[melaniejs (OP)]

David asks:

Have we ever created/witnessed a new species or is it just a hypothesis based on a lot of evidence?

Anyone know?

[Kryptid]

I want to say yes, but it may require a bit of digging. What could count as effective speciation has been done for fruit flies in the laboratory, where different populations were artificially selected for differing traits over a series of generations. When those populations were recombined, there was a significant tendency for the fruit flies to mate with the population that they came from instead of crossbreeding with the other population. That would be a form of reproductive isolation. Whether any such experiments have been successful in making the two populations literally infertile to each other, I do not know.