Many many species pairs only have pre-zygote isolation[1], meaning they could have common offspring but avoid doing so, as such mixed offspring would be at disadvantage.

1. https://en.wikipedia.org/wiki/Reproductive_isolation#Pre-cop...

I thought “species” meant their offspring was not going to be fertile, such as mules for example.

So how can they use this term “species”, isn’t it a contradiction? So they are NOT distinct species, then? Like dogs?

Species do not exist, but are a useful concept, anyways. See https://en.wikipedia.org/wiki/Species_problem. https://en.wikipedia.org/wiki/Ring_species, linked from there, also may be educational for you.

https://en.wikipedia.org/wiki/Lumpers_and_splitters#Biology also may be a good starting point.

That’s the simple definition. Unfortunately there are enough edge cases that it doesn’t work very well.

This, ring species, asexual reproduction, the small number of fertile mules: http://news.bbc.co.uk/1/hi/sci/tech/2290491.stm

Often the issue isn't two organisms can mate and have fertile offspring but whether or not they often do. A species can still be "real" if their gene pool is not shared to a great degree. Yes, wolves, dogs, and coyotes can all interbreed, but there are real behavioral differences due to differing genetics -- their gene pools are not the same.

It may make sense to say two populations should be considered separate species if they are capable of interbreeding to produce fertile offspring if they almost never do. But that doesn't seem to be the case here. 15% "hybrids" is huge.

Right, so is this kind of a non-story? They are basically not distinct species, according to the story, so its premise is wrong.

the categories were made for man, not man for the categories

"There’s a lot of promiscuity taking place in Gombe National Park. Red-tails are mating with blues, blues are mating with red-tails, blues are mating with blues, red-tails are mating with red-tails, and hybrids are mating with everyone?"

Replace "Red-tails" and "blues" with black, white, asian, hispanic, etc... and quickly you see that the definition os "species" is pretty ill-defined.

There are evolutionary benefits to isolating into groups, and there are benefits to cross-breeding between those groups.

That's how the species count goes down without any going extinct.

Actually true, even amongst dinosaurs.

Jack Horner is decreasing species counts: https://youtube.com/watch?v=kQa11RMCeSI

That's a great talk, thanks for pointing it out.