“Woman seems to differ from man in mental disposition, chiefly in her greater tenderness and less selfishness,” wrote Charles Darwin in The Descent of Man.
Now scientists claim that the stereotype is supported by evidence that the brain’s reward system may be geared towards more “prosocial” behaviour in women.
“It was known that women and men behave differently, but it was not known why, or how this comes about in the brain,” said Philippe Tobler, associate professor of neuroeconomics and social neuroscience at the University of Zurich, and co-author of the research.
The team note it is not clear whether the gender differences they see in the brain’s reward system are in any way “innate”, or whether they are the result of social pressures, but in short: women seem to get more of a chemical reward for being generous than men do.
“It is known that girls receive different kinds of feedback than boys for being prosocial,” said Tobler. “It is perfectly conceivable that [the root of the differences here are] only cultural – we simply don’t know.”
Writing in the journal Nature Human Behaviour, Tobler and colleagues from Germany, Switzerland and the Netherlands carried out two studies looking at whether dopamine, a neurotransmitter that plays a crucial role in the brain’s reward system, is linked to different social behaviours in men and women.
In the first, a group of 56 men and women were randomly allocated to two groups, and either given a placebo or amisulpride – a drug that blocks the action of dopamine in the brain. Neither the scientists nor the participants knew which pill was taken.
The participants were then presented with a hypothetical situation in which they could either claim a wad of cash for themselves, or split a chunk of money evenly with another person, ranging from someone close to a complete stranger. After completing the task, the experiment was repeated with participants taking the alternative pill.
The results revealed that when taking the placebo, 51% of the time women chose to share the money, while for men the figure was lower, at 40%. But after taking the amisulpride, women were less keen to share, while men became more prosocial, opting to split the cash 45% and 44% of the time respectively.
In the second study, the team looked at data from 40 men and women who had undergone brain imaging while undertaking decisions on whether to share money, focussing on the activity of a value-processing region of the brain that relies on dopamine signalling.
The team found that when making prosocial choices, activity in this brain region was stronger for women than men, suggesting a greater dopamine response.
The researchers say that, taken together, the studies support the idea that the dopamine-based reward system is geared towards sharing behaviour in women and more selfish behaviour in men.
But others are far from convinced by the findings.
Gina Rippon, professor of cognitive neuroimaging at Aston University who was not involved in the work, said that while intriguing, the results were “questionable”.
Among her concerns, she notes that the data from the first study does not show that women are particularly prosocial, pointing out under placebo they were split almost 50:50 for prosocial and selfish choices, adding that the effects of taking amisulpride were small.
Rippon also pointed out that the imaging study pooled results from two different groups of participants, using two different scanners and two slightly different versions of the task.
However, Angela Saini, author of Inferior: How Science Got Women Wrong said that the results showed how closely intertwined biology and culture are.
“We know that girls and women are socially expected to behave in different ways from boys and men. We encourage girls to be kinder, gentler and more generous, because these are seen as female virtues,” she said. “It shouldn’t really come as a surprise that research like this shows that women tend to show a greater reward response to this kind of behaviour.”