Younger siblings with older brothers may have an increased propensity to become more aggressive with time as opposed to siblings with older sisters, according to a recent study's results.

451 sibling pairs were studied by California researchers (ages nine through 18), and such factors like aggressive behavior, family economic pressures and the hostility of the parents towards the kids were observed.

The conclusions showed that the younger males with older brothers exhibited more aggressive behavior over time, as well as older siblings with younger sisters becoming less aggressive over time. Quite naturally, another conclusion to the study said that parents' hostility also played a role in the aggression development in their kids.