[stainablesteel]

my understanding of what classifies something as being a part of the same species is the fact that they can make children that are viable to have children themselves

horses and donkeys can breed to make mules, but the mules usually cant reproduce, this is the same with tigons and ligers but sometimes the females are viable

so if they can produce children that can produce children, they're the same species. where this line is blurred, so is the species line. geographical barriers have nothing to do with it.

[Vaphell]

> my understanding of what classifies something as being a part of the same species is the fact that they can make children that are viable to have children themselves

things are a bit more complicated than that, because having fertile offspring is not a transitive property. Ring species: population A can mate with B, B with C, C with D, and D with E, but A and E cannot mate, even though they are part of the same continuous chain.

Ensatina eschscholtzii salamanders in California exhibit this non-transitive behavior. Populations at the ends of the coastal ranges can interbreed with their neighboring populations, but where they meet in the south, the "ends" of the ring do not interbreed.

[rolph]

if you consider that geographic barrier is an environment of immediate lethality, or infecundity, that is physiological incompatability, and would be a speciation.

if you consider that geographic barrier, simply precludes, interaction between individuals, then you will have founder effect, thus one population will be genetically decended from a sample of the larger population.

https://en.wikipedia.org/wiki/Founder_effect