Sunday, February 24, 2008

Why do Males Exist? An Unanswered Question in Science

Mysteries of the male

Why do males exist? If you look at any standard biology textbook, you will probably read that the point of having males as well as females is to promote variation by the exchange of different mutations, and hence to increase the chances of species survival. Unfortunately, most evolutionary biologists stopped believing in this explanation over 20 years ago. From a reproductive point of view, no individual is interested in anything beyond donating genes to the next generation, while species survival happens more or less at random, according to the whims of climate and geology. You don't actually need sexes in order to mutate and produce variation. In any case, most mutations have no effect, or mainly deleterious ones. John Maynard Smith talks of ‘the twofold cost of males’. Firstly, it is incomprehensible that any female should want to chuck away half her genome. Secondly, the males of many species are useless at doing anything except sitting around, getting fat at the females’ expense, and—in the words of Richard Dawkins—duffing up other males. Among some animals, such as elephant seals, the vast majority die as wasteful, disappointed virgins.

Given the cost of males, it is perhaps not surprising that there are at least 40 species where the female kills the male during or after sex. In the case of the praying mantis, she literally bites his head off as part of foreplay, and he carries on in a delighted reflex of posthumous orgasm. Females of other species are equally imaginative: male scale insects have been demoted to microscopic excrescences on their females’ legs, while female angler fish carry their mates on their backs as tiny dwarves. More pertinently, there are many effective ways of reproducing apart from sex as we understand it. These include simple division and gene exchange, which have served prokaryotes so well that they have produced the longest-enduring of all species on the planet, as well as comprising the greatest number of species, and probably constituting most of the biomass as well.


Among other organisms, alternative methods of reproduction include budding, hermaphroditism and isogamy (i.e. two individuals, not distinguished as males and females, combining their genes). There are asexual variants among all sorts of creatures, including jellyfish, dandelions, lichens and lizards. Of the creatures who do reproduce sexually, some species have two sexes, but others have three, or thirteen, or 10 000, if you are a fungus. Many species alternate between sexual and asexual reproduction, either on a regular basis or occasionally, as the circumstances require. Bdelloid rotifers—tiny invertebrates who live in drains and puddles—went off sex about 80 million years ago, and have cheerfully diversified into several hundred species since then, without regaining the inclination. Maynard Smith described them an ‘an evolutionary scandal’.

The various current theories about why males evolved and still remain in existence are nicely set out in Matt Ridley's book ‘The Red Queen’. They are also covered in Olivia Judson's racy and wonderfully informative book ‘Dr Tatiana's Sex Advice to All Creation’. Different theories rejoice in names like Muller's ratchet, Kondrashov's hatchet, and the eponymous red queen of Ridley's book (named after the character in Alice in Wonderland who perpetually runs without getting very far because the landscape moves with her). This last theory seems to be the front runner at the moment. It is based on W.D. Hamilton's idea that sex is part of a continual race to outwit external pathogens. What is clear, however, is that the consensus that existed on this topic from Darwin until the 1980s has totally broken down. The purpose of males has instead become one of the biggest unanswered questions in science. My guess is that we will eventually come to understand fertilization by males in a similar way to how we now understand the appearance of ancient autonomous organisms such as mitochondria or chloroplasts in the eukaryotic cell. In other words, we will see it as an evolutionary compromise poised half way between invasion and alliance, parasitism and symbiosis, or genetic rape and informed consent. There is already much evidence to show how females resist the process physiologically (for example by stripping male gametes of all extra-nuclear DNA) and how males try to control reproduction against their females’ will (for example, by killing off competitor sperm or genetic material in the female genital tract, or alternatively killing the competitors and their offspring directly).

If the status of males in evolutionary terms is an equivocal one, the consequences of sexual dimorphism are not reassuring for males either. In a review of the evidence relating to human males, my colleague and mentor Sebastian Kraemer has set out the scale of the problem. Throughout life, men are more vulnerable than women on most measures. This starts with the biological fragility of the male foetus, leading to ‘a greater risk of death or damage from almost all the obstetric catastrophes that can happen before birth’. If they survive these catastrophes, boys then have a far greater susceptibility to developmental disorders than girls. These are magnified in turn by our cultural assumptions about masculinity, and by our low expectations of males. The toxic interaction of biological and social ingredients shows itself in far higher rates of suicide and deaths through violent crime. Males also do worse in (among other things) scholastic achievement, emotional literacy, alcoholism, substance abuse, circulatory disorders, diabetes, and of course in longevity. Kraemer looks at how male disadvantage is ‘wired in’ from infancy and persists to the grave, but he suggests that we shouldn't necessarily conclude that maleness is a genetic disorder. Instead, he argues, we should show more curiosity about the reasons for boys and men being so vulnerable, and should pay more attention to redressing this in child-rearing and in medicine.

It may be no coincidence that questions about the ‘raison d’etre’ for males, and concerns about their relative deficiencies, should have arisen at this point in history; enough of the relevant information behind them would probably have been available to an observer in Darwin's time. The recent appearance of these scientific preoccupations may well be the consequence of understandable male anxiety. In the last few generations of our species, female control over fertility has developed at a rate so phenomenal that it may justify comparison with the sudden emergence of male-female reproduction itself, around a thousand million years ago. In evolutionary terms, it has taken only the twinkling of an eye from the introduction of the vaginal diaphragm and the contraceptive pill in the middle of the last century, to the widespread use of frozen sperm and extracted eggs, and hence to the actualization of human oocyte cloning. Within the span of just one lifetime, women have advanced through several enormous stages of biological liberation and have reached the threshold of elective parthenogenesis.

Assuming that the minor technical problems of gene damage during cloning can soon be overcome, and that legal constraints will in time be removed—assumptions that seem reasonable by any standard—it is possible that the women of our species will soon have the overall choice of doing with very few men, or with none at all. If, in the mean time, they can prevent males from destroying any environment in which to survive, they might be forgiven if they choose to follow the path that has already been pioneered by the bdelloid rotifers. Attempts to understand maleness or to redress its difficulties will then become entirely academic.


QJM: An International Journal of Medicine

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