Sperm

From Wikipedia, the free encyclopedia

Diagram of a human sperm cell

Sperm is the male reproductive cell and is derived from the Greek word (σπέρμα) sperma (meaning "seed"). In the types of sexual reproduction known as anisogamy and its subtype oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell. A uniflagellar sperm cell that is motile is referred to as a spermatozoon, whereas a non-motile sperm cell is referred to as a spermatium. Sperm cells cannot divide and have a limited life span, but after fusion with egg cells during fertilization, a new organism begins developing, starting as a totipotent zygote. The human sperm cell is haploid, so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell. In mammals, sperm develops in the testicles, is stored in the epididymis, and released from the penis.

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Video of human sperm cells recorded by an affordable home microscope.

Sperm in animals

Function

The main sperm function is to reach the ovum and fuse with it to deliver two sub-cellular structures: (i) the male pronucleus that contains the genetic material and (ii) the centrioles that are structures that help organize the microtubule cytoskeleton.

Anatomy

Sperm and egg fusing

The mammalian sperm cell can be divided in 4 parts:

• head: it contains the nucleus with densely coiled chromatin fibres, surrounded anteriorly by an acrosome, which contains enzymes used for penetrating the female egg. It also contains vacuoles;
• neck: it contains one typical centriole and one atypical centriole such as the proximal centriole like;
• midpiece: it has a central filamentous core with many mitochondria spiralled around it, used for ATP production for the journey through the female cervix, uterus and uterine tubes;
• tail or "flagellum": it executes the lashing movements that propel the spermatocyte.

During fertilization, the sperm provides three essential parts to the oocyte: (1) a signalling or activating factor, which causes the metabolically dormant oocyte to activate; (2) the haploid paternal genome; (3) the centriole, which is responsible for forming the centrosome and microtubule system.

Origin

The spermatozoa of animals are produced through spermatogenesis inside the male gonads (testicles) via meiotic division. The initial spermatozoon process takes around 70 days to complete. The spermatid stage is where the sperm develops the familiar tail. The next stage where it becomes fully mature takes around 60 days when it is called a spermatozoan. Sperm cells are carried out of the male body in a fluid known as semen. Human sperm cells can survive within the female reproductive tract for more than 5 days post coitus. Semen is produced in the seminal vesicles, prostate gland and urethral glands.

In 2016 scientists at Nanjing Medical University claimed they had produced cells resembling mouse spermatids artificially from stem cells. They injected these spermatids into mouse eggs and produced pups.

Sperm quality

Human sperm stained for semen quality testing.

Sperm quantity and quality are the main parameters in semen quality, which is a measure of the ability of semen to accomplish fertilization. Thus, in humans, it is a measure of fertility in a man. The genetic quality of sperm, as well as its volume and motility, all typically decrease with age.

DNA damages present in sperm cells in the period after meiosis but before fertilization may be repaired in the fertilized egg, but if not repaired, can have serious deleterious effects on fertility and the developing embryo. Human sperm cells are particularly vulnerable to free radical attack and the generation of oxidative DNA damage.

The postmeiotic phase of mouse spermatogenesis is very sensitive to environmental genotoxic agents, because as male germ cells form mature sperm they progressively lose the ability to repair DNA damage. Irradiation of male mice during late spermatogenesis can induce damage that persists for at least 7 days in the fertilizing sperm cells, and disruption of maternal DNA double-strand break repair pathways increases sperm cell-derived chromosomal aberrations. Treatment of male mice with melphalan, a bifunctional alkylating agent frequently employed in chemotherapy, induces DNA lesions during meiosis that may persist in an unrepaired state as germ cells progress though DNA repair-competent phases of spermatogenic development. Such unrepaired DNA damages in sperm cells, after fertilization, can lead to offspring with various abnormalities.

Sperm size

Related to sperm quality is sperm size, at least in some animals. For instance, the sperm of some species of fruit fly (Drosophila) are up to 5.8 cm long — about 20 times as long as the fly itself. Longer sperm cells are better than their shorter counterparts at displacing competitors from the female’s seminal receptacle. The benefit to females is that only healthy males carry ‘good’ genes that can produce long sperm in sufficient quantities to outcompete their competitors.

Market for human sperm

Some sperm banks hold up to 170 litres (37 imp gal; 45 US gal) of sperm.

In addition to ejaculation, it is possible to extract sperm through TESE.

On the global market, Denmark has a well-developed system of human sperm export. This success mainly comes from the reputation of Danish sperm donors for being of high quality and, in contrast with the law in the other Nordic countries, gives donors the choice of being either anonymous or non-anonymous to the receiving couple. Furthermore, Nordic sperm donors tend to be tall and highly educated and have altruistic motives for their donations, partly due to the relatively low monetary compensation in Nordic countries. More than 50 countries worldwide are importers of Danish sperm, including Paraguay, Canada, Kenya, and Hong Kong. However, the Food and Drug Administration (FDA) of the US has banned import of any sperm, motivated by a risk of transmission of Creutzfeldt–Jakob disease, although such a risk is insignificant, since artificial insemination is very different from the route of transmission of Creutzfeldt–Jakob disease. The prevalence of Creutzfeldt–Jakob disease for donors is at most one in a million, and if the donor was a carrier, the infectious proteins would still have to cross the blood-testis barrier to make transmission possible.

