Whether there exist differences between boys and girls is passionately debated (for example, see this debate about gender disparity between Stephen Pinker and Elizabeth Spelke). Some studies have found that girls are more sociable than boys, but prefer to play with just one other person, while boys prefer a larger group to play with.
However, it is very difficult to say whether differences that we see in boys' and girls' behaviour has a biological basis, as boys and girls are also treated differently. Even before a baby is born, parents have often painted its room pink or blue, and bought gender-differentiated toys. A mother is more likely to under-estimate her female babys crawling abilities, and over-estimate her male babys (hes a boy, of course hes going to be stronger and better at crawling?!). Perceptions on the personality and abilities of a baby also differ depending on whether the adult is told that the child is male or female. Given these differences in how people treat male and female children, it can be difficult to say whether the behaviours we see are have a biological basis or not.
However, we can look for certain clues to biological differences in child behaviour from our cousins the chimpanzees. Chimpanzees live in communities of 20 to 180 individuals, with sub-groups within this. One recent study looked at the behaviour of eight female and twelve male chimpanzee infants to see if their behaviour differed from each other. They found that the young males were more sociable than the young females.
Male infants interacted more with others than female infants, even when the males mothers werent particularly sociable (it wasnt just that they were following their mothers around and copying their behaviour). However, infant chimpanzees do generally stay close to their mothers for the first five years of their lives, so it is difficult to disentangle the possibility that mothers with sons just have more interactions than mothers with daughters. However, it seems likely that the males are initiating the interactions, and then their mothers are following them, rather than the other way around. The male infants also interacted more with adult males than did the female infants.
These sex differences last throughout a chimpanzees life, so it is interesting that they appear so early on. The researchers involved in this study argue that the differences seen in young humans may then also have a biological basis.
Of course, no one single study like this can tell us whether human infant behaviour has a strong biological basis or not. Further studies should look further into why such differences between the sexes may exist (both in chimpanzees and in humans), and see how widespread human infant behavioural differences are across different cultures.
Children playing: Aislinn Ritchie
girls and boys toys: Janet McKnight
chimpanzee photos: Tambako the Jaguar
Lonsdorf, E. V., Anderson, K. E., Stanton, M. A., Shender, M., Heintz, M. R., Goodall, J., & Murray, C. M. (2014). Boys will be boys: sex differences in wild infant chimpanzee social interactions. Animal Behaviour, 88, 79-83.