Coral reefs primarily to marine invertebrates in the phylum Cnidaria (related to jellyfish and sea anemones) that form colonies of polyps. These build some of the most diverse and important ecosystems on Earth—coral reefs—often called the "rainforests of the sea."
Biology of Corals
Corals are animals, not plants or rocks. Individual units are polyps: tiny, soft-bodied organisms with a mouth surrounded by tentacles for catching plankton and defense. They live in colonies of hundreds to thousands (or more).
Hard corals (stony or scleractinian corals): These build reefs by secreting rigid skeletons of calcium carbonate (limestone/aragonite). Polyps have six-fold symmetry (6 tentacles or multiples). They form the structural backbone of reefs. Examples include brain coral, staghorn, elkhorn, and massive boulder types.
Soft corals (e.g., sea fans, sea whips, gorgonians): These lack rigid skeletons (instead using flexible protein structures like gorgonin and sclerites). They have eight-fold symmetry (eight tentacles) and sway with currents. They don't build reefs but add to reef biodiversity and habitat.
Many shallow-water hard corals have a symbiotic relationship with photosynthetic algae called zooxanthellae living in their tissues. The algae provide food (carbohydrates) and oxygen via photosynthesis; corals offer protection and nutrients. This gives corals their vibrant colors. Without it, they appear white (bleached).
Deep-sea corals often lack zooxanthellae and feed on plankton/organic matter in colder, darker waters.
Corals reproduce sexually (broadcast spawning of eggs/sperm) and asexually (budding or fragmentation). Growth is slow—millimeters to centimeters per year for colonies, with reefs building over thousands of years.
Coral Reefs: Formation and Types
Reefs are massive structures of accumulated coral skeletons, cemented by coralline algae and other organisms. Most formed after the Last Glacial Period as sea levels rose.
Main types of reef formations (per Charles Darwin's observations):
Fringing reefs: Grow directly near shorelines of islands/continents, separated by narrow lagoons. Most common type.
Barrier reefs: Parallel to shore but farther out, with deeper/wider lagoons. They can act as barriers (e.g., Great Barrier Reef).
Atolls: Ring-shaped reefs surrounding lagoons, often forming after volcanic islands subside completely.
Patch reefs: Smaller, isolated patches.
Reefs thrive in warm (20–28°C), clear, shallow tropical waters with sunlight for photosynthesis, though some exist in deeper/colder areas.
Distribution and Importance
Coral reefs cover ~0.1% of the ocean but support ~25% of marine species, including fish, invertebrates, turtles, and sharks. They provide:
Coastal protection from storms/waves.
Food and livelihoods for millions.
Tourism revenue.
Biodiversity hotspots and potential sources for medicines.
The Great Barrier Reef off Australia is the largest: ~2,300 km long, visible from space, with thousands of reefs, ~600 coral species, 1,500+ fish species, and more. It's a UNESCO World Heritage Site.
Threats and Coral Bleaching
Coral reefs face severe pressures:
Climate change: Warming oceans cause bleaching—corals expel zooxanthellae under stress (e.g., +1–2°C for weeks). Bleached corals starve or die if conditions don't improve. Mass events are more frequent/intense.
Local threats: Pollution, overfishing, destructive fishing, sedimentation, disease, and physical damage.
Many reefs have lost significant coral cover; recovery is possible but harder with repeated stresses.
Conservation and Restoration
Efforts include marine protected areas, reducing emissions, local pollution controls, reef restoration (e.g., coral gardening, breeding heat-resistant strains), and research into resilience. Organizations like NOAA, Coral Reef Alliance, and others monitor and protect reefs.
Other Meanings of "Coral"
Gemstone/jewelry: Precious coral (e.g., red/pink from Corallium species) is harvested for jewelry. It's organic (calcareous) and valued for color, though overharvesting raises sustainability concerns.
Color: A pinkish-orange hue.
Fossils: Ancient corals provide paleoclimate data.
Corals are remarkable engineers of underwater worlds, but they are highly vulnerable to human impacts. Protecting them requires global action on climate and local stewardship. For deeper dives, check resources from NOAA, IUCN, or the Coral Reef Alliance.
