Wall Street Journalさんのインスタグラム写真 - (Wall Street JournalInstagram)「The development of bigger brains has long been considered a hallmark of our species’ increased intelligence and subsequent dominance on this planet. The last two million years of our evolution were marked by a nearly fourfold increase in brain volume. ⁠ ⁠ But a growing body of evidence suggests our brains recently changed in an unexpected way: They diminished in size sometime following the end of the last Ice Age.⁠ ⁠ “Most people think of brain evolution happening in this linear way. It grows, plateaus and stops,” said Jeremy DeSilva, a professor of paleoanthropology at Dartmouth College. “But we’ve lost brain tissue equal to the volume of a lime—it isn’t a tiny little sliver we’re talking about.”⁠ ⁠ Many anthropologists had initially posited the changes coincided with the advent of agricultural practices around 10,000 years ago, and a global shift away from hunting and gathering.⁠ ⁠ The more-recent dates from DeSilva’s group point to booming eras for ancient civilizations in North Africa, the Middle East and South America—complex societies that they think may have played a role in the shrinkage.⁠ ⁠ Researchers suggested that perhaps our need to maintain a large brain—to keep track of information about food, social relationships, predators and our environment—has also relaxed in the past few millennia because we could store information externally in other members of our social circles, towns and groups.⁠ ⁠ “We’re so social that we don’t have to know everything anymore,” DeSilva said. “And we collectively then operate as a pretty functional society.”⁠ ⁠ DeSilva’s group calculated that human brains had remained roughly the same size in average volume, about 1,450 cubic centimeters, for roughly the past 150,000 years. That average rapidly dropped by around 10%, or up to 150 cubic centimeters, over the course of the last few millennia.⁠ ⁠ Read more at the link in our bio.」9月15日 4時01分