There are important evolutionary reasons that explain the differences between men and women, and understanding them can help us live longer, healthier lives, scientists say.
The battle of the sexes has been raging on earth for millions of years, and it’s all down to sexual antagonism, the evolutionary genetic variants that are good for one sex but bad for the other.
In obvious one is longevity – no matter how advanced medicine becomes, on average women still live longer than men.
‘It is important to remember that evolution maximises Darwinian fitness rather than longevity,’ explained Dr Alexei Maklakov, at the Department of Animal Ecology of Uppsala University’s Evolutionary Biology Centre in Sweden.
He explained that this meant that one sex can live longer than the other. ‘Males and females have very different reproductive strategies, meaning that the trade-off between reproduction and longevity can be optimised differently between the sexes.’
Those aged 65 years or over are projected to account for 28.7 % of the EU’s population by 2080, compared with 18.9 % in 2015, according to EU data. As the global population ages, it is more important than ever to study this subject.
‘There is a massive research effort underway to find treatments that can improve the human condition in late life,’ said Dr Maklakov. ‘However, because of the fundamental biological differences between the sexes, men and women are likely to respond differently to the same treatments.’
As part of the EU-funded AGINGSEXDIFF project, he has done tests on roundworms and fruit flies - organisms commonly used by biologists - to look at the factors which affect longevity.
The project also analysed human data to help explain the variation in longevity between species, populations, sexes and individuals.
Dr Maklakov gives the example of female beetles, where longevity is positively associated with fitness, meaning longer-lived females produce more offspring. In male beetles it’s a different story, successful males invest a lot in early-life reproduction and die young.
The same principle explains how shifts in demographics are giving human females longer average lifespans than males.
In the past, women paid a higher cost than men in terms of longevity for having children. A historical shift to smaller families has therefore increased longevity among women but not among men, Dr Maklakov explains.
The project has helped to explain the link between evolutionary biology and biogerontology – the science of why and how we age.
Sex-specific
‘For biogerontologists, our results imply that lifespan- and healthspan-extending treatments in humans will likely always affect men and women differently, suggesting that we need more research on sex-specific effects of the new treatments,’ said Dr Maklakov.
Sexual antagonism may also help to explain a longstanding paradox for evolutionary biologists – why there is so much genetic variation in many natural populations.
‘Any gene variants that are good should spread throughout the population, and any bad ones should be lost,’ said Dr Jessica Abbott at Lund University’s Department of Biology in Sweden. ‘So why do we see so much variation?’
She has selected successive generations of fruit flies and flatworms in a sex-specific manner and is now setting about genetic and genomic analysis of the changes she has observed in the subjects as part of the EU-funded ComplexSex project.
Sexual antagonism can explain how sex chromosomes evolve, how males and females evolve to be different from one another, and how genetic conflicts shape evolution, Dr Abbott adds.
The findings of the ComplexSex project will apply specifically to flatworms and fruit flies, but Dr Abbott believes the broader evolutionary mechanisms the research highlights should be relevant to many species, including humans.
‘Lots of diseases with a genetic component have different prevalence in men and women. My colleagues and I have speculated that this might be partially due to sexual antagonism,’ she said.
‘The better we understand sexual antagonism as a phenomenon, the more we might be able to understand the reasons for these differences between men and women in disease and ageing.’
By Helen Massey-Beresford
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