Older Is Better for Whale Moms: Study
Reuters
February 2, 2009
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An orca, or killer whale, speeds towards the beach before launching itself onto the sand
to hunt baby sea lions in Argentina's Patagonian area of Punta Norte March 21, 2008.
(Enrique Marcarian/Reuters)
WASHINGTON (Reuters) – Older mothers may do a better job raising their children than
younger, less-experienced moms, at least among killer whales, researchers reported on
Monday.
They studied 30 years of data to show that calves born to the oldest killer whales were
10 percent more likely to survive the critical first year of life than calves born to younger
mothers.
"Older mothers appear to be better mothers, producing calves with higher survival
rates," Eric Ward of the Northwest Fisheries Science Center in Seattle and colleagues
wrote in the journal Frontiers in Zoology.
Killer whale females become mature at around 15 and stop reproducing at around 40.
"Our work supports previous research showing that menopause and long postreproductive lifespans are not a human phenomenon," the researchers said.
For years researchers thought humans were the only creatures that had evolved
menopause, and one theory was that having a healthy and unencumbered grandmother
around to help take care of the babies benefited babies and mothers alike.
But killer whales, Orcinus orca, also have menopause. The mammals live long lives, with
males living up to 50 years and females living to be as old as 90.
Ward's team used 30 years of data on the charismatic black-and-white carnivores to see
which mothers did the best at raising calves.
"Older females may be more successful in raising young because of maternal
experience, or they may allocate more effort to their offspring relative to younger
females," the researchers wrote in their study, available on the Internet at
http://www.frontiersinzoology.com/.
(Reporting by Maggie Fox, Editing by Sandra Maler)
In Killer Whales and Humans, Older Moms May Be Best
By Andrea Thompson, LiveScience.com
February 6, 2009
Killer whales that are nearing menopause make the best moms, a new study finds. This
could be the case among humans, though it's less clear.
Killer whales (Orcinus orca) are extremely long-lived marine mammals. While males can
live as many as 50 years, female killer whales can live much longer - scientists have
even found one female that is thought to be more than 90.
Females can have their first calves (as baby killer whales are called) as early as age 10,
and can continue having offspring until their early 40s, when menopause can start to
kick in.
Just as in humans, menopause ends a female killer whale's ability to reproduce. Just
why humans, whales and other mammals have evolved this trait is unknown. Some
scientists think menopause could simply be due to physiological deterioration that comes
with age, while others think it could increase the fitness of older females.
Eric Ward of the Northwest Fisheries Science Center in Seattle and a team of
researchers studied killer whales living off the coasts of Washington and British
Columbia, Canada, to see what benefits menopause might have on females, including
on their calf-rearing abilities.
Older is better
The researchers used 30 years of data collected by the Center for Whale Research and
Canada's Department of Fisheries and Oceans that includes information on all of the
whales living in the area.
"During annual photographic surveys, nearly every individual in the population has been
recorded. Each animal has unique pigmentation, scars, and fin shapes, allowing us to
track the survival and reproductive performance of each female over time," Ward said.
The researchers didn't find any direct benefit of menopause for mothers (or
grandmothers), but they did find an impact on the survival of calves: Calves born to older
mothers had a 10 percent higher survival rate than other calves.
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"We found that the oldest mothers may also be the best mothers," Ward said. "Older
females may be more successful in raising young because of maternal experience, or
they may allocate more effort to their offspring relative to younger females," which are
splitting their attention between their calves and mating.
The results of the research, which was partially funded by the National Research
Council, were detailed in the Feb. 3 issue of the online journal Frontiers in Zoology.
The researchers also found that 3-year-old killer whales may benefit from helpful
grandma whales; studies of humans have also shown a positive grandmother effect on
newly-weaned infants, the researchers said in their study.
Biology and sociology
Human females of course also become infertile once they reach menopause, but their
ability to bring a pregnancy to term and have a healthy baby can be affected long before
that, as problems in the reproductive system can begin to accumulate after about age
40.
"Biologically you've got a pretty sharp ceiling," said retired sociologist John Mirowski,
formerly of the University of Texas, Austin. Mirowski was not involved in the new whale
study.
But a mom's age isn't the only factor that affects the health and development of her
children.
"There's a tradeoff between biology and sociology," Mirowski told LiveScience. And for
child-rearing socially speaking, "the later the better," Mirowski said.
Older women are more likely to have careers and college degrees, which means they've
had "time to develop personally," which can contribute to the quality of a marriage and
the economic stability of a household, all of which can have a positive impact on a child.
When biological and sociological factors are taken into account, there's a "just right" age
range of about 25 to 35 or 40 where there is minimum risk to the mother and baby and
maximum benefit, Mirowski said. Though that doesn't mean that older women can't have
healthy children, or that "we can't push that ceiling back," he added.
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