PARENTS hoping to shield their children from sex stereotypes by giving them gender-neutral toys may be fighting a losing battle, especially if their offspring are boys. It seems that hormones released both before birth and well into the first few months of life may dictate the type of toys and play that boys are drawn to.
By the age of 3, boys and girls show differences in their play preferences. Boys are more strongly drawn to balls, vehicles and construction toys than girls and tend to prefer playing with larger groups, whereas girls are more likely to prefer play with a few individuals. To what extent these differences are biologically programmed rather than a result of social pressure is hotly debated.
Recent research hints that exposure to differing levels of hormones in the uterus might sway the preferences that both boys and girls have for 鈥渂oy-like鈥� toys later on. No one had looked at whether the surges in testosterone and oestrogen that boys and girls experience in the early months of life also affect behaviour. 鈥淲e tend to think of early development as a time when hormones aren鈥檛 having effects,鈥� says Gerianne Alexander of Texas A&M University in College Station and colleagues.
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To investigate the effects of these hormone surges on behaviour, Alexander and her colleagues used eye-tracking software to measure levels of interest in animations of a ball versus a doll and a group of figures versus an individual figure, in 21 boys and 20 girls aged 3 to 4 months. The researchers measured levels of oestrogen in the girls鈥� saliva and testosterone in the boys鈥� and compared the lengths of their index and middle fingers 鈥� a guide to prenatal testosterone exposure.
鈥淏oys exposed to more prenatal testosterone showed a pronounced preference for the ball鈥�
Girls鈥� behaviour appeared unaffected by current or prenatal hormone levels. Boys鈥� preferences, however, seemed affected by both, in slightly different ways. Those with higher circulating levels of testosterone had a stronger preference for the groups of figures over the individuals, while those whose finger lengths indicated that they had been exposed to more testosterone in the uterus showed a more pronounced preference for the bouncing ball over the doll (Hormones and Behavior, ).
The children in the experiment were too young for these preferences to translate into actual choices about how they play. However, Alexander says that even at the tender age of 3 months, such innate visual preferences could drive future behaviour. The next step is to test if visual preferences at 3 months predict behaviour later on.
鈥淚t鈥檚 a very interesting paper and I think it will motivate a lot of additional research,鈥� says Melissa Hines of the University of Cambridge, who researches the role of hormones in prenatal development.
If confirmed by larger groups of children, the results would also suggest that aspects of behaviour or even gender identity might be skewed by exposure to hormone-disrupting chemicals like phthalates or pesticides, both in the womb and early in life.