The diet of known human ancestors varies dramatically over time. Strictly speaking, according to evolutionary anthropologists and archaeologists, there is not a single hominin Paleolithic diet. The Paleolithic covers roughly 2.8 million years, concurrent with the Pleistocene,
and includes multiple human ancestors with their own evolutionary and
technological adaptations living in a wide variety of environments. This
fact with the difficulty of finding conclusive evidence often makes
broad generalizations of the earlier human diets very difficult. Humans'
pre-hominin primate ancestors were broadly herbivorous,
relying on either foliage or fruits and nuts and the shift in dietary
breadth during the Paleolithic is often considered a critical point in
hominin evolution. A generalization between Paleolithic diets of the
various human ancestors that many anthropologists do make is that they
are all to one degree or another omnivorous and are inextricably linked with tool use and new technologies.
Due to the variety of environments inhabited, physiologies
of the humans and human ancestors alive during the Paleolithic over 2.8
million years, we can’t ascribe a single set diet to any species,
regional or cultural group. Larger brain sizes required a greater caloric intake. In colder climates meat might be necessary due to the decreased
availability of plant based foods, and in hotter tropical climates a
wider range of plants would be available.
Recent estimates of the last common ancestors of humans and chimpanzees are around 12 million years ago. After this split the first bipedal hominins appeared around 4 million years ago in the genus Australopithecus. The first appearance of genus Homo takes place around 2.8 million years ago with Homo habilis, followed by Homo erectus at around 1.8 million years ago, Homo neanderthalensis by 400,000 years ago and finally the first appearance of Homo sapiens by 200,000 years ago. In each new species of hominin, particularly genus Homo
there is a general trend of increasing brain size and decreasing
dentition, these patterns are inextricably linked with an evolving diet.
Lines of evidence to uncover the diet of human ancestors
There are numerous difficulties in detecting and understanding the
ancient diet of human ancestors. The Paleolithic begins around 2.6
million years ago and ends only around 12,000 years ago with the onset
of the Holocene and Neolithic.
The enormous time scale, variable environments inhabited by human
ancestors and issues with preservation ensure that direct evidence is
often very difficult to come by.
Evolutionary anthropologists who study the evolution of human
origins and diet use a variety of methods to determine what human
ancestors ate. As a starting point comparative analysis of the diets of
humans closest living relatives, great apes such as chimpanzees, bonobos and other great apes,
though these comparison are limited. Through environmental
reconstruction of the areas ancient humans lived, inferences of
available resources can be made. A common method of analysis is through
the study of dentition and toothwear, as different foods will leave different markers that can be studied. There is also direct archaeological evidence, different types of tools
would be used to process and consume different types of food and often
be associated with faunal remains and evidence of fire. Human coprolites can also reflect direct evidence of diet.
More recent techniques have been introduced such as carbon isotopic analysis
of recovered bones, which can be used as direct evidence of diet, and
life history traits. An example would be the expensive tissue
hypothesis, linking a decrease in gut size with an increase in brain
size. Recently genetic studies of differences between Homo sapiens and other related hominins to determine adaptations related to diet.
Hominin diet before the Paleolithic
Generally speaking, inferring feeding adaptations in fossil hominins
is not a simple task, and hence diet reconstructions have relied on
diverse techniques (e.g. microwear, stable isotopes, functional
morphology, etc.) that have provided different or even contradictory
results. The direct predecessors to genus Homo, Australopithecus are thought to have broadly been frugivores or herbivores. The dental and jaw morphology of Australopithecus afarensis
have often been assumed to indicate a diet of harder brittle foods,
however tooth wear analysis from some specimen reflect a diet of tough
grasses and leaves. This is corroborated by stable carbon isotopic
evidence indicating the consumption of plants found along riversides and
under tree cover. A recent study that analysed several hominin taxa has shown that they
were probably not hard-food specialists, most likely relying on a softer
diet.
Homo naledi, Homo habilis, Homo floresiensis and Homo erectus
Homo naledi
Almost half of H. naledi teeth have one or more chips on the
enamel surface, caused by teeth coming into contact with hard foods or
environmental grit during life. These antemortem enamel fractures
are predominantly small and on the surfaces between molars, suggesting
either a small hard dietary item was commonly consumed, or, more likely,
environmental grit was incorporated into their diet when eating foods
such as tubers. Two other studies support the suggestion that H. naledi
consumed large quantities of small hard objects, most likely in the
form of dust or grit. Crown shape supports this finding, with taller
crowned and more wear resistant molars, potentially evolving to protect
against abrasive particles. Microwear on the molars of H. naledi also suggests they regularly consumed hard and abrasive items. Overall, it is likely H. naledi differed substantial from other African fossil hominins in terms of diet, behaviour, or masticatory processing.
