It's easy to understand why early humans domesticated (驯养)dogs as their new best friends, domesticated dogs can guard against fierce animals and provide warmth during cold nights. But those benefits only come following domestication. Despite more than a century of study, scientists have struggled to understand what caused the domestication process in the first place.
A new theory given by Maria Lahtinen, a senior researcher, might be able to explain this puzzle. She made this theory when studying die diet of late Pleistocene hunter-gatherers in Arctic and sub — Arctic. At that time, around 20,000 to 15,000 years ago, the world was buried in the coldest period of the last ice age. In cold environments then, as today, humans tended to gain the majority of their food from animals. Nutritional deficiencies (缺失) came from the absence of fat and carbohydrates (碳水化合物), not necessarily protein. Indeed, if humans cat too much meat, they can develop protein poisoning and even die. "Because we humans are not fully adapted to an all-meat diet, we simply cannot digest protein very well," Lahtinen says.
During the coldest years of the last ice age — and especially in lough Arctic and sub-Arctic winters — reindeer, wild horses and other animals that humans killed for food would have been struggling to live. Using previously published early fossil records, Lahtinen and her colleagues calculated that the game captured by people in the Arctic and sub-Arctic during this time would have provided much more protein than they could have safely consumed.
