You might begin by reading a 2013 post I wrote about an extremely influential study and its reception. Those argued that we have finally figured out why girls have pink brains and boys have blue brains, and that post is my response to the tidal wave of similar popularizations in all sorts of places.
More about why they were a tidal wave can be learned in this post (which also has useful stuff about Simon Baron-Cohen's work). And this post talks about one of the many pertinent studies which never get reported at all. They don't qualify for the tidal wave, because they are not about sex or gender and don't necessarily support innate views of gender.
Finally, Anne Fausto-Sterling writes about the question whether girls innately like pink and boys blue (we know the answer to that, of course, given that the colors were assigned to the genders quite recently). But more importantly, she notes:
My research shows that, even at a young age, “nature” and “nurture” already interact.3 The first three years of a child’s life mark a period of extraordinary brain development and synapse growth. Like a sponge, the child absorbs everything around it, etching a record of its sensory experiences in its developing neurons. Social and cultural cues children experience during this period can influence their physiological development, establishing bodily patterns that set the stage for later phases of development.
One of my studies focuses on the belief that boy infants are more physically active than girl infants.4 While the babies in the study show no sex-related differences in their own spontaneous activity, we discovered through detailed observation that the mothers interact with the boys in a more physically active way. They move boy infants, help them sit up, and touch them more often than they do girls.
The impact of the mothers’ behavior may go much deeper than just setting cultural expectations – it could actually have biological consequences. While more testing is needed to understand these biological effects, it is possible that the sensory, motor, and neuromuscular systems of boys develop differently than those of girls, at least partly in response to different patterns of maternal handling.
If biological development is influenced by a child’s environment in this way, “nature” and “nurture” are no longer distinct. They are a developmental unit, two sides of the same coin. Rather than talking about nature versus nurture, we should ask: How is nature being affected by certain kinds of nurturing events?(c) And instead of viewing gender as something inherent and fixed, we should understand it as a developmental process involving the ongoing interaction of genes, hormones, social cues, cultural norms, and other factors.5
Moving beyond the nature versus nurture dichotomy allows us to have a more nuanced, accurate understanding of gender.