Homo habilis
By 3 million years ago the broad pattern of human dentition was in
place with reduced canines and a jaw morphology implying heavier
chewing. Stone tools and butchered animal remains dating to 2.6 million years ago have been found together in Ethiopia.
This finding provides both the clearest evidence of meat eating by
early human ancestors and the association of earliest stone tools with
the butchering of animals for meat and marrow. This co-occurrence of stone tools is clearly linked with the butchering of animals and earliest identifiable appearances of Homo habilis. Tooth wear from Homo habilis
indicates a relative lack of hard foods such as nuts, tubers or other
hard brittle plant material being consumed. This is not to say that no
tougher foods were eaten by H. habilis, only that it was likely not a regular part of the diet. By contrast, Homo erectus teeth generally reflect a much higher degree of wear, indicating tougher plant foods being eaten. While likely able to consume a variety of plant and animal resources, it seems that H. habilis was not able to exploit the wide array of resources and ecological niches its descendants would be able to.
Homo erectus
In contrast to Homo habilis, H. erectus left its ancestral environment of Africa and spread through much of the old world. Homo erectus appears to have avoided other large predators. Several interpretations of Homo erectus
diet have been made, usually contrasting between primarily plant based
foragers and scavengers or opportunistic hunters. However, as H. erectus dispersed across Eurasia some behaviors in some areas appear to have changed. The trajectory of diets between Homo habilis and Homo erectus can be described as a diversification of diet as Homo erectus spread within Africa and beyond into Asia. Meat played a critical role in the evolution of H. habilis, but as Homo erectus evolved the diet broadened to include tougher foods that H. habilis did not consume regularly.A broad diet alone however is not Homo erectus'
sole contribution to evolution of the human lineage. Genetic evidence
of reduced jaw muscles implies the adoption of cooking by humans prior
to the branching of H. sapiens and H. neanderthalensis, placing the first use of fire for cooking firmly during the time of Homo erectus.
Fire presents clear advantages to a species diet, in that cooking
allows a greater range of foods to be eaten and improves the caloric
content of both animal protein and plants. Another hypothesis is that H. erectus used tools to slice up their food even before they started to cook it, making it easier to chew.
Homo floresiensis
Homo floresiensis is thought to have diverged from humanity's ancestral branch prior to the evolution of Homo erectus. The direct ancestor of Homo floresiensis is currently thought to be Homo habilis, but this is subject to change with new information. Tooth wear from Homo floresiensis implies a tough, fibrous diet requiring powerful mastication. There is some evidence of meat eating associated with Homo floresiensis, but current evidence indicated that a plant based diet dominated. The specific plant species available to H. floresiensis is currently unknown. This complicates H. floresiensis relationship to H habilis, due to the latter’s association with intensive meat eating diet. That being the case, more than enough time passed for H. floresiensis diet to specialize to its given environment.
Homo heidelbergensis and Homo neanderthalensis
Homo heidelbergensis
Homo heidelbergensis, the likely predecessor of Homo neanderthalensis, has few direct clues to its diet. Two adult incisors, likely from H. heidelbergensis have been found in England
in an environment that at death would have been a spring fed wetland.
The teeth themselves are heavily worn, implying heavy wear in the
individual’s diet. Wooden spears dating to between 380,000 and 400,000 years BP were found in Germany, indicating that H. heidelbergensis was a big game hunter with sophisticated technology.
