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Friday, December 24, 1999Having children really does lead to an early grave: study
At last, science has proven what parents have suspected all along: Having kids makes us age faster.
A new British study with fruit flies suggests reproduction can lead to a wave of early death. Published today in the journal Science, the finding may shed light on why human parents tend to die off more quickly than childless people -- usually about 35 years after their offspring are born.
However, the researchers say the time-delay mechanism that causes this is unclear.
"Reproduction may cause damage directly, and the effects may accumulate with time," says biologist Linda Partridge, of University College in London.
It may also divert nutrients from DNA repair and defence against disease, resulting in a more rapid accumulation of genetic damage.
Evolutionary biologists say the finding may also answer one of the most baffling questions in ageing research: Why do so many parents die in their late 60s?
The most common theory of ageing suggests genes that are beneficial in youth mutate to become harmful later, elevating the risk of death as years pass. Except death doesn't follow this pattern.
"Mortality rates should continue to accelerate with age," says David Reznick, a University of California biologist. "But instead, mortality rates plateau or decelerate in organisms as diverse as yeast, nematodes, insects and humans."
In other words, a huge group of people die around their 68th birthday. The rest linger for years, with their funeral dates strung further apart.
Ms. Partridge and her colleague Carla Sgro think the mystery can be explained by the harmful effects of reproduction.
To test their theory, they bred lines of "old" and "young" fruit flies. The "old" flies came from breeding adults at an older age, whereas "young" ones were propagated from young breeders.
For the first 30 days, the death rates were similar.
Then the "young" flies, who laid more eggs, experienced a wave of death that peaked at 40 to 50 days, which suggests reproduction can trigger a premature wave of death. The "old" flies, who laid fewer eggs, lived much longer.
When the researchers stopped the "young" group from laying eggs (by irradiation or inducing a genetic mutation), they began to live as long as their "old" counterparts.
The researchers said parents who survived this initial wave of mortality tended to live as long as the childless individuals, suggesting the harmful impact of breeding may wear off over time.
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