Ligers and tigons are created through humans' intentional mating of lions and tigers, or because the parent animals were housed together in human-controlled enclosures. Most tigon offspring don't reach full term or are stillborn because the mother tiger's womb isn't big enough to hold the big tigon cubs, which are larger than what the male tiger's cubs would be. Tigons are often smaller when full-grown than either of their parents. Big cat experts surmise that lions and tigers are able to breed because they're genetically similar enough that their chromosomes can pair and produce offspring. Both lions and tigers have 38 chromosomes. The ability of two separate species -- lions and tigers -- to produce offspring raises questions about just what defines a "species." Generally the term species refers to a group of genetically similar animals that can successfully produce offspring. However the word "successfully" is a sticking point when it comes to ligers and tigons -- many of these hybrid animals have genetic disorders and die at an unnaturally young age. Because of this, scientists believe it's safe to say that lions and tigers are clearly two different species that would not breed in the wild even if given the opportunity.