Scientists identify reason behind brain shrinkage 3,000 years ago

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After analyzing skull fossils, scientists have identified the reason the human brain shrank 3,000 years ago.

The study, published in the journal Frontiers in Ecology and Evolution, shows that our ancestors had larger brains than we do.

According to the study’s lead author, Jeremy DeSilva, an anthropologist at Dartmouth College in the United States, “This is much younger than we anticipated. We expected something 30,000 years ago.”

The brain, which throughout history has been humans’ greatest asset in surviving disasters and subjugating other species, contains 86 million neurons.

For comparison: the brain of an ant has a volume of about one tenth of a cubic millimeter and contains only 250,000 neurons.

“The assumption was that the evolution of the brain essentially took place in the Pleistocene. So if you find a skeleton or skull that’s 4,000 years old, people don’t run to measure brain size. The assumption is that it will be the same as people living today and the same as people who lived in the late Pleistocene,” DeSilva said.

“What we’ve found is that the downtrend is best positioned around 3,000 years ago.”

The human brain, which weighs about 1.4 kg and is made up mostly of water, is the building block of the nervous system, and each neuron in the brain can send up to 1,000 signals at an impressive speed of up to 250 miles an hour.

“As these social insects become more social, their neural ganglia get larger, but they reach a point where there are so many of them that they specialize and rely on each other through collective intelligence,” DeSilva said.

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He added: “Our interpretation is that people have become more social and may be experiencing something similar. If you have a smaller brain and are able to store more information externally and then interact with it in more complex ways, you can have the best of both worlds where your collective intelligence increases as a society and as a population, although both the individual brain might get a little smaller .”

And since a single neuron can connect to at least 1,000 other neurons, a single brain can have a total of at least 100 trillion connections. But brain signals that run on electricity have less than a tenth the voltage of an ordinary flashlight battery.

“As people moved into more sedentary communities, we see an increase in disease with the onset of agriculture,” DeSilva said.

“More people in close quarters means infectious diseases spread more easily, and when your body is exposed to these pathogens, you expend a lot of energy on the immune system, which means less energy on brain growth,” he added.

(With contributions from agencies)

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