Sexuality is complicated across the animal kingdom. In humans, there are predominantly two genetic sexes, with a very small percentage of chromosomal divergence (e.g. XXY, X, XYY, XXX). There are predominantly two anatomical sex configurations, with a small percentage of anatomically different presentations. These non-binary variations are generally called 'intersex' for want of a better word.
When it comes to physiological sex, there is a broad spectrum with two broad peaks corresponding to normative male and female. The spectrum is broad because it involves both genetic and developmental influences.
A peaked distribution also applies to sexual preference and gender identity, which are also the result of genetic and developmental influences (gender identity is the personal sense of one's own gender). The peaks roughly correspond to normative physiological male & female (reversed for sexual preference).
For those outside the normative peaks of those distributions, problems arise, not just from general ignorance and cultural inertia, but for the many who are between those normative peaks and either extreme of the spectrum, there are conflicting social and psychological pressures, and the physiological and psychologically pressures of puberty just serve to complicate things.
Categorising the world and dividing continua into arbitrary blocks helps us understand and organise the world by simplifying it, particularly socially and culturally, but they're often crude approximations that don't always mesh with individual experience.
