My personal belief when it comes to this subject is that like most things, gender roles are a combination of nature and nurture. As was well explained by TLM and abygail, there are biological differences, however, how those differences are manifested in the environment is largely, but not completely, a result of socialization within their specific culture.
For example, in American culture we constantly have conflicts between a gender's capabilities and its culturally assigned gender roles. Women who took part in fighter jet training easily outperformed men due to their higher dexterity which allowed them greater joystick mobility and their extra layer of body fat which allowed them to sustain higher Gs than their male counterparts. However, the Air Force decided rather than allow women to excel as fighter pilots from their biological advantage, to instead reclassify the position as a "combat position" thereby keeping women out of the pilot's seat altogether.
To lack an ability to discern a biological capability from a culturally assigned role is far from irrelavant when it results in an individual not being allowed to succeed at what they naturally do best.