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Menopause and its side effects can all be blamed on men, Canadian experts suggest.

Evolutionary geneticists from McMaster University say men’s tendency to choose younger mates meant fertility became pointless for older women.

According to a PLOS Computational Biology article, experts say men’s preferences eventually led to the menopause.

However, a UK expert said that was the “wrong way round” and men chose younger women because older women were less fertile.

Researchers have long been puzzled as to why it appears that human are the only species where females cannot reproduce throughout their lives.

Previous theories had proposed a “grandmother effect”. This suggests that women lose their fertility at an age where they might not live to see a child grow, and instead are available to care for younger women’s children.

The menopause was therefore seen as the block to older women from continuing to reproduce.

But this latest theory suggests things work the other way around, and that it is the lack of reproduction that has given rise to menopause.

Evolutionary geneticists from McMaster University say men's tendency to choose younger mates meant fertility became pointless for older women

Evolutionary geneticists from McMaster University say men’s tendency to choose younger mates meant fertility became pointless for older women

Using computer modelling, the team from McMaster’s concluded “preferential mating” was the evolutionary answer – men of all ages choosing younger women as partners.

That meant there was “no purpose” in older women continuing to be fertile.

Prof. Rama Singh, an evolutionary geneticist who led the study, said men choosing younger mates were “stacking the odds” against continued fertility.

He said: “There is evidence in human history; there was always a preference for younger women.”

Prof. Rama Singh stressed they were looking at human development many thousands of years ago – rather than current social patterns,

He said this extended longevity – plus later childbirth – could potentially alter the timing of the menopause, over a significant period of time.

“The social system is changing. There are women who are starting families later, because of education or a career.”

Prof. Rama Singh suggested this trend would mean those women would have a later menopause, and those genes would be passed on to their daughters “with the possibility of menopausal age being delayed”.

However, Dr. Maxwell Burton-Chellew, an evolutionary biologist in the department of zoology at the University of Oxford, challenged the theory.

“The authors argue that the menopause exists in humans because males have a strong preference for younger females.

“However, this is probably the wrong way round – the human male preference for younger females is likely to be because older females are less fertile.

“I think it makes more sense to see the human male preference for younger females largely as an evolved response to the menopause, and to assume that ancestral males would have been wise to mate with any females that could produce offspring.”

Dr. Maxwell Burton-Chellew added: “Evolutionarily-speaking, older females
faced an interesting ‘choice’: have a child that may not reach adulthood before your own death, or stop reproducing and instead focus on helping your younger relatives reproduce.”

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Canadian researchers, who examined the impact of the medications on the whole body, say common anti-depressants could be doing patients more harm than good.

Researchers at McMaster University examined previous patient studies into the effects of anti-depressants and determined that the benefits of most anti-depressants compare poorly to the risks, which include premature death in elderly patients.

“We need to be much more cautious about the widespread use of these drugs,” said study leader and evolutionary biologist Paul Andrews.

“It’s important because millions of people are prescribed anti-depressants each year, and the conventional wisdom about these drugs is that they’re safe and effective.”

Anti-depressants are designed to relieve the symptoms of depression by increasing the levels of serotonin in the brain, where it regulates mood.

The vast majority of serotonin that the body produces, though, is used for other purposes, including digestion, forming blood clots at wound sites, reproduction and development.

The researchers, whose study was published in the online journal Frontiers in Psychology, found that anti-depressants had negative health effects on all processes normally regulated by serotonin.

This included a higher risk of developmental problems in infants, problems with sexual function, digestive problems and abnormal bleeding and stroke in the elderly.

The authors reviewed three recent studies showing that elderly anti-depressant users are more likely to die than non-users, even after taking other important variables into account. The higher death rates indicate that the overall effect of these drugs on the body is more harmful than beneficial.

The higher death rates among anti-depressants users indicate that the overall effect of these drugs on the body is more harmful than beneficial

The higher death rates among anti-depressants users indicate that the overall effect of these drugs on the body is more harmful than beneficial

“Serotonin is an ancient chemical. It’s intimately regulating many different processes, and when you interfere with these things you can expect, from an evolutionary perspective, that it’s going to cause some harm,” Paul Andrews said.

Millions of people are prescribed anti-depressants every year, and while the conclusions may seem surprising, Paul Andrews says much of the evidence has long been apparent and available.

“The thing that’s been missing in the debates about anti-depressants is an overall assessment of all these negative effects relative to their potential beneficial effects,” he says.

“Most of this evidence has been out there for years and nobody has been looking at this basic issue.”

In previous research, Paul Andrews and his colleagues had questioned the effectiveness of anti-depressants even for relieving depression. They found patients were more likely to suffer relapse after going off their medications as their brains worked to re-establish equilibrium.

Paul Andrews says it is important to look critically at their continuing use.

“It could change the way we think about such major pharmaceutical drugs,” he said.

“You’ve got a minimal benefit, a laundry list of negative effects – some small, some rare and some not so rare. The issue is: does the list of negative effects outweigh the minimal benefit?”

 

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