History

Sperm were first observed in 1677 by Antonie van Leeuwenhoek using a microscope, he described them as being animalcules (little animals), probably due to his belief in preformationism, which thought that each sperm contained a fully formed but small human.

Forensic analysis

Ejaculated fluids are detected by ultraviolet light, irrespective of the structure or colour of the surface. Sperm heads, e.g. from vaginal swabs, are still detected by microscopy using the "Christmas Tree Stain" method, i.e., Kernechtrot-Picroindigocarmine (KPIC) staining.

Sperm in plants

Sperm cells in algal and many plant gametophytes are produced in male gametangia (antheridia) via mitotic division. In flowering plants, sperm nuclei are produced inside pollen.

Motile sperm cells

Motile sperm cells of algae and seedless plants.

Motile sperm cells typically move via flagella and require a water medium in order to swim toward the egg for fertilization. In animals most of the energy for sperm motility is derived from the metabolism of fructose carried in the seminal fluid. This takes place in the mitochondria located in the sperm's midpiece (at the base of the sperm head). These cells cannot swim backwards due to the nature of their propulsion. The uniflagellated sperm cells (with one flagellum) of animals are referred to as spermatozoa, and are known to vary in size.

Motile sperm are also produced by many protists and the gametophytes of bryophytes, ferns and some gymnosperms such as cycads and ginkgo. The sperm cells are the only flagellated cells in the life cycle of these plants. In many ferns and lycophytes, they are multi-flagellated (carrying more than one flagellum).

In nematodes, the sperm cells are amoeboid and crawl, rather than swim, towards the egg cell.

Non-motile sperm cells

Non-motile sperm cells called spermatia lack flagella and therefore cannot swim. Spermatia are produced in a spermatangium.

Because spermatia cannot swim, they depend on their environment to carry them to the egg cell. Some red algae, such as Polysiphonia, produce non-motile spermatia that are spread by water currents after their release. The spermatia of rust fungi are covered with a sticky substance. They are produced in flask-shaped structures containing nectar, which attract flies that transfer the spermatia to nearby hyphae for fertilization in a mechanism similar to insect pollination in flowering plants.

Fungal spermatia (also called pycniospores, especially in the Uredinales) may be confused with conidia. Conidia are spores that germinate independently of fertilization, whereas spermatia are gametes that are required for fertilization. In some fungi, such as Neurospora crassa, spermatia are identical to microconidia as they can perform both functions of fertilization as well as giving rise to new organisms without fertilization.

Sperm nuclei

In almost all embryophytes, including most gymnosperms and all angiosperms, the male gametophytes (pollen grains) are the primary mode of dispersal, for example via wind or insect pollination, eliminating the need for water to bridge the gap between male and female. Each pollen grain contains a spermatogenous (generative) cell. Once the pollen lands on the stigma of a receptive flower, it germinates and starts growing a pollen tube through the carpel. Before the tube reaches the ovule, the nucleus of the generative cell in the pollen grain divides and gives rise to two sperm nuclei, which are then discharged through the tube into the ovule for fertilization.

In some protists, fertilization also involves sperm nuclei, rather than cells, migrating toward the egg cell through a fertilization tube. Oomycetes form sperm nuclei in a syncytical antheridium surrounding the egg cells. The sperm nuclei reach the eggs through fertilization tubes, similar to the pollen tube mechanism in plants.

Sperm centrioles

Most sperm cells have centrioles in the sperm neck. Sperm of many animals has 2 typical centrioles known as the proximal centriole and distal centriole. Some animals like human and bovine have a single typical centriole, known as the proximal centriole, and a second centriole with atypical structure. Mice and rats have no recognizable sperm centrioles. The fruit fly Drosophila melanogaster has a single centriole and an atypical centriole named the Proximal Centriole-Like (PCL).

Sperm tail formation

The sperm tail is a specialized type of cilium (aka flagella). In many animals the sperm tail is formed in a unique way, which is named Cytosolic ciliogenesis, since all or part of axoneme of the sperm tail is formed in the cytoplasm or get exposed to the cytoplasm.

Egg cell

From Wikipedia, the free encyclopedia

Egg cell
A human ovum with corona radiata surrounding it

Human Ovum Cell

The egg cell, or ovum (plural ova), is the female reproductive cell (gamete) in oogamous organisms. The egg cell is typically not capable of active movement, and it is much larger (visible to the naked eye) than the motile sperm cells. When egg and sperm fuse, a diploid cell (the zygote) is formed, which rapidly grows into a new organism.

