before 1939 were not under the court's jurisdiction because the prosecution had not proven a connection to aggressive war.

Four organizations were ruled to be criminal: the Leadership Corps of the Nazi Party, the SS, the Gestapo, and the SD, although some lower ranks and subgroups were excluded. The verdict only allowed for individual criminal responsibility if willing membership and knowledge of the criminal purpose could be proved, complicating denazification efforts. The SA, Reich Cabinet, General Staff and High Command were not ruled to be criminal organizations. Although the Wehrmacht leadership was not considered an organization within the meaning of the charter, misrepresentation of the verdict as an exoneration would become one of the foundations of the clean Wehrmacht myth. The trial had nevertheless resulted in the coverage of its systematic criminality in the German press.

Sentences were debated at length by the judges. Twelve defendants were sentenced to death: Göring, Ribbentrop, Keitel, Kaltenbrunner, Rosenberg, Frank, Frick, Streicher, Sauckel, Jodl, Seyss-Inquart, and Bormann. On 16 October, ten were hanged, with Göring killing himself the day before. Seven defendants (Hess, Funk, Raeder, Dönitz, Schirach, Speer, and Neurath) were sent to Spandau Prison to serve their sentences. All three acquittals (Papen, Schacht, and Fritzsche) were based on a deadlock between the judges; these acquittals surprised observers. Despite being accused of the same crimes, Sauckel was sentenced to death, while Speer was given a prison sentence because the judges considered that he could reform. Nikichenko released a dissent approved by Moscow that rejected all the acquittals, called for a death sentence for Hess, and convicted all the organizations.

Subsequent Nuremberg trials

Telford Taylor opens for the prosecution in the Ministries trial, 6 January 1948.
Monowitz prisoners unload cement from trains for IG Farben, presented as evidence at the IG Farben trial.

Initially, it was planned to hold a second international tribunal for German industrialists, but this was never held because of differences between the Allies. Twelve military trials were convened solely by the United States in the same courtroom that had hosted the International Military Tribunal. Pursuant to Law No. 10 adopted by the Allied Control Council, United States forces arrested almost 100,000 Germans as war criminals. The Office of Chief Counsel for War Crimes identified 2,500 major war criminals, of whom 177 were tried. Many of the worst offenders were not prosecuted, for logistical or financial reasons.

One set of trials focused on the actions of German professionals: the Doctors' trial focused on human experimentation and euthanasia murders, the Judges' trial on the role of the judiciary in Nazi crimes, and the Ministries trial on the culpability of bureaucrats of German government ministries, especially the Foreign OfficeAlso on trial were industrialists—in the Flick trial, the IG Farben trial, and the Krupp trial—for using forced labor, looting property from Nazi victims, and funding SS atrocities. Members of the SS were tried in the Pohl trial, which focused on members of the SS Main Economic and Administrative Office that oversaw SS economic activity, including the Nazi concentration camps; the RuSHA trial of Nazi racial policies; and the Einsatzgruppen trial, in which members of the mobile killing squads were tried for the murder of more than one million people behind the Eastern Front. Luftwaffe general Erhard Milch was tried for using slave labor and deporting civilians. In the Hostages case, several generals were tried for executing thousands of hostages and prisoners of war, looting, using forced labor, and deporting civilians in the Balkans. Other generals were tried in the High Command Trial for plotting wars of aggression, issuing criminal orders, deporting civilians, using slave labor, and looting in the Soviet Union.

These trials emphasized the crimes committed during the Holocaust. The trials heard 1,300 witnesses, entered more than 30,000 documents into evidence, and generated 132,855 pages of transcripts, with the judgments totaling 3,828 pages. Of 177 defendants, 142 were convicted and 25 sentenced to death; the severity of sentencing was related to the defendant's proximity to mass murder. Legal historian Kevin Jon Heller argues that the trials' greatest achievement was "their inestimable contribution to the form and substance of international criminal law", which had been left underdeveloped by the IMT.

Contemporary reactions

Press at the International Military Tribunal
Germans read Süddeutsche Zeitung reporting the verdict, 1 October 1946

In all, 249 journalists were accredited to cover the IMT and 61,854 visitor tickets were issued. In France, the sentence for Rudolf Hess and acquittal of organizations were met with outrage from the media and especially from organizations for deportees and resistance fighters, as they were perceived as too lenient. In the United Kingdom, although a variety of responses were reported, it was difficult to sustain interest in a long trial. Where the prosecution was disappointed by some of the verdicts, the defense could take satisfaction.

