“I’ve read these papers fairly carefully, looking for weak points ... but I can’t find any.”
See, now that’s how science works. An article by Carl Zimmer in the New York Times (I expect you’ll need to register; it is too fresh for Aaron’s Link Generator) describes a couple of recent papers about how new species arise. One is about the kentia palm (Howea forsteriana) and its kissing cousin H. belmoreana, the other about two Nicaraguan cichlid fish, the Midas cichlid (Amphilophus citrinellus) and the slender arrow cichlid (A. zaliosus).
The two papers in Nature show pretty conclusively that the two palms and the two cichlids arose as independent species while occupying the same physical location. That’s called sympatric speciation, as opposed to allopatric speciation, where two populations become physically separated and evolve their separate ways, to the point where they no longer interbreed to produce fertile offspring.
There has been a long debate within evolutionary science as to whether sympatric speciation could actually happen. Mathematical models suggest it could, but in real life, skeptics charged, the two fledgling proto-species would continue to breed, eradicating any nascent differences between them.
The debate is about a wrinkle within evolutionary theory. Neither side has ever said that its doubts cast doubt on the truth of evolution by natural selection. Those who oppose sympatric speciation are not saying that new species never arise from existing species.
And when evidence arrives in support of one view or the other, real scientists, such as the eminent Douglas Futuyma of the State University of New York at Stony Brook, quoted above from the article, examine it.
Alas, from that quote alone one can’t tell whether he actually accepts sympatric speciation now. Time will tell.
p.s. Bizarrely, while searching for a link, I found a blog that simply cut and pasted Zimmer's entire article. Why is anybody’s guess. But it is kind of handy. So thanks, and nice headline, Mama Bear.