"There seems to be something about the darkness that is like a blanket that ties people together," said professor of anthropology, Polly Wiessner. When humans started regularly using fire, perhaps 350,000 years ago, it didn't just give warmth or cooking ability, says Wiessner. It meant more time awake — but unlike the bright light of day, these hours couldn't be used to gather food or make tools. "This is economically unproductive time," she said. "So my question was, what is it that goes on at night that's so important that would have made these changes in our sleeping patterns?" Read full article.