When compared with other animals of a similar size, our brains are extremely large. The human brain has nearly become four times bigger in size in the six million years. However, studies show this trend has reversed in Homo sapiens (智人). In our species, average brain sizes have shrunk over the course of the last 100,000 years.
How can we explain this striking reduction? Ian Tattersall suggests that the shrinkage in brain size began around 100,000 years ago, which corresponds to a period of time in which humans switched from a more intuitive (直觉的) style of thinking to thinking in a more abstract way to better understand your surroundings. Tattersall believes that what caused this change in thinking style was the invention of language. This led to the brain being reorganised in a more efficient way, allowing humans to get more “bang for their buck”.
However, Stibel believes that a changing climate, and not language, could explain our smaller brains. In a 2023 study, he analysed the skulls (头骨) of 298 Homo sapiens over the past 50,000 years. He found that human brains have been shrinking for about the last 17,000 years or so — since the end of the last ice age. When he carefully examined the climate record, he found that decreasing brain sizes were closely linked to periods of climate warming. Smaller brains could have allowed humans to cool down quickly. It’s well known that humans in hot climates have evolved thinner and taller bodies to increase heat loss. It’s possible that our brains could have evolved in a similar fashion.
Perhaps the most well-known theory put forward to explain our shrinking brains is that it began when our ancestors stopped being hunter-gatherers, laid down roots, and began to build complex societies. Jeremy DeSilva suggests that the birth of complex societies meant that knowledge and tasks could be spread out. People no longer had to know everything, and as individuals no longer had to think as much to survive, their brains reduced in size. But not all are convinced.
So where does that leave us?
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