Hi, two answers:

Firstly,

> how do you conclude that these two populations can still interbreed?

I'm saying that people shouldn't spend time asking that question of allopatric populations.

Secondly you're right that I didn't read up on these monkeys. I wanted to rant about species concepts, but I was doing it in a discussion about some doubtless wonderful and very interesting monkeys and I am definitely guilty of not doing justice to them or to the people studying them.