Fish made us human

How its consumption helped our primal brains evolve

Minke van Voorthuizen/Leiden UniversityArtist impression of H. erectus with a carved shell.

Bart Braun

Eating fish had a major impact on human evolution. Archaeologist and biologist José Joordens is investigating that premise by studying fossil fish remains from the Kenyan desert and shells from Java – and visiting fishmongers on Leiden market.

Elephants have large noses, ducks have enormous willies … and humans? Human have gigantic heads in proportion to their bodies. We use them for thinking with and that’s something we do better than any other animal. Such large heads make giving birth a bit of a challenge and humans are helpless infants for years until their brains are truly up and running. But it’s worth the wait: we have plays by Shakespeare, the Sistine Chapel and processed cheese in tubes.

We still haven’t come close to unravelling the exact origins of man but when you arrange the skulls next to each, you can see that they grew larger and larger, posing two questions: why did they develop that way and what caused it? Both archaeologists and biologists think these questions belong to their fields. Not surprisingly, José Joordens, the Leiden scientist studying this matter, is a biologist at the Faculty of Archaeology.

She made global headlines late last year after discovering a zigzag marking, almost certainly drawn by Homo erectus, an extinct species of human, on a fossilised shell from Java. It is the oldest picture ever found, four to five times the age of the oldest pictures produced by Homo sapiens a hundred thousand years ago.

Why would someone researching large brains examine a collection of fossilised freshwater mussels? It has to do with the composition of brains: remember the scene from Breaking Bad, when Jesse tries to dissolve a corpse in a bathtub of acid? He can’t get rid of the brains due to their fat content. To build brains, you need fats – more specifically, unsaturated fats with long-chain fatty acids. And your diet must contain enough iodine – until 2009, Dutch bakers were legally obliged to add iodine to their bread for this reason. Aquatic food – fish, seaweed, shellfish and crustaceans – is a good source of those substances.

There is growing evidence that primitive man appreciated that source too. In 2010, a South African archaeologist revealed that catfish and crocodiles were eaten by proto-humans in Kenya’s Turkana Basin, the cradle of humankind, two million years ago. Joordens’ shells caught the public’s interest because of the zigzag, but her Nature paper revealed that Homo erectus also used them as tools and as food. "The scratches were just a bonus", as she herself says.

The Journal of Human Evolution recently published a special issue on the role of water in the evolution of the brain, behaviour and human diet. Joordens and a number of her colleagues wrote their contribution on the fatty acid composition of various species of fish. One colleague took samples of local freshwater fish and marine fish in Africa and, looking for material for comparison, the researchers bought fish from Dutch inland waters and from the North Sea on the market here. Together, they determined the unsaturated fat content of 59 species. There are considerable differences between the species: sardines are as oily as a politician’s smile while the elephant-snout fish, Mormyrus kannume, from Tanzania isn’t fatty at all. But if your diet includes a varied range of fish, your intake of unsaturated fat will be the same overall, whether it comes from rivers and lakes or the sea, from tropical or temperate waters.

That explains the "how" question: primitive man, spreading out across the globe from Africa, discovered the building blocks for larger brains in water.

The "why" question poses more difficulties. Human brains did not expand just because fish was available – if your brains grew from eating fish, fish themselves would have larger brains. "We should distinguish between facilitating factors and steering factors", Joordens continues. "I think the availability of fatty acids was a facilitator." There are books full of theories on the steering factor: impressing the other sex, increasingly complicated social behaviour, cooking with fire, collaboration with other animals and so on. "With this topic, everyone tends to focus on a single issue but it’s likely that very many factors all had a small part in it."

She is convinced that if she can reach further back in time, she will find proof of fish consumption there too. That means she should return to the Turkana Basin where she did her PhD research. "What was the role of the East African coast five to two-and-a-half million years ago, before Homo erectus? I think there are fossils that could tell us more; we just haven’t found them yet. My larger research project focuses on finding those fossils. I keep stressing the importance of water, because we are discovering more and more about the importance of eating fish."

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Fish made us human

Eating fish had a major impact on human evolution. Archaeologist and biologist …