human origin debate (out-of-africa?)

Gcle Again, that we may all have a common ancestor doesn't prove (or even indicate) there was only one common ancestor

How can we not have "one common ancestor", we havn't existed since eternity so we must have had a starting point.


Edited by Bulldog - 28-Jan-2009 at 16:13

Originally posted by konstantinius I tend to support Wolpoff's Multiregional Hypothesis based on the fact the humans have maintained genetic continuity and species cohesiveness. There are multiple, not one, migrations out of Africa, beginning of course with H. erectus. Genetic drift quarantees persistence of regional populations that are further away from the 'center' of radiation (Africa). In these cases, interbreeding takes place; elsewhere replacement is possible. Big question: does interbreeding happens with Neaderthals? Recent DNA extracted from nead. says no. But in Asia local populations persist.

No- planted here by aliens from Mars after Planet X wreaked havoc upon the Martian surface. Or according to a guest on coast to coast am radio-

calvo, no one (at least not me) is arguing against the well-attested fact that modern humans originated in South Africa. It is the concept of a "single mother" that is becoming increasingly unfathomable. What Cann has done in her research is take the DNA of MODERN humans and deduce that of a single living being approx. 150,000 ya. by tracing back the number of mutations in the mtDNA. "Eves" DNA remains a mystery, never to be deciphered since we can't go and take hers. ALL we know is about the DNA of the modern sample. To extend that back is highly assumptive and scientifically erroneous since truly, "Eves" DNA will never be known, i.e. Cann's is a hypothesis that can never be truly tested. Theories of a single anything are highly dubious in uman evolution. With the known biodiversity of humans I consider it naive to think of "single mothers" or "single driving force" or single anything for that matter. Let me ask you this: what about "Eve's" ancestors? Why the cut-off point there? What if the ancestors had a recessive mutation that shows up every few generations? How Cann would know unless she went back in time?   

Actually, sample size in hypothesis testing is related to Type II error, not Type I. Someone doesn't know their stats around here obviously but that's not me. Type II error occurs when, because of the non-representational nature of the sample, the hypothesis is rejected while it's true.

Edited by Beylerbeyi - 29-Jan-2009 at 11:23

Well, that's not the partial replacement theory I and most other anthropologists I talk to have in mind. The debate is not concerned with ORIGIN (so far firmly set to have taken place in Africa ca. 90 kya) but with rates and modes of migration. Are you sure you understand the extend of the debate? In a purely scientific sense, Cann's assertions can never be tested therefore they remain implications at best. Projecting today's population genetic make up back through time is science-by-proxy, especially in view of the most recent DNA research (Cann conducted hers 20-something years ago). In particular, we just know are starting to understand the role of non-coding DNA and especially that of the "junked" introns. Of course those are not part of mtDNA; but still, many issues remain in association with Y and X chromosome DNA polymorphisms such as restriction fragment length (RFLP's). Many technical points have arisen for which Cann had no idea about: a) some regions of mtDNA are less susceptible to change while others fix mutations at a higher rate, contributing to higher variability within a population b) the fact that all 37 genes of the mtDNA are closely linked limits their usefulness of the mitochondria in EVOLUTION studies (Spuhler, 1988) c) there is considerable difficulty in calculating a molecular "clock". On this last one, some calibrations assume a steady mutation rate (constant, steady change in base sequences) at 2%/million years while others point to a much slower rate of less than 1%. These calibrations are obtained by comparisons of LIVING human and ape mtDNA, mainly chimpanzee. The faster rate assumes that apes and humans diverged from a "common ancestor" some five million years ago (Templeton, 1985). The slower rate is mainly attested by paleontological evidence that places the time of the divergence much earlier, approx. 9 mya. This pushes the "eve" theory much further back and in accordance with the fossil record.  Regardless, no one is arguing the origin of H. sapiens. But to embrace a far-fetched theory of a 'single mother' is  naive, especially in the light of our constantly changing knowledge of DNA and genetics (what I've written is probably already obsolete).

Just to clarify, I am not saying that the Cann study is correct, or the number samples it has is enough. Maybe it is not a powerful study. What I am saying is, he provided no proof of that.

Edited by es_bih - 03-Feb-2009 at 14:55

Bey and Konstantinius I am sure you two gentlemen can keep the discussion going in a more professional manner (lay off the personal attacks). This thread is interesting lets keep i so. 

I am just asking both of you to keep the discussion in a gentlemanly manner. Thanks. No reason for personal insults from either side. 

Well, we can't get Asian H. erectus DNA. DNA decays rapidly and they were barely able to extract the European Neanderthal DNA at about 40,000 BCE. We'll never know about the genetic make up of H. erectus, except by comparison with modern populations which is not really conclusive.