EVOLUTION:
Male Mating Blocks New Cuckoo Species
Virginia Morell
Cuckoos lay their eggs in the nests of many other bird species, leaving the unwitting hosts to raise their young, but individual females specialize in nests of just one kind of host bird. Such specialization should lead to the formation of new cuckoo species but has mysteriously failed to do so. Now, a study on page 471 shows why: Male cuckoos mate with females that parasitize many different hosts, homogenizing the cuckoo genes and preventing the development of new species.