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Why the Human Brain is Shrinking

Fact: our brains are 10% smaller than they were 10,000 to 20,000 years ago. Anthropologists and psychologists across the world have advanced various explanations sharing the common threads discussed below.

One driver of brain shrinkage they seem to agree on is domesticity. As this theory’s lead proponent, Bruce Hood of the University of Bristol, explains: “We have been self-domesticating through the invention of culture and practices that ensure that we can live together.” These anthropological shifts obviated the need to hunt for our own food or evade predators. As Hood points out, the same decrease in brain size is observable in all domesticated animals, whose reduced testosterone triggered a decrease in the size of all organs. Indeed, where a wolf would solve a problem through cunning, a dog simply solicits help from its master, often a decidedly less cognitively intensive task.

Another driver of brain shrinkage is a reduction in average human body size. As paleoanthropologist Christopher Stringer from the Natural History Museum in London explains, bigger bodies require larger nervous systems. As body size decreased, so did the pelvic size in females, which in turn fostered the delivery of smaller-headed babies.  Mr. Stringer attributes the decrease in human body size to warmer weather since the last Ice Age, as colder conditions favor bulkier bodies.

Finally, there are experts that believe that the brain shrinkage marks dwindling intelligence (David Geary at the University of Missouri) and experts that believe it manifests increased brain efficiency (John Hawks at the University of Wisconsin).

Although the advent of computing technology may be too recent to be thrown into this mix of anthropological hypotheses, this author can’t help but wonder whether our increased reliance on external information storage/processing and automated processes/robotics might have something to do with it…

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