A scientist finds what she thinks is a new species of rodent on a small Pacific island. However, some similar-looking rodents inhabit some nearby islands. She mates the new rodent with the nearby rodents and gets viable but infertile offspring. Why

Charles Darwin's theory of evolution states that evolution happens by natural selection. Individuals in a species show variation in physical characteristics.  As a consequence those individuals most suited to their environment survive and, given enough time, the species will gradually evolve

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