Many Germans at the time of the trials focused on finding food and shelter. Despite this, a majority read press reports about the trial. In a 1946 poll, 78 percent of Germans assessed the trial as fair, but four years later that had fallen to 38 percent, with 30 percent considering it unfair. As time went on, more Germans considered the trials illegitimate victor's justice and an imposition of collective guilt, which they rejected—instead considering themselves victims of the war. As the Cold War began, the rapidly changing political environment began to affect the effectiveness of the trials. The educational purpose of the Nuremberg Military Tribunals was a failure, in part because of the resistance to war crimes trials in German society, but also because of the United States Army's refusal to publish the trial record in German for fear it would undermine the fight against communism.

The German churches, both Catholic and Protestant, were vocal proponents of amnesty. The pardon of convicted war criminals also had cross-party support in West Germany, which was established in 1949. The Americans satisfied these wishes to bind West Germany to the Western Bloc, beginning early releases of Nuremberg Military Tribunal convicts in 1949. In 1951, High Commissioner John J. McCloy overturned most of the sentences and the last three prisoners, all convicted at the Einsatzgruppen trial, were released in 1958. The German public took the early releases as confirmation of what they saw as the illegitimacy of the trials. The IMT defendants required Soviet permission for release; Speer was not successful in obtaining early release, and Hess remained in prison until his death in 1987. By the late 1950s, the West German consensus on release began to erode, due to greater openness in political culture and new revelations of Nazi criminality, including the first trials of Nazi perpetrators in West German courts.

Legacy

Benjamin Ferencz, chief prosecutor of the Einsatzgruppen trial, in the Palace of Justice courtroom, 2012

The International Military Tribunal, and its charter, "marked the true beginning of international criminal law". The trial has met a mixed reception ranging from glorification to condemnation. The reaction was initially predominantly negative, but has become more positive over time.

The selective prosecution exclusively of the defeated Axis and hypocrisy of all four Allied powers has garnered the most persistent criticism. Such actions as the German–Soviet pact, the expulsion of millions of Germans from central and eastern Europe, deportation of civilians for forced labor, and violent suppression of anti-colonial uprisings would have been deemed illegal according to the definitions of international crimes in the Nuremberg charter. Another controversy resulted from trying defendants for acts that were not criminal at the time, particularly crimes against peace. Equally novel but less controversial were crimes against humanity, the conspiracy charge, and criminal penalties on individuals for breaches of international law. Besides these criticisms, the trials have been taken to task for the distortion that comes from fitting historical events into legal categories.

The International Military Tribunal for the Far East (Tokyo Trial) borrowed many of its ideas from the IMT, including all four charges, and was intended by the Truman Administration to shore up the IMT's legal legacy.[263][271] On 11 December 1946, the United Nations General Assembly unanimously passed a resolution affirming "the principles of international law recognized by the Charter of the Nuremberg Tribunal and the judgment of the Tribunal".[272] In 1950, the International Law Commission drafted the Nuremberg principles to codify international criminal law, although the Cold War prevented the adoption of these principles until the 1990s.[273][274] The 1948 Genocide Convention was much more restricted than Lemkin's original concept and its effectiveness was further limited by Cold War politics.[274][275] In the 1990s, a revival of international criminal law included the establishment of ad hoc international criminal tribunals for Yugoslavia (ICTY) and Rwanda (ICTR), which were widely viewed as part of the legacy of the Nuremberg and Tokyo trials. A permanent International Criminal Court (ICC), proposed in 1953, was established in 2002.

The trials were the first use of simultaneous interpretation, which stimulated technical advances in translation methods. The Palace of Justice houses a museum on the trial and the courtroom became a tourist attraction, drawing 13,138 visitors in 2005. The IMT is one of the most well-studied trials in history, and it has also been the subject of an abundance of books and scholarly publications, along with motion pictures such as Judgment at Nuremberg (1961), The Memory of Justice (1976) and Nuremberg (2025).

Transgenerational epigenetic inheritance

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