I wonder how long until human evolution produces humans genetically incapable of interbreeding. Wikipedia says that even some intergeneric (genus) hybrids may be fertile!
Here is some unsettling information about "humanzees" and "chumans", hypothetical intergeneric hybrids between humans and chimpanzees:
Hybrids between different subspecies within a species (such as between Bengal and Siberian tigers) are known as intra-specific hybrids. Hybrids between different species within the same genus (such as between lions and tigers) are sometimes known as interspecific hybrids or crosses. Hybrids between different genera (such as between sheep and goats) are known as intergeneric hybrids. Extremely rare interfamilial hybrids have been known to occur (such as the guineafowl hybrids). No interordinal (between different orders) animal hybrids are known.
Here is some unsettling information about "humanzees" and "chumans", hypothetical intergeneric hybrids between humans and chimpanzees:
https://secure.wikimedia.org/wikipedia/en/wiki/Humanzee
Also:
Hybrids between different subspecies within a species (such as between Bengal and Siberian tigers) are known as intra-specific hybrids. Hybrids between different species within the same genus (such as between lions and tigers) are sometimes known as interspecific hybrids or crosses. Hybrids between different genera (such as between sheep and goats) are known as intergeneric hybrids. Extremely rare interfamilial hybrids have been known to occur (such as the guineafowl hybrids). No interordinal (between different orders) animal hybrids are known.