History

While the non-mammalian animal egg was obvious, the doctrine ex ovo omne vivum ("every living [animal comes from] an egg"), associated with William Harvey (1578–1657), was a rejection of spontaneous generation and preformationism as well as a bold assumption that mammals also reproduced via eggs. Karl Ernst von Baer discovered the mammalian ovum in 1827, and Edgar Allen discovered the human ovum in 1928. The fusion of spermatozoa with ova (of a starfish) was observed by Oskar Hertwig in 1876.

Animals

In animals, egg cells are also known as ova (singular ovum, from the Latin word ovum meaning egg or egg cell). The term ovule in animals is used for the young ovum of an animal. In vertebrates, ova are produced by female gonads (sexual glands) called ovaries. A number of ova are present at birth in mammals and mature via oogenesis. White et al. disproved the longstanding dogma that all of the ova are produced before birth. The team from the Vincent Center for Reproductive Biology, Massachusetts, Boston showed that oocyte formation takes place in ovaries of reproductive-age women. This report challenged a fundamental belief, held since the 1950s, that female mammals are born with a finite supply of eggs that is depleted throughout life and exhausted at menopause.

Human and mammal ova

Diagram of a human egg cell

 

Ovum and sperm fusing together

 

The process of fertilizing an ovum (Top to bottom)

In all mammals the ovum is fertilized inside the female body.

The human ova grow from primitive germ cells that are embedded in the substance of the ovaries. Each of them divides repeatedly to give secretions of the uterine glands, ultimately forming a blastocyst.

The ovum is one of the largest cells in the human body, typically visible to the naked eye without the aid of a microscope or other magnification device. The human ovum measures approximately 0.1 mm in diameter.

Ooplasm

Ooplasm (also: oöplasm) is the yolk of the ovum, a cell substance at its center, which contains its nucleus, named the germinal vesicle, and the nucleolus, called the germinal spot.

The ooplasm consists of the cytoplasm of the ordinary animal cell with its spongioplasm and hyaloplasm, often called the formative yolk; and the nutritive yolk or deutoplasm, made of rounded granules of fatty and albuminoid substances imbedded in the cytoplasm.

Mammalian ova contain only a tiny amount of the nutritive yolk, for nourishing the embryo in the early stages of its development only. In contrast, bird eggs contain enough to supply the chick with nutriment throughout the whole period of incubation.

Ova development in oviparous animals

In the oviparous animals (all birds, most fish, amphibians and reptiles) the ova develop protective layers and pass through the oviduct to the outside of the body. They are fertilized by male sperm either inside the female body (as in birds), or outside (as in many fish). After fertilization, an embryo develops, nourished by nutrients contained in the egg. It then hatches from the egg, outside the mother's body.

The egg cell's cytoplasm and mitochondria are the sole means the egg is able to reproduce by mitosis and eventually form a blastocyst after fertilization.

Ovoviviparity

There is an intermediate form, the ovoviviparous animals: the embryo develops within and is nourished by an egg as in the oviparous case, but then it hatches inside the mother's body shortly before birth, or just after the egg leaves the mother's body. Some fish, reptiles and many invertebrates use this technique.

Plants

Nearly all land plants have alternating diploid and haploid generations. Gametes are produced by the gametophyte, which is the haploid generation. The female gametophyte produces structures called archegonia, and the egg cells form within them via mitosis. The typical bryophyte archegonium consists of a long neck with a wider base containing the egg cell. Upon maturation, the neck opens to allow sperm cells to swim into the archegonium and fertilize the egg. The resulting zygote then gives rise to an embryo, which will grow into a new diploid individual (sporophyte). In seed plants, a structure called ovule, which contains the female gametophyte. The gametophyte produces an egg cell. After fertilization, the ovule develops into a seed containing the embryo.

In flowering plants, the female gametophyte (sometimes referred to as the embryo sac) has been reduced to just eight cells inside the ovule. The gametophyte cell closest to the micropyle opening of the ovule develops into the egg cell. Upon pollination, a pollen tube delivers sperm into the gametophyte and one sperm nucleus fuses with the egg nucleus. The resulting zygote develops into an embryo inside the ovule. The ovule in turn develops into a seed and in many cases the plant ovary develops into a fruit to facilitate the dispersal of the seeds. Upon germination, the embryo grows into a seedling.

Gene expression pattern determined by histochemical GUS assays in Physcomitrella patens. The Polycomb gene FIE is expressed (blue) in unfertilised egg cells of the moss Physcomitrella patens (right) and expression ceases after fertilisation in the developing diploid sporophyte (left). In situ GUS staining of two female sex organs (archegonia) of a transgenic plant expressing a translational fusion of FIE-uidA under control of the native FIE promoter

In the moss Physcomitrella patens, the Polycomb protein FIE is expressed in the unfertilised egg cell  as the blue colour after GUS staining reveals. Soon after fertilisation the FIE gene is inactivated (the blue colour is no longer visible) in the young embryo. 

