Homo saps secret weapon against Neanderthal man
Do the Eyes Have It?
Dog domestication may have helped humans thrive while Neandertals declined
We all know the adage that dogs are man’s best friend. And we’ve all heard heartwarming stories about dogs who save their owners—waking them during a fire or summoning help after an accident. Anyone who has ever loved a dog knows the amazing, almost inexpressible warmth of a dog’s companionship and devotion. But it just might be that dogs have done much, much more than that for humankind. They may have saved not only individuals but also our whole species, by “domesticating” us while we domesticated them.
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Earning Their Keep
Would a good dog really have been so important that it would inspire ritual significance—and give modern humans a crucial edge over Neandertals? We can’t observe how ancient, but anatomically modern, humans used dogs in their daily life, but there are some interesting possibilities. We know from their bones that the Paleolithic dogs were very large, with a body mass of at least 32 kilograms and a shoulder height of at least 61 centimeters, about the size of a modern German shepherd. Germonpré and her colleagues suggest that these early dogs might have been beasts of burden. They cite ethnographic examples of peoples like the Blackfeet and Hidatsa of the American West, who bred very large, strong dogs specifically for hauling travois or strapped-on packs.
All but one of the six Paleolithic dog sites that have so far been identified preserve large quantities of mammoth bone which, with meat attached, must have been lugged from the kill site to where the group was living. If the dogs carried the meat, humans would have saved a lot of energy, so each kill would have provided a greater net gain in food—even after feeding the dogs. Additional food generally has marked effects on the health of a group. Better-fed females can have more babies, can provide them with more milk and can have babies at shorter intervals. Before long, using pack dogs could have caused the human population to increase.
Dogs may also have contributed more directly to human hunting success. To discover how big a difference dogs could make, Vesa Ruusila and Mauri Pesonen of the Finnish Game and Fisheries Institute investigated what may be the closest easily studied analog to a mammoth hunt: the Finnish moose hunt. Finns use large dogs such as Norwegian elkhounds or Finnish spitzes to find moose and keep them in place by barking until humans can approach and shoot them. In hunting groups of fewer than 10 people, the average carcass weight per hunter without dogs was 8.4 kilograms per day. With dogs, the yield went up to 13.1 kilograms per hunter per day—an increase of 56 percent.
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The dogs improved hunting success by increasing the rate at which the hunters encountered game. Finding game “is often the hardest skill to learn for human hunters,” Koster and Tankersley write. The encounter rate for agoutis—rodents weighing 2 to 8 kilograms—was nine times better if dogs were used; for armadillos, the encounter rate was six times better with dogs. The most successful hunts of all involved killing tapirs using both dogs and firearms.
Karen Lupo of Washington State University conducted a similar study among the Bofi and Aka forest hunters of the Central African Republic. These foragers hunt with spears, bows, crossbows and nets; most of their prey animals weigh less than 10 kilograms each. Although dogs had little effect on the proportion of successful hunts, they markedly reduced the time required to make a kill. In hunts that captured giant pouched rats, for instance, dogs reduced the amount of time expended before a kill by 41 percent (29 minutes with dogs versus 49.5 minutes without dogs). Similarly, when porcupine was caught, dogs reduced the time before a kill by 57 percent (44 minutes versus 101.33 minutes). Faster hunts lowered the energy expended by humans during hunting and increased the yield. The dogs were not treated as pets or companions, and the very idea of doing so was considered laughable by Lupo’s informants. Lupo titled her paper “A dog is for hunting.”
Domesticating dogs clearly improves humans’ hunting success and efficiency—whether the game (or the dog) is large or small. The same must have been true in the Paleolithic. If Neandertals did not have domestic dogs and anatomically modern humans did, these hunting companions could have made all the difference in the modern human–Neandertal competition.
I can’t help wondering whether the process of domesticating dogs was connected to changes in human anatomy and communication abilities. Domestication is a two-way street, as we know from examples such as the genetic changes that make adult humans able to digest milk. Those mutations arose several times in different human populations after the domestication of cattle. I have no evidence that the change I am about to discuss did or did not occur between 45,000 and 35,000 years ago. But it might have.
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Wide-Eyed Cooperation
A study by Hiromi Kobayashi and Shiro Kohshima of the Tokyo Institute of Technology showed that modern humans are unique among extant primates in having highly visible white sclerae surrounding the colored irises of their eyes, as well as eyelids that expose much of the sclerae. In other primates, the dark sclerae, similarly colored skin and concealing eyelids tend to mask the direction in which the animal is looking, according to the Japanese team. In humans, the white sclerae and open eyelids make the direction of a person’s gaze visible from a distance, particularly if that glance is directed in a more or less horizontal direction. The changes in the human eye may be adaptations to enhance the effectiveness of the gaze signal.
Michael Tomasello and colleagues at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, developed this idea as the “cooperative eye hypothesis.” They suggested that cooperation among humans was facilitated by the ability to recognize where others were looking. Apes will follow gaze less often than human infants, they found. If the direction of gaze and the direction of the head conflicted, apes tended to follow head direction. In a humorous aside, the researchers noted that they tried their experiment with 14 chimpanzees, 4 gorillas, 4 bonobos and 5 orangutans—but dropped the results of tests on three chimps and all five orangutans because they “did not pay attention to the gaze cues sufficiently for their skills to be reliably assessed.” Following gaze was apparently not a high priority to the apes.
The mutation causing white sclerae is universal in humans, but it turns up occasionally in apes, too. In decades of observations at Gombe National Park in Tanzania, Jane Goodall observed two chimps, probably brothers, who had white sclerae. A third, female chimp developed white sclerae as an adult. But the trait has not spread or reappeared in that population. The advantage of the white sclerae must be related to something that ancient humans did commonly and chimps don’t do or do rarely. Although chimps hunt small prey, often cooperatively, meat makes up less than 2 percent of their diet, whereas Paleolithic humans hunted much larger game that apparently provided a significant part of their diet. Obviously, silent communication among humans would be advantageous for hunting in groups. But there is another skilled gaze-reader: the domestic dog.
A dog will follow the gaze of a videotaped human if the human first attracts the dog’s attention by speaking to it and looking at it, according to results published by Ernõ Téglás, of the Central European University in Budapest, Hungary, and his colleagues. Indeed, dogs perform as well as human infants at following the gaze of a speaker in tests in which the speaker’s head is held still.
It does make a lot of sense to me, and I’m sure that Cinnamon would agree. If I woke her up from her bed on the living room floor.
