Human hunters bagged more game than they could safely eat during the last Ice Age.
Rather than waste the excess meat, they fed it to wolves, which evolved into domesticated dogs over time, a new study suggests.
It's hard to resist dogs when they beg for scraps from the table. The act of feeding leftovers to hungry canines may have jump-started dog domestication during the last Ice Age, new research suggests.
A study published Thursday in the journal Scientific Reports suggests that humanity's bond with dogs began in northern Eurasia between 14,000 and 29,000 years ago, when much of the Earth was covered in ice.
Plants were scarce and prey was lean during those harsh Ice Age winters. Our hunter-gatherer ancestors could only get all 45% of the calories they needed to survive from eating lean meat, since too much can cause protein poisoning (human livers aren't well-adapted to metabolizing protein). In the absence of plant-based carbs, our ancestors relied on animal fat and grease to supplement their diet.
To get enough fat, though, hunters had to kill more lean animals like deer and moose than they could eat in their entirety.
So Ice Age hunters fed the excess meat to wolves, according to Maria Lahtinen, the lead author of the new study and an archaeologist with the Finnish Food Authority.
"The wolf and human can form a partnership without competition in cold climate. This would easily promote domestication," Lahtinen told Business Insider.
The descendants of the leftover-eating wolves eventually became the first domesticated dogs, her study suggests.
There are plenty of benefits to domesticated dogs: They can pull sleds, protect livestock, or provide protection from other predators.
But none of those benefits became apparent until long after dogs' wolf ancestors had been domesticated. So scientists long wondered about the initial reasons for dog domestication.
The question was especially perplexing given that ancient humans and the northern wolves that occupied Eurasia tens of thousands of years ago subsisted on the same prey, like caribou, rabbits, and deer. It struck many researchers as unlikely that the two species would have willingly chosen to cooperated given the limited food sources during the Ice Age.
"Humans have a tendency to try to eliminate other competitors," Lahtinen said, adding, "it has never been explained before that why humans joined their forces with a competitor."
Before this new study, one hypothesis was that wolves were opportunistic scavengers that were so attracted to the food waste humans left behind that the two species eventually adapted to live alongside one another. The problem with that thinking, however, was that Ice Age humans didn't settle in any one place long enough to leave consistent, scavengeable scraps, according to Lahtinen and her coauthors.
So it may be more plausible that our ancestors simply caught more prey than they could safely consume, and chose to satiate their fellow predators rather than kill them off.
That led the four-legged predators to stick closer and closer to people over time until they evolved into dogs, a process that took place sometime between 20,000 and 14,000 years ago, Lahtinen's research suggests.
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