Let’s hear it for the female of the species and (more guardedly) for her second X-chromosome! Female superiority in colour vision, immune response, longevity, even basic survival from birth to death are illustrated in Sharon Moalem’s The Better Half. After decades, if not centuries, of bad press for women and their vulnerable biology, this book argues that in fact “almost everything that is biologically difficult to do in life … is done better by females”.

Moalem, a Canadian-born physician, is a research geneticist who has identified two new rare genetic conditions. He has worked across the world in paediatric medicine, including clinics for HIV-infected infants and is also a biotechnology entrepreneur and bestselling author. The Better Half is his latest foray into the field of popular science, and presents a general argument for the superiority of women’s biology to men’s.

In most circumstances, a human female has two X-chromosomes, one from her father and one from her mother; a male has just one, inherited from his mother, which is paired with a Y-chromosome, inherited from his father. Moalem believes that the X-chromosome has always received a poor press, and that it is time this negative view is counteracted. He draws on swathes of medical and historical data to show that, in many instances, the superiority of women’s biology is explicitly linked to their possession of the second X-chromosome. The greater complexity of women’s biology, he claims, is the secret of their success – it is more difficult to make a female but, once made, she trumps the male in her lifelong survival skills, for instance in her hyperefficient immune system shrugging off infection and maximising the benefits of vaccination – which means that females can avoid the consequences of a wide range of life threatening events ranging from starvation and cancer to, Moalem has cautiously concluded, Covid-19.

In mainstream genetics it was long held that, despite having two X-chromosomes, female cells only made use of one: the second randomly switched off or deactivated early on in embryonic development, a process rather summarily described as an instance of “genetic redundancy”. There was some evidence that the deactivation reduced female chances of succumbing to X-linked problems, due to the availability of an undamaged back-up. It was acknowledged, for example (though rather grudgingly), that women generally escaped being colour blind. Moalem notes that when he was studying genetics there was much emphasis on the tiny Y-chromosome as “what makes a man”. He observes wryly that maybe this positivity was related to the fact that “most of the people who were speaking breathlessly about the Y had one as well”.

Now a new spin on the X-inactivation story is emerging in genetics. Via a process called “escape from X-inactivation”, it turns out that the silenced X-chromosome is not so silent after all – there are escapees which may continue to offer back-up services, for instance providing extra cellular recovery options in the face of traumatic injury. It is to the benefits offered by this flexible availability within different cells that Moalem attributes the secrets of women’s biological superiority.

Statistics going back as far as 1662 show women living longer than men, and today’s figures show that 95% of people who have reached the age of 110 and over are female. In sport, women’s success in races such as ultra-marathons offer a different perspective on what it means to be physically superior. In the spirit of Angela Saini’s book Inferior, Moalem notes that this superiority has largely been ignored by medical science. And he discusses the medical trial data whose absence is observed by Caroline Criado-Perez in Invisible Women, her exploration of how the world is designed for men. Medicine needs to stop ignoring the secrets of women’s biological successes, Moalem argues, and find ways of harnessing them to improve the survival chances of the whole of the human race.

Imagine you live in a world where most individuals can see 1m colours. But in one group of these people (let’s call them males), about 8% cannot tell the difference between colours such as red and green, and a smaller number are totally colour blind. In a second group in this population (let’s call them females), almost all can see the standard 1m colours, but some (perhaps as many as 15%) can see 100m colours. Would you excitedly rave about the amazing talent of this latter group? Or would you just describe them as “not usually colour blind”? This same group has an immune system that has a profound talent to fight off many forms of infection and reap major benefits from vaccinations – with the down side that sometimes such hyperefficiency can lead to autoimmune disorders such as multiple sclerosis. Would you celebrate the former or emphasise the latter? For years, it is the drawbacks that have been underlined.

The Better Half is an eye-opening book. In explaining why the advantages that accompany females’ greater genetic options have to date been largely ignored, Moalem points to “paradigm blindness”, and to the fact that research geneticists rarely get out in the field to notice, for example, the much greater survival rates of girls in paediatric ICUs (rates which, he discovers, have been clearly obvious to the nurses doing the frontline caring).

I take issue with one part of his chapter on “The Male Brain”, for the moment setting aside the unproven assumption that the brains of men are different from the brains of women. Moalem chooses to consider autism, and it appears as a given in his book that autism is more common in boys than girls (itself an assumption that is increasingly being challenged). Yet at the more impaired end of the autism spectrum, it is possible that there are as many girls as boys, and his suggestion that females have a different “kind” of autism doesn’t quite prove his wider argument. The X-linked disorders such as “fragile-X” or Rett syndrome receive only a passing mention – not surprisingly perhaps as they run counter to his argument about the superiority of the X-chromosome.

What about hormones? Moalem has perhaps missed a good opportunity to counter oestrogen’s frequently negative press, and to laud its potentially neuroprotective effects. The greater susceptibility of women to Alzheimer’s disease is put down by Moalem to a form of anti-inflammatory process linked to an overefficient immune system; their lesser susceptibility to Parkinson’s disease (surely a possible inclusion in the list of female genetic successes) is unexplained.

One section of the book focuses on “why women’s health is not men’s health”, and considers the failures of drug companies to test their products on females as well as males. For sure this has had detrimental consequences on, for example, the accuracy of dosage rates. But in at least one of the examples he gives, that of Ambien, body mass and blood volume are key factors in calculating dosage rates: because people vary enormously in size and shape, simply dividing test participants into males and females still risks inaccuracy. He is talking about averages, it’s true, but even so Moalem seems firmly wedded to the notion that genetic females and genetic males can be neatly categorised into two distinct types, and that the understanding of genetic sex will provide all the answers we need.

The impression given in The Better Half is that there is a lifelong
free-ranging choice between X-chromosomes available to the female, her cells dancing back and forth between the best options that will help her to heal quicker after a car crash or to overcome the bacterial infection that might lead to an ulcer. There are brief and tantalising hints about the “escapees” from X-inactivation in several chapters of Moalem’s book, but it is a shame that we are never given a full, head-on account.

Yet this book is full of wonderful titbits of information – from the existence of a female prostate gland to the number of honey bee flying miles it takes to make 1lb of honey. The celebration of the genetic diversity offered by the female’s second X-chromosome is wholehearted and the examples Moalem gives are highly effective. He has written a powerful antidote to the myth of the “weaker sex”.