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Genes whose deleterious effects are not manifest
until after reproductive maturity are not as effectively selected against
as those manifest before reproductive maturity. Alleles increase in a
population when they are subject to positive natural selection, and by
genetic drift if they are not subject to negative selection. [Chuck Dunn
in sci.bio.evolution]
That is about the size of it. If it doesn't kill you before you breed
it is invisible to evolution. My father has a heart condition, by the
time anybody, including any evolutionary pressures, found out he had seven
grandchildren. He has been a genetic success, and may have spread a late
acting lethal genetic condition.
It is in the nature of nature to do just enough to get by. For us breeding
is the finishing line. After that any illnesses that we have or bad things
that happen to us have no effect on the evolution of us as a species unless
they impact on the lives or success of our children, or perhaps our tribe.
Actually living until about 70, long enough to help the grandchildren
a bit and passing on our culture to other generations is about as far
as our usefulness goes. If we limped on to 150 we would be more of a handicap
to our children than an asset. So basically that is what happens, our
bodies repair themselves well up to the point we have reached full breeding
age then they slacken off, they succumb to entropy.
A good question to ask is about the evolution of the menopause, think
about that one. It pays your genes to stop the risky project of trying
to pass an object the size of a human baby through such an obviously inadequate
passage once the woman would be better off looking after grandchildren
than putting her life in great danger trying to have another child herself.
Human babies are right on the limit of what is possible to give birth
to without the female pelvis being too wide for bipedalism. As it is the
human baby is born effectively prematurely, incapable of walking or even
riding on its mother's back. A gorilla mother is twice the human size
and her baby is half the size, but much more capable. It is all down to
our enormous brains. We have to be born when we are or mother and child
would be killed by the expanding head. In contrast there is no big risk
for the elderly father, apart from the increased risk of genetic mutation
in his senile testicles.That explains why female reproductive capacity
dries up and male capacity just gradually declines, with the rest of his
body.
Any quest for the secret of eternal youth is doomed to failure. The only
way to do it would be to select for long life over many generations, only
breeding from the long lived. It would probably work to some degree but
the question will have to arise as to why bother? The desire to live for
ever is one thing, but where would the desire for our great great great
grandchildren who we may never meet to live for ever come from? Apart
from some dodgy pseudo-religious / destiny vision.
Which is the stronger evolutionary trait?
1. The desire of the organism to replicate (Mechanisms
for reproducing the organism)
2. The desire of the organism to stay alive (Mechanisms
for keeping the organism alive)
Any comments?
[moderator's comment: Sure, I'll bite. When I was
a wee sprat I was fortunate enough to be taught from a NSF-developed curriculum
titled "Man - A Course Of Studies" (which I initially thought was something
titled "manacoursive studies", but when I couldn't find manacoursive in
the dictionary...), where I was taught the three rules, in order, which
guide a critter's life:
1) Eat,
2) Avoid being eaten,
3) Reproduce.
Three of the four F's of animal behavior. I suppose
one might roll two of 'em into number three there. - JAH]
Which is the strongest evolutionary trait? It has got to be an optimum
trade-off between the two. An organism [NEVER use the word critter, a
terrible folksy abbreviation of creature, a thing that has been created,
presumably by Our Lord Jesus's dad urghh, ban both these words] sorry,
where was I? Yeah, an organism must strike the optimum trade off between
eating, sex and everything else. It does no good for an organism to be
eating all the time and growing but not reproducing. At least it does
no good for the genes of that organism. Although it can benefit the genes
of parasites of that organism.
Evolution is very rarely about maximizing anything, the key is always
the optimum trade-off. A bird whose courtship dance is so spectacular
than everything within a quarter of a mile notices will probably have
its genes consigned to the stomach of a passing predator. Moderator: for
the crime of using that terrible word I suggest you copy out the whole
of Darwin's Origin of Species as a pennance ;-)
Martin
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The following is in response to a posting that was effectively
a republishing of the evolution
page.
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Very nice note.
Thank you for taking the time to write and
post it. If you could answer a few question I would be grateful.
I've tried to keep the format simple and
short, in the hopes you will answer the questions. This is not a
test, I will not grade you.
These questions reflect my own gaps in information
on evolution. And though you may or may not be an expert, I hope
a series of responses to this questionnaire will be somewhat self
correcting.
Please delete the response that least matches
your opinion. Leave the one response that most closely approximates
your opinion.
Thank you for your time.