Other organisms

In algae, the egg cell is often called oosphere. Drosophila oocytes develop in individual egg chambers that are supported by nurse cells and surrounded by somatic follicle cells. The nurse cells are large polyploid cells that synthesize and transfer RNA, proteins and organelles to the oocytes. This transfer is followed by the programmed cell death (apoptosis) of the nurse cells. During the course of oogenesis, 15 nurse cells die for every oocyte that is produced. In addition to this developmentally regulated cell death, egg cells may also undergo apoptosis in response to starvation and other insults.

How Supercomputers Can Help Fix Our Wildfire Problem

by Matt Simon

11.29.18 08:00 am

Original link:   https://www.wired.com/story/how-supercomputers-can-help-fix-our-wildfire-problem/?mbid=social_gplus&utm_brand=wired&utm_campaign=wired&utm_medium=social&utm_social-type=owned&utm_source=google-plus

David McNew/Getty Images

Fire is chaos. Fire doesn’t care what it destroys or who it kills—it spreads without mercy, leaving total destruction in its wake, as California’s Camp and Woolsey fires proved so dramatically this month.

But fire is to a large degree predictable. It follows certain rules and prefers certain fuels and follows certain wind patterns. That means its moves with a complexity that scientists can pick apart little by little, thanks to lasers, fancy sensors, and some of the most powerful computers on the planet. We can't end wildfires altogether, but by better understanding their dynamics, ideally we can stop a disaster like the destruction of Paradise from happening again.

You could argue that a wildfire is the most complicated natural disaster, because it’s both a product of atmospheric conditions—themselves extremely complex—and a manipulator of atmospheric conditions. So for instance, California’s recent fires were driven by hot, dry winds coming from the east. These winds dried out vegetation that was already dry due to lack of rainfall, fueling conflagrations that burn more intensely and move faster.

But wildfires also create their own weather patterns. Blazes produce hot air, which rises. “You can imagine that if something moves from the surface up, there must be some kind of horizontal movement of air filling the gap” near ground level, says Adam Kochanski, an atmospheric scientist at the University of Utah. Thus the fire sucks in surface winds.

Researchers are using supercomputers and lookout stations like this to model the dynamics of wildfires in real time.

Los Alamos National Laboratory

Wildfires don’t yet have the equivalent of a grand unified model to explain their behavior. The contributing factors are just so different, and work on such different scales—air dynamics for one, the aridity of local vegetation for another.

“That's what's really difficult from a modeling standpoint,” says Kochanski. You can’t hope to model a 50-square-mile wildfire with millimeter-scale resolution. So researchers like Kochanski simplify things. “We don't really go into looking at how every single flame burns every single tree and how it progresses. No, we assume fuel is relatively uniform.”

Still, advances in computing are allowing researchers to crunch ever more data. At Los Alamos National Laboratory, atmospheric scientist Alexandra Jonko is using a supercomputer and a system called FIRETEC to model fires in extreme detail. It models, among other things, air density and temperature, as well as the properties of the grass or leaves in a particular area.

Jonko runs a bunch of simulations with different wind speeds, typically on the scale of 40 acres. “It'll probably take me about four hours to simulate between 10 and 20 minutes of a fire spreading,” she says.

FIRETEC produces valuable physics-based data on fire dynamics to inform how fire managers do prescribed burns. This is pivotal for controlling vegetation that turns into fuel for fires. Wildfire agencies know generally the ideal conditions—low winds, for instance—but this type of modeling could help give even more granular insight.

FIRETEC's modeling a portion of the 2011 Las Conchas fire near Los Alamos

Los Alamos National Laboratory

To figure out where to do these burns, researchers are experimenting with lidar, the same kind of laser-spewing technology that helps self-driving cars find their way. This comes in the form of airborne lidar, which lets researchers visualize trees in 3D, supplemented with ground-based lidar, which details the vegetation underneath the trees.

That information is essential. “If we don't know what the fuels are, then it's a pretty big guess whether or not you've got dangerous fuels at a site,” says the University of Nevada, Reno’s Jonathan Greenberg.

The visualizations that come from lidar blasts are as stunning as they are useful. With this kind of data in hand, managers can more strategically deploy prescribed burns. California in particular has a serious problem with fire resources—in just the last year, the state has seen seven of its 20 most destructive fires ever. Money, then, goes to constantly fighting the infernos, leaving fewer resources for proactive measures like prescribed burns.

Another way to go about modeling fires is with reinforcement learning. You might have heard of researchers using this to get robots to learn—instead of explicitly showing a robot how to do something like putting a square peg in a square hole, you make it figure it out on its own with random movements. Essentially, you give it a digital reward when it gets closer to the correct manipulation, and a demerit when it screws up.

A model showing wind. The faster the wind, the longer and redder the arrows.

Los Alamos National Laboratory

Turns out you can do the same thing with virtual fire. “It's kind of like Pavlov's dog,” says computer scientist Mark Crowley of the University of Waterloo. “You give it a biscuit and it will do that trick again.”

