How do you decide if two populations separated in time are a distinct species (some of our ancestors come to mind)? What about species that reproduce asexually?
A dandelion can’t “mate” with anything, is each individual plant its own species?
Tom and Arnold let this go by?
Have Mamas stopped telling their kiddies about the birds and the bees?
Where is aha when you need him?
On why the world doesn’t contain dozens of distinct species of hominids: I think it’s probably because there simply isn’t much room for variations on the basic theme.
Speciation occurs when you have a generalized ancestor from which descend separate populations that specialize in varying ways. For example, in felines you get a very large range of sizes, from wildcats to lions, because there are econiches for predators of very different body masses.
By contrast, genus Homo has pretty much stuck with one basic theme: a bipedal, tool-using hunter/gatherer. Physically there isn’t a lot you could do to vary the design. About the furthest spread is between four-foot pygmies and seven-foot Watusi. And because humans use technology, our variation tends to be cultural rather than biological. Inuit (Eskimos) didn’t evolve fur, they invented warm clothing.
Tomndebb, uh, the acid test would be if there’d be some sort of controlled study done. I’m not sure how the study should be set up, though.
Daniel (and others), I don’t feel this is an accurate portrayal of the current scientific view. The latest DNA evidence seems to indicate no mitochondrial DNA contribution from the Neanderthals. Therefore, Homo Sapiens likely did not interbreed with the Neanderthals to any significant degree.
jally
For an true comparison, you must contrast a poodle with a doberman, with a boxer, etc. These are all of the same species, as are humans. There is far more variety in the facial characteristics of dogs than humans.
There’s a paleoanthropologist from Finland who wrote a couple of novels (something about “Tiger”) to demonstrate his theory of how Neanderthals vanished.
It wasn’t that they fought Homo sapiens, but rather the opposite: they loved them too much. The H. sapiens face with its large forehead, lack of brow ridges, and relatively flat plane resembled the infantile Neanderthal face. Ethologists know that the infantile-type face inspires feelings of love in the eye of the beholder. The Neanderthals couldn’t help falling in love with H. sapiens; they kept mating with them. But, being of different species, the offspring were sterile. When eventually all the Neanderthal’s offspring wound up sterile, the result was extinction.
" And I’ve noticed that there is MUCH more variation in facial appearance between humans (doppelgangers excluded), than there is, say, between one poodle & another, or between one chihuahua and another, or between one cat & another "
Just to add another aspect in addition to what tomndebb said. Don’t forget that dog breeds (and cat breeds) were made by a series of selective breedings. The crosses were done to choose and maintain certain traits in the dog. Sometimes these traits were appearance. But even when they were not, the breed was chosen from a smaller gene pool which could result in a more limited variety with regard to appearance.
John
Actually, it can. It just doesn’t have much fun doing it, and requires insects to help. Lends some veracity to looking at your lawn and complaining about all the f***ing dandelions.
Don’t confuse “sexual reproduction” with copulation.
BTW, somebody has observed a difference in suburban dandelions vs. those that grow in the wild - the ones in suburbia tend to flower very close to the ground, then spring up when going to seed. The one’s from wild areas grow tall while flowering so as to compete with surrounding plants. As the study put it, we’ve evolved the first lawnmower distributed species.
I love it! Evolution in action, folks!
I’m not, that’s why I put “mate” in quotes. I do realize that sexual reproduction occurs in most plants. The reason that I chose dandelions as my example is because dandelions are all female, and reproduce by aparthogenesis. I love the lawnmower example, BTW.
As to humans being in a genus by themselves: The tuatara (a lizard-like reptile) is in a whole order by itself, and I think that the ginko tree might be a whole class.
Curious. Before I posted I did a quick check and found references to how dandelions were pollinated (by bees, apparently, and apple growers worry about the bees paying attention to the dandelions instead of the apple blossoms).
Is that the dandelion’s only mode of reproduction?
That appears to be right about Ginkos - class Ginkgoopsida contains only 1 surviving species, though there are extinct members of the class.
well, with regard to variations in species, I must say that I don’t know of any encyclopedia which depicts different varieties of human faces, the way they depict different varieties of birds, butterflies, dogs & so on.
As an aside, I did once mention on these boards about the study by Bouchard & N.Segal of the Univ.of Minn. on MZ twins separated at birth. And I mentioned that the study was incomplete in that it studied related look-alikes & related “non” lookalikes.
Yet it left another aspect unaddressed:
Non-related (perhaps gene-related?) look-alikes. I read an article once about celebrity lookalikes & how they compared their tendencies to the celebrities’. It made for an interesting article, but wasn’t all that scientific. No thorough study has ever yet been done on the phenomenon (that I know of).
OK, I may be wrong about dandelions, maybe it’s just that they’re capable of aparthogenesis (and come to think of it, why would they have sweet flowers if they didn’t depend on insects sometimes?). The point is, though, that there definitely are some species (and apparently I don’t know which ones) that reproduce exclusively asexually, and for them, the interfertility criterion is useless.
Then why, (according to science magazines I’ve read… no pretense to being an anthropological maven) don’t any tested modern humans show any evidence of Neandertal DNA? I thought that was the big deal with the test/study they completed last year that pretty much said we don’t have any N-tal DNA (or mitochrondria or whatever) and concluded they weren’t “absorbed” but did indeed die out.
