It’s a curious fact that Homo sapiens, despite a global distribution of population and a wide variation in physical appearance, has less genetic diversity than chimpanzees. The currently prevailing theory to explain this is the “Toba catastrophe” – http://en.wikipedia.org/wiki/Toba_catastrophe_theory:
Suppose it had never happened? Science knows of at least twelve species in the genus Homo other than Homo sapiens.http://en.wikipedia.org/wiki/Human_evolution (N.B.: Not all of these were still extant at the time of the Toba catastrophe, and at least two – Homo neanderthalensis and Home floresiensis lived on for several millennia afterwards.) If there had never been a Toba catastrophe, would we have had to share this world with other “human” races? Or would we eventually have wiped them all out? (Or is it possible one of them would have wiped us out?) Or would we have made slaves of the intellectually inferior species? (Harry Turtledove explored that theme in the alternate-history novel A Different Flesh, in which the Europeans discover a New World inhabited not by Indians but by Homo erectus.) Also, what would be the long-term effects of a wider, pre-Toba range of genetic diversity within Homo sapiens itself?
Unlikely. There isn’t any evidence that the “Toba catastrophe” had anything to do with the extinctions of the Neanderthals, and they aren’t around any more. I doubt that our “less enlightened” ancestors would have allowed a seperate species of *Homo *to survive. Unless that species was extremely isolated somewhere, they’d be toast.
Homo erectus too, which may have survived up to 27,000 years ago on Java. H. neanderthalis survived to at least 30,000 years ago, and* H. floresiensis* to 18,000 years ago. So at least four species of *Homo * survived at least 45,000 years after the Toba event. It doesn’t sound likely that it was responsible for the extinction of three of them. More likely it was *H. sapiens * that did the others in.
Didn’t the australopithecines die out long before 75,000 years ago? By that time I thought pretty much there was only one genus of hominid left (neanderthals afaik being simply a subspecies or a cold weather adapted version). I could be totally wrong about both of these, as its been over a decade since my college anthropology classes…and they were only electives anyway.
According to the Wikipedia article on “Human evolution” (linked in the OP), and pages linked from it:
The Australopithecus genus of hominids first appeared roughly 3.9 million years ago and was extinct long before the Toba catastrophe. A. africanus once was thought ancestral to the Homo genus, but hominid fossils apparently belonging to genus Homo have been discovered which predate A. africanus. The split might have been with A. afarensis.
The first human (defining human as any member of genus Homo) species was H. habilis, which lived from 2.4 to 1.5 MYA.
H. egaster lived from about 1.8 to about 1.25 MYA.
H. rudolfensis is a proposed species that might or might not be distinct from habilis.
H. georgicus, known from fossils discovered in Georgia (in the Caucasus) and dated to 1.8 MYA, might transitional between habilis and erectus.
H. erectus lived from about 1.25 MYA to 70,000 years ago.
H. heidelbergensis (common ancestor of both H. neanderthalensis and H. sapiens) lived from about 500,000 years ago to about 300 TYA.
H. sapiens idaltu is a subspecies of H. sapiens that lived over 160 TYA in Africa.
H. floresiensis (the “hobbit”) survived until at least 12,000 years ago.
Six skeletons of an extinct species, H. antecessor, were discovered in Spain in 1994.
H. neanderthalensis (classed as a separate species, not a subspecies of H. sapiens, but that question remains controversial) lived from about 250 to 30 TYA.
Our species, H. sapiens, appeared 200 TYA.
The article also mentions H. cepranensis and H. rhodesiensis but no information is provided.
Based on timeline alone, erectus and possibly sapiens idaltu might have been wiped out by the Toba catastrophe – or perhaps they were merely displaced/marginalized/exterminated by the H. sapiens diaspora from Africa, as neanderthalensis almost certainly was.
On the other hand, it seems to be the Toba catastrophe that is responsible for the narrow range of genetic diversity within H. sapiens. And there might well have been other human species living at the time of the Toba catastrophe, and wiped out by it, that have not yet been discovered. The existence of H. floresiensis, after all, was not even suspected until a few months ago.
Yeah, but wasn’t floriensis discovered on an isolated island, thus making it more or less moot? Also, given that the island floriensis was discovered on was in Indonesia, presumably much nearer to the Toba eruption than African or European humanoids, wouldn’t it have been mujch more likely to be wiped out by Toba than other species?
I guess what I am saying is that floriensis is probably a moot point in the argument, re: Toba. But it does lead me to wonder if the floriensis pop. isn’t a remnant population of a species that once had much wider geographical dispersal, whose remains were discovered precisely because they were relatively recent.
