“The human genetic constitution has changed relatively little since the appearance of truly modern human beings, Homo sapiens sapiens, about 40,000 years ago,” S. Boyd Eaton and Melvin Konner wrote.
The authors reasoned that human bodies have been shaped more by our prolonged time as hunter-gatherers than by the brief span since the advent of farming. Meat, probably lots of it, as well as fruits and vegetables were in. The staples of agriculture -- breads, cereals, milks and cheeses -- were not.
Three decades later, that academic ripple is now a popular tidal wave. We have not just Paleo diets -- the subject of multiple bestsellers -- but Paleo exercise, Paleo sleeping and Paleo toilets. They’re all based on the premise that our bodies are more suited for Paleo-era habits.
But even as the “caveman” diet rose to become the most Googled diet in 2013 and 2014, evolutionary biologists, with much less advertisement, were using advanced DNA techniques, sometimes on ancient bones, to suggest that the original Paleo premise may be off the mark: In fact, it seems, we have evolved.
Over the last year alone, prominent scientific journals have published evidence of genetic shifts in humans over the last 10,000 years -- apparently in response humankind’s transition to agriculture.
Two relatively recent gene variants help humans survive with deficiencies characteristic of agricultural diets; another genetic shift appears to help fight the dental cavities that arose with farm-based staples; another changes the way humans digest fats; dozens of others help fight the diseases that came with living at higher densities.
Those new findings add to previously known adaptations to mankind's changing diet. After the domestication of milking animals, many humans evolved to digest milk. Humans also appear to have developed better ways to digest the starches characteristic of agricultural diets.
“It drives me crazy when Paleo diet people say that we’ve stopped evolving -- we haven’t,” said Anne C. Stone, a professor of human evolution at Arizona State University who has shown that genes related to starch digestion appear to have changed in number, apparently in response to farming. “Our diets have changed radically in the last 10,000 years, and, in response, we have changed, too.”
While all this new evidence challenges the Paleo diet argument, it doesn’t necessarily disprove it. And Eaton and Konner, for their part, maintain that their central hypothesis -- that there is a mismatch between our bodies and our diets -- remains sound.
Yes, Konner acknowledged in an interview, there is more research that humans have evolved recently.
“There’s evidence that there’s been a lot more selection and genetic change in the last five to 10,000 years than previously thought,” he said. “This is a challenge to the Paleo diet claims -- including mine and Boyd Eaton’s over the years.”
“But,” he said, “I don’t think it’s much of one.”
For one thing, he and Eaton say, the newly discovered genetic differences between Paleo hunter-gatherers and modern humans are not very numerous. While there may be some ways in which humans have adapted to agricultural diets, those are far outnumbered by the ways in which human bodies are suited for the Paleo era.
“There are -- no question -- genetic differences” between Paleo people and us, Eaton said. “But our metabolism is controlled by hundreds of genes and maybe more than that. So while there are differences, they do not affect our nutritional needs in a significant way.”
Moreover, Konner said, even if one concedes that there has been significant genetic change over the last 10,000 years, those changes would only catch us up to human diets from 10,000 years ago. But our diets have changed radically over the last 300 years alone -- we consume less fiber, more refined grains, etc. -- and evolutionary forces can’t have altered our bodies so quickly over that time.
“The bulk of the chronic degenerative disease in our population is due to dietary changes in the last few centuries; they’re not necessarily related to the shift from hunter-gatherers to agriculture,” Konner said. “The biggest culprit with the current epidemic of diabetes, a looming problem worldwide, is refined carbohydrates. There’s no way humans could have adapted to that because they haven’t been around long enough.”
Moreover, the idea that we may be better suited for a Paleo diet has been validated in part by recent shifts in the government's Dietary Guidelines for Americans. For example, the hunter-gatherer diets touted by Eaton and Konner included large amounts of cholesterol; with the 2015 Dietary Guidelines, the government dropped its sternest warning and numerical limit for cholesterol intake.
The outcome of the debate over their idea, however, rests for now on the ongoing research, which has accelerated markedly in recent years.
When Eaton and Konner wrote in the '80s, the human genome had not been fully sequenced, and it was far more difficult to detect evidence of recent human evolution.
Take, for example, the discovery that humans got the ability to digest milk -- lactose tolerance -- as they began to domesticate milking animals.
