[John O]

When the two groups can no longer interbreed, or just prefer not to, they stop exchanging genes and eventually go their own evolutionary ways, thus forming separate species.

According to this Negros and Caucasians in the early 1700's were different species. But then we became one species again in the 1960's.

Either they neeed to do a lot more work on this or they have to phrase things much better

[PatrickHenry]

Thank you for your thoughtful contribution.

[Modernman]

When the two groups can no longer interbreed, or just prefer not to, they stop exchanging genes and eventually go their own evolutionary ways, thus forming separate species.

That is kind of an unclear statement. I don't think it really refers to preferences (i.e., I prefer to exchange genes with redheads but that doesn't mean that my descendants will form a separate species from brunettes) but rather talks about different species that CAN interbreed but do not do so under natural conditions (such as tigers and lions, who can create liger and tigon hybrids)

[AntiGuv]

Actually, it's a rarely discussed phenomenon that Australian aborigines who conceive children with non-aborigines tend to have extremely high rates of miscarriage and stillbirth. This is likely attributable to the 70,000-50,000 year genetic separation of aborigines from the rest of mankind.

[Right Wing Professor]

According to this Negros and Caucasians in the early 1700's were different species.

Boy, do you need to read some history.

Ever wonder why African Americans are, on average, much lighter than West Africans?

[VadeRetro]

According to this Negros and Caucasians in the early 1700's were different species. But then we became one species again in the 1960's.

Bad history, never mind the bad model.