Re: Extremely OT, But Very Good News (For Me, Anyway)
- From: "AusWendy" <no@xxxxxxxxxxxxx>
- Date: Wed, 26 Sep 2007 23:25:00 +1000
"Bo Raxo" <crimenewscenter@xxxxxxxxx> wrote in message
news:1190769002.239283.59090@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
...and for Snyder. Those 20 somethings I date, I'm doing it for the
good of all humanity. It's a sacrifice, but hey, I'll take one for
Team Humanity. Oh, give give give, that's all I do.
Bo Raxo
And you know it takes a lot to get this Cal alum to post something
published by the hated Trees.
http://news-service.stanford.edu/news/2007/september12/men-091207.html
It turns out that older men chasing younger women contributes to human
longevity and the survival of the species, according to new findings
by researchers at Stanford and the University of California-Santa
Barbara.
Evolutionary theory says that individuals should die of old age when
their reproductive lives are complete, generally by age 55 in humans,
according to demographer Cedric Puleston, a doctoral candidate in
biological sciences at Stanford. But the fatherhood of a small number
of older men is enough to postpone the date with death because natural
selection fights life-shortening mutations until the species is
finished reproducing.
[...]
"Why Men Matter: Mating Patterns Drive Evolution of Human Lifespan,"
was published Aug. 29 in the online journal Public Library of Science
ONE. Shripad Tuljapurkar, the Morrison Professor of Population Studies
at Stanford