Homo neanderthalensis
Neanderthals were almost certainly effective hunters. Multiple sites associated with H. neanderthalensis
also have the remains of butchered animals. More direct stable isotope
evidence from Neanderthal bodies also indicates a heavy, though by no
means exclusive reliance on animal protein.The degree to which Neanderthals rely on meat in their diet is
extensively debated with contradictory evidence found often at very
similar sites. Worn teeth from Neanderthal remains at a variety of sites
imply use of plant and other abrasive foods, while other researchers find that Neanderthal tooth wear in general indicates a varied diet of both plants and meat. There is clear evidence of the consumption and processing of ancestors
of wheat and barley by Neanderthals from starch analysis of dental
calculus, while in Belgium, a species related to Sorghum was consumed along with other unknown plants. At the site of Shanidar in Iraq, in addition to the ancestors of wheat and barley, Homo neanderthalensis
is known to have consumed dates, legumes and a variety of other unknown
plant species. In addition, evidence exists from the same teeth of
Neanderthals to support the increased use of fire in their diet in
addition to the wide variety of plant and animals in their diet. Evidence from Neanderthal coprolites from a Middle Paleolithic site in Spain
support a diet of animal protein and plants at that site, though there
is a lack of indicators for the consumption of starchy tubers. Neanderthals at El Sidron cave
in Spain appear to have a more limited diet of meat when compared to
other Neanderthal groups. In February 2019, scientists reported
evidence, based on isotope studies, that at least some Neanderthals may have eaten meat. Nonetheless, instead of diet dominated by meat eating, the genetic and
microbiological evidence from dental calculus implies reliance on mushrooms, pine nuts and a species of moss.
The implications of this array of evidence is important due to the
evidence that the “broad spectrum” of plant use is not unique to Homo sapiens. Homo neanderthalensis had, for all intents and purposes, a complex diet similar to many hunter-gather groups of Homo sapiens. The critical factor in this diet was that it varies significantly based on the local environment.
Homo sapiens
The evidence of early Homo sapiens diet stems from multiple
lines of evidence, and there is a relative abundance of information due
to both a larger relative population footprint and more recent evidence.
A key contribution to early human diet likely was the introduction of
fire to hominins toolkit. Some studies indicate a correlation with the
introduction of fire and the reduction of tooth and gut size, going so
far as to indicate their reduction as clear evolutionary indicators of
the widespread introduction of fire.
A key difference between the diets of Homo sapiens and our closest extinct relatives H. neanderthalensis is the ability to effectively digest cooked starches, with some evidence found linking cooked starch and a further increase in H. sapiens brain size. Roots and tubers were introduced into the broader human diet, and can
likely be assumed to be associated with fire as cooking would likely be
necessary for many tubers to be digested. The use of root and tuber species in some Hunter Gatherer cultures
makes up a critical component of diet. This is not only for the
nutritional value of the species, but the relative annual stability of
the species. This buffer effect would be important for many groups that
relied on tubers. In addition to the exploitation of tubers, another dietary innovation (this far) of Homo sapiens is the introduction of coastal and other marine resources. Some researchers have argued that the introduction of shellfish and other marine species play a significant role in the evolution of modern Homo sapiens.
By the Upper Paleolithic,
more complex tools and a higher proportion of meat in the human diet
are assumed to correlate with an expansion of population in Europe. Though the diet of modern humans is not consistent through the Upper Paleolithic, from the Middle to Late Pleistocene
there is a general shift in many areas towards a less abrasive diet.
This is accompanied by changing technologies that would aid in the
processing of abrasive plant species. Ethnographic comparisons with contemporary groups of Hunter Gatherers
broadly imply a high reliance on animal protein supplemented with a
wide range of available plant foods. While a reliance on animal protein
is often seen as typical, it is by no means universal.
By the time of the Upper Paleolithic and modern Homo sapiens,
not only was a wide variety of plants consumed, but a wide variety of
animals, snails and fish. In order to exploit the many different species
consumed, there was a wider variety of tools made than ever before
available to humans. The shift to a higher quality diet and the technology to process a wide
array of foods is reflected in modern humans by both the relatively
larger brain size and reduction in gut size. The trend of larger brain size, the eating of animal protein, fire use
and diversification of exploited foods is key to understanding the
changing diets of human ancestors.
Archaeologist James Cole investigated the nutritional value of the
human body and found it to be similar to that of animals of similar
size. He notes that, according to ethnographic and archaeological records,
nearly all edible parts of humans were sometimes eaten – not only skeletal muscle tissue ("flesh" or "meat" in a narrow sense), but also "lungs, liver, brain, heart, nervous tissue, bone marrow, genitalia and skin", as well as kidneys. For a typical adult man, the combined nutritional value of all these edible parts is about 126,000 kilocalories (kcal). The nutritional value of women and younger individuals is lower because
of their lower body weight – for example, around 86% of a male adult
for an adult woman and 30% for a boy aged around 5 or 6.
