I believe this does indeed have a biological basis. The hormones that prepare the egg to be released also have the effect of increasing libido. Testosterone increases as the egg matures, so that is partly responsible. Progesterone also begins to increase, and that is also partly responsible. According to this link
the brain also plays a large part of sexual drive. But as a person with severe hormone imbalances, I know without doubt that my lack of libido is related to the improper balance of hormones that keeps me from ovulating.
I saw a show on PBS once, Evolution, I think? they did a study of young women out clubbing. They would dress more sexily while ovulating.Show more skin. More tank tops and mini skirts.
This is why natural family planning would not have worked for me as BC. You are only supposed to have intercourse while not ovulating! Try and get me into the mood when I am not ovulating. Not easy. Not natural.