By Craig Weatherby
Scientists have been debating why and how the human brain started outgrowing the brains of other mammals, starting about two million years ago.
The human brain is built from fatty acids, and omega-3 DHA, which is essential to brain cell structure and to thinking and memory, constitutes about 60 percent of the fatty acids in our brains.
Humans can convert plant source omega-3s into DHA, but do so very inefficiently. The only foods naturally rich in omega-3 DHA are fish, shellfish, algae, and animals that eat heavily aquatic diets (amphibians, crocodiles, hippos, etc.).
Accordingly, some researchers—led by renowned British brain researcher Michael Crawford, Ph.D.—have suggested that our immediate evolutionary ancestors must have eaten diets rich in DHA.
(Paleoanthropologists refer to humans and human ancestors as members of the “hominin” family: a category that encompasses all of the Homo species—including Homo sapiens—the Australopithecines, and other ancient ancestors.)
But other scientists have complained about a lack of evidence for the “DHA theory” of brain evolution.
To date, most paleoanthropologists still hew to the traditional “savannah theory,” which posits that pre-humans evolved into big-brained humans on diets consisting of green plants, nuts, seeds, roots, and small land animals.
Brain expert's evolutionary theory accrues evidence
Dr. Crawford's hypothesis gained important support three years ago, when a team led by Arizona State University researchers published evidence of early humans living on the South African coast about 164,000 years ago.
That date was far earlier than any ever documented for shore-dwelling humans, and sits smack in the center of the time period when anatomically modern humans emerged (See “Omega-3 Brain Evolution Theory Gets a Boost ”).
(Dr. Crawford's proposal is very different from one called the “aquatic ape” hypothesis of human evolution, which was critiqued in the February, 2010 issue of Scientific American, in an article titled “The Naked Truth” …for our summary of the aquatic ape idea, see “Were Human Ancestors Aquatic Apes?”.)
We first heard Dr. Crawford present his case at the 2005 Seafood & Health conference in Washington, D.C. … and Vital Choice founders Randy and Carla Hartnell just heard Dr. Crawford and others discuss it at two European conferences on omega-3s.
Coincidentally, Dr. Crawford's hypothesis just received a major boost from a study reported online June 1, 2010 in the Proceedings of the National Academy of Sciences (PNAS).
In short, an international team of scientists has uncovered evidence that bolsters the “DHA theory” of brain evolution
Landmark study finds human ancestors ate diets rich in omega-3s
Starting about two million years ago, the brains of human ancestors began to grow into the large, uniquely powerful thinking organ possessed by prehistoric and modern people.
Now, archeologists working in Kenya have unearthed evidence that our human ancestors ate a wide variety of animals including fish, turtles and even crocodiles. Based on analyses of animal bones and stone tools they excavated, the research team found that our early ancestors incorporated aquatic “brain food” into their diet (Braun DR 2010).
“These aquatic foods are really important sources of the long-chain polyunsaturated fatty acids and docosahexaenoic acid [omega-3 DHA] that are so critical to human brain growth,” said co-author and paleoanthropologist Dr. Brian Richmond. “Finding these foods in the diets of our early ancestors suggests they may have helped to lift constraints on brain size and fuel the evolution of a larger brain.” (GWU 2010)
The discovery of such a diverse animal diet is important because early human brain size increased dramatically starting about two million years ago. Growing a large brain requires an enormous investment in calories and nutrients and places considerable costs on the mother and developing infant.
Anthropologists have long considered meat in the diet as key to the evolution of a larger brain. However, until now, there was no evidence that human ancestors this long ago had incorporated into their diets animal foods, from lakes and rivers, rich in brain nutrients.
Scientists from Kenya, the United States, the U.K., Australia and South Africa discovered a 1.95 million-year-old site in northwestern Kenya in 2004, and the excavated site was so remarkably well-preserved that the team was able to develop a detailed reconstruction of the environment.
Over four years, the scientists excavated thousands of fossilized bones and stone tools, and were able to determine that at least 10 individual animals, and perhaps many more, were butchered by early humans at this site.
Many of these bones showed evidence of cut marks made by early human ancestors as a result of using sharp stone tools to cut meat from the bones or crush long bones to access the fat-rich bone marrow.
“At sites of this age we often consider ourselves lucky if we find any bone associated with stone tools, but here we found everything from small bird bones to hippopotamus leg bones,” said archeologist David Braun of the University of Cape Town in South Africa, who was the lead author on the research (GWU 2010).
Gaining access to smaller animals like turtles and fish may have allowed these early humans to increase the protein in their diet without the danger of interacting with dangerous carnivores, such as lions and hyenas.
These early humans were relatively small and not well-suited to compete with the large carnivores that lived at that time. Stumbling upon brain-fueling food may have been a fortunate side effect of finding foods at lakes and rivers.
The international team will return to northern Kenya to find more answers to questions about the diets of our earliest ancestors.
Stay tuned for more updates on this fascinating search for the evolutionary source of human's big brains!
- Braun DR et al. Early hominin diet included diverse terrestrial and aquatic animals 1.95 Ma in East Turkana, Kenya. PNAS June 1, 2010 vol. 107 no. 22 10002-10007. doi: 10.1073/pnas.1002181107
- George Washington University (GWU). Archeologists Discover “Brain Food” in Early Human Ancestors' Diet. May 28, 2010. Accessed at http://www.newswise.com/articles/archeologists-discover-brain-food-in-early-human-ancestors-diet