WHAT鈥橲 the point of old men? We women have had our postmenopausal existence justified, in evolutionary terms, by the grandmother hypothesis. But the same cannot be said for men. The mystery is why they live long past their physical prime, with muscles turning to flab and potency waning.

In How Men Age, we have an answer. Biological anthropologist Richard Bribiescas covers some interesting uncharted territory. This is not a mere description of ageing. Instead, by considering male ageing in the light of natural selection, it aims to answer big questions including why men鈥檚 lifespans are shorter than women鈥檚, why baldness, prostate disease and erectile dysfunction are so prevalent, and how humans as a species have benefited from men鈥檚 tendency to run to fat.

From an evolutionary perspective, nothing matters more than sex. And as far as men are concerned, nothing influences sexual power more than testosterone. It increases libido, promotes muscle growth and encourages risk-taking behaviour 鈥� all of which help attract a mate. But testosterone peaks in early adulthood, so that men are past their physical prime by the age of 30. It鈥檚 tempting to see it as all downhill from there. But with wit and insight, Bribiescas shows convincingly that鈥檚 not the case.

He points out that testosterone has a dark side 鈥� it can increase a man鈥檚 metabolic rate and suppress the immune system. In other words, there鈥檚 a trade-off, or as Bribiescas puts it: 鈥渕acho makes you sick鈥�. High levels of the hormone early in life help explain why men don鈥檛 live as long as women and why they are prone to prostate cancer later on. So waning testosterone can be seen as a positive development. It may make older men less physically competitive against younger ones, but men can produce offspring throughout their lives and, argues Bribiescas, as they age they develop new reproductive strategies to achieve this.

For a start, although they may lack raw strength, their experience and guile often make them better providers than their younger counterparts. Bribiescas has done fieldwork with the Ache people of Paraguay, and points to research showing that men鈥檚 hunting success peaks in their 40s, long after their testosterone levels peak.

What鈥檚 more, older men tend to become more nurturing. As testosterone decreases, a man鈥檚 girth increases, and the metabolic changes associated with growing adiposity promote care of offspring. Bribiescas calls this the 鈥減udgy dad hypothesis鈥�, and argues that it has implications for the evolution of our species as a whole.

Humans live far longer than other primates. For longevity to evolve, natural selection must favour long-lived individuals. Older women cannot reproduce, so they are out of the running. But if, throughout human history, pudgy older men have been fathering children, then they will have passed on genes associated with longevity to both daughters and sons.

Old men, therefore, could be the reason we all live so long. It would appear there is some point to them after all.

This article appeared in print under the headline 鈥淕olden oldies鈥�

This lion king (pictured above) is a queen. And she鈥檚 not the only one.

Five lionesses in Botswana have grown a mane and are showing male-like behaviours. One is even roaring and mounting other females.

Male lions are distinguished by their mane, which they use to attract females, and they roar to protect their territory or call upon members of their pride. Females lack a mane and are not as vocal.

But sometimes lionesses grow a mane and even behave a bit like males. However, until now, reports of such maned lionesses have been extremely rare and largely anecdotal. We knew they existed, but little about how they behave.

Now, Geoffrey D. Gilfillan at the University of Sussex in Falmer, UK, and colleagues have reported five lionesses sporting a mane at the Moremi Game Reserve in Botswana鈥檚 Okavango delta.

Gilfillan started studying these lionesses back in March 2014, and for the next two years he focused on recording the behaviour of one of them, called SaF05. She had an underdeveloped mane and was larger than most females.

鈥淲hile SaF05 is mostly female in her behaviour 鈥� staying with the pride, mating males 鈥� she also has some male behaviours, such as increased scent-marking and roaring, as well as mounting other females,鈥� says Gilfillan.

鈥淎lthough females do roar and scent-mark like males, they usually do so less frequently,鈥� he says. 鈥淪aF05, however, was much more male-like in her behaviour, regularly scent-marking and roaring.鈥�

A likely explanation is an increased level of testosterone as these lionesses mature, says , president and chief conservation officer at the global wild cat conservation organisation Panthera.

In lions, testosterone directly affects the development of manes. Castrated males, for example, lose their ability to produce testosterone and promptly lose their mane, too.

In 2011, a at the National Zoological Gardens of South Africa developed a mane. Tests revealed high levels of testosterone due to a problem in her ovaries, and once they were removed she reverted to a typical lioness.

The idea that testosterone is implicated in the Botswana lionesses is also backed by observations of their reproductive success, says at Virginia Tech in Blacksburg.

