Cambridge University neuroscientist Joe Herbert on testosterone, sex, power and the will to win
It's the molecule that made history and the subject of Professor Herbert's new book
Without testosterone, none of us would exist. Neither would any other mammals, birds, fish, amphibians or reptiles.
Testosterone is not only a mightily important hormone, it’s also a great evolutionary success. Its function: to enable reproduction in males by making them fertile but also sexy. But for all species, getting a mate is highly competitive; which makes it dangerous, since it may involve fights.
Males must enjoy competition and taking risks, and be prepared for aggression when necessary.
Testosterone is such a successful hormone because it equips males for the robust world of competitive sex.
Claws, long sharp teeth, horns, well-developed muscles and a liking for competition and risky behaviour are some of the tools that testosterone gives males of different species.
Testosterone prepares them not only for sex but for combat.
The effects of such a powerful hormone can’t be let loose. So all animal societies have controls on males’ behaviour. These vary according to species, but they all have a similar purpose: to direct or limit the sexual activity of males.
Selection by female partners is one potent one, with males having to compete for their attention.
Coloured plumage, red faces, even bright blue genitals are some of the ways testosterone makes males attractive.
Males of all vertebrate species strut their testosterone-fuelled stuff.
Have humans shrugged off all these ancient roles of testosterone? Not at all. As with many other features of their life, humans have complicated a basic biological inheritance to degrees unknown in other species.
Humans use sex for purposes that may have little to do with reproduction (e.g. advertising).
We can see the tendrils of testosterone all over human life. Laws, social customs, religion, tradition: all have much to say about how male sexual behaviour should be regulated.
While humans do what other species do, they do it in ways unimaginable to other animals.
Human regulation of testosterone-dependent sexuality has varied throughout history, and today varies across cultures.
Compare UK attitudes to male sexual activity today with those of Victorian times, or between the UK and some other countries. You won’t see such variation within other species: chimpanzees 10,000 years ago almost certainly regulated sex in their societies much as they do today.
The behavioural effects of testosterone are all brought about by the brain. But testosterone affects only some parts of the male brain: those concerned with other basic functions, such as eating, drinking, keeping warm and so on, as well as the areas responsible for emotions.
This explains why the hormone’s effects on behaviour are so similar in humans and other species.
Castrate a human (eunuchs were common in ancient times) and sexual activity diminishes or, if it is done before puberty, sex never appears – just as in dogs or rats.
The human brain is distinguished by the enormous development of its outer layers, the cortex.
This more recently evolved area is responsible for all those mental qualities we call humanity. And, importantly, it controls the more ancient testosterone-sensitive brain regions.
But this control is not always perfect. Walk down a Cambridge street on a Friday night and you may see some testosterone-related behaviour released from the control of an alcohol-impaired cortex.
Testosterone has begun its pervasive action long before the male is proving his masculinity in the pub.
Early in pregnancy, the male embryo’s tiny testes are starting to produce testosterone.This has profound effects, as we know from one striking example. A rare genetic condition exists in which the male brain cannot respond to testosterone: it’s as if the hormone was absent. Such individuals are born looking like females. They think of themselves as female, and may only be discovered to be genetic ‘males’ at puberty.
This says a lot about what testosterone during early life does to the male brain: it makes it ‘male’, though there are strongly-held ideas about the definition of ‘male’.
A second surge of testosterone occurs in the few months after birth (which would surprise the babies’ mothers if they knew about it): what this does is still mysterious. Then the testes stop making testosterone until puberty.
Puberty is simply an even greater surge of testosterone. This transforms a boy into a man in a couple of years. He’s now ready and eager for sex. But his brain hasn’t caught up.
At the front of the brain lie the frontal lobes, responsible for many of those qualities we call ‘higher’ mental functions, such as personality, social behaviour, planning and ‘insight’.
The frontal lobes don’t become fully mature until the man’s early twenties, well after puberty (females mature earlier).
Young males have characteristic patterns of behaviour that we all know about: loud, laddish, rebellious and difficult to control. They also love taking risks – like skiing off-piste, hang-gliding and other extreme sports.
The combination of lots of testosterone and an immature frontal lobe may be a biological advantage. Males need to take risks to be successful in sex but also in other contexts.
Those that innovate – for example, inventors and entrepreneurs – have to take risks.
Societies need young men to take risks in their defence if they are attacked.
Immature frontal lobes may release young males from the inhibitions that might deter older ones. Young men are expendable, biologically speaking: it doesn’t need many to fertilise all available females.
In the Second World War, 75 per cent of those killed in action were under 35. Young males readily form clubs, gangs, regiments and other associations that are so important for concerted action – although these don’t always have beneficial results.
Street gangs are usually formed of groups of young males with a common background and they take a hostile approach to other gangs, particularly those of similar backgrounds. Although they are regarded as a menace by the rest of society, they have similarities with football fan clubs (who may also be violent), but also fraternities, golf clubs and other institutions that have entry requirements, loyalty demands and internal hierarchies. But there are circumstances in which this becomes pathological.
Most suicide bombers are young men, who are also responsible for most acts of terrorism. Their brain seems to facilitate youths to joining a group, usually led by an older, charismatic male with simple and strong beliefs or objectives. Hitler Youth was an example: jihadists are another.
It seems likely that this aberration of an otherwise beneficial social quality may be one, perhaps inevitable, consequence of young males’ immature brain and their testosterone.
Understanding a potent hormone
Joe Herbert is emeritus professor of neuroscience at Cambridge University and a fellow of Gonville and Caius College.
His areas of expertise include the role of hormones in the ability of the adult brain to make new nerve cells, or neurons, and repair the brain, how hormones regulate behavior, the neuroscience of stress, how hormones, genes and the social and psychological environment interact to promote the risk for depression, and the way that hormones and genes influence financial decision-making. He has authored or co-authored about 250 scientific papers,
His new book, ‘Testosterone, The molecule behind power, sex, and the will to win’ will be published by Oxford University Press on September 28, priced £12.99, and has received glowing reviews.
Dr Ian Miller, of the Times Literary Supplement, said: “Testosterone... provokes its readers into considering the role of our biological inheritance in influencing how we cope with modern society.”
It explores the nature of this potent hormone, how it operates in mammals in general and in humans in particular, what we know about its role in influencing various aspects of behaviour in men, and what we are beginning to understand of its role in women.
Understanding the workings of testosterone can help us manage its effects - not least its role in rape and gang warfare among youths,
The paperback, published on September 28, also features expanded material reflecting the latest research on the role of testosterone in women and in street gangs.