Homo sapiens, only species under homo?

Why is it that all other species under our genus have become extinct... does that mean anything in regards to the validity of evolution, and are there other single specie genus instances?

IIRC, Lineaus had gorillas and chimps under the same genus. This has been suggested since. We are much closer, as I understand, to them than other species are to ones in the same genus. It is because of our anthropormorphic view that we are not.It doesn't mean anything for evolution. All groupings of life above the species level are for convenience and constructed for that convenience only. The whole Linnean system is just one way of naming things. So haveing a few genera with only one species shouldn't be too surprising.There are other groups but I can't give examples. I'm pretty darn sure there are a number of one species genera even one species families and maybe higher levels than that.What is odd is the validity question. I don't understand why you would ask that? Can you explain what you were thinking?

Well, I understood taxonomy to be for the sake of convenience with no impact on the validity of evolution... a creationist asked me, "where are all the intermediates today? extinct!" and I was curious how that was supposed to be a rebuttal, that's why I asked.
Thanks for the genetics info, that answers my question!

L. had chimps and orang-utans in Homo initially - gorillas weren't known to Swedes and such in his day.
The pronghorn "antelope" is one example that leaps (yuk yuk) to mind of a species that's the only one in its genus and family. I think I remember more, too, Ned, but my unauthorized and unintentional access to Walker's "Mammals of the World" got terminated, so I can't readily find examples.

That is an excellent question, and one which merits a bit of time to seek out an answer and evaluate the available data.One difficulty, as NosyNed points out, is that the term "genus" is an arbitrary ranking. The term "species" has considerable ambiguity and alternative definitions exist, but it is a taxonomic rank for which there is at least a grounded basis for trying out definitions and applying them. "Genus" has no such basis; it is basically a convenient convention with no good basis for comparison across different instances.Even so, the question is still meaningful, I think. I'm not going to attempt a full answer here. Perhaps a biologist in the house might step up to the plate.However, I will note that S.J. Gould considered the question. He pointed out that a sign of evolutionary success could reasonably be a widespread and diverse famility of many closely related species. But in the wax and wane of living forms, extinction marks the end of the line. Large groups can become extinct as well as smaller groups. The dinosaurs are a dramatic example, involving total extinction of many large groups of related species, which had been highly successful and diverse in the past. Birds may be the only survivors; from a small outgroup of therepod dinosaurs.A classic example is the horse. Horses used to be a very diverse group of species; now all that remains of a great evolutionary bush is a small twig. In the past, it was common to considered (for example) the horse as a success, and trace their long lineage as an example of inevitable evolutionary progress. The resulted in that now notorious example (often siezed by creationists as an example of flaws in evolution) of the mistaken attempt to rank a whole range of horses into a kind of progression.We now know a bit better, and tend to trace many diverging lineages of related species, expanding in parallel into diverse niches. Most of these, however, are now extinct, with only a few little twigs of that once great bush still with living descendents; modern horses, donkeys and zebras. This is an indication of the waning of a group of organisms, not an example of success.The other dramatic example Gould points out, are apes. The Miocene, some 25 million years ago or so, was the heyday of the apes, with many diverse species over greater ranges than today. What we have in modern times is only a fragment of a once much larger group of species.The obligate bipedal apes are a dramatic subcase. 3 million years ago there were quite a number of species living in this group; various species of robust and gracile australopithicenes. But alas, this group also has waned; with only one species still living. Homo sapiens.It is an interesting perspective. It suggests we might not be a great example of evolutionary success, but the tail end of what was mostly a failed evolutionary experiment. I don't remember the essay in which Gould discussed this notion; it might have been in "Hen's Teeth and Horses Toes".The development over the last 100,000 years of distinctively human behaviours of culture and civilization, on the other hand, are something quite new for our biosphere. This one species is now amazingly successful. But in the long terms of species, the future remains unclear.Cheers -- Sylas

There was an article a while back that had new genetic information on this.See Chimps Belong on Human Branch of Family Tree, Study Says (National Geographic News - May 20, 2003): Bonobos are the "pygmy chimps" a different species with very "left bank" behavior ... and they engage in some kinky behavior that would make a normal person blush.There is some controversy on which is the closer cousin, but little doubt that both are close.Enjoy.

There's actually a fair selection of single-species genera. Usually, the single species is a relict or remnant of a once-widespread clade. A couple of examples were discussed in this post. There are a bunch of others, especially among plants. Sylas covered most of the explanation - let us know if you have other questions on it.

Didn't the rediscovery of the Coelecanth make it a one species order?

Sorry, TL, it's a two species order: Latimeria chalumnae and L. menadoensis.

Yeah, I got told that in another thread, too. Oh, well, live and learn.Hey, do you happen to know what taxonomic level the monotremes are? I looked up the spiny anteater, thinking it was one of only two egg-laying mammals, and I found out there's two species of spiny anteater. However, there are only three egg-laying mammals, the duck-billed platypus being the other. They're called monotremes, but I didn't know whether they belonged to an order by themselves or a family or something. They must be class mammalia, since they're mammals (wow, you can see how deep my knowledge of taxonomy is ). I poked around several web sites, but they just didn't want to give me the classification of monotremes.

IIRC the monotremes diverged from the marsupials before the marsupials diverged from the placental mammals.Ah, here we go: Mammalia[This message has been edited by Mr Jack, 03-30-2004]

Thanks, MrJack.What totally cool animals!