- Meat-eating and animal domestication separated humans from other apes.
- Taking in animals is uniquely human and seems counterproductive at first.
- Hunting and caring for animals drove the development of technology and languages.
Dogs, cats, cows and other domesticated animals played a key role in human evolution, according to a theory being published by paleoanthropologist Pat Shipman of Penn State University.
The uniquely human habit of taking in and employing animals -- even competitors like wolves -- spurred on human tool-making and language, which have both driven humanity's success, Shipman says.
"Wherever you go in the world, whatever ecosystem, whatever culture, people live with animals," Shipman told Discovery News.
For early humans, taking in and caring for animals would seem like a poor strategy for survival. "On the face of it, you are wasting your resources. So this is a very weird behavior," Shipman said.
But it's not so weird in the context something else humans were doing about 2.6 million years ago: switching from a mostly vegetarian diet to one rich in meat. This happened because humans invented stone hunting tools that enabled them to compete with other top predators. Quite a rapid and bizarre switch for any animal, Shipman said.
"We shortcut the evolutionary process," said Shipman, who published her ideas in the latest issue of Current Anthropology and in an upcoming book. "We don't have the equipment to be carnivores."
So we invented the equipment, learned how to track and kill, and eventually took in animals who also knew how to hunt -- like wolves and other canines. Others, like goats, cows and horses, provided milk, hair and, finally, hides and meat.
Managing all of these animals -- or just tracking them -- requires technology, knowledge and ways to preserves and convey information. So languages had to develop and evolve to meet the challenges.
Tracking game has even been argued to be the origin of scientific inquiry, said Peter Richerson, professor emeritus in the Department of Environmental Science and Policy at the University of California, Davis.
One of the signs that this happened is in petroglyphs and other rock art left by ancient peoples. At first they were abstract, geometric patterns that are impossible to decipher. Then they converge on one subject: animals.
"Think what isn't there: people, landscapes, fruit and edible plants," said Shipman. This implies that animals and information about animals was of great importance.
There have also been genetic changes in both humans and our animals, Shipman argues.
For the animals those changes developed because human bred them for specific traits, like a cow that gives more milk or a hen that lays more eggs.
But this evolutionary influence works both ways. Dogs, for instance, might have have been selectively taken in by humans who shared genes for more compassion. Those humans then prospered -- a.k.a. reproduced -- with the dogs' help in hunting and securing their homes.
All this and more Shipman breaks down and addresses in view of the archeological evidence.
"The overall message is highly plausible," Richerson said.