Crowley begins with satellite thermal images that show how a wildfire has burned over an area. Think of this as the simulated fire’s “goal,” like a robot’s goal is to get the peg in the hole. This approach is still in its early days, and Crowley is busy helping his artificial flames learn the art of being fire. If it accurately mimics how a real fire ended up traveling, the algorithm gets a digital reward—if not, it gets a demerit. “Then over time you update this function so it learns how to travel properly,” Crowley adds. In a sense, he can create a digital fire infused with artificial intelligence.

Out in the field, researchers are using a supercomputer at UC San Diego to confront the immediate threat of wildfires, with a program called ALERTWildfire. On mountaintops across California, lookout stations are loaded with sensors like high-def cameras and wind and moisture detectors. If the camera catches a fire breaking out, the system can pipe that atmospheric data to the supercomputer, which does real-time modeling of the blaze for fire agencies.

A terrestrial laser scanner image of a forest after a fire.

UNR/USFS RSL/USFS FBAT/UMD/UE

“They can see where the fire is going, what it's going to look like in the near term and long term, and then continue to receive live updates,” says Skyler Ditchfield, co-founder and CEO of GeoLinks, a telecom that’s partnered with the project.

Why a supercomputer? “The magic word here is fast,” says Ilkay Altintas, chief data science officer at the San Diego Supercomputer Center. Wind-driven fires move quickly, and the bigger a fire gets, the more data it produces. “The computational complexity can depend on how big the fire is, how complicated the topography is, how the weather is behaving.”

As the detection network grows—85 cameras are deployed right now, but the researchers hope to expand to over 1,000 across California—so too does the torrent of data. Also, at the moment, human eyes have to watch the camera feeds to detect fires, though the idea is to get AI to do that in the future.

Tech won’t solve all our wildfire problems—we need to band together to reinforce our cities, for instance. But with ever more data and computing power, and ever better models, we can get better at confronting the wildfire menace. Fire is chaos, but it’s not impossible to understand.

Preformationism

From Wikipedia, the free encyclopedia

A tiny person inside a sperm, as drawn by Nicolaas Hartsoeker in 1695

 

Jan Swammerdam, Miraculum naturae sive uteri muliebris fabrica, 1729

In the history of biology, preformationism (or preformism) is a formerly-popular theory that organisms develop from miniature versions of themselves. Instead of assembly from parts, preformationists believed that the form of living things exist, in real terms, prior to their development. It suggests that all organisms were created at the same time, and that succeeding generations grow from homunculi, or animalcules, that have existed since the beginning of creation.

Epigenesis (or neoformism), then, in this context, is the denial of preformationism: the idea that, in some sense, the form of living things comes into existence. As opposed to "strict" preformationism, it is the notion that "each embryo or organism is gradually produced from an undifferentiated mass by a series of steps and stages during which new parts are added" (Magner 2002, p. 154). This word is still used, on the other hand, in a more modern sense, to refer to those aspects of the generation of form during ontogeny that are not strictly genetic, or, in other words, epigenetic.

Furthermore, apart from those distinctions (preformationism-epigenesis and genetic-epigenetic), the terms preformistic development, epigenetic development and somatic embryogenesis are also used in another context, in relation to the differentiation of a distinct germ cell line. In preformistic development, the germ line is present since early development. In epigenetic development, the germ line is present, but it appears late. In somatic embryogenesis, a distinct germ line is lacking. Some authors call Weismannist development (either preformistic or epigenetic) that in which there is a distinct germ line.

The historical ideas of preformationism and epigenesis, and the rivalry between them, are obviated by our contemporary understanding of the genetic code and its molecular basis together with developmental biology and epigenetics.

Philosophical development

Pythagoras is one of the earliest thinkers credited with ideas about the origin of form in the biological production of offspring. It is said that he originated "spermism", the doctrine that fathers contribute the essential characteristics of their offspring while mothers contribute only a material substrate.  Aristotle accepted and elaborated this idea, and his writings are the vector that transmitted it to later Europeans. Aristotle purported to analyse ontogeny in terms of the material, formal, efficient, and teleological causes (as they are usually named by later anglophone philosophy) – a view that, though more complex than some subsequent ones, is essentially more epigenetic than preformationist. Later, European physicians such as Galen, Realdo Colombo and Girolamo Fabrici would build upon Aristotle's theories, which were prevalent well into the 17th century.

In 1651, William Harvey published On the Generation of Animals (Exercitationes de Generatione Animalium), a seminal work on embryology that contradicted many of Aristotle's fundamental ideas on the matter. Harvey famously asserted, for example, that ex ovo omnia—all animals come from eggs. Because of this assertion in particular, Harvey is often credited with being the father of ovist preformationism. However, Harvey's ideas about the process of development were fundamentally epigenesist. As gametes (male sperm and female ova) were too small to be seen under the best magnification at the time, Harvey's account of fertilization was theoretical rather than descriptive. Although he once postulated a "spiritous substance" that exerted its effect on the female body, he later rejected it as superfluous and thus unscientific. He guessed instead that fertilization occurred through a mysterious transference by contact, or contagion.

