On Human Evolution

by TD 77 Replies latest jw friends

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  TD

  Thank you DD. You are the only one who accepts creation that responded. --And this wasn't a trick question. It was a matter of perception question.

  I'm not whining here, but I'd like to point out as a general observation that facial appearance and morphology-based taxonomy aren't quite the same thing. The latter is much more of a science than people might realize.

  Pongid cranial features are very, very distinctive. Many of them you can't see until after the creature is dead and you have the actual skull in hand, but even when the creature is alive, some of them are still observable:

  The sulcas. Apes don't just have bigger brow ridges than us. The skull constricts just behind the brow ridge to form a furrow that goes all the way down to the cheek.

  Prognathisism. The maxilla of an ape protrudes well beyond the coronal plane to form a snout.

  Lack of a parietal bulge. At the back, the widest point of a human skull is near the top, in the parietal region. The widest point of an ape's skull is near the bottom in the auditory region.

  Palate shape. The widest point of an ape's palate is near the front where the canines are located. The widest point of a human palate is at the very back where the third set of molars (Wisdom teeth) are located.

  Lack of the mental eminence. The human manidble has a roughly triangular protrubence of bone that gives is a chin.

  Sometimes we joke about the way certain people look. (Like Nicolai Valeuv, the Russian boxer in Moshe's picture) but in the criteria I've listed above, the shape of his skull is definitely human and wouldn't fool anybody.

  We wouldn't let an evolutionist base an argument on a fossil that has never been found. We would say, "That's an ad hoc argument buddy. Run along and discover your fossil and then we'll talk."

  Similarly, we can't postulate the existence of a phenomenon in humans that has never, ever been observed. Humans in all their shapes and sizes do not have these pongid characteristics and there are no known diseases that can cause them.
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  Deputy Dog

  TD

  I'm certainly not an expert, but, I'm sure we would agree on much, if we're only speaking in general terms about modern humans and modern apes.

  Similarly, we can't postulate the existence of a phenomenon in humans that has never, ever been observed. Humans in all their shapes and sizes do not have these pongid characteristics and there are no known diseases that can cause them.

  I know its only one example and not quite the same, but, look at the controversy with "Homo floresiensis". Is it variation within a species or not?

  With anything short of a romantic encounter, I don't know how you could know for sure.
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  Cadellin

  I think the recent explosion in gene sequencing technology, particularly with respect to ancient DNA, will seal the deal. Modern human genomes fall within a fairly limited range and it's now known that Neanderthals fall outside that range (making them a separate, though related species), as do the most recent discovery, the Denisovians.

  What's interesting is that interbreeding happened way long ago, which means that researchers theorize that we're carrying around something like 3-4% Neanderthal DNA and a whopping 5% Denisovian. Not all of us, though. These species arose after leaving Africa, so it would be expected that indigenous African peoples like the !Kung would not share Neanderthal or Denis. DNA. And they don't.
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  Nickolas

  The skull sequence presents a certain clarity to the dynamic that some will be unable to see because it challenges what they otherwise believe. It's just the way it is. The evidence for our evolution is plentiful and virtually conclusive (adjective chosen deliberately) and is more logical than the alternative proposition. Good thread.
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  Deputy Dog

  Cadellin

  I think the recent explosion in gene sequencing technology, particularly with respect to ancient DNA, will seal the deal. Modern human genomes fall within a fairly limited range and it's now known that Neanderthals fall outside that range (making them a separate, though related species), as do the most recent discovery, the Denisovians.

  If interbreeding could happen (which seems to be the case), that would seem to me to be the best arguement for variation within a species, not evolution into a new one.

  What's interesting is that interbreeding happened way long ago, which means that researchers theorize that we're carrying around something like 3-4% Neanderthal DNA and a whopping 5% Denisovian. Not all of us, though. These species arose after leaving Africa, so it would be expected that indigenous African peoples like the !Kung would not share Neanderthal or Denis. DNA. And they don't.

  Interbreeding would point to these all being of one species not three.
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  Abaddon

  Whether Sapiens, Neanderthals and Denisovians are species or subspecies doesn't change the very good evidence pointing to them evolving from a common ancestor that was a completely different species.

  Scientific names are given based on the knowledge available at the time. If we knew what we will know in 50 years then maybe Hominids back to Hidelbergensis might all be seen as sub-species. But again all as descending from another species.

  And it should go without saying that members of a species can breed with immediate ancestors and descendants, no matter what classification we put them under later. And by immediate, I mean many generations. 'Interbreeding' between species happens on evolutionary time scales, otherwise you would have to insist that at some point direct offspring would not be genetically compatible with their parents.
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  Cadellin

  Members of a species can breed with immediate ancestors and descendants, no matter what classification we put them under later

  That's the idea. The very limited interbreeding occurred around 60,000 years ago (b/w H. sapiens and H. neanderthalensis). The species had already diverged, but were very closely related. Researchers are able to identify specific places in our genome that appeared after we diverged from Neanderthals, including gene variants for cognitive development. I'm quoting from the recent Discover article here (May 2011, "Meet the New Human Family").

  That two species can interbreed doesn't mean they're actually a single species. For instance, golden retreivers can be mated with grey wolves. Same species? No, there are a host of behavioral and physiological differences. I don't mind sharing my quarters with a golden retriever but I know a wolf will want to spray urine around the place at a distance of about three feet from the floor. That trait can't be trained out of it. It will challenge me at a certain point in its development--the golden retriever not so much. Also, the wolf has a bite strength of about 1500 lbs per squ. inch, the golden about half that. These traits all point to separate species, albeit closely related ones--hence the ability to mate and produce a hybrid.

  THe point is is that the term "species" is a cultural construct that resists an absolutely precise definition in the real world. We like the idea as humans of a nature that is finely ordered and easily categorized. But that's not how life works. Evolution is sloppy, imprecise and fuzzy around the edges.
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  Deputy Dog

  That two species can interbreed doesn't mean they're actually a single species. For instance, golden retreivers can be mated with grey wolves. Same species? No,

  Without defining species there isn't much more to talk about.
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  bohm

  DD, why do you think a definition of species is particular relevant in the evolution/creation controversy in light of Feynmans 3 steps? It does not at all seem to me clearly defined species is a consequence of evolution, on the contrary, evolution would predict the species-boundaries must be vanishing when the temporal development of the gene pool is taken into account.
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  TD

  Without defining species there isn't much more to talk about.

  That's why I raised the question of what we all consider to be human. We've discussed the limitations of the term "Species" and the lack of a good working definition for the term "Kind" before.

  Personally, I wouldn't consider a creature with cognitive abilities on par, or maybe just slightly above a chimpanzee to be human regardless of whether it could hybridize with modern man or not.