Humanity's Mysterious Brain Growth Spurt

At a point in human evolution between about 2.6 million and 0.2 million years ago, the human brain grew incredibly rapidly, doubling in size in just 2 million years, and no one knows why. During this stretch, early Homo species gave way to forms like Homo erectus, and fossil skulls show their cranial capacity expanding from ape-sized brains to volumes approaching those of modern humans. Scientists have suggested that a shift toward calorie-dense, difficult-to-obtain foods may have helped drive this rapid encephalization.

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