It must have been the first all-you-can-eat sushi bar. About 1.95 million years ago, a group of early human ancestors assembled on the shores of an ancient lake or river in Kenya and gathered fish and other aquatic animals from the shore and shallow water. Using stone tools, they deboned a catfish, eviscerated a turtle, and defleshed the foot of a crocodile.
Today, their leftovers—in the form of hundreds of bones and several thousand stone tools—are the earliest “definitive evidence” of hominins butchering and eating aquatic animals, which are rich in fatty acids essential for growing bigger brains. The findings are published  online today in the Proceedings of the National Academy of Sciences.
The first markedly bigger human brains appear with Homo erectus, about 1.8 million years ago, and researchers have long thought that our ancestors began eating more meat by 2 million years ago to fuel the dramatic boost in gray matter. Some have suggested that fish and shellfish must have appeared on the menu at about the same time because seafood is rich in docosahexaenoic acid and arachidonic acid, also known as omega-3 and omega-6 fatty acids, which are essential for human brain growth . But except for the bones of two catfish dated to about 1.8 million years ago at Olduvai Gorge in Tanzania, there has been scant evidence of fish eating this early in human evolution. Surely, hominins were eating fish when they could catch or collect them easily—but where was the evidence?
Just north of H. erectus’s home at Koobi Fora, Kenya, in fact. The new fossil site was discovered in 2004 when archaeologist David Braun was surveying the barren lands northeast of Koobi Fora as part of a field school run by Rutgers University in New Jersey, where he was a graduate student. He and his adviser Jack Harris found thousands of primitive stone flakes, cores, and modified fragments made of basalt and dated them to 1.95 million years ago. Braun, Harris, and their colleagues also found a diverse array of bones of at least 48 aquatic and terrestrial animals, including 10 butchered at the site over the course of several weeks or months. In addition to 41 bones of catfish and 15 from other fish, they found cut marks on the bones of other freshwater animals, including crocodiles and turtles.
“Here we see the first conclusive evidence of hominins eating fish before there were dramatic increases in brain growth,” says co-author Brian Richmond, a paleoanthropologist at George Washington University in Washington, D.C. But apparently the diners weren’t picky: They also ate antelopes, hippos, and rhinoceros—"any kind of animal tissue they could get their hands on," Richmond says.
Studies of carbon isotopes in the animals' teeth by geochemist Naomi Levin of Johns Hopkins University suggest that the butchery site was in a wet, wooded habitat with palm trees, perhaps a thin strip of forest along the banks of a river or lake. The identity of the early fish-eaters is still a mystery—no hominin bones have been found at the site so far. Both australopithecines and early members of the genus Homo, such as H. habilis, have been found in east Turkana, so either could have left the tools.
But both hominins have relatively small brains. That suggests that our ancestors expanded their diet 1.95 million years ago, paving the way for the expansion of their brains and, perhaps, the reduction in size of their teeth and jaws—something also seen in H. erectus—because these foods are relatively easy to chew, even raw. “The importance of the site is the confirmation that hominins at this early time period had a very diverse diet ... [including] turtles and fish,” says Leslie Aiello, president of the Wenner-Gren Foundation for Anthropological Research in New York City. “It all fits very nicely with hypotheses for brain expansion at this time period.”