Homo sapien sapiens (modern man)
have been an individual group for about 130,000 years.
strongly disagree
disagree
I don't know
slightly agree
strongly agree
Humans descended from a single female born
at that time.
strongly disagree
disagree
I don't know
slightly agree
strongly agree
This primary female human, lived in southern
Africa
strongly disagree
disagree
I don't know
slightly agree
strongly agree
The human race migrated from this area to
spread to the rest of the world through migration
strongly disagree
disagree
I don't know
slightly agree
strongly agree
These humans migrated along the continuous
beach that stretches from southern Africa to the bearing straight
strongly disagree
disagree
I don't know
slightly agree
strongly agree
Racial features are the result of small
groups of humans becoming isolated geographically for several millennia
and then reinforcing certain superficial physical traits within
the group through descendants.
strongly disagree
disagree
I don't know
slightly agree
strongly agree
Humans are 99.9% the same genetically.
strongly disagree
disagree
I don't know
slightly agree
strongly agree
The most diverse genetic "pool" (the genes
with the largest number of genetic variations) of humans, is in
Africa, then in descending order of complexity progresses through
the middle east, Asia and the Americas.
strongly disagree
disagree
I don't know
slightly agree
strongly agree
Thank you for your time. I hope you found
this survey interesting.
writer@ime.net
Richard Rust
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I don't like forms. My medium is words, not options.
I don't agree with the simplistic idea of African Eve as a single
female that gave birth to us all. That is a misunderstanding of
the African Eve mitochondrial DNA evidence. There has to
be a single latest common universal female-line only direct ancestor
to us all, that is elementary evolutionary logic. What is open to
question is how far back she lived; was she an ape, a fish, a four
foot high early hominid, an African shoreline scavenger or the Queen
of Atlantis?
Another equally valid question is why should you assume that the
latest common human ancestor was
1] female and
2] even more bizarrely, the female-line-only ancestor.
It is far more likely that our latest common ancestor was male
and from a mixed-sex line of direct decent. Males have a much higher
chance of having many or no descendants, females have much less
variation in the number of offspring. While it does not necessarily
follow that our most recent common ancestor must have been especially
fertile it would seem to be a not unreasonable assumption.
As an exercise contemplate OUR most recent common ancestor. [assuming
we are both white and British] Chances are we have one a lot closer
to home than Africa 130,000 years ago. He or she probably lived
in Europe within the last thousand years or two. I read once that
there was a Mr Willett who lived in London in 1640 or so and had
11 surviving children, and he is an ancestor of a substantial proportion
of the British population. That may or may not be true. But if we
had to trace the female only line of common descent we might
have to go back ten times further into the roots of our family trees.
Or try this one, your father's brother's daughter is your first
cousin, by definition. How far back is your latest common ancestor?
You share a grandmother or grandfather and maybe both. But how far
back is your latest FEMALE LINE ONLY relative? Chances are you and
I could be as closely related by that route as you and your first
cousin.
I don't fall for this nice easy we-are-all-relatives idea. It is
too convenient. Always ask yourself who benefits. Who benefits from
science that proves that races are trivial artefacts of no underlying
significance? Scientific researchers. They stay employed.
Homo sapien sapiens
(modern man) have been an individual group for about 130,000 years.
I don't know
Humans descended from a single female born
at that time.
slightly agree
This primary female human, lived in southern
Africa
This statistical nonentity probably did live in Southern Africa,
yes. Who knows where the latest common ancestor of us all lived?
Probably in the same place as his great-great-great-great grandmother,
"Eve".
The human race migrated from this area to
spread to the rest of the world through migration
strongly agree.
Where they met other people and did what comes naturally... Kill,
drive off, shag or eat depending on how different the people were
and how much they resisted. To what degree they followed each strategy
I don't know, but I am curious.
These humans migrated along the continuous
beach that stretches from southern Africa to the bearing straight
Agree.
Seashore is seashore, a habitat that does not require much adaptation,
if you've survived on one beach you are fitted to survive on most
beaches.
Racial features are the result of small groups
of humans becoming isolated geographically for several millennia
and then reinforcing certain superficial physical traits within
the group through descendants.
Racial features could come from sexual selection (isn't red hair
sexy?), founder effect within small semi-isolated populations, regular
natural selection and the effect of interbreeding with other (earlier)
populations. I doubt whether any one of those explains more than
90% of the phenomenon.
Humans are 99.9% the same genetically.
I don't know, I would not be surprised.
The most diverse genetic "pool" (the genes
with the largest number of genetic variations) of humans, is in
Africa, then in descending order of complexity progresses through
the middle east, Asia and the Americas.
I don't know, but I see no reason to doubt it.
Martin
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Dear Martin Willett,
Thank you very much for your very generous
answer to my query.
You note was very interesting and has helped
to clarify several points in my own thinking. You've been of great
help. Once again, thank you for taking the time to write back.
Writer@ime.net
Richard Rust
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I hope you are serious in that reply. I am no an expert, I don't
have enough spare time to be so, but I am interested in both evolution
and the bastardization of science so I have some idea of what I
am going on about. But at any time I would love to be corrected
if I get anything wrong, that is a sentiment I share with true scientists.