Harvey's epigenesis, more mechanistic and less vitalist than the Aristotelian version, was, thus, more compatible with the natural philosophy of the time. Still, the idea that unorganized matter could ultimately self-organize into life challenged the mechanistic framework of Cartesianism, which had become dominant in the Scientific Revolution. Because of technological limitations, there was no available mechanical explanation for epigenesis. It was simpler and more convenient to postulate preformed miniature organisms that expanded in accordance with mechanical laws. So convincing was this explanation that some naturalists claimed to actually see miniature preformed animals (animalcules) in eggs and miniature plants in seeds. In the case of humans, the term homunculus was used.

Elaboration

After the discovery of spermatozoa in 1677 by Dutch microscopist Antonie van Leeuwenhoek, the epigenist theory proved more difficult to defend: How could complex organisms such as human beings develop from such simple organisms? Thereafter, Joseph de Aromatari and then Marcello Malpighi and Jan Swammerdam made observations using microscopes in the late 17th century, and interpreted their findings to develop the preformationist theory. For two centuries, until the development of cell theory, preformationists would oppose epigenicists, and, inside the preformationist camp, spermists (who claimed the homunculus must come from the man) to ovists, who located the homunculus in the ova.

Dutch microscopist Antonie van Leeuwenhoek was one of the first to observe spermatozoa. He described the spermatozoa of about 30 species, and thought he saw in semen "all manner of great and small vessels, so various and so numerous that I do not doubt that they be nerves, arteries and veins...And when I saw them, I felt convinced that, in no full grown body, are there any vessels which may not be found likewise in semen." (Friedman 76-7)

Leeuwenhoek discovered that the origin of semen was the testicles and was a committed preformationist and spermist. He reasoned that the movement of spermatozoa was evidence of animal life, which presumed a complex structure and, for human sperm, a soul. (Friedman 79)

In 1694, Nicolaas Hartsoeker, in his Essai de Dioptrique concerning things large and small that could be seen with optical lenses, produced an image of a tiny human form curled up inside the sperm, which he referred to in the French as petit l'infant and le petit animal. This image, depicting what historians now refer to as the homunculus, has become iconic of the theory of preformationism, and appears in almost every textbook concerning the history of embryological science.

Philosopher Nicolas Malebranche was the first to advance the hypothesis that each embryo could contain even smaller embryos ad infinitum, like a Matryoshka doll. According to Malebranche, "an infinite series of plants and animals were contained within the seed or the egg, but only naturalists with sufficient skill and experience could detect their presence." (Magner 158-9) In fact, Malebranche only alleged this, observing that if microscopes enabled us to see very little animals and plants, maybe even smaller creatures could exist. He claimed that it was not unreasonable to believe that "they are infinite trees in only one seed," as he stated that we could already see chickens in eggs, tulips in bulbs, frogs in eggs. From this, he hypothesized that "all the bodies of humans and animals," already born and yet to be born, "were perhaps produced as soon as the creation of the world."

Ova were known in some non-mammalian species, and semen was thought to spur the development of the preformed organism contained therein. The theory that located the homonculus in the egg was called ovism. But, when spermatozoa were discovered, a rival camp of spermists sprang up, claiming that the homunculus must come from the male. In fact, the term "spermatozoon," coined by Karl Ernst von Baer, means "seed animals."

With the discovery of sperm and the concept of spermism came a religious quandary. Why would so many little animals be wasted with each ejaculation of semen? Pierre Lyonet said the wastage proved that sperm could not be the seeds of life. Leibniz supported a theory called panspermism that the wasted sperm might actually be scattered (for example, by the wind) and generate life wherever they found a suitable host.

Leibniz also believed that “death is only a transformation enveloped through diminution,” meaning that not only have organisms always existed in their living form, but that they will always exist, body united to soul, even past apparent death.

In the 18th century, some animalculists thought that an animal's sperm behaved like the adult animal, and recorded such observations. Some, but not all, preformationists at this time claimed to see miniature organisms inside the sex cells. But, about this time, spermists began to use more abstract arguments to support their theories.

Jean Astruc, noting that parents of both sexes seemed to influence the characteristics of their offspring, suggested that the animalcule came from the sperm and was then shaped as it passed into the egg. Buffon and Pierre Louis Moreau also advocated theories to explain this phenomenon.

Preformationism, especially ovism, was the dominant theory of generation during the 18th century. It competed with spontaneous generation and epigenesis, but those two theories were often rejected on the grounds that inert matter could not produce life without God's intervention.

Some animals' regenerative capabilities challenged preformationism, and Abraham Trembley's studies of the hydra convinced various authorities to reject their former views.

Lazaro Spallanzani, Trembley's nephew, experimented with regeneration and semen, but failed to discern the importance of spermatozoa, dismissing them as parasitic worms and concluding instead that it was the liquid portion of semen that caused the preformed organism in the ovum to develop.

Criticisms and cell theory

Caspar Friedrich Wolff, an epigenicist, was an 18th-century exception who argued for objectivity and freedom from religious influence on scientific questions.