As the daily energy need of an adult man is about 2,400
kilocalories, a dead male body could thus have fed a group of 25 men for
a bit more than two days, provided they ate nothing but the human flesh
alone – longer if it was part of a mixed diet. The nutritional value of the human body is thus not insubstantial, though Cole notes that for prehistoric hunters, large megafauna such as mammoths, rhinoceros, and bison
would have been an even better deal as long as they were available and
could be caught, because of their much higher body weight.
Archeological and historical evidence
Debates over the frequency of cannibalism
in ancient humanity have been sporadic, usually erupting on the
discovery of humans with cut and break marks reflective of being
processed as food. Many theories of cannibalism amongst humans rely on a
lack of available prey, crowding and fears of potential starvation.
There are clear biological drawbacks of cannibalism including disease,
and in addition instances of ritual cannibalism that have nothing to do
with nutrition drawn from the ethnographic record.
The oldest firm evidence of Homo eating other hominins comes from cut marks on bones uncovered in Turkana, Kenya
from 1.45 million years ago, and is a plausible early case of
cannibalism. However, at this time and place multiple species of
hominins coexisted, so it is not certain that this specific incident was
undertaken by the same species. Cannibalism by Homo antecessor has also been uncovered, and it has been suggested to possibly have been a strategy employed against rival groups, though H. antecessor is a relative rather than an ancestor of Neanderthals and modern humans.
Evidence of cannibalism in the Pleistocene has also been firmly tied to both Homo sapiens and Homo neanderthalensis.
Extensive evidence from Human bones that have been "de-fleshed" by
other humans dates back over 600,000 years, including the first H. sapiens bones from Ethiopia. For instance in humans, the Magdalenian culture practiced the consumption of deceased relatives as a ritual funerary practice, and also appear to have used skull cups. Similarly, conclusive evidence amongst Neanderthals from remains in Belgium features cracked bones, cut marks and other indicators of processing for food. Some bones were then modified into bone tools. Notably, reindeer
remains from the same site have the same types of butcher marks. The
degree to which these remains reflect a ritual behavior, regular diet or
isolated instances of dietary distress is not known.
Cannibalism continued after the end of the Paleolithic, as shown by hunter-gatherers of the Mediterranean Mesolithic from 10,200–9,000 years ago, who would have still had a relatively similar lifestyle. Bones uncovered in Castell de Castells, Spain
show marks of human teeth gnawing on them. Nineteen of these bones also
show burns from cooking, apparently after the meat was removed, but
prior to the bones being broken down. Furthermore, human feces uncovered
inside the cave contained fragments of human bones.
Neolithic adaptations
The evolution of the human diet has not stopped since the end of the
Paleolithic. Major functional adaptations have arisen in the last few
thousand years as human technology has altered the environment. The most
prevalent dietary adaptation since the Neolithic is lactase persistence,
an adaptation that allows humans to digest milk. This adaptation
appears roughly 4000 years ago in Europe. For populations more dependent
on agriculture and domesticated animals, the importance of being able
to add another edible resource should be noted.[47]
General trends
Many specifics of the evolution of the human diet change regularly as
new research and lines of evidence become available. Through the
Paleolithic across the last 2.8 million years there has been a pattern
of human and human ancestors' biology adapting to an additionally
available food source with resulting greater brain size, with the
subsequent broadening and diversification of human diet. Homo habilis incorporated larger amounts of animal protein and fat into its diet, then as Homo erectus evolved it increased the breadth of its diet through fire and more advanced tool use. Homo sapiens
in turn evolved the ability to consume cooked starch and marine life,
which led to a further increase in brain size then greater technological
diversification that ultimately allowed modern humans to adapt to a
wide variety of ecological niches. The initial technological and
biological adaptations each have knock on effects that allow a greater
range of species to be used as food. This culminates in the Neolithic
when suites of plants and animals are ultimately domesticated.
This article is about a modern-day diet. For information on the dietary practices of Paleolithic humans, see Paleolithic § Diet and nutrition.
