If you had to buy gifts for young children this year, you probably noticed the bombardment of pink stuff for girls and almost every other colour for boys. A new book this year is challenging the notion that boys will be boys as the aggressive, dominant, risk-takers, and girls will be girls as the safe nurturers.

Back in the stone age, it was useful for men to go out and hunt and the women to stay home and nurture. The thought, until very recently, was that our X and Y chromosomes determine gender, with the hormone testosterone as the fuel for this masculine divide.

The book, written by Dr. Cordelia Fine, a Canadian-born professor of history and philosophy of science from the University of Melbourne in Australia, is called, Testosterone Rex: Myths of Sex, Science, and Society. It won the U.K.'s Royal Society Science Book of the Year for 2017.

Stores often stock a bombardment of pink toys for girls and almost every other colour for boys. (Carlo Allegri/Reuters)

"Testosterone Rex" is a nickname Fine penned for what she says is an outdated, familiar idea that males have evolved to be risk-taking and competitive, which supposedly enhanced reproductive success, and that those traits are hard-wired in the male brain and fueled by testosterone.

"When you look up you see many more men than women in positions of power and status," said Fine. "So it's a scientific story that seems to offer us an explanation of why those inequalities still exist." But like the Tyrannosaurus Rex, what Fine calls "Testosterone Rex," is a story that she says is scientifically extinct.

Men are not from Mars, nor are women from Venus

One of the reasons Fine wanted to write the book is because through her academic research, she was seeing how these "Testosterone Rex" scientific ideas were changing.

Instead of men and women having different and complementary behavioural characteristics, Fine said that what you tend to find in the scientific literature is a very large degree of overlap between the sexes, even in quintessentially masculine or feminine traits like empathy, competitiveness, or risk taking.

If someone's not taking enough risks for our liking we tell them to "grow some balls," for example, that in itself is quite telling. - Dr. Cordelia Fine

"While you do see average differences at the population level, there is a lot of overlap," said Fine. "Knowing that someone's a man or a woman actually isn't a great guide to knowing whether they're more likely or less likely to take risks on a particular kind of task or to be interested in competing. When you start to think about testosterone driving sex differences in competition or risk-taking, it starts to get a bit difficult because when you think in a very simple way, 'Men are risk-taking and women are risk-averse,' then you think, 'Oh yeah, testosterone must be the reason.' But when you start to look at the actual literature more carefully, some men in some contexts are sometimes more risk-taking than women, but not in other contexts. Then testosterone doesn't seem quite such an obvious explanation of the differences that you sometimes see."

It's surprisingly difficult to link sex differences in the brain to sex differences in behaviour. (Pixabay)

Psychologists used to think of risk-taking as a uni-dimensional personality trait. So you either were a risk-taker or not. And if you're a risk taker, then you're as willing to jump out of a plane with a parachute as you are to invest in high-risk stocks. "It turns out that this isn't actually how risk taking plays out. We're quite idiosyncratic in the kinds of risks that were willing to take. So someone who's willing to take financial risks, for example, may be very unwilling to take physical risks."

We're quite idiosyncratic in the kinds of risks that were willing to take. So someone who's willing to take financial risks, for example, may be very unwilling to take physical risks. - Dr. Cordelia Fine

Fine said what seems to explain why some people are willing to take certain kinds of risks and not others are the perceptions of the perceived costs and benefits to taking that risk, which she said can be influenced by any number of things. "Part of it's going to be things like experience and knowledge and familiarity, which make risk-taking seem less risky and more likely to be beneficial. Some of it may be actual real differences to do with your place in the world. So if you have a lot of wealth, then taking a risk on a particular kind of stock or share may be sort of intrinsically less risky in the sense that you've got that financial buffer in case it doesn't work out. But of course gender norms are a really important part of that as well because people are always aware when they're behaving how they're going to be perceived as others."

Our stereotype, despite the lack of good evidence, is that we expect men to take more risks. "So we talk about, you know, if someone's not taking enough risks for our liking we tell them to 'grow some balls,' for example, that in itself is quite telling."

