Diverse Dogs and Cats and fertile offspring

[dichotomy]

I find it interesting that lions and tigers can reproduce with each, yet produce sterile male offspring. Dogs, on the other hand, to my knowledge, can successfully reproduce fertile male and female offspring, from wolf to pug.

 

Why are very physically different dogs successful with producing fertile offspring of either sex, while cats don’t seem to have the same success? Is it the nomadic Man and dog companionship that has made this possible?

 

I also find it interesting that homosapiens are in the same boat as dogs: We can successfully reproduce from Pigmy to Chinese oriental. So I assume, in general, if other creatures travel with man long enough they too can look pretty diverse (like man and dogs), yet continue to reproduce successfully.

[Sisyphus]

It's not too mysterious. You're just talking about breeds vs. species. Two breeds of dogs are not analogous to lions and tigers. Different breeds of dogs might look very different because they've been artificially selected for superficial qualities, but genetically the difference is tiny compared with two different true species. Ultimately it's just a matter of scale: different dog breeds are divergent by at most a few hundred generations, and usually much less than that, not to mention sporadic interbreeding along the way. Lions and tigers are divergent by millions of years, and there is not natural interbreeding. That they're able to mate and have anything happen is actually pretty remarkable.