BG: You have to be careful when reading something like Wikipedia about a subject like human sepciation. There are many “species” floating around in the literature that aren’t widley accepted. Species designations keep changing, and new are added almost ever time a new fossil is discovered. You get a lot more press and recognition when you announce “New species of hominind discovered” as opposed to “New fossil of existing species discovered”. It wasn’t that long ago that Neanderthals were considered a subspecies of Sapiens, but most anthropologists now recognize it as a distinct species. Even still, the designation of an extinct population as a separate species is always going to be somewhat arbitrary.
Homo floresiensis, for example, has been PROPOSED, but still has lots of question marks associated with it. The fossils have not been widely circulated for other scientists to study and until that happens, there is always going to be an “*” by its species designation.
If you believe every proposed species is real, it would appear that the human line speciated every 100k years or so. That’s just not realisitic. If you look at other extant large mammals with lifespans on the order of humans, you’d be hard pressed to find two different species in the same genus that didn’t branch off from each other at least a million years ago. And even then, those “species” are likely to be cross fertile even if mating in the wild is rare.
A good example of this is the red wolf. Scientists are in disagreement if this wolf is truely a distinct species or just a population of grey wolf/coyote hybrids. In this case, the species designation takes on a political aspect, since that determines whether or not the population can be considered “endangered”.
I know that most experts agree, but I have never fully understood this.
It’s easy to see why H. sapiens could kill off the primitive Neanderthals if they were competing for the same food and shelter. But why did they have to compete? Neanderthals had technology and physiology that enabled them to survive the ice age and hunt woolly mammoths–they could have run away from the new homo sapiens spreading thru Africa, and migrated to the colder climates. The planet is one huge place for cave men who didn’t have broadband access. It seems like there should have been room for the smaller brained, but physically stronger Neanderthals to live separately from H. Sapiens.
(And if Neanderthal had survived, we probably would have kept 'em as slaves.Sure would make for an interesting comparison with whatever alien creatures we may one day encounter…)
I wouldn’t say “most experts agree.” Like most things about early humans, the idea that H. sapiens might have done in the other species of Homo it encountered is pretty much speculation. But that speculation is based largely on what happened when different groups of sapiens of differing cultural levels have encountered one another. The more primitive group was as often as not wiped out, or at the very least subjugated. And this probably happened not just recently, but tens of thousands of years ago as well.
Of course they were often competing for the same food and shelter. Early sapiens hunted big game and lived in caves, just as Neanderthals seem to have done. And I don’t know how neanderthalensis could have “'run away.” Sapiens was perfectly capable of living anyplace that neanderthalensis could.
For the record, *neanderthalensis * had a larger brain than the average sapiens, although it was somewhat differently shaped. And just because there might be “enough room” wouldn’t necessarily prevent conflict from occurring. Certainly there was “enough room” in Tierra del Fuego and in Tasmania for primitive groups to survive there in company with Europeans, but those groups were pretty much eradicated anyway.
Nitpick: We call prehistoric humans “cavemen” because a lot of their remains have been found in caves – but that’s because caves naturally preserve bones, artifacts and wall paintings. A lot of them probably lived in tents or huts (it’s not exactly a major technological challenge to build one – the pre-Columbian American Indians, whose technology was purely stone-age, had their teepees and wigwams), but the elements gradually destroyed all trace of them.
I know, I know . . . but the Wiki article was more plain and readable than anything else I could find on the same subject. Do you know of any site that makes clear exactly how many known human species were living 75,000 years ago?
Not sure I follow you . . . there’s no question the fossils exist, is there? Or do you mean they still might decide to classify the “hobbits” as a subspecies of H. sapiens? Hard to see that, if their braincases were really that small.
BG: At 75k years ago, there probably is concensus on Sapiens, Neanderthal and Asian Erectus. Floresiensis is still too new to be broadly accepted, but for the sake of argument we can probably say that some different species existed on the Flores Island. It’s the earlier species that I question. For instance, do we really need a H. antecesor given that we have erectus, ergaster, rudolfensis, and heidelbergensis?
As for floresiensis: there is no doubt that the fossils exist. But they are being held in Indonesia (can’t remember the name of the Indonesian scientist in charge) and not being made available for study. Yes, the discovering crew has claimed they are a new species, but not enough other scientists have looked at the actual fossils and until that happens, it’s unclear how the chips will eventually fall. The case looks pretty strong for a new species, but it’s still too early to say definitively.
