kent@xanth.UUCP (Kent Paul Dolan) (10/13/87)
I guess I'm just feeling exceptionally stupid this morning, but there seems to be a gaping hole in this argument somewhere. Somebody enlighten me. Years ago, I learned that just by the propagation of the number of needed ancestors, versus the diminishing size of the human species as you go backward in time, there is a point not that far back where everybody now is the descendent of everybody then who left descendents. Now we discover, after this argument is well known, that there is something that everyone inherits only from their mother, and zappo, all but one of the women back then suddenly have no living descendents? I don't believe it. How about, instead, that by the usual same set of circumstances that eventually extinguishes family names, all but one of the lines somewhere passes only through the male side. So, sure, there's some lady back then who is mother to us all in the sense that the mothers of everyone living today can trace their ancestry back entirely on the maternal side to her, but this doesn't seem to be too big of a surprise; we knew it all along. This doesn't mean that the other ladies of that era don't also have lots of descendants, male and female, alive today, though. Just remember that tracing ones ancestry back entirely through the female side represents a vanishingly small portion of all your ancestors as you go further back in time. Look at it another way. If tomorrow we discover something which is inherited entirely from the father (an inclusion from the sperm coat, for example ;-), we will immediately discover that there was also an "Adam". Doesn't mean all the other fellows didn't leave descendents, though, just that somewhere along the way they were all daughters. Does this make sense, or is it just low blood sugar at work? Kent, the man from xanth.
felsenst@entropy.ms.washington.edu (Joe Felsenstein) (10/13/87)
In article <317@dg-rtp.UUCP> throopw@dg-rtp.UUCP (Wayne A. Throop) writes: >> dd@beta.UUCP (Dan Davison) >>> dhesi@bsu-cs.UUCP (Rahul Dhesi) >>> All living people (or at least ~99% of them) have a single common >>> female ancestor on their purely maternal line.... >> A small correction: this refers ONLY to mitochondrial DNA, not nuclear DNA, >> and so for the vast majority of the population says nothing about a single >> common female ancestor. > >How does the fact that mitochondrial DNA was used in this evaluation >escape the conclusion of a single common female ancestor (SCFA for >short)? Mitochondrial DNA comes exclusively from the female parent, and >if there was a single common original human mitochondrial DNA, it must >(barring unusually bizarre co-incidences) have come from a single female >at some point in time. The evidence supports a single common ancestral >mitochondrial DNA, hence an SCFA. > >> Nor does it imply a population bottleneck 200,000 years ago. > >True. There may have been any number of male ancestors, and the fact >that only one maternal line survived doesn't mean that it was the only >maternal line *at* *that* *time*. Dan Davison is right about the "Eve" publicity having spawned an amazing amount of misinformation. Yes, there was a single female who was the ancestor of all of our mitochondria. But she was NOT the ancestor of all of our nuclear genes as well (at least, there is no indication she was). Your nuclear genes come from both parents, and their nuclear genes from both their parents and so on back, with parents dropping out randomly owing to the randomness of mendelian segregation and recombination. So ten generations ago you may have had one ancestor up the strictly female line, but many who were ancestors of your nuclear genes. Similarly with "Eve". The years she lived there probably lived around her many men AND WOMEN who bore nuclear genes that are represented in the present human population. The incredible reaction to the "Eve" story is probably due to its similarity (accidental) to the biblical story, and to the attractiveness of notions of an earth-mother-goddess. Since mitchondria are all that were involved these are, needless to say, overreactions! -------------- Joe Felsenstein, Dept. Genetics SK-50, Univ. of Washington, Seattle, WA 98195 UUCP: ... uw-beaver!uw-entropy!uw-evolution!joe BITNET: uw-entropy!uw-evolution!joe%uw-beaver.ARPA@UWAVM ARPANET: uw-entropy!uw-evolution!joe@beaver.cs.washington.edu