I think I can tell you about this little question.
DNA just isn’t available from Neanderthals. That DNA is gone, long gone and so far there is little reason to hold out hope that we’ll get a little chunk someplace.
mtDNA is what’s being tested - and that’s only because many mitochondria are found in each cell and fossils of Neanderthals do contain enough of the mtDNA to construct enough to compare.
There is some question that we (Hss) could have Neanderthal DNA (the real DNA) and yet not have Neanderthal mtDNA. To many this does not seem logical but is doesn’t look as if the proof (Neanderthal DNA) will ever come to be examined let along proven.
IMO the Neanderthals weren’t absorbed. And I do think that is the theory that is “winning” at this time.
A seemingly “innnocent” idea sometimes is mentioned at this point - that the population what did interbreed with the Neanderthals is no longer represented in the current European population - they were all replaced by subsequent groups, like the agriculture populations that went east to west about 5000 BC. Somehow it being easier to accept that Hss interbred with Neanderthals but their offspring were killed off by the agriculture populations. I think the original Hss saved the aggies the trouble.
It’s quite possible that (to steal a line from many a bad Western) this planet wasn’t big enough for the two of us.
In spite of the popular image of Neanderthals as big, clumsy, stupid half-humans, they were really a lot like our ancestors - and a lot like us now. They made similar tools, had big brains (bigger than modern H. sapiens in fact), lived in tribal groups, etc. H. sapiens and H. neanderthalensis shared the same evolutionary niche. The explanation for why only H. sapiens is still around could simply be that the combined populations of H. sapiens and H. neanderthalensis were at some point larger than the environment could support, and that this problem continued long enough for the slight differences between the two groups to become significant. H. sapiens may have neither annihilated nor absorbed H. neanderthalensis, but just moved onto their turf, ate their food, and made babies faster than the Neanderthals could cope with. Even a small evolutionary competitive advantage can add up over generations.
This hypothesis isn’t as exciting as some of the others, but then, evolution is terribly dull 90% of the time.
Maybe, but per the PBS show I show I saw (yeah I know great cite) on the N-tals, based on the time dated evidence for similar co-temporaneous N-tal and Hss excavated sites it seems that Hss really was much cleverer than the N-tals in producing art-weapons-etc per the hallmarks of the more advanced skill sets necessary for “civilization”.
N-tals have a rep. for being a little behind the curve and appparently, based on archeological findings to date this rep. is not entirely undeserved.
It is hard to see how all breeding populations of N-tals were wiped from the face of the earth though. You’d have thought some N-tal group somewhere would have hung on in some remote location.
For a bit more on that Neanderthal mtDNA stuff, read this article, from the journal Nature in which the mtDNA study was published.
The most recent theory (from Oxford) about the demise of Neanderthals is that they had too selective a diet, mostly meat with few nuts and grains.
The evidence for this comes from analysing the ratios of carbon and nitrogen isotopes in Neanderthal bones. Because plants and animals have different isotopic ratios, they leave different signatures in the bones when eaten.
The results were compared with results from contemporary carnivores (bears) and herbivores (bison). And lo, it was discovered that 90% of a Neanderthal’s protein came from meat.
If anything were to interrupt the supply of game, this would naturally have an effect on a group that relied almost exclusively on hunting.
Personally, however, I can’t imagine Neanderthals would be so stupid as to be unable to find a new source of food. And surely any serious depletion would have an effect on all predators including early humans.
no it isn’t - the infertility crierion is based on “this species is the same as species x, y or z if they can have fertile offspring with species x, y or z”
If they reproduce solely by asexual reproduction (many simple sea creatures & 99% plus of single celled creatures (not getting into issues about bacteria etc swapping dna)), then they obviously can’t produce a fertile offspring with species x, y or z as they can produce no offspring with x,y, or z.
Creatures that can interbreed but are becoming very different tend to be called “demes” - this usually happens because of genetic isolation (eg group of beavers arrive in a valley, big rock-slide, get trapped there. Different conditions in the valley from outside lead to different offspring types surviving and passing on a differently selected pool of genes. It probably takes millions of years before you can call them a separate species, but they can become very different from the original. If the land slip disappears quickly, they’ll just breed back into the original population & disappear.)
Fi.
I do know that mitochondrial dna is only passed on through the female (it is found inside the cell & the only male genetic info passed on to the next generation is half of its chromosomes, as that is all that enters the egg cell).
While unlikely, it is possible that the only children from ntal/sap species that survived to breed were from a male n’tal/fem sapiens pairing - the xntal-xsap could have had a lethal combination that a y-ntal x-sap pairing avoided & so no ntal mitochondria were ever passed on. They could have bred into the population but not carried any ntal mitochondria that way.
Fi.
Fierra, I think some may nurse that hope - male Neanderthals and female Hss would have the mtDNA but it would depend on how generic mtDNA is and how necessary the absolutely correct mtDNA is for survival even in the foetal stage.
Have you looked at the studies that compare our mt DNA to our various “next of kin” chimps, apes, bonobos? It may change right along with the species.
And the possibility that the terms of pregnancy may have been different between Hss and Neadnerthals. I don’t think I’ve seen that soundly backed up or chopped down, yet.