A meal compatible with the Paleolithic diet
The Paleolithic diet, Paleo diet, caveman diet, or Stone Age diet is a modern fad diet consisting of foods thought by its proponents to mirror those eaten by humans during the Paleolithic era.
The diet avoids food processing and typically includes vegetables, fruits, nuts, roots, and meat and excludes dairy products, grains, sugar, legumes, processed oils, salt, alcohol, and coffee. Historians can trace the ideas behind the diet to "primitive" diets advocated in the 19th century. In the 1970s, Walter L. Voegtlin popularized a meat-centric "Stone Age" diet; in the 21st century, the best-selling books of Loren Cordain popularized the "Paleo diet". As of 2019 the Paleolithic diet industry was worth approximately US$500 million.
In the 21st century, the sequencing of the human genome and DNA analysis of the remains of anatomically modern humans have found evidence that humans evolved
rapidly in response to changing diet. This evidence undermines a core
premise of the Paleolithic diet—that human digestion has remained
essentially unchanged over time. Paleoanthropological evidence
has indicated that prehistoric humans ate plant-heavy diets that
regularly included grains and other starchy vegetables, in contrast to
the claims made by proponents of the Paleolithic diet.
Advocates promote the Paleolithic diet as a way of improving health. There is some evidence that following it may lead to improvements in body composition and metabolism compared with the typical Western diet or compared with diets recommended by some European nutritional guidelines. On the other hand, following the diet can lead to nutritional deficiencies, such as an inadequate calcium intake, and side effects can include weakness, diarrhea, and headaches.
History and terminology
Adrienne Rose Johnson writes that the idea that the primitive diet
was superior to current dietary habits dates back to the 1890s with such
writers as Emmet Densmore and John Harvey Kellogg, the founder of the eponymous breakfast cereal company. Densmore proclaimed that "bread
is the staff of death", while Kellogg supported a diet of starchy and
grain-based foods in accord with "the ways and likings of our primitive
ancestors". Arnold DeVries advocated an early version of the Paleolithic diet in his 1952 book, Primitive Man and His Food. In 1958, Richard Mackarness authored Eat Fat and Grow Slim, which proposed a low-carbohydrate "Stone Age" diet.
In his 1975 book The Stone Age Diet, gastroenterologist Walter L. Voegtlin
advocated a meat-based diet, with low proportions of vegetables and
starchy foods, based on his declaration that humans were "exclusively
flesh-eaters" until 10,000 years ago.
In 1985 Stanley Boyd Eaton and Melvin Konner published a controversial article in the New England Journal of Medicine
proposing that modern humans were biologically very similar to their
primitive ancestors and so "genetically programmed" to consume
pre-agricultural foods. Eaton and Konner proposed a "discordance
hypothesis" by which the mismatch between modern diet and human biology
gave rise to lifestyle diseases, such as obesity and diabetes.
The diet started to become popular in the 21st century, where it
attracted a largely internet-based following using web sites, forums and
social media.
This diet's ideas were further popularized by Loren Cordain,
a health scientist with a Ph.D. in physical education, who trademarked
the words "The Paleo Diet" and who wrote a 2002 book of that title.
In 2012 the Paleolithic diet was described as being one of the
"latest trends" in diets, based on the popularity of diet books about
it; in 2013 and 2014 the Paleolithic diet was Google's most searched weight-loss method.
The Paleolithic or Paleo diet is also sometimes referred to as the caveman or Stone Age diet.
Foodstuffs
Roast beef. Some recent paleo diet variants emphasize the consumption of unprocessed animal products.
The basis of the diet is a re-imagining of what Paleolithic people
ate, and different proponents recommend different diet compositions.
Eaton and Konner, for example, wrote a 1988 book The Paleolithic Prescription with Marjorie Shostak,
and it described a diet that is 65% plant based. This is not typical of
more recently devised paleo diets; Loren Cordain's – probably the most
popular – instead emphasizes animal products and avoidance of processed food. Diet advocates concede the modern Paleolithic diet cannot be a faithful
recreation of what Paleolithic people ate, and instead aim to
"translate" that into a modern context, avoiding such likely historical
practices as cannibalism.