lindsay@K.GP.CS.CMU.EDU (Donald Lindsay) (10/15/87)
In article <2567@sigi.Colorado.EDU> pell@boulder.Colorado.EDU (Anthony Pelletier) writes: >The notion of a group of organisms going off into a secluded area and >evolving together into a new species seems absurd to me. I can buy that >selection on all of them is the same, but the random element of evolution, >mutation, cannot possibly occur in them all. No no no. The "punctuated equilibrium" theory says that a subgroup becomes genetically different. It doesn't say that they all simultaneously mutate, no doubt while touching a black monolith. One creature, born with a nonfatal mutation, tries to pass the change on to his available genetic pool. If the pool is small, then there is a good chance the change can become universal, even if it has no value (or even negative value) simply by the probabilities of gene pools. If a group of creatures becomes cut off from the main pool, then for the duration, they constitute a small pool. Hence, the laws of chance begin to dabble with them, and they MAY diverge in a useful direction. When-and-if the isolation is over, they may replace the parent species, or merge back into it, or coexist as a new species. That's the theory. -- Don lindsay@k.gp.cs.cmu.edu CMU Computer Science
daver@sci.UUCP (Dave Rickel) (10/17/87)
So, has anyone compared the mitochondria of caucasians with australian bushmen? As i remember, the rest of the human race diverged from the bushmen before the common ancestress. Scale of events according to one article i have handy--split from the bushmen, about 400,000 years ago, orientals split off about 100,000 years ago, blacks and whites, 40,000 years ago. Hmm. This article goes on to say that "Eve" lived about 300,000 years ago--a little after the split with the bushmen. It doesn't say anything about whether or not the bushmen mitochondria show the same lack of diversity as the rest of mankind's. david rickel decwrl!sci!daver
felsenst@entropy.ms.washington.edu (Joe Felsenstein) (10/21/87)
In article <7034@sgi.SGI.COM> rmr@chefchu.SGI.COM (Robert Reimann) writes: >In article <10107@sci.UUCP>, daver@sci.UUCP (Dave Rickel) writes: >> >> I remember >> that humans, gorillas, and chimpanzees all seem to be about equidistant from >> some common ancestor on the evolutionary tree--that gorillas are as closely >> related to man as they are to chimpanzees; ditto with chimps. >> > >This was a matter of contention until recent comparisions of human, chimp, and >gorilla DNA showed that gorillas were closer, as in the diagram below. If I >remember correctly, the point where the gorilla/human ancestor split from >chimps is not very far from the point where gorilla and human lines split. > [diagram omitted] > Robert Reimann. You misremember. Actually that's the one tree no one backs. The recent studies of Sibley and Ahlquist (Journal of Molecular Evolution, 1984) using DNA hybridization strongly back humans being (slightly) closer to chimps than either is to gorillas. There are other evidences that this is true, but some studies contradicting it and putting chimps closest to gorillas and both equidistant from humans. To really settle the matter more data are needed, but one thing that is clear from all studies is that the tree is nearly a three-way split (trifurcation). Additional data analyses are on the way; the ones I know about back human-chimp. Sibley and Ahlquist have an expanded paper coming out in early 1988 in JME and I have a paper accompanying it analyzing this expanded data set. --- Joe Felsenstein, Dept. Genetics SK-50, Univ. of Washington, Seattle WA 98195 BITNET: uw-entropy!uw-evolution!joe%uw-beaver.ARPA@UWAVM uw-entropy!uw-evolution!joe%uw-beaver.ARPA@UWAVM.ACC.WASHINGTON.EDU uw-entropy!uw-evolution!joe%uw-beaver.ARPA@WISCVM.WISC.EDU (**) ARPANET: uw-entropy!uw-evolution!joe%uw-beaver uw-entropy!uw-evolution!joe@beaver.cs.washington.edu UUCP: ... uw-beaver!uw-entropy!uw-evolution!joe (**) after 1 Dec. 1987 the third BITNET address will be invalid when WISCVM.WISC.EDU ceases to be a network gateway machine