Question for the biology experts

[Adam]

The thread "Do different human races exist?" got me wondering about this. In any other species, has there ever been any observation or discovery which indicates that two entirely separate chains of evolution have produces two separate species capable of interbreeding? Say, two creatures develop in separate parts of the world, don't have any contact through millions of years of evolution, and now are observed breding, for example. Has there ever been any genetic evidence of observation which would indicate this possibility?

It seems to me this question is very important to the question in the other thread I mentioned.

 

[James R]

One commonly used definition of the word "species" is "a group which can interbreed and produce fertile offspring".

Using this definition, if any two groups can successfully interbreed and produce offspring which can also breed, then the two groups are part of the same species.

 

[Adam]

However, even among humans, there are many who can not breed with humans. Some are infertile. Some fertile couples just don't work together. It is an insufficient definition.

 

[paulsamuel]

reply to adam

That's a good question adam, and very clarifying. the answer is emphatically NO! It cannot happen. All hybridization is between species that have (relatively) recently diverged from a common ancestor.

on species: The fact that some individual humans are infertile due to some genetic problem or pathology, is NOT the reason that the species concept has problems. All humans, infertile or not, are at least potentially able to interbreed, therefore, same species.

James is right in the most literal interpretation of the species concept, but there are exceptions. i.e. inter-species hybridizations with fertile offspring, but are without question separate species.

The species concept is problematic. It is not clear that species are biological entities or constructs of human desire for classification. There are alternate hypotheses for species constructs including the phylogenetic species concept. one problem is that many look at species as some 'thing' but species are constantly changing and are different from one generation to the next. one question one could ask, 'is an extant species interfertile with the same species that was extant 100, 1000, or 100,000 years ago?' are they the same species?