Mate Choice and the Origin of Menopause

Mate Choice and the Origin of Menopause

Abstract

Human menopause is an unsolved evolutionary puzzle, and relationships among the factors that produced it remain understood poorly. Classic theory, involving a one-sex (female) model of human demography, suggests that genes imparting deleterious effects on post-reproductive survival will accumulate. Thus, a ‘death barrier’ should emerge beyond the maximum age for female reproduction. Under this scenario, few women would experience menopause (decreased fertility with continued survival) because few would survive much longer than they reproduced. However, no death barrier is observed in human populations. Subsequent theoretical research has shown that two-sex models, including male fertility at older ages, avoid the death barrier. Here we use a stochastic, two-sex computational model implemented by computer simulation to show how male mating preference for younger females could lead to the accumulation of mutations deleterious to female fertility and thus produce a menopausal period. Our model requires neither the initial assumption of a decline in older female fertility nor the effects of inclusive fitness through which older, non-reproducing women assist in the reproductive efforts of younger women. Our model helps to explain why such effects, observed in many societies, may be insufficient factors in elucidating the origin of menopause.

Author Summary

The origin and evolution of menopause is understood poorly and explanations remain contentious. Virtually ignored among explanations is the effect that mate choice can exert on an evolving population. We designed and used a computational model and computer simulation to show that male mating preference for younger females in humans could have led to the accumulation of mutations deleterious to female fertility and thereby produced menopause. Our model demonstrates for the first time that neither an assumption of pre-existing diminished fertility in older women nor a requirement of benefits derived from older, non-reproducing women assisting younger women in rearing children is necessary to explain the origin of menopause.



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Study blames men for menopause

Study blames men for menopause

    POSTED: 15 Jun 2013 7:44 AM
   
Men and their preference for younger female mates may have led to the phenomenon of menopause in women, according to a controversial study by Canadian researchers published this week.

WASHINGTON: Men and their preference for younger female mates may have led to the phenomenon of menopause in women, according to a controversial study by Canadian researchers published this week.

"If women were reproducing all along, and there were no preference against older women, women would be reproducing like men are for their whole lives," said evolutionary geneticist Rama Singh, a professor at McMaster University.

Singh said the conventional "grandmother theory," which holds that older women grow infertile so that they can assist the survival of their kin by helping to raise their children's offspring, did not make sense to him.

Instead of age leading to infertility, Singh theorised that the dwindling pool of male mates for older women - because many older men seek to mate with younger women - led to a lack of reproduction that gave rise to menopause.

His work, backed up by computer models, suggests that a male mating preference for younger females could have led to the accumulation of genetic mutations that would harm female fertility and bring on menopause.

The study was published on Thursday in the open-access, peer-reviewed journal PLOS Computational Biology.

But while the assertion raised many eyebrows, not all experts are convinced by Singh, who questioned why menopause appears to be mainly a human phenomenon.

"I cannot agree with the theory put forth," said Steven Goldstein, professor of obstetrics and gynaecology at New York University School of Medicine.

"There are other primates who do experience menopause, although life expectancy after menopause is extremely limited," said Goldstein, who was not involved in the research.

"The same was true of humans until roughly the 1850s. In 1850 the average age of menopause was 46 and life expectancy was 50, which more closely parallels that of chimpanzees or gorillas.

Rather, a more accurate explanation would be that scientific advances like water purification and antibiotics have led to much longer lives among humans, he said.

"The cessation of reproductive capabilities in higher primates has always come shortly before the life span ends. It is only the advances of modern society that have women living so very long," he told AFP.

- AFP/fl

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JEM attracts more than 10,000 shoppers within first hour of opening

JEM attracts more than 10,000 shoppers within first hour of opening

    By Alvina Soh
    POSTED: 15 Jun 2013 12:35 PM
  
The much-awaited opening of suburban mall JEM took place on Saturday morning and attracted more than 10,000 shoppers within an hour of its opening.

SINGAPORE: The much-awaited opening of suburban mall JEM took place on Saturday morning and attracted more than 10,000 shoppers within an hour of its opening.

However, not all shops were shipshape, with some, including retailer Topshop and restaurant Ding Tai Fung, closing in the afternoon due to water leakages, according to their staff.

Plastic bags were seen placed over store mannequins and towels on the floor inside Topshop, barely hours after its opening in the morning.

A sales assistant there also told Channel NewsAsia that the building's aircon was leaking.

Queues were seen snaking outside the mall with some shoppers showing up as early as 5.30am.

The suburban mall finally opened its doors after delaying its opening on June 11 due to the lack of fire permits.

The delay did not discourage shoppers who came from all over the island to throng the 818,000 square feet mall.

One thousand early-bird shoppers also received S$10 vouchers which were quickly put to good use inside the 241-store mall.

Shoppers can also look forward to shops like bookstore Kinokuniya which opened its first branch here in 14 years.

The mall did not open as scheduled early this week after the Singapore Civil Defence Force said it did not receive safety applications for some of the 241 units.

Fire safety certificates are necessary for commercial premises and their units to operate.

- CNA/fa

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