intersex is considered a very normal
To a quantitative biologist, maybe. But that's the wrong point of reference, as they don't make mainstream culture.
Sexual reproduction so as to perpetuate
humanity is the single most important function a society
executes. All human culture directly or indirectly relates to
this task.
One of the key tasks in this context is the choice of partner(s)
whom to reproduce with.
Alas, not any two humans can reproduce
together. Indeed, an exact determination who can successfully
reproduce with whom is still not possible in 2016, although we are much better at this task than say 1000 years ago.
Given that we can't predict mate compatibility perfectly,
humanity needs heuristics to make this decision efficiently. The
following heuristics are being used in practise:
- Divide humans into two, male and female, based on the shape of
their genitalia.
- Have sex with members of the opposite group.
Humans use additional heuristics for deciding with whom to mate,
e.g. social status, age, but the male/female binary is by a large
margin the most important.
As you correctly point out, not all humans neatly fall
into the genital-shape based classification between. But it doesn't matter, because the heuristic works so well that humans can reproduce successfully by ignoring those outliers. That means outliers must be
infrequent enough (say > 99% fit the binary).
I can't overemphasise this: the heuristic has been extremely successful.
The very concept intersex makes sense only in contradistinction from binary normalcy. To see this, consider the fact that most humans have 10 fingers, but not all. Yet, there is no socially relevant concept of 'interhanded' people, no pressure groups, nobody claims to have been born with the wrong number of fingers, no finger reassignment surgery etc. That's because the number of fingers is not all that important.
In the future we might have a refined classification, as
our understanding of human reproduction has
improved immeasurably in the last century. But note that a finer classification
still relates to biological facts about human bodies. It would probably be something along the lines of
- Can give birth to children, i.e. falls in the category woman, despite non-standard genitalia.
- Can father children, i.e. falls in the category man, despite non-standard genitalia.
- Can neither father children, nor give birth to children.
In other words, it would be a refinement of the male/female binary.