elt@astrovax.UUCP (Ed Turner) (11/18/83)
------------------------------------------------------------------------------- In my original article I stated the following result based on some recent results in comparative studies of human mitochondrial DNA: > All living people (or at least ~99% of them) have a single common female > ancestor on their purely maternal line. In other words, tracing back to > one's mother's mother's mother's ... mother will bring everyone back to a > single individual woman. She is estimated to have lived between 50,000 and > 500,000 years ago. This article has generated considerable comment and some confusion. In order to resolve some of the confusion let me try to state the same result in a slightly different and more direct way: The mitochondrial inclusions in human (and other animal) cells contain their own separate genetic material which is independent of the chromosonal DNA which otherwise controls inheritance. This mitochondrial DNA reproduces asexually (i.e., no mixing with the DNA of other mitochondria). In human (or other sexual) reproduction the offspring inherit mitochondria totally from their mother; they simply get the mitochondria in and descended from those in the egg cell because the sperm contains no mitochondria. Thus mitochondria may be thought of as asexual symbiotic organisms living in human (and other animal) cells. The exciting new result is that all (or at least ~99% of) present day human mitochondria are the descendants of a single mitochondria which existed 50,000 to 500,000 years ago. The evidence for this assertion is that mutations would have produced differences between independent lines of mitochondria greater than those observed in present day humans in any longer period of time. This does not 1) imply that our species appeared that recently, 2) mean that the single mitochondria (and woman) in question had no ancestors 3) follow from the fact that we must be at least distantly related to *all* people who lived at early times (because there were so few of them) 4) follow from the fact that homo sapiens emerged as a separate species at some point (if it did, the same arguement would apply to all species) 5) suggest that our ancestors slaughtered anyone, or 6) require that there were men long before there were women! It does suggest that, at least in a statistical sense, we have had a close brush with extinction. Ed Turner astrovax!elt