jcrawford wrote:I wouldn't go so far as to theorize that H. heidlebergensis is ancestral to everyone in the world, because such early/archaic H. sapiens fossils are dated to have been living contemporaneously in Asia, Africa and Europe, and, using neo-Darwinist logic about one or more mutations leading to their developing "modern" characteristics, their inter-sterility with other racial groups, and these new characterisics not spreading throughout the rest of the heidelbergensis racial groups, we inevitably end up with these guys reproducing and their population increasing to the point of fighting for survival with other racial groups in the world for world domination.
As I see it, H. heidlebergensis was contemporaneous with other racial groups within H. erectus in China, H. ergaster in Africa, H. antecessor in Spain, H. neandertalensis and other H. sapiens throughout Eurasia, the Middle East, Africa and the rest of the world, and no human evolution from one species to another ever occurred.
OK, here's a question for which I would like a very seriously-considered answer. As a biology professor and perpetrator (if that's the word I want) of professional development workshops for secondary science teachers, I'm always on the lookout for someone who is articulate enough to help me see things I don't understand. Here's the question:
how, or why, should it matter if two species are contemporaneous? What I'm getting at here is the model that you have in mind for how evolution is "supposed to happen." If you have one thing in mind, and I have something else in mind, we'll end up talking about different things when we
think we're talking about the same thing. Rather than have either of us imagine that the other guy is an idiot for "not getting it," we might want to deal with this kind of thing whenever it comes up.
I am reminded of a cute little conversation I had with a faculty recruit years ago. He was an ecologist; I'm a molecular biologist. We speak different languages. We
thought we were having a conversation, but ended up each thinking the other was a complete idiot. Years later, after we'd become friends and learned enough about each other's fields that we could actually communicate, we looked back on that conversation with a certain amount of mirth. We'd each assumed that we'd known what the other was saying, but it turned out that neither of us had actually had any idea. It's no wonder we'd failed to communicate.
But back to the issues. I think that it is inappropriate "lumping" to jump to the conclusion that someone (e.g. myself) is automatically using "neo-Darwinist logic" when interpreting data or describing a scenario. That, after all, would be assuming the interpretation before assessing the data. I won't play that game. However, because I know what mutations are, and how they lead to morphological or biochemical changes, and how new alleles may or may not spread through a population over time, I can, and do, develop my own models for how things happen. Sometimes, those models happen to be similar to the models that others have described. Other times, they differ. What I described concerning the acquisition of mutations in a population is simply the only way that it can happen and remain consistent with the chemistry and biology. If that scenario happens to match "neo-Darwinist logic," why, then I'd have to conclude that maybe their logic might be OK.
jcrawford wrote:In these cases we would be using members of the same species (Crawford and Jose) as outgroups, so it's not similar to using a chimp at all. Using a chimp as the outcrop influences the genetic data in the diagram.
It turns out that
it actuall is quite similar. In fact, we'd get the identical result for the jcrawford and Jose trees using chimp DNA as the outgroup as we would if we used each other, or if we used Bill Clinton for the outgroup. I've prepared a little figure to make this more clear:
The arrows identify the "root" of the tree. The Jose tree can have its root defined by jcrawford (tree A, black) or by a chimp (tree C, red). The root comes out in the same place. (I've drawn the vertical line connecting the tree to the outgroup as rather longer for the chimp, to indicate that chimps are rather different from us.) The jcrawford tree has its root in the same place, whether defined by Jose (tree B, blue) or by a chimp (tree D, green). Of course, if we used chimps for the outgroup, then we could build a larger tree in which we can link
both of our trees onto a single tree that we could call a human tree (tree E, purple). It turns out that it doesn't matter who we use for the outgroup; we still end up with the same relationships for everyone in the jcrawford family.
jcrawford wrote:How do we know that you "redrew the figure" accurately?
Two ways. (1) I said so.
(2) I gave you the reference to the source, so you can look it up.
jcrawford wrote:How do we know that 'similar' sequences to humans in fossils are not overlooked and rejected because they are thought to be the result of contamination by modern humans doing the fossil examination?
As I noted for the folks in my building who do this, they have samples of DNA from everyone who is likely to be anywhere near their lab, so if they get a sequence that looks "modern," they check their database. If it's Jenny's DNA, then Jenny has to move to a desk in a different lab (indeed, Jenny
did have to move to a different lab for this reason--but they'll never put that into the paper). They won't just take the first sequence they get and call it quits, either. They'll get as many as they can to have statistical confidence that they are looking at something real.
Nonetheless, your point is valid. A modern sequence cannot be distinguished from contamination
unless it is in a region that has lots of polymorphisms, and they can rule out its being DNA from one of the investigators. If it's non-polymorphic DNA (ie, conserved among humans), then they cannot distinguish between contamination and the fossil actually having the same sequence. I'd conclude that it was contamination, and that we didn't get sequencable DNA from the fossil.
So, modern sequence (say, from Cro-Magnon) is uninterpretable. Different sequence (say, from neanderthals) can be interpreted with more ease. If it's different sequence, and doesn't match any of the polymorphisms known, and can be "theoretically constructed" only by a separate route from a theoretical ancestral sequence, then it seems likely that it's from an individual in a different lineage.
This is pretty much the same as what Kahn and Gibbons said.
jcrawford wrote:Jose wrote:We're asking who our ancestors were, and we really don't care whether we find the ancestral Mom or Dad.
Speak for yourself here, Jose, since billions of folks wouldn't mind knowing for sure who the real mother and father of us all were in the beginning.
If we really want to know who the absolute first anatomically-modern human was, then we need to find a technique that can figure it out. While it may be the case that many people would like to know, they're just going to have to wait. This method can't get it. That's why I say "we don't really care"--because
we can't answer that question.
The question is even more difficult than you suggest here. Suppose we pretend that we have found the "ancestral Mom" identified in a great big DNA tree of all humans. Who was
her Mom? The way genetics works is that every organism reproduces according to its kind. So, she had to have parents. This type of data can only go back a little ways into the past--but there is no indication that the past wasn't much, much longer than that. So, our "mitochondrial Eve" had parents, who had parents, who had parents, and so on until the beginning of life. 450 million years ago, there was plenty of life, but none of it was what we have today. Genetic continuity, and the fact that fossils can be found in all ages of rock after its inception, suggest that among those living things 450 MYA were some of our ancestors--another Eve, if you will, and she too had to have parents.
Where did the first anatomically modern humans arise? Probably in one place, in one small group. Where did their human-like ancestors live? Probably in that area, and probably in other areas as well, if they could walk. Where did their pre-human-like ancestors live, and what were they like? What about their ancestors? I think the immediate questions of this thread are the first couple of these; however, all such questions are really a part of it.
Anyone need a snack?
