“Years ago, speaking in a tone of subdued irony for my benefit, Donn Rosen, a curator of ichthyology at the American Museum of Natural History, wryly summarized what is involved: Darwin said that speciation occurred too slowly for us to see it. Gould and Eldredge said it occurred too quickly for us to see it. Either way we dont see it.
From an American Spectator review of “Darwin’s Doubt”
In fact, evolution can be seen every day in DNA studies mapping the occurrences and transmissions of mutations in everything from plants & animals to human beings.
When, precisely, all these observed mutations add up to separate races & breeds (i.e., dogs), sub-species, species, genera & families, etc. -- these are all matters of careful scientific definitions and debates.
For example, you might remember that Polar Bears & Brown Bears were recently reclassified from separate genera down to just separate species of the same genus.
Reason: it was discovered that Polar & Brown (Grizzly) Bears can and occasionally do interbreed in the wild.
By biological definition, natural interbreeding means they can still be separate species, but not different genera.