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Live Long and Reproduce

Insect queens have it all: colonies of workers that cater to their every need, security befitting a monarch, and, to top it all off, time to enjoy their royal perks. Some queens live 100 times longer than solitary insects. In today's Nature, two researchers claim that the queens' sheltered lives may have helped them evolve their extraordinary longevity.

Aging seems to be an inevitable consequence of living, since cells die after DNA is damaged by replication mistakes and the chemical by-products of turning food into energy. Consequently, many biologists have argued that cellular factors, such as metabolic rate, figure greatly in fixing an animal's natural life-span. Hence, elephants with their slow metabolism outlive mice, which burn calories much faster.

But other biologists believe that natural selection has the larger hand in setting the rate of aging. In plants and animals that are at high risk of dying young, mechanisms to repair the DNA damage incurred in a long life don't have a big evolutionary payoff. Such organisms have a better chance of passing on their genes if they reproduce early. Organisms with more protection, on the other hand, should be more likely to reap a benefit from the repair mechanisms by living--and reproducing--into old age.

Working out whether aging is mainly a by-product of metabolism or is controlled by natural selection has been difficult, though, because many of the small animals that live dangerous lives also tend have higher metabolic rates. But evolutionary biologists Laurent Keller of the University of Lausanne in Switzerland, and Michel Genoud of the University of Bern in Switzerland, thought they might be able to disentangle these effects by looking at insect queens. Queens, who lay millions of eggs for their colonies, have high metabolic rates, but most live a very sheltered life. Keller and Genoud reasoned that if natural selection is at work, the best-protected queens--having no need to rush their reproduction--should have the longest life-span.

When they dug through the published scientific literature and compared the laboratory life-spans of nearly 150 insect species from eight orders, they found that while no solitary insects live more than a year on average, the queens of social insects live an average of 10 years, and queens of one ant species live nearly 30 years. Worker members of social species had intermediate life-spans. They also found that well-protected queens tend to live as much as seven times longer than those whose colonies move frequently and expose the queen to danger.

Geneticist Ross Crozier of La Trobe University in Bundoora, Australia, says the evidence "will significantly tip the balance" toward evolutionary theories of aging. But Keller says the findings will do little to aid humans searching for a scientific fountain of youth. During human evolution, he says, "there has not been selection to live more than 70 years." As a result, many mutations have accumulated that limit the average human life-span. It is unlikely, he says, that a single gene or chemical will be able to overcome all of them and dramatically increase life expectancy.