Foodstuffs that have been described as permissible include:
"vegetables, fruits, nuts, roots, meat, and organ meats";
"vegetables (including root vegetables), fruit (including fruit oils, e.g., olive oil, coconut oil, and palm oil),
nuts, fish, meat, and eggs, and it excluded dairy, grain-based foods,
legumes, extra sugar, and nutritional products of industry (including
refined fats and refined carbohydrates)"; and
"avoids processed foods, and emphasizes eating vegetables, fruits, nuts and seeds, eggs, and lean meats".
The diet forbids the consumption of all dairy products. This is because milking did not exist until animals were domesticated after the Paleolithic era.
Adopting the Paleolithic diet assumes that modern humans can reproduce the hunter-gatherer diet. Molecular biologist Marion Nestle
argues that "knowledge of the relative proportions of animal and plant
foods in the diets of early humans is circumstantial, incomplete, and
debatable and that there are insufficient data to identify the
composition of a genetically determined optimal diet. The evidence
related to Paleolithic diets is best interpreted as supporting the idea
that diets based largely on plant foods promote health and longevity, at
least under conditions of food abundance and physical activity." Ideas about Paleolithic diet and nutrition are at best hypothetical.
The data for Cordain's book came from six contemporary
hunter-gatherer groups, mainly living in marginal habitats. One of the
studies was on the !Kung, whose diet was recorded for a single month, and one was on the diet of the Inuit. Due to these limitations, the book has been criticized as painting an incomplete picture of the diets of Paleolithic humans. It has been noted that the rationale for the diet does not adequately account for the fact that, due to the pressures of artificial selection,
most modern domesticated plants and animals differ drastically from
their Paleolithic ancestors; likewise, their nutritional profiles are
very different from their ancient counterparts. For example, wild almonds produce potentially fatal levels of cyanide, but this trait has been bred out of domesticated varieties using artificial selection. Many vegetables, such as broccoli, did not exist in the Paleolithic period; broccoli, cabbage, cauliflower, and kale are modern cultivars of the ancient species Brassica oleracea.
Trying to devise an ideal diet by studying contemporary
hunter-gatherers is difficult because of the great disparities that
exist; for example, the animal-derived calorie percentage ranges from
25% for the Gwi people of southern Africa to 99% for the Alaskan Nunamiut.
Descendants of populations with different diets have different genetic
adaptations to those diets, such as the ability to digest sugars from
starchy foods. Modern hunter-gatherers tend to exercise considerably
more than modern office workers, protecting them from heart disease and
diabetes, though highly processed modern foods also contribute to
diabetes when those populations move into cities.
A 2018 review of the diet of hunter-gatherer populations found
that the dietary provisions of the Paleolithic diet had been based on
questionable research, and were "difficult to reconcile with more
detailed ethnographic and nutritional studies of hunter-gatherer diet".
Researchers have proposed that cooked starches met the energy
demands of an increasing brain size, based on variations in the copy
number of genes encoding amylase.
Health effects
The methodological quality of research into the Paleolithic diet has been described as "poor to moderate". Some of the paleo diet's proponents have made exaggerated health claims, such as the claim that the diet can reverse diabetes and cure autoimmune diseases, miring the diet in controversy.
Following the Paleolithic diet results in the consumption of
fewer processed foods, less sugar, and less salt. Reduced consumption of
such is consistent with mainstream advice about diet. Diets reflecting a Paleolithic pattern of nutrition also share some similarities with traditional ethnic diets, such as the Mediterranean diet, which has been found to result in more health benefits than the Western diet. Following the paleolithic diet can lead to nutritional deficiencies, such as those of vitaminD and calcium, which can in turn lead to compromised bone health. The increased fish consumption suggested by the diet can also lead to an elevated risk of exposure to toxins.
There is some evidence that the diet can help in achieving weight loss, due to the increased satiety from the foods typically eaten. One trial of obese
postmenopausal women found improvements in weight and fat loss after
six months, but the benefits had ceased by 24 months. Side effects among
these participants included "weakness, diarrhea, and headaches". As
with any other diet regime, the Paleolithic diet leads to weight loss
because of overall decreased caloric intake, rather than any specific feature of the diet itself.
The Paleolithic diet is similar to the Atkins diet, in that it encourages the consumption of large amounts of red meat, especially meats high in saturated fat. Increased consumption of red meat can lead to a higher incidence of cardiovascular disease.
