DHA and human brain evolution
I read a review recently in The Economist of Clive Finlayson’s The Improbable Primate: How Water Shaped Human Evolution and it prompted me to buy the book. This subject has fascinated me ever since I saw Michael Crawford give a talk on the importance of DHA omega-3 to the human brain and how its dietary availability may be a prime factor in the evolution (and potentially devolution) of the human brain. However, the more I have read about brain evolution, the more controversial every theory in this field seemed to be.
The camp that believes DHA played an important role in evolution of the human brain has migrated towards the Aquatic Ape theory of human development. This theory basically says that our ancestors migrated from the plains of Africa to the coasts and began consuming seafood as a result, which gave us access to the DHA and other nutrients that were needed for the human brain to grow in size and complexity. At its core, though, the Aquatic Ape theory was not based on human brain development, instead it became popular in the 1970s because the prevailing theories of evolution at the time believed males in the human predecessor species lost their fur because they were expending more energy hunting and needed to sweat to cool down, but this did not address the loss of hair in females. The Aquatic Ape theory was seen as more balanced at the time. The root idea of the Aquatic Ape theory was that our ancestors were forced from the trees by competition for food into the oceans where shellfish and other shallow-water seafood was plentiful. This adjustment to spending time in water caused us to lose our hair and potentially even develop a more bipedal walking structure. It just happens that the DHA theory fits nicely into this narrative, but many paleoanthropologists say there is no fossil evidence to support Aquatic Ape evolution.
Finlayson proposes a new theory of human evolution that he says attacks the Aquatic Ape theory and many other theories of evolution, but he argues that water plays the key role of human development and is the primary condition of existence required for human evolution. His primary argument is that humans moved from the forests to nearby marshes and lakes, rather than to the ocean. As the climate changed and parts of Africa became more arid, it was humans’ search for water that led them to migrate to new areas, rather than new food sources. He does note, however, that in the transition from trees to land, human ancestors had the physical structure to eat soft foods, not tough meats. As a result, they likely ate fish, mollusks and other sources of seafood from the marshes and lakes to complement the fruits they were harvesting from trees.
The prime criticism I have seen of all the theories of evolution is that they basically try to create a single unifying explanation for how humans evolved, but the process is likely much more complex than that. Scientists who have studied the human brain believe a specific set of nutrients were needed in the diet for the brain to evolve because they are structural components of the brain and the human body cannot produce them. This is their manifesto, and the Aquatic Ape theory is the only one that came close to fitting this evidence. The new theory from Finlayson is interesting and is another theory that also seems to fit this manifesto.
There is additional evidence that has just emerged for this as well. Joordens et al just published a study in the Journal of Human Evolution that measured the fatty acid composition of African lake fish and found that these species could supply enough DHA to the human diet to potentially kick off the evolution of the human brain, but not enough for the rapid growth seen in later stages of evolution.
This new evidence and new theory indicates that the truth is somewhat complex and is perhaps somewhere in between. I do have to say that all of the paleoanthropological theories of evolution being advanced all seem to have a bias toward a specific area of research like fossil evidence, archaeology, biology, or behavioral evidence, but few seem to think about all of these factors together. Given that human evolution is complex, it seems like a more holistic approach is required to get to the bottom of how humans evolved. Finlayson’s book is interesting and provides another theory in which the DHA evidence fits. However, he discusses the evolution of the brain throughout the book and does not make a single mention of any of the nutrients required by the brain, nor does he mention any of the structural components of the brain. It seems like this would need to be a fundamental piece of evidence to support any theory of evolution.