Despite careful observation of developing embryos, epigenesis suffered from a lack of a theoretical mechanism of generation. Wolff proposed an "essential force" as the agent of change, and Immanuel Kant with Johann Friedrich Blumenbach proposed a "developing drive" or Bildungstrieb, a concept related to self-organization.

Naturalists of the late 18th century and the 19th century embraced Wolff's philosophy, but primarily because they rejected the application of mechanistic development, as seen in the expansion of miniature organisms. It was not until the late 19th century that preformationism was discarded in the face of cell theory. Now, scientists "realized that they need not treat living organisms as machines, nor give up all hope of ever explaining the mechanisms that govern living beings." (Magner 173)

When John Dalton's atomic theory of matter superseded Descartes' philosophy of infinite divisibility at the beginning of the 19th century, preformationism was struck a further blow. There was not enough space at the bottom of the spectrum to accommodate infinitely stacked animalcules, without bumping into the constituent parts of matter. (Gee 43)

Roux and Driesch

Near the end of the 19th century, the most prominent advocates of preformationatism and epigenesis were Wilhelm Roux and Hans Driesch. Driesch's experiments on the development of the embryos of sea urchins are considered as deciding the case in favor of epigenesis.

Homunculus

From Wikipedia, the free encyclopedia

A homunculus (/hoʊˈmʌŋkjʊləs/; Latin for "little person") is a representation of a small human being. Popularized in sixteenth-century alchemy and nineteenth-century fiction, it has historically referred to the creation of a miniature, fully formed human. The concept has roots in preformationism as well as earlier folklore and alchemic traditions.

History

Alchemy

Astadi with the first mention of the homunculus in De homunculis (c. 1529–1532), and De natura rerum (1537).

The homunculus first appears by name in alchemical writings attributed to Paracelsus (1493–1541). De natura rerum (1537) outlines his method for creating homunculi:

That the sperm of a man be putrefied by itself in a sealed cucurbit for forty days with the highest degree of putrefaction in a horse's womb, or at least so long that it comes to life and moves itself, and stirs, which is easily observed. After this time, it will look somewhat like a man [sic], but transparent, without a body. If, after this, it be fed wisely with the Arcanum of human blood, and be nourished for up to forty weeks, and be kept in the even heat of the horse's womb, a living human child grows therefrom, with all its members like another child, which is born of a woman, but much smaller.

Comparisons have been made with several similar concepts in the writings of earlier alchemists. Although the actual word "homunculus" was never used, Carl Jung believed that the concept first appeared in the Visions of Zosimos, written in the third century AD. In the visions, Zosimos encounters a priest who changes into "the opposite of himself, into a mutilated anthroparion". The Greek word "anthroparion" is similar to "homunculus" – a diminutive form of "person". Zosimos subsequently encounters other anthroparion in his dream but there is no mention of the creation of artificial life. In his commentary, Jung equates the homunculus with the Philosopher's Stone, and the "inner person" in parallel with Christ.

In Islamic alchemy, Takwin (Arabic: تكوين‎) was a goal of certain Muslim alchemists, a notable one being Jābir ibn Hayyān. In the alchemical context, Takwin refers to the artificial creation of life in the laboratory, up to and including human life.

The homunculus continued to appear in alchemical writings after Paracelsus' time. The Chymical Wedding of Christian Rosenkreutz (1616) for example, concludes with the creation of a male and female form identified as Homunculi duo. The allegorical text suggests to the reader that the ultimate goal of alchemy is not chrysopoeia, but it is instead the artificial generation of humans. Here, the creation of homunculi symbolically represents spiritual regeneration and Christian soteriology.

In 1775, Count Johann Ferdinand von Kufstein, together with Abbé Geloni, an Italian cleric, are reputed to have created ten homunculi with the ability to foresee the future, which von Kufstein kept in glass containers at his Masonic lodge in Vienna. Dr. Emil Besetzny's Masonic handbook, Die Sphinx, devoted an entire chapter to the wahrsagenden Geister (scrying ghosts). These are reputed to have been seen by several people, including local dignitaries.

Folklore

References to the homunculus do not appear prior to sixteenth-century alchemical writings; however, alchemists may have been influenced by earlier folk traditions. The mandragora, known in German as Alreona, Alraun or Alraune is one example.

In Liber de imaginibus, Paracelsus however denies that roots shaped like men grow naturally. He attacks dishonest people who carve roots to look like men and sell them as Alraun. He clarifies that the homunculus’ origins are in sperm, and that it is falsely confused with these ideas from necromancy and natural philosophy.

The homunculus has also been compared to the golem of Jewish folklore. Though the specifics outlining the creation of the golem and homunculus are very different, the concepts both metaphorically relate man to the divine, in his construction of life in his own image.

Preformationism

A tiny person inside a sperm as drawn by Nicolaas Hartsoeker in 1695

Preformationism is the formerly-popular theory that animals developed from miniature versions of themselves. Sperm were believed to contain complete preformed individuals called "animalcules". Development was therefore a matter of enlarging this into a fully formed being. The term homunculus was later used in the discussion of conception and birth.

