"Sex redefined"

"Sex can be much more complicated than it at first seems. According to the simple scenario, the presence or absence of a Y chromosome is what counts: with it, you are male, and without it, you are female. But doctors have long known that some people straddle the boundary — their sex chromosomes say one thing, but their gonads (ovaries or testes) or sexual anatomy say another. Parents of children with these kinds of conditions — known as intersex conditions, or differences or disorders of sex development (DSDs) — often face difficult decisions about whether to bring up their child as a boy or a girl. Some researchers now say that as many as 1 person in 100 has some form of DSD²... What's more, new technologies in DNA sequencing and cell biology are revealing that almost everyone is, to varying degrees, a patchwork of genetically distinct cells, some with a sex that might not match that of the rest of their body."
http://www.nature.com/news/sex-redefined-1.16943

A must read; so fascinating, so many questions to explore.

There is a lot of interesting stuff going on in terms of sex differences in the brain, and basically (paraphrasing from a talk I went to back in November and slightly forget the details of) there are a lot of places in the brain that have clear differences between the "average male" and the "average female" human but within an actual individual, all the different regions of a single brain will vary in their sex-ed-ness and there is a huge amount of overlap. Like, a given woman might have a ~neutral amygdala and a super feminine visual cortex. So, there are absolute differences, but they are all relative, and they mix-and-match within individuals.