hybrid

Offspring from a cross between individuals of two different species, or two inbred lines within a species. In most cases, hybrids between species are infertile and unable to reproduce sexually. In plants, however, doubling of the chromosomes (see polyploid) can restore the fertility of such hybrids.

Hybrids between different genera were believed to be extremely rare (an example is the Cupressocyparis leylandii cypress which, like some hybrids, shows exceptional vigour, or heterosis) but research in the late 1990s shows that hybridization is much more common than traditionally represented. One British evolutionary biologist estimated in 1999 that approximately 10% of animal species and 20% of plant species produced fertile offspring through interspecies mating. Blue whales, for example, hybridize with fin whales and different species of birds of paradise also hybridize. In the wild, a ‘hybrid zone’ may occur where the ranges of two related species meet.