Nicolas Hartsoeker postulated the existence of animalcules in the semen of humans and other animals. This was the beginning of spermists' theory, who held the belief that the sperm was in fact a "little man" that was placed inside a woman for growth into a child. This seemed to them to neatly explain many of the mysteries of conception. It was later pointed out that if the sperm was a homunculus, identical in all but size to an adult, then the homunculus may have sperm of its own. This led to a reductio ad absurdum with a chain of homunculi "all the way down". This was not necessarily considered by spermists a fatal objection however, as it neatly explained how it was that "in Adam" all had sinned: the whole of humanity was already contained in his loins. The spermists' theory also failed to explain why children tend to resemble their mothers as well as their fathers, though some spermists believed that the growing homunculus assimilated maternal characteristics from the womb environment in which they grew.

Terminological use in modern science

The homunculus is commonly used today in scientific disciplines such as psychology as a teaching or memory tool to describe the distorted scale model of a human drawn or sculpted to reflect the relative space human body parts occupy on the somatosensory cortex (the "sensory homunculus") and the motor cortex (the "motor homunculus"). Both the motor and sensory homunculi usually appear as small men superimposed over the top of precentral or postcentral gyri for motor and sensory cortices, respectively. The homunculus is oriented with feet medial and shoulders lateral on top of both the precentral and the postcentral gyrus (for both motor and sensory). The man's head is depicted upside down in relation to the rest of the body such that the forehead is closest to the shoulders. The lips, hands, feet and sex organs have more sensory neurons than other parts of the body, so the homunculus has correspondingly large lips, hands, feet, and genitals. The motor homunculus is very similar to the sensory homunculus, but differs in several ways. Specifically, the motor homunculus has a portion for the tongue most lateral while the sensory homunculus has an area for genitalia most medial and an area for visceral organs most lateral. Well known in the field of neurology, this is also commonly called "the little man inside the brain." This scientific model is known as the cortical homunculus.
In medical science, the term homunculus is sometimes applied to certain fetus-like ovarian cystic teratomae. These will sometimes contain hair, sebaceous material and in some cases cartilagous or bony structures.

In popular culture

Early literature

19th-century engraving of Goethe's Faust and Homunculus

Homunculi can be found in centuries worth of literature. These fictions are primarily centred around imaginative speculations on the quest for artificial life associated with Paracelsian alchemy. One of the very earliest literary references occurs in Thomas Browne's Religio Medici (1643), in which the author states:

I am not of Paracelsus minde that boldly delivers a receipt to make a man without conjunction, ...

The fable of the alchemically-created homunculus may have been central in Mary Shelley's novel Frankenstein (1818). Professor Radu Florescu suggests that Johann Conrad Dippel, an alchemist born in Castle Frankenstein, might have been the inspiration for Victor Frankenstein. German playwright Johann Wolfgang von Goethe's Faust, Part Two (1832) famously features an alchemically-created homunculus. Here, the character of Homunculus embodies the quest of a pure spirit to be born into mortal form, contrasting Faust's desire to shed his mortal body to become pure spirit. The alchemical idea that the soul is not imprisoned in the body, but instead may find its brightest state as it passes through the material plane is central to the character. William Makepeace Thackeray wrote under the pen name of Homunculus.

Contemporary literature

The homunculus legend, Frankenstein and Faust have continued to influence works in the twentieth and twenty-first century. The theme has been used not only in fantasy literature, but also to illuminate social topics. For instance, the British children's writers Mary Norton and Rumer Godden used homunculus motifs in their work, expressing various post-war anxieties about refugees, persecution of minorities in war, and the adaptation of these minorities to a "big" world. W. Somerset Maugham's 1908 novel The Magician utilises the concept of the homunculus as an important plot element. David H. Keller’s short story "A Twentieth-Century Homunculus" (1930) describes the creation of homunculi on an industrial scale by a pair of misogynists. Likewise, Sven Delblanc’s The Homunculus: A Magic Tale (1965) addresses misogyny and the Cold War industrial-military complexes of the Soviet Union and NATO.

Other media

Homunculi appear in fantasy based television, film, and games in a manner consistent with literature. Examples can be found in numerous mediums, such as the films Homunculus (1916), Bride of Frankenstein (1935), The Golden Voyage of Sinbad (1973), the television movie Don't Be Afraid of the Dark (1973), Being John Malkovich (1999), Guillermo del Toro's The Devil's Backbone (2001), J.K. Rowling’s Fantastic Beasts: The Crimes of Grindelwald (2018), and the big-screen remake of Don't Be Afraid of the Dark (2011), fantasy role-playing games (such as Dungeons & Dragons), video games (such as Ragnarok Online, Valkyrie Profile, Shadow of Memories, The Legend of Heroes series, Cabals: Magic & Battle Cards), books (such as The Secret Series), graphic novels (such as Bureau for Paranormal Research and Defense) and manga (such as Homunculus, Fullmetal Alchemist, Fate/Zero, and Gosick).