Proposed rationale and reception
Melvin Konner, co-author of a 1985 paper setting out a hypothetical basis for the Paleolithic diet
The stated rationale for the Paleolithic diet is that human genes
today are not different from human genes of 10,000 years ago, and that
the diet of that time is therefore the best fit with humans today. Loren Cordain has described the paleo diet as "the one and only diet that ideally fits our genetic makeup".
The argument is that modern humans have not been able to biologically adapt to contemporary circumstances. According to Cordain, before the agricultural revolution,
hunter-gatherer diets rarely included grains, and obtaining milk from
wild animals would have been "nearly impossible". Advocates of the diet argue that the increase in diseases of affluence
after the dawn of agriculture was caused by these changes in diet.
Others, however, have countered that it may be that pre-agricultural
hunter-gatherers did not suffer from the diseases of affluence because
they did not live long enough to develop them.
According to the model from the evolutionary discordance hypothesis, "many chronic diseases and degenerative conditions evident in modern Western populations have arisen because of a mismatch between Stone Age genes and modern lifestyles." Advocates of the modern paleo diet have formed their dietary
recommendations based on this hypothesis. They argue that modern humans
should follow a diet that is nutritionally closer to that of their
Paleolithic ancestors.
The evolutionary discordance is incomplete, since it is based
mainly on the genetic understanding of the human diet and a unique model
of human ancestral diets, without taking into account the flexibility
and variability of the human dietary behaviors over time. Studies of a variety of populations around the world show that humans
can live healthily with a wide variety of diets and that humans have
evolved to be flexible eaters. Lactase persistence, which confers lactose tolerance
into adulthood, is an example of how some humans have adapted to the
introduction of dairy into their diet. While the introduction of grains,
dairy, and legumes during the Neolithic Revolution
may have had some adverse effects on modern humans, if humans had not
been nutritionally adaptable, these technological developments would
have been dropped.
Since the publication of Eaton and Konner's paper in 1985, analysis of the DNA
of primitive human remains has provided evidence that evolving humans
were continually adapting to new diets, thus challenging the hypothesis
underlying the Paleolithic diet. Evolutionary biologist Marlene Zuk
writes that the idea that our genetic makeup today matches that of our
ancestors is misconceived, and that in debate Cordain was "taken aback"
when told that 10,000 years was "plenty of time" for an evolutionary
change in human digestive abilities to have taken place. On this basis
Zuk dismisses Cordain's claim that the paleo diet is "the one and only
diet that fits our genetic makeup".
Paleoanthropologist Peter Ungar
has written that the paleo diet is a "myth", on account both of its
invocation of a single suitable diet when in reality humans have always
been a "work in progress", and because diet has always been varied
because humans were spread widely over the planet.
Anthropological geneticist Anne C. Stone
has said that humans have adapted in the last 10,000 years in response
to radical changes in diet. In 2016, she was quoted as saying "It drives
me crazy when Paleo-diet people say that we've stopped evolving—we
haven't."
Melvin Konner has said the challenge to the hypothesis is not
greatly significant since the real challenges to human non-adaptation
have occurred with the rise of ever-more refined foodstuffs in the last
300 years.
Environmental impact
A 2019 analysis of diets in the United States ranked consumption of a
Paleolithic diet as more environmentally harmful than consumption of an
omnivorous diet, though not so harmful as a ketogenic diet.
Elizabeth Kolbert
has written the Paleolithic diet's emphasis on meat consumption is a
"disaster" on account of meat's comparatively high energy production
costs.
Popularity
A lifestyle and ideology have developed around the diet. "Paleolithic" products include clothing, smartphone apps, and cookware. Many Paleolithic cookery books have been bestsellers.
As of 2019 the market for products with the word "Paleo" in their
name was worth approximately $US500 million, with strong growth
prospects despite pushback from the scientific community. Some products
were taking advantage of the trend by touting themselves as
"paleo-approved" despite having no apparent link to the movement's
tenets.
Like many other diets, some proponents promote the Paleolithic diet by an appeal to nature and a narrative of conspiracy theories
about how nutritional research, which does not support the supposed
benefits of the paleolithic diet, is controlled by a malign food industry. Paleolithic diet advocate John Durant has blamed suppression of the
truth about diet in the United States on "the vegetarian lobby".
