The development of man is characterized by the exponential growth of his brain. Early humans like Australopithecus It was the brain of a chimpanzee. In the space of two to three million years, our brains have grown four times their size. Less well known is that it shrunk a little later. Our brains are about 10 percent smaller than the brains of Neanderthals or sane man From fifty thousand years ago.

The big question: When did they shrink and why? There is a hypothesis that the reversal occurred about ten thousand years ago, at the beginning of the Holocene, when the Earth was warming and man as a whole became somewhat younger. American anthropologists write in a professional journal, but that can’t be the whole story Frontiers in ecology and evolution. The brain has shrunk fivefold.

The downturn came later than expected

In their search for a better explanation, the Americans first tried to capture this tipping point with greater accuracy. From a large database they extracted the data of nearly a thousand fossil and modern skulls. There were very old skulls – from Homo sahelanthropus from Ardipithecus – To contemporaries, as well as some strangers such as Floresmens or the newfound Homo naledi.

They put all the sizes on a timescale, let their computer draw a line through it, and then saw three kinks. The first was 2.1 million years ago, when the first specimens of the genus Homo erectus (Homo erectus) appeared on the scene. Then it turned out that there was a second, slight acceleration in brain development one and a half million years ago. Both kinks can be explained by the invention of tools, fire (which allowed people to prepare their own food), and then the growth of group size. After all, more social interaction requires more brain activity.

According to their calculations, the downturn began three thousand years ago. This is much later than previously thought and as a result all kinds of theories are discarded. Some have suggested that this shift coincided with the rise of agriculture. Then the brain shrinkage could be the result of a different diet, or of self-domestication. Pets often have smaller brains than their wild ancestors. Perhaps the same thing happened to humans when they settled down and lost their unruly hair. But man began farming ten thousand years ago. So that cannot be the case.

For many ant species, the tasks are divided

so what? In their search, the Americans make a surprising journey here: to the realm of ants. Not exactly an animal that can rival humans in terms of intelligence, but ants form complex societies. Ants plant too, they do it together and they learn from each other.

And very important: with many species of ants, the tasks are divided. One maintains inbred cultivation, the other monitors offspring. You can see differences in brain size in these types of ants.

From here the Americans begin to speculate. Brain activity consumes a lot of energy; With us, half of the consumption goes to the brain. If you can save some money on that, for example by splitting tasks, that provides an evolutionary advantage. Perhaps humans can handle a smaller brain when society is organized in such a way that everyone has their own task and can leave large parts of the work to others.

Putting energy into the immune system

What happened three thousand years ago that allowed an individual to use group intelligence? Writing! The researchers enthusiastically suggest. Although that originated five thousand years ago, it is still within the bandwidth of their calculations. When a person has learned to write down his thoughts, he no longer has to master all knowledge, but can entrust part of it to the group. And his brain could shrink.

Americans write that there are other conceivable explanations. As societies grew, more infections appeared and people had to put more energy into their immune system. Which could have been at the expense of his brain. But at the end of their article, they still called on their colleagues to further investigate the ant brain hypothesis and the wisdom of the masses.

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