PASADENA—When early humans first encountered wolves after leaving Africa 140,000 years ago, the two species may have established a partnership that allowed Homo sapiens to eventually dominate the entire world, a Caltech biologist says in a new book.
According to John Allman, Hixon Professor of Psychobiology and professor of biology, recent DNA evidence from both modern dogs and humans suggests that the human departure from Africa occurred at roughly the same time as the domestication of wolves. Though his evidence is circumstantial, Allman writes in his new book Evolving Brains that the early partnership could have allowed Homo sapiens to displace the other competing hominids—the Neanderthals of Europe and Homo erectus of Southeast Asia—and proliferate throughout the habitable areas of the world.
"Several things came together," says Allman, who specializes in evolutionary biology. "Recently, Robert Wayne at UCLA has shown through mitochondrial DNA that dogs are basically domesticated wolves, and that their domestication occurred much earlier than previously thought—as much as 135,000 years ago.
"Other DNA evidence also shows that Homo sapiens first left Africa about 140,000 years ago," Allman continues. "And since there were no wolves in Africa and no modern humans in Eurasia before this time, I conjecture that the two species got together soon afterward and became remarkably successful hunting partners."
Allman notes that much of Europe was populated by the bigger, heartier Neanderthals when modern humans first left East Africa. The ancestors of Neanderthals also originated in Africa but migrated at a much earlier time, more than a million years ago.
But Homo sapiens and Neanderthals apparently were isolated during the next few hundred thousand years, until the former arrived from Africa.
Neanderthals in the meantime had evolved into more hearty creatures to deal with the harsher climate of Europe, but there is no evidence to suggest that they ever domesticated wolves. Nor is there evidence that Neanderthals ever bred with Homo sapiens.
Migrating even earlier from Africa were the hominids known as Homo erectus. These people departed from Africa about 2 million years ago, and like their close relatives the Neanderthals, continued to evolve when they reached their new habitats. But Homo erectus didn't do particularly well outside Africa, and by 140,000 B.C. was confined to Southeast Asia. And the possibility of Homo erectus domesticating wolves is a moot point, for wolves have never inhabited Southeast Asia.
Allman doesn't go so far as to suggest that the Homo sapiens–wolf partnership directly caused the extinction of Neanderthals and Homo erectus, but he nonetheless says that such a hunting collaboration would have made the two highly developed species an unbeatable combination. Thus, it could be that the partnership was a significant factor in making life more difficult for the other hominids, regardless of whether direct conflict occurred.
"Wolves and humans are two of the most geographically widespread and successful of all mammals," Allman says. "And wolves have a lot in common with early humans, especially in their tendency to prey on ungulates—that is, big meaty creatures with hooves—the stuff we dogs and humans still like to eat."
Too, wolves and early humans were virtually unique in their tendency to live in extended families, Allman says. In other words, all adult members of the social group participated in caring for offspring.
Even in the modern world, humans and wolves are two of the very few types of mammals that live in extended families in which the impetus exists to look out for the other fellow's welfare. Thus, it was easy for humans and domesticated wolves to accept each other as family/pack members.
As for the partnership itself, Allman says that humans got a good deal in that they were able to contend with the harsh climates of Eurasia after eons of balmy weather in Africa. Being a successful hunter of ungulates meant that humans had access to furs and skins for protection against whatever environments they found in their new habitats. And later, when humans took up agriculture, they again found they had a ready and willing ally to watch over the crops and domesticated livestock.
Allman thinks the DNA evidence for his hypothesis is persuasive, even though the notion of the collaboration could be falsified in several ways. For one, additional work on the DNA of modern dogs might show that the domestication of wolves occurred much sooner or much later than human migration from Africa into Asia.
But new DNA work could also strengthen the hypothesis if it shows a more detailed timeline for domestication. As for the archaeological evidence, any results showing that Neanderthals indeed domesticated dogs would be troublesome. But no such evidence has been uncovered so far.
On the other hand, Allman thinks the best endorsement of the hypothesis would come from new archaeological work in remote regions such as Siberia. The hypothesis would predict that the human alliance with dogs enabled humans to expand into these inhospitable areas and ultimately invade the New World. If evidence of domesticated wolves and dogs were found in Homo sapiens living sites some 20 to 50 thousand years old, then the argument would be stronger that humans indeed proliferated throughout the world with the cooperation of wolves.
Allman's book Evolving Brains is being published this week by Scientific American Library/W.H. Freeman. The book will be available in bookstores in time for Christmas.