The article didn't say that they couldn't interbreed. It said that they had "changes in courtship behavior." It also said that "positive assortative mating"* was observed.
You're correct, the two varieties did occasionally interbreed.
So the speciation was only partial.
Maybe we can get the DI to perform the same experiment over 400 generations instead of 40.
Any predictions?
After 4000 generations?
...deviant sexual attitudes...
I don't think it's proper to talk about flies having attitudes. They're not smart enough, at least IMO.
*A situation in which like phenotypes mate more commonly than expected by chance.
It also said that "positive assortative mating"* was observed.
Ok above are two species of Helens.
Now do I have to lock you in a jar for 49 generations before you will demonstrate "positive assortative mating" tendencies between these two species?
Remember the experiment started out with mutant flies not normal flies. Let's say we did the experiment with humans and you had a jar of Helen Thomas offspring in one jar and a jar of Helen Hunt offspring in the other. Now 40 generations later do you think the Helen Hunt jar men are going to have any desire whatsover to engage in mating rituals with the Helen Thomas jar women?
Now, are they a different "species" because they don't want to mate?