First, scientists had to discover that lactose tolerance is an inherited trait. This came about after scientists noticed similarities within families. Once that was established, scientists were forced to look for clues from geography and anthropology. What they found is that in populations where cattle had been long domesticated, most people could easily digest milk; in populations without domesticated milking animals, most could not.
“This trait seems to be common or extremely common only in populations which have established the custom of having milk regularly in their diet after weaning,” Stanford geneticist Luigi Luca Cavalli-Sforza wrote in 1972. “It is rare or absent in others.”
Eaton and Konner acknowledged this dietary adaptation in their 1985 paper but said that “very few other examples are known.”
Since then, however, the pace of evolution research accelerated rapidly, especially with the ability to sequence the entire human genome. It allowed researchers, for example, to compare the DNA of populations with different diets -- new and old -- and look for signs of adaptation.
Stone and her colleagues, for example, were interested in the varying abilities of people to digest diets loaded with starch. After the transition to agriculture, which brought steady supplies of wheat, corn, rice, barley and other crops, the ability to digest starches likely became more useful. Did human bodies adapt?
To answer that question, the researchers compared the DNA from peoples with high-starch diets and contrasted it with remote peoples who had low-starch diets.
The high-starch groups included European Americans, Japanese and the Hadza, hunter-gatherers who rely on starch-rich roots. The low-starch groups were African pygmies, some African cattle farmers and a Russian ethnic group known as the Yakut.
As the DNA analysis showed, individuals from the high-starch groups were roughly twice as likely to have inherited many extra copies of the AMY1 gene. People with more copies of the AMY1 gene tend to have more of an enzyme known as amylase in their saliva, which allows them to better digest starch.
This benefit, Stone said, may have been particularly critical for the survival of children.
"In populations where starch was a major component of the diet, being able to extract as many calories as possible as quickly as possible likely was a lifesaver for kids who suffered from bouts of intestinal illness," she said.
More recently, another advance gave scientists a direct way of comparing contemporary humans to our Paleolithic ancestors. They were able recover DNA from ancient bones.
In November 2013, for example, researchers announced that they had sequenced the DNA of a Siberian boy who lived 24,000 years ago. Then in October 2014, researchers announced that they had sequenced DNA from the bone of a human -- a thigh discovered in Siberia -- believed to be 45,000 years old. It is currently the oldest modern human genome.
“We now have some idea how people who lived 45,000 years before present were related to present-day people,” one of the researchers, Janet Kelso, said at the time.
One of the largest, most significant recent critical finds came from excavations done in advance of a railway project in Motala, Sweden.
In what were once wetlands and a shallow lake, workers led by archaeologist Fredrik Hallgren uncovered the remains of at least 11 humans. It was a strange find: skulls resting on wooden stakes. There were also, apparently as grave offerings, tools carved of bone and antler. One item was a knife made from a wild boar tusk.
While the cultural significance of the burial remains unclear, the DNA extracted from the remains is unequivocal.
In a paper that appeared in December in the journal Nature, scientists looked at the DNA that has been recovered from the Motala remains and from those of more than 200 other ancient Eurasian humans. The ages ranged from 8,000 years old to about 2,000 years old -- a span of time that covers ancient hunter-gatherers as well as early farmers.
In analyzing the DNA from those ancient remains, the scientists noted thousands of distinct places where there were DNA changes that didn’t seem just random. That is, the changes didn’t seem to be merely a case of genetic drift but a sign that the human species was actually adapting to some aspect of its environment.
Out of those thousands of places, the scientists then highlighted 12 places in the DNA where the signs of selection were clustered. One of those clusters related to the digestion of milk -- a confirmation of previous findings. Another related to how humans digest fatty acids. Two others may have a link to celiac disease. Others were related to skin color, which got lighter as humans moved northward from Africa, and disease resistance.
“Europeans of 4,000 years ago were different in important respects from Europeans today, despite having overall similar ancestry,” the authors concluded.
Those findings, like the others, challenge the Paleo assumption that humans have not changed. What remains unanswered is how much. As good as the research techniques have become, and as far as the technology has advanced, the validity of the central premise of the Paleo movement remains uncertain. As Eaton and Konner said in 1985, any diet proposals, to be validated, must be tested with experiments.
“My overall opinion of this is that we don’t really know,” said Iain Mathieson, a Harvard med school researcher and a co-author of the Nature paper. “We do know there are some specific changes in humans. But they are a relatively small in number. To me, it’s an open question. It’s a hypothesis.”