Razib and GNXP writes about polar bears, concludes with an interesting thought
"If the polar bear goes extinct today, what will happen when the next Ice Age opens up more opportunities? Likely the "polar bear" will reappear, assuming that human intervention does not forestall such evolutionary responses. In fact there may be an eternal recurrence in the cases of bears and sticklebacks over the past few million years of Ice Ages whereby cold adapted morphs emerge, and go extinct, repeatedly. What would happen if all non-African populations were exterminated? Likely Africans would resettle the rest of the world, and de-pigmentation and Bergmann's would produce lighter populations all around the temperate zones within 10,000 years. The specific details might vary, consider how light skinned populations in Britain and Japan are rather different. It illustrates how evolution is both contingent and deterministic."