Behavioural sex differences in the brain

When it comes to sex differences in the brain, a good way to think about that is like a Venn diagram with male brains in one circle that overlaps with the female brain circle.

"So if you compare a male and female brains, you will find average differences between them," said Fine. Our brains are not asexual. "Genetic and hormonal components of sex do influence brain development and brain function at every level, from sort of cellular to the sort of larger, structural level, so there are average differences between the male and female brains. Where you have to be careful though is to not sort of directly leap from that to your kind of masculine and feminine behaviour."

It's time to say goodbye to the outdated notion of Testesterone Rex, said author Cordelia Fine. (WelkerMedia)

One reason we can't make that leap is because it's actually surprisingly difficult to link sex differences in the brain to sex differences in behaviour.

Fine described a study that was done out of Tel Aviv University a few years ago that looked at a number of different large data sets of brains from men and women. "And they identified the 10 largest differences between the brains of men and the brains of women. And [the scientist] actually found that the Top 10 list wasn't consistent across these different populations, showing that there are other factors that must be contributing to creating those differences. And the obvious candidates would be age, environment, and genetics, and so on."

Our brains are plastic and respond to different experiences, so there's no way to tell where a sex difference in the brain might have come from. But the fact remains that when it comes to behaviour, which most people would expect to come from the brain, men and women are very similar.

The behavioural science shows that there is a lot of similarity in how men and women often behave and the importance of norms in how those similarities can become greater or smaller over time. - Dr. Cordelia Fine

"Sometimes these sex differences in the brain that we see may actually be compensating for other physiological differences to enable similarity of behaviour," said Fine. "The behavioural science shows that there is a lot of similarity in how men and women often behave and the importance of norms in how those similarities can become greater or smaller over time."

Behavioural sex differences from testosterone

When it comes to people's testosterone levels, there are generally quite large differences between men and women with only a bit of overlap. "So if there is a kind of direct relationship between the level of testosterone in people's blood and how they behaved, we would see much larger sex differences in behaviour than we actually do," said Fine. "That's already telling us that simply looking at the fact that there's more testosterone in men than in women is not the whole story. And in fact, you know, testosterone is just one part of this incredibly complex neuro-endocrine system. There are many other different factors involved, you know, aspects to do with the receptors for the hormones in the brain, where they're located, their sensitivity, there are many other different kinds of chemicals involved. There can be obviously epigenetic changes and so on."

(Penguin Random House Canada)

While it looks like testosterone doesn't contribute to stereotypical gendered behavioural characteristics we once thought it did, it does affect behaviour for both men and women. Scientists now see testosterone as a hormone that puts us in a better position to compete for resources, partners, or even to protect our offspring. Testosterone is no longer just important for male behaviour.

"Competition is increasingly recognized in evolutionary biology as important for female reproductive success as well. So studies find that our testosterone levels are actually responsive to the situations that we find ourselves in. And that kind of fits with how behavioural endocrinologists understand the role of hormones, like testosterone, which is kind of adapting us to our particular kind of environment."

What they found was that whether you were from that culture of honour influenced both how aggressively you responded to that situation or how much your aggressiveness increased following that situation and also whether your testosterone levels rose in response to that situation. - Dr. Cordelia Fine

Our view of testosterone's evolutionary role is changing from one that gives rise to gendered behaviours to one that helps us adapt to our situations and circumstances. One study in particular looked at the effect society's gender constructions have on testosterone levels. This study compared how American students from southern parts of the U.S. with a strong "honour" culture to students from northern parts of the country to see how their testosterone levels would respond to being insulted. "What they found was that whether you were from that culture of honour influenced both how aggressively you responded to that situation or how much your aggressiveness increased following that situation and also whether your testosterone levels rose in response to that situation," said Fine. This, she said, is an example of how social norms can influence a person's hormonal state.

Saying goodbye to Testosterone Rex

Fine said it's time to let Testosterone Rex die. "I would like to see is a moving away from drawing on these outdated scientific ideas about men and women being fundamentally and immutably and inevitably different as a way of kind of explaining and justifying the inequalities that we see, particularly in the workplace."