What lets dogs interbreed and create odd and crazy-looking pups when most birds can’t do the same? If dogs can interbreed and you can make a cockapoo, why don’t birds interbreed where you could have a robin-crow?
A species is a group of animals that gives birth to live, fertile offspring when its members interbreed. Dogs all belong to a single species. On the other hand, birds — like robins and crows — come from different species.
Species are created by a combination of behavior and genetics. Many birds are very picky — they’ll only mate with another bird if the bird looks the same. Dogs aren’t so choosy.
Genetics also plays a role. If the genetic make-up of two animals is quite different, and there’s a big difference in the number of chromosomes, the animals can’t mate successfully.
The many different dog breeds are relatively new. They’ve only been around since humans created them. There hasn’t been time for a schnauzer’s genes to look much different from a Great Dane’s. Meanwhile, bird types have been evolving for millions of years.
How many chromosomes? Curious? Check out GenomeSize.com
One cool thing about species is that there are levels of “protection” against interbreeding, as it would certainly be a waste of effort if individuals from different species were always attempting to mate with each other, only to never produce offspring. some of these protections are mechanical – parts simply won’t fit together. some are behavioral: individuals are not attracted to each other. basically, one bird’s mating dance (or song) is another bird’s nonsense. these behavioral isolating mechanisms (as they are officially known), keep like with like, a process which further isolates species from each other.