More science >

The Old Smart Diet

Updated 4 May 2021

How humankind could have evolved our big brains has long been a mystery. A large brain needs a large skull, and that means a thin-walled and weak one. The muscles attached to it cannot be too strong. So our jaws cannot bite as hard as other apes and we must eat softer foods. That means cooking all that tough meat and hard vegetation. but such controlled use of fire needs brains, which needs... and we have gone round in a circle. All these things could not possibly have simply evolved together. Yet they all seem dependent on each other. How did we break the vicious cycle?

But there is one very obvious solution when you stop and think about it. One class of highly nutritious but naturally soft food exists in abundance. You have to go down to the seashore to find it; almost all seafood is either soft already or needs only a couple of rocks to crack open its carapace.

Theories of an aquatic stage in human evolution are not new. But as long as palaeoanthropologists thought we evolved inland, that seemed untenable. Almost all the fossils and other traces they were digging up certainly came from inland communities. This brought many theories as to how humanity might have migrated across the land to spread around the world. But none of those theories really worked.

We now know that those palaeoanthropolgists were missing the obvious. As the ice ages came and went, the sea shore fell and rose with them. Today's shoreline is well above the ice age levels. Underwater palaeoanthropology is revealing a rich cultural heritage on ancient submerged lands such as Doggerland under the North Sea and on many shallow-water sites which follow the shorelines around the world.

A powerful new understanding hits us in the face, beguiling in its simplicity and hard to argue down. That first tribe of upright apes struggled to find food in the harsh climate changes of the ice ages. They retreated to the water margins where seafoods remained in abundance. With the land barren, they wandered the shores looking for food and a place safe from their more aggressive tribal relatives. As each ice age came and went, jaw muscles softened, opening up the evolutionary path to intelligence. The need for social cohesion, adaptation to new environments and more sophisticated hunting methods drove the evolution of intelligence and set the wheel turning.

When the ice melted and the waters rose again, no palaeoanthropological trace was left of how we had spread or of what we had eaten on the way. Only those who wandered inland, following the newly-melted waterways, would leave their traces for the landlubber palaeoanthropologists.

Today, the omega-three oils found in seafood remain an essential part of our diet. We can get them from some green vegetables, seeds and nuts, but they must be the right ones and they take more metabolic processing than the seafoods do. Some of the richer sources, such as flax and hemp seeds, are among our oldest inland staple diets. Many animals can synthesise these oils for themselves; somewhere in the murky period of our emergence from the apes, we lost the ability to. The simplest and most obvious explanation for all this is that we did not need to any more. We spent so long surviving on seafoods, through the many ice ages and interglacials, that we could lose the genes for making them and suffer no ill effects. The problems only came later, when the last interglacial ended and increases in numbers drove us inland.

All my life I have read the accounts of those landlubbers, extolling the complexities of their latest analysis of land-based evolution and migration patterns, bickering over whose theory is the worse and assasinating the careers of anybody who suggested a marine phase. The other day I read a piece in a science journal, by a young lady palaeoanthropologist. She commented on how her generation have moved beyond that old paradigm, to appreciate the fundamental nature of the coastal margins as the focus of that period of human emergence and migration. I forgot to note your name (as is my failing these days), but if you read this, I hope you will add the evolutionalry consequences of a seafood diet to your theories. And next time you meet one of those antedeluvian alpha males, do pass on a good kicking from one of his own kind.

There is another longstanding puzzle, of how we lost our fear of fire. All wild animals are afraid of it; only we and our house pets - dogs and cats - have lost it. But a species cannot simply lose its fear of fire overnight. The loss has to be gradual, over generations, before anybody dare actually start using it. How could that have happened? I'd like to suggest one idea. There are places where the Earth's crust is split open and the hot magma from below wells up constantly. Most are under the sea, but a few are on land and accessible to the brave. At least one may be found in north east Africa. Apes, especially unusually intelligent upright apes fresh from the water margins, might find it convenient to live nearby, with the fire providing warmth and frightening off the lions and other predators. Over the generations they would slowly lose their fear and move closer, leaving the outliers to the bravest and hungriest lions. Soon they learned that a pointed stick left in the red heat just long enough becomes usefully hardened. Eventually they made the opposite breakthrough discovery; tough foodstuffs left in there proved softer and more edible. And the essential omega oils in them were more accessible to our digestive systems. Anyway, it's a thought. If I were an palaeoanthropologist, that is where I would go looking for signs of emerging humanity.