The best explanation you will get is from a medical doctor. They will explain to you how there are multiple sexes. Gender is not biological so there is no biological explanation.
For people who are downvoting me and are either too lazy to talk to a doctor or use Google: Fine, here are some links. Please educate yourselves about simple biology you should have learned in school.
Would you please not break the HN guidelines by (a) arguing snarkily and superciliously or (b) going on about downvotes? Trainwrecks though these recent threads have been, we're still trying for a higher standard of discussion on HN, and comments like this one make take us all in the wrong direction.
Someone posts an ignorant comment. I provide a relevant, actually helpful and fact-based reply and get downvoted. So I get pissed off, say something pissy, and then provide a ton of supporting evidence in response. But it doesn't affect the votes, and probably hasn't changed any minds at all.
Comments are the problem if you find civility more important than rationality.
> Gender is not biological so there is no biological explanation.
There is considerable evidence of gender identity different from biological sex lining up with biological features in several areas more typical of the other sex, so it seems that gender identity is tied to biology.
Which, if you think about it, it has to be: humans are biological machines, everything about them is biology, on one level or another. All of psychology is, ultimately, biology.
Biology is the study of living organisms. Psychology is the study of the human mind and its functions. A mind is a part of an organism, not a discrete one itself. The study of the part is not the same thing as the study of the whole. Psychology is not biology. This is not a controversial thing, every person who has graduated college in the past 30 years should know this, besides it being illogical.
Your first sentence seems like it's conflating correlation with causation.
As for the second, saying psychology is ultimately biology is reductionist in a way that dismisses the context and environment biology gets expressed in. You would be a much different person if the same set of genes was born in a different place, or at a different time, or if your life circumstances were different in any mild way.
I wouldn't go that far, but there are many studies that have looked at the genetic (biological) basis for brain function/behavior [0]. Once you're at the level of gene expression, which some of those studies go into, you're at a level of acetylation, methylation, etc., which is easily categorized as chemistry.
The bigger argument I get into with coworkers is the blurry line between brain function/behavior stuff and psychology.
> by that same token, all of psychology is also physics.
Yes, it is, which would be relevant if someone suggested there was no physical explanation for a psychological phenomenon (which is, in fact, what they are usually claiming when they claim it is not biological.)
For people who are downvoting me and are either too lazy to talk to a doctor or use Google: Fine, here are some links. Please educate yourselves about simple biology you should have learned in school.
https://www.quora.com/Scientifically-how-many-sexes-genders-...
http://www.nytimes.com/1993/03/12/opinion/how-many-sexes-are...
https://en.wikipedia.org/wiki/Intersex
http://www.who.int/genomics/gender/en/index1.html
https://en.wikipedia.org/wiki/Sex_and_gender_distinction