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Scientists examine the ‘evolutionary paradox’ of menopause in mammals like killer whales and humans

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Menopause in women and females from a few other “higher” species is probably a fluke of nature rather than evolution at work, according to a study published Wednesday.

Biologists have long puzzled over why women lose the capacity to reproduce during roughly the last third of their lives.

Another, less polite, way scientists frame the question is this: why do females from a handful of species — including killer whales — continue to live well beyond the age when they can bear offspring?

“Menopause is an evolutionary paradox,” said Hazel Nichols, a biologist at Liverpool John Moores University and lead author of the study.

“An early end to reproduction seems contrary to the laws of natural selection, where passing on genes to the next generation is the main purpose of life.”

In most mammals, she pointed out, females reproduce until a ripe old age.

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Evolutionary biologists have put forward competing explanations for this extended “post-reproductive lifespan,” or PRLS.

The “grandmother hypothesis” suggests women outlive their fertility in order to help raise grandchildren, thereby strengthening the likelihood that their own genes will survive.

In this scenario, “grandmothers… encouraging their sons to have more children” are driven by a biological imperative, Nichols told AFP.

Even among orcas, scientists have shown that females remain with their male offspring, and probably teach them hunting techniques and where to apply them.

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– Evolutionary tinkering –

Another theory says that menopause does not, in fact, confer any advantage in the Darwinian struggle to pass on genes from one generation to the next, but is just an accident resulting in a “mismatch” in the ageing process.

“Different parts of the body are likely to age at different rates, in the same way that some part of a car wear out before others,” Nichols said.

In this argument, modern medicine and nutrition has helped outpace the evolutionary process, extending human life beyond its “natural” limits.

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To find out who might be right, Nichols and colleagues examined data from 26 different mammal species, including three tribal or historical human populations.

In each case, they tested for the effects of lifespan, group size, and the tendency of post-menopause females to stay within either a male- or female-dominated group.

What they found is that neither school of thought could adequately explain the menopause puzzle, but that when combined, a coherent picture began to emerge.

“Post-reproductive lifespan appears to arise by chance,” Nichols said by email.

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“But then evolutionary ‘tinkering’ comes into play to extend PRLS in species that benefit from females caring for their sons and grandchildren.”

Among orcas the bond is so strong that “many killer whale sons die in the year after their mother’s death,” she said.

The findings were published in Biology Letters, a journal of Britain’s Royal Society.

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Virginia Democrats are so fired up that the party chair had to scold them: ‘Sit down — be quit’

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Democrats in Virginia are fired up as they gathered in Richmond for their annual gala dinner.

Political analysts believe the Democratic Party of Virginia has a good chance to win control of the state legislature in 2019's election, before setting their sights on the Commonwealth continuing its recent trend of voting Democratic in presidential elections.

Patrick Wilson, a political reporter for the Richmond Times-Dispatch, attended the event.

He reported that Democrats were so "noisy" that it was hard to hear the speakers, which include presidential candidates Sen. Amy Klobuchar (D-MN) and South Bend Mayor Pete Buttigieg.

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‘Everyone knows what to expect’ at Trump’s Amway Center re-election kickoff

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Donald Trump considers himself a legendary salesman, but can he really sell America on giving him four more drama-filled years at the White House?

Tuesday, he'll make his big pitch.

The 2020 reelection kickoff rally is being held in Orlando, Florida and campaign operations chief Michael Glassner says the "historic" event "has already generated tens of thousands of ticketing requests."

There's little mystery about how the night will go down.

Expect Trump, the self-promoting hero of his ghost-written book "The Art of the Deal," to claim the US economy is richer, the military stronger, and the country more respected than ever in history.

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Florida man’s own family blasts him after he was arrested for racist threats: ‘This isn’t how we were raised’

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After a Florida man was arrested for trying to start a race war, a member of his own family slammed his values.

"A Florida man’s social media posts that threatened violence against African-Americans, Jews and homosexuals and that urged his followers to start a race war netted him a $1 million bond," the Miami Herald reported Saturday. "And then there’s another $100,000 bond he would have to pay to get out of Lee County Jail because of a weapons charge."

Joshua Leff, 40, is being held in the Lee County Jail.

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