Food for Thought: Fish Fossils and Evolution of the Human Brain

I am now in Kenya, continuing my study of fossil fish. As I wrote in my previous blog from Ethiopia, studying the fossil fish of East Africa reveals much about the environment in which our earliest human ancestors lived.

Entrance of the Nairobi National Museum, which includes a courtyard with sculpture in front.

Main entrance of the Nairobi National Museum. Image: Scott Rufolo © Canadian Museum of Nature.

Knowing the habitat preferences of the species in the fossil record can be used to reconstruct the types of lakes, rivers, streams, and other waterways that once dotted the Horn of Africa 2 to 4 million years ago.

These fossils could also reveal whether hominins have a long history of exploiting fish as a food resource. Hominins are the group that includes modern humans plus all of our closest relatives, following the evolutionary divergence between chimpanzees and humans over 7 million years ago.

The head of a fish mounted on a wall.

Head of a Nile perch (Lates niloticus) mounted in the Natural History Museum of Addis Ababa, Ethiopia. These fish can grow to be quite large, reaching up to 2 metres in length, and are still eaten today in many countries. Image: Scott Rufolo © Canadian Museum of Nature.

Now I am at the Nairobi National Museum, the flagship institution of the National Museums of Kenya. I have spent a week examining the fish fossils collected in 2014 at the site of Kanapoi, which is located south of Lake Turkana in northwestern Kenya.

View of trees in a courtyard surrounded by a building with white walls.

A courtyard of the Directorate of Research and Collections at the Nairobi National Museum. The fish fossils are stored among the palaeontology collections housed on the third floor overlooking this court. Image: Scott Rufolo © Canadian Museum of Nature.

At just over 4 million years old, these fossils predate the appearance of the earliest member of our genus by at least 1.5 million years. As can be appreciated from the photos included here, these fossils represent a diverse assemblage that is very interesting from a palaeontological perspective alone. So what is their relevance to human evolution?

Fossil fish bones on a blue background.

(left) Cranium fragments from a member of the catfish genus Clarotes. The distinctive texture on the outer surface is characteristic of this type of catfish, which is still represented by two modern species in Africa. (right) Vertebrae from the Nile perch (Lates niloticus), a fish species still present in the waters of East Africa. Images: Scott Rufolo © Canadian Museum of Nature.

Within palaeoanthropology, it has long been debated when our ancestors regularly began to utilize fish and other aquatic animals as a source of nutrition. Until recently, good evidence for the human consumption of fish did not stretch back more than 50,000 years; active fishing on any appreciable scale is only well-documented in the archaeological record for the last 10,000 years.

Fossil fish teeth.

(left) Fossil fish teeth rank among the most diagnostic elements. These are teeth from Gymnarchus, a genus of fish represented today by the aba or African knifefish. (right) These blade-like teeth belong to a species of the genus Hydrocynus and represent a relative of the modern African tigerfishes. The modern species are famed for their ferocity and have even been observed leaping out of the water to take birds in mid-flight. Images: Scott Rufolo © Canadian Museum of Nature.

In 2014, however, a study provided evidence for the capture and consumption of both fish and turtles from the Kenyan site of Koobi Fora dating to about 1.95 million years ago.

It has been proposed in the palaeoanthropological literature that the incorporation of fish into the diet of early hominins may have launched the evolutionary trend towards larger brain size that characterizes the human line. This is partly because fish are rich in docosahexaenoic acid, which plays an important role in brain chemistry and function.

A traditional Kenyan village.

A Luo village at the Bomas of Kenya, an outdoor museum where representatives of Kenya’s tribes have constructed buildings according to traditional designs. The fenced area would be used to confine livestock overnight. My guide, a member of the Kikuyu tribe, told me that the Luo are known for producing Kenya’s most intelligent people, and he attributed their braininess to their diet of fish! The Luo live along the shores of Lake Victoria and are one of the few tribes to include fish regularly in their diet. Image: Scott Rufolo © Canadian Museum of Nature.

The role and effects of fish in the early hominin diet remain a contested subject, but any evidence of the early consumption of fish by early human ancestors will help to fill out the picture. The material I studied this year provides no such evidence, but in future seasons we may be able to target sites that would have the best chances of yielding the necessary clues.

In the meantime, fully analyzing the data I have gathered over the past few weeks will keep me busy, and I’ll update you on the results in another blog post in the not-too-distant future.

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