After reading the article, Stephan requested his grandfather to take him to a zoo. Overthere he saw an animal which resembled a horse and a donkey. He thought that donkey and horse are of the same species. But his grandfather corrected him by saying that no they are not. Identify the reason why they are not of the same species.
They do not produce fertile offspring.
Species are defined as a group of individuals that can reproduce and produce fertile offspring. Fertile offspring are defined as the babies who grow up and then mature and can reproduce organism of the same kind. For e.g.: Two humans are of the same species. One woman and one man can reproduce to give a child who will be capable of reproduction. The horse and donkey together can produce offsprings called mules. However, mules are sterile and incapable of reproduction. Thus, horses and donkeys form separate species.