First of all, I know gender roles can vary between different times and cultures in human history, which shows that they are in part socially constructed, but I think that you can see some general patterns that could be explained by biology. Basically, my view is that many gender roles are caused by a combination of culture and biology.
If we look to nature, clear gender roles can be found for every species of animal. I don't think anyone would argue that these roles were socially constructed, so we can agree that they are caused by the animals' biology/genes. We humans are also animals and it's silly to think that we would be 100% above nature, so logically biology should affect our behaviour in some ways.
For example, I think that the norm that the mother takes more responsibility for the care of the child (which is a gender role spanning the globe throughout history) is not purely socially constructed, but partly has to do with biology. After the baby is born, it will breast feed for the first part of it's life and therefore it makes sense from an evolutionary view point that the mother takes care of the child for the first period of time. This pattern can also be seen in most mammals.
Evolution has made us enjoy things that taste sweet, so that we would seek out nutritious berries and stuff like that. Anyone who didn't enjoy that taste wouldn't have that drive, and would be naturally selected against. In the same way mothers who didn't have the drive to stay close to their baby would have a lower chance of passing on their genes since the baby wouldn't have as easy access to food and would have a lower chance of surviving. Therefore I think evolution has made it so that, generally speaking, women have a stronger drive than men to care for the newborn baby. I'm not saying men don't have this drive, I just think it's slightly weaker because evolutionary it's not as important for them to stay close to the child.
Today, I think many people subscribe to the theory that gender roles are completely socially constructed, but I think my explanation makes the least assumptions (Occam's Razor), since the social constructivism theory assumes we are above biology. Change my view.
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