It’s All About The DNA
DNA appears to be the key to the mystery. There are 62 chromosomes in a donkey and 64 in a horse, hence a mule is the result of the two matings. Consequently, the offspring of the two animals have an odd number of chromosomes. And, of course, this has its own set of repercussions. An egg or sperm must include 50% of an animal’s chromosomes in order for sexual reproduction to work, hence this odd number indicates that the species has a “defective” genetic coding that precludes it from reproducing further.
Gorillas And Orangutans
Gorillas and orangutans, for example, have the same number of chromosomes. Then, some scientists believe, it will be simpler for them to have healthy children. At various stages in their evolutionary history, there is evidence that bonobos and chimpanzees have interbred with each other.