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Sunday, March 13, 2011
Study chips away further at humans' uniqueness
By ROWAN HOOPER
Time for some self-love, people: We're pretty damn cool. As animals, we're special.
Right. But it's just that we're not quite as special as we once thought. That's because, although we can do lots of things better than other animals, it's hard to think of things we can do that are unknown among our dumber cousins.
Let us count some ways in which we thought ourselves unique.
Tool use: In the 1960s, thanks to Jane Goodall's work in the Gombe National Park in Tanganyika (now Tanzania), we learned that chimps can use tools. Since then, a host of other animals — including crows, for goodness sake — have been found to be able to wield tools to solve problems. Chimps have even been shown to use sharpened sticks as lethal weapons when hunting.
How about culture, the ability to pass learning down the generations? Other animals have this, too. To take two examples, dolphins teach other dolphins how to forage in sand using a sponge over their nose to protect the skin, and Japanese macaques famously teach others how to wash sweet potatoes before eating them.
What about the ability to deceive? It might not be noble, but at least it was ours — or so we thought. Then it was shown that chimps and other great apes, and even some monkeys, have the ability to deceive.
For instance, a chimp named Georgia at the Yerkes National Primate Research Center in Atlanta, Georgia, plays tricks on her ape companions — she mingles with them quietly then sprays water from her mouth at them — and jays have been seen to retrieve buried food and re-cache it when they know they have been observed by other jays.
So it is that morality, personality, emotion, deception, culture and toolmaking — all these traits, once thought to be uniquely human, have been seen to a greater or lesser extent in other animals.
And, you've guessed it, this month's column will reveal another aspect of human nature that is not, as we've thought until now, unique: Aging — or, to be specific, the rate of aging.
Compared with some other animals, humans grow old gracefully. We live for a relatively long time, and that's especially true in Japan — as of 2010, the life expectancy of a Japanese man was 78.87 years, while for a Japanese woman it was 85.66 years.
It was long thought that our long lifespans, combined with good nutrition and medical care, explained why we were apparently different from other animals. But no one had properly looked at other animals. Now they have.
The first multispecies comparison of human aging patterns with those of chimps, gorillas and other wild primates suggests that the pace of our aging is not so different after all.
"There's been this argument in the scientific literature for a long time that human aging was unique, but we didn't have data on aging in wild primates besides chimpanzees until recently," said Susan Alberts, of the National Evolutionary Synthesis Center in Durham, North Carolina, who is also a biologist at the city's renowned Duke University.
Alberts and her colleagues combined data from long-term studies of seven species of wild primates: capuchin monkeys from Costa Rica; muriqui monkeys from Brazil; baboons and blue monkeys from Kenya; chimpanzees from Tanzania; gorillas from Rwanda; and sifaka lemurs from Madagascar.
Instead of focusing on the decline in health or fertility that comes with age, the team looked at the risk of dying. When they compared human aging rates — measured as the rate at which mortality risk increases with age — to similar data for nearly 3,000 individual monkeys, apes and lemurs, the human data fell neatly within the primate continuum.
Human patterns of mortality, it turns out, are surprisingly similar to those of other primates — even though wild primates don't have health-care programs, and are exposed to sources of mortality from which we may be protected, the scientists said. The results of the study are published in the journal Science.
In addition, there are also animals that live longer than us. Parrots, clams, some whales and tortoises can surpass our mortal span, and even some fish. In Japan, meanwhile, there was a famed koi carp given the name Hanako that was reported hatched in feudal Japan, in 1751. After outliving the samurai era and several owners, it died 226 years later, in 1977, when it was owned by a Dr. Komei Koshihara. Nonetheless, we humans are the longest-lived primates.
However, even despite Japan having the longest human longevity worldwide, you will have noticed a difference in the life expectancy of its men and women — a difference widely reflected globally. At the time of writing, the oldest person in Japan is a woman named Chiyono Hasegawa, who was born in 1896 and is 114 years old. The greatest age that any human has reached, incidentally, is 122 — that being how old one Frenchwoman named Jeanne Calment was when she died in 1997.
This pattern observed in humans is similar elsewhere in the animal kingdom: As males age, they die sooner than their female counterparts.
But here's an interesting point: The new study found that, in primates, the mortality gap between males and females is narrowest for the species with the least amount of male-male aggression. That species is a monkey called the muriqui, also known as the woolly spider monkey. The New World's largest monkeys, muriqui are only found in the Atlantic Forest of southeastern Brazil.
Of the seven wild primates in the study, muriquis are the only species in which males do not fight with one another for access to mates. This might mean that the reason why males of other species die faster than females is the stress and strain of competition.
If so, that would confirm what I always suspected was true: It's better to be a lover than a fighter.
Follow Rowan Hooper on Twitter @rowhoop. The second volume of Natural Selections columns translated into Japanese is published by Shinchosha at ¥1,500. The title is "Hito wa Ima mo Shinka Shiteru" ("The Evolving Human").