You're operating under a false dichotomy, and frankly, it's the type of misguided reasoning in the face of new evidence that leads to farces like the Scopes trial and decades of perceived conflict between science and humanity.
Of course it can be both. That's why it's disturbing that the article completely discards the majority of human experience of sexuality, while literally saying "To understand sex completely, we need an explanation that goes back to the primordial soup of very early complex organisms and the immediate survival pressures they were under."
