When the ranges of two different species meet, a stable "hybrid zone" occupied by hybrid individuals may form. How is this possible? When the ranges of two different species meet, a stable "hybrid zone" occupied by hybrid individuals may form. How is this possible? Two diverged populations are capable of mating and producing viable and fertile offspring. Hybrid individuals may have reduced fitness and thus be strongly selected against. Hybrid individuals are always allopolyploid and are thus unable to mate with either of the original species. One species has a selective advantage, so as hybridization continues, the other species will go extinct.

Two diverged populations are capable of mating and producing viable and fertile offspring.

Explanation:

Although the biological concept of species says that two different species can not mate and produce viable fertile descendants, the hybrid zones are characterized for being an area where two different genetically groups meet and reproduce. These groups might be the same or different species.

This is a frequent phenomenon in nature, and widely common geographically and among taxonomic groups. It is not rear that different sympatric populations, with a short time of divergence and similar reproductive strategies, can hybridize and even generate new populations that get reproductively isolated from their parentals.

When talking about sympatry we refer to two similar species that coincide in part or their whole distribution area.  

These new populations are even morphologically different from the parental forms, which allow them to colonize new habitats and niches, promoting diversification.

Hibridation zones are very important to conserve, just because they are points of genetic diversity generation and diversification areas.

d. organisms have cells with different shapes and functions.