鈥淲hile some of the maned lionesses were observed mating, none of them became pregnant, suggesting they are infertile, a known consequence of high levels of androgens such as testosterone in females,鈥� she says. 鈥淭he behavioural changes suggest this is likely the case.鈥�

Hunter suspects this explanation applies to the animals studied by Gilfillan and his colleagues. 鈥淕iven all five known maned females come from the Okavango region, there must be a genetic component in this population underlying the phenomenon,鈥� he says.

鈥淚 don鈥檛 think this is anything to be concerned about,鈥� says Hunter. 鈥淎lthough the females are apparently infertile, they otherwise appear to live long, healthy lives. And from a conservation perspective, there is nothing to suggest the pattern is increasing or will ever be anything more than a rare, local phenomenon.鈥�

No one seems to be studying the exact genetic and hormonal causes of this phenomenon at the moment. 鈥淚 guess there are just one or a few genes altered,鈥� says at Imperial College London, who had a student briefly work on the possible causes. 鈥淚 believe some masculinised genes have been documented in domesticated cats 鈥� it would be good to look into this, especially given that the cat genome is available as reference.鈥�

Could the masculinised females in fact be a boon to the pride when it comes to competing with other prides? It鈥檚 possible, it seems.

Gilfillan says he once saw SaF05 bring down a zebra. 鈥淎 neighbouring pride stole the zebra from SaF05, but in return SaF05 killed two of their cubs.鈥�

Cub-killing behaviour is rare in females but common in males.

IT COULD be the biggest killer you鈥檝e never heard of: the weakening and loss of muscle that happens as we get older.

Muscle loss is no longer seen as just a side effect of disease and frailty 鈥� it鈥檚 also a prime cause. As well as contributing to falls, muscle loss has serious knock-on effects on metabolism (see 鈥�Life-saving muscle鈥�). In future, muscle-boosting drugs could aid those unable to maintain muscle mass through exercise such as weight training. Although researchers stress this isn鈥檛 about bodybuilding, but keeping muscles in your limbs at a healthy level.

Muscle loss, also known as sarcopenia, is increasingly being seen as an important facet of ageing, according to several speakers at a held in Basel, Switzerland, last month. 鈥淭reatments will eventually get into the market,鈥� said Dan Perry of the patient lobby group .

However, the mechanisms behind muscle ageing are still poorly understood 鈥� although new research suggests it involves damage from free radicals.

Mice that have been genetically modified to produce fewer free radicals in their mitochondria are known to . So a team led by Andrew Marks at Columbia University in New York investigated how this affected the ageing of their muscle tissue.

They found that a key player is calcium, the release of which triggers our muscles to contract. The molecule responsible for this release 鈥� ryanodine receptor 1 鈥� is damaged by free radicals, and as the rodents age, calcium begins to leak out when it shouldn鈥檛, weakening muscle fibres.

The modified mice experienced less free radical damage to the ryanodine receptor 1. They also had stronger muscles, and, in old age, chose to run on their exercise wheels more than unmodified mice 鈥� by about an extra kilometre a day ().

鈥淚t helps point to the role that mitochondria play in the muscle ageing process,鈥� says Daniel Moore of the University of Toronto, Canada.

Marks has founded a firm called to develop several compounds aimed at preventing calcium leakage, which are in early-stage clinical trials.

鈥淧eople think of muscle as the body鈥檚 mover, but it鈥檚 really a huge metabolic organ鈥�

Other drugs are in development that combat sarcopenia in different ways. Muscle fibres are in a constant state of turnover, being simultaneously broken down and regrown, so any compound that tips the balance towards growth could help build muscle mass.

One class of drug includes the compound , which works by blocking a signalling pathway targeted by an inhibitor of muscle growth called myostatin. Others work by .

鈥淭here鈥檚 a lot of interest in trying to come up with something for sarcopenia because at the moment there鈥檚 no treatment,鈥� says Marks.

Indeed, it鈥檚 only within the last six months that US researchers have even agreed on how to define the condition 鈥� essential before a drug treatment can be approved. The US National Institutes of Health .

鈥淲e have come a long way in how to approach this,鈥� says of the University of Maryland, who was involved in the defining process.

In the meantime, there is already a natural way to boost muscle: exercise. 鈥淭he mitochondrial function of lifelong exercisers is like that of someone half their age,鈥� says Moore. 鈥淥ne of the best anti-ageing pills is to stay active.鈥�

This article appeared in print under the headline 鈥淏eefing up can keep you healthy鈥