A lot has been made of the study of mitochondrial DNA, which is
passed on by female only lines of decent because it is not part
of the cell nucleus, it comes from the tamed bacteria that are our
mitochondria, and passes down through the cell contents and via
the egg cell only, never part of the nucleus of any cell. Studying
the variation in m-DNA among people of differing racial backgrounds
(using race in the everyday sense) has shown more variation
among African people than among any other people, suggesting that
they are the most diverse and hence the oldest populations, all
other groups show decent from a limited range of African genes.
That is consistent with a recent out-of-Africa explanation of racial
origins.
It is not yet fully vindicated research. I would like to see the
equivalent research done on the Y chromosome as well. This shows
male line only heritability in the way a surname does. I would anticipate
that this research may also show an out of Africa result, with an
even more recent date for the latest common universal human ancestor,
no doubt to be dubbed African Adam.
Such research would have more problems though. Nobody is in danger
when their female line of decent is investigated, the identity of
your mother is very rarely controversial. This kind of research
could prove very alarming, given the rate of false attribution of
paternity in our species. I can easily imagine scientists shying
away from doing it, or rather, hoping that somebody else does it
first. My mind fills with images of hungry penguins desperate to
go into the sea but fearing predators, they jostle about on the
edge of the ice hoping that they can "accidentally" knock another
bird in first to test the waters...
Martin
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Dear Martin Willett,
Thank you again for writing. My last note
was quite sincere. I am always amazed when complete strangers will
take time out of their busy lives are willing to write back and
answer my unsolicited queries. It is something that confirms my
belief that humans are basically good and always looking for the
truth as best they can.
Below is some information about the male
counter part to "Mitochondrial Eve." Normally I take Web sources
with a grain of salt, but the note listed below, cites a periodical
(November, 2000 issue "Nature Genetics") which can give independent
confirmation of the web page's assertion.
Once again thank you for your note.
writer@ime.net
Richard Rust
----------BEGIN FORWARD HERE-------------
http://www.academicpress.com/inscight/11012000/graphb.htm
DATE: 1-November-2000 The Eden Chronicles:
Tracking 'Y Chromosome Adam'
The fundamentalists aren't going to like
this, but Eve was an older woman--by about 81,000 years. By tracing
the lineages of Y chromosomes back through the stone age, researchers
have estimated how long ago humans' oldest paternal ancestor lived.
The results support the idea that modern humans originated in Africa,
and they help track where humans wandered from there.
Mutations that accumulate in DNA are like
molecular clocks. Over time, harmless mutations accrue and are passed
down through generations. By comparing mutations from enough people,
researchers can construct family trees with roots that reach back
to the earliest modern humans. A decade ago, analysis of mitochondrial
DNA, which is passed down through the mother's egg cell, showed
that humans' earliest common maternal ancestor lived 140,000 years
ago. She was dubbed "Mitochondrial Eve."
Now, researchers report that they have traced
the Y chromosome lineage to modern humans' earliest common paternal
ancestor, "Y Chromosome Adam." The team, led by molecular biologist
Peter Underhill of Stanford University, looked at 167 mutations
in 1062 men from 21 geographical regions. The researchers calculate
that the Y chromosomes carried by modern men are versions of the
Y chromosome carried by a common ancestor who lived in Africa about
59,000 years ago, they report in the November issue of Nature
Genetics.
The Y chromosome lineages also provide a
finer resolution of early human migration than mitochondrial DNA
analysis. Following the molecular footsteps of males, Underhill
says early humans left Africa more than once. Some migrated down
the coast of Africa and over to Australia; others to India and Asia;
and some migrated from there back toward Europe. The researchers
also found that fewer Y chromosome lineages survived to the present
day than mitochondrial DNA lineages. Perhaps males were more likely
to die before passing along their Y chromosome than females, thus
preventing some Y chromosome lineages from making it to the modern
age. Alternatively, as Underhill delicately puts it, "nonrandom
mating patterns," in which only a few males pass their Y chromosomes
to many females, could explain the difference.
The Y chromosome lineage will have a big
impact on the emerging field of "archaeogenetics," the reconstruction
of human history from molecular genetics, says archaeologist Colin
Renfrew of the McDonald Institute for Archeological Research in
Cambridge, United Kingdom. As more Y chromosome mutations are discovered,
he says, researchers will be able to paint an ever higher resolution
picture of human prehistory--the when, where, and Y of human evolution.
MARY BECKMAN
----------------END FORWARD HERE---------
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Isn't it wonderful to get your suspicions confirmed?
That is exactly what I expected, well, maybe not quite as recent,
but certainly that pattern.
I couldn't be certain that you weren't setting me up for something
but I thought I'd do it anyway, I'm a bit impulsive.
Martin
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