Is gender biologically or socially determined? I guess the word "gender" needs to be defined, but that is part of the problem I suppose, since it can mean many different things to many different people. By gender, I do not mean anatomical physical sexual structures( like breasts, or a penis). Maybe the best definition I could conceive is: whether one identifies as man or women or w/e gender intermediate. 

The question is in the title, and I am aware that it could be due to both effects, and was curious about this question due to the existence of transgender people, which in my mind means gender is more of a social concept. But then some transpeople claim they have "felt" that they were a women or man at birth, which implies a biological origin. And even though both are "story-based" evidence, I was hoping for something more conclusive from this stackexchange.
There has been a lot of debate amongst scientist, and they are not in agreement on any one argument. In general, there is a trend towards thinking that gender identity is based on biology.

Argument that gender identity is based on biology:


http://www.sciencedaily.com/releases/2015/02/150213112317.htm
https://www.psychologicalscience.org/index.php/news/releases/transgender-kids-show-consistent-gender-identity-across-measures.html
http://www.scienceworldreport.com/articles/21032/20150109/gender-identity-determined-brain-region-cross-links.htm


The arguments here are that the brain patterns of transgendered people are more similar to the brain patterns of people of the gender that they identify with, which seems to indicate that gender identity is based in biology.

Argument that there is a lot more to be understood:


http://steinhardt.nyu.edu/opus/issues/2011/spring/gender_identity_development



  "Neither the affects of prenatal and puberty hormones nor socialization alone are enough to explain gender identity development, the process must lie in a brain structure."