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.
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
lindsay@K.GP.CS.CMU.EDU (Donald Lindsay) (10/15/87)
Several of the postings seemed to be a bit weak on just what it means
to be Eve. Think of it this way:
Mitochronidal family trees are (in the computer science sense) N-ary trees.
Represent each woman as a node, and the number of descendant nodes is the
number of female children she bears.
Any random mutations are passed down into the subtrees. Other than that,
everybody gets a faithful copy from above.
If "a" is Eve, then suppose that "d" has no daughters. We can erase that
part of the diagram:
a a
/ \ \
/ \ \
b c => c
/ / \ / \
/ / \ / \
d f g f g
...and suddenly, at the moment that "d" dies, "c" becomes Eve !
This may in general happen long after "c" dies. Our current Eve may not
have been Eve for very long: perhaps her sister's mitochrondial DNA was
with us until modern historical times. When Eve was born, someone else
held the title - perhaps her mother, or perhaps her great**N maternal
grandmother. And before that Eve, another, and another, all the way back
to the invention of mitochrondia, where we get into other issues.
--
Don lindsay@k.gp.cs.cmu.edu CMU Computer Sciencedaver@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