>I have a question for those on the list who know more about genetics than I do. In other words anyone. Is it possible to show by DNA studies that it is genetically impossible for humanity to have descended from two individuals, say Adam and Eve?<
It is probably impossible to utterly rule out some weird scenario that could generate the observed human genetic diversity from almost any starting point. At most DNA work might suggest that this is improbable.
> Is it possible to show genetically that all human ancestry cannot be traced through two individuals, who were the first to have a spirit?<
Determining this requires two things: tracing the genetic common ancestry of humans and pinning down the origin of spirituality.
Population genetics indicates that a new species, etc. is most likely to arise from a small, isolated starting population. Two individuals would be a very small population, but distinguishing this from a slightly larger population would be very difficult.
Comparison of the different alleles found for each DNA segment in humans gives a measure of the total genetic variability. Obviously, an exhaustive measurement would require sequencing the entire genome of everyone, past and present, but a good sample is available for many genes. Using an estimate of the mutation rate for each gene (which probably incorporates a lot of guesswork), we can figure out how long it would take to generate this range of variation starting from the number of sequences found in a single couple. These typically give a minimum of a few tens of thousands of years and a maximum of a few million. Thus, it seems genetically plausible, though by no means proven, that humanity goes back to a single couple sometime in the past few million years.
Additionally, there is the paleontological evidence for human populations having been established in various regions for a long period of time. If we are looking for a common ancestor of all modern humans, it would need to be old enough to pre-date the dispersal.
Pinning down the origin of spirituality is rather difficult. If you use Glenn's approach of looking for traces of behaviors that seem to reflect mental abilities qualitatively better than animals or things that seem to reflect post-Adam features (religion, clothing, difficult childbirth, etc.), then this points to a relatively early date for Adam, possibly in keeping with being the physical ancestor. If you put emphasis on the genealogies, assuming minimal gaps, or on the cultural and geographic features suggestive of the ancient Near East a few thousand BC, then such a relatively late date for Adam would rule out being our common ancestor.
One line of molecular evidence that would be difficult to reconcile with a single common ancestor of humans would be the presence of multiple alleles for a single DNA sequence shared between humans and other primates. If the variation was unlikely to have arisen convergently, this would suggest that multiple individuals carrying different alleles all contributed to our ancestry. However, transspecies allele transmission is possible, and convergence is likely in some cases. I do not know of a definite example of such allele sharing, but my research focuses on mollusks and so I could easily miss a study on primates.
I hope this helps.
Dr. David Campbell
Old Seashells
University of Alabama
Biodiversity & Systematics
Dept. Biological Sciences
Box 870345
Tuscaloosa, AL 35487 USA
bivalve@mail.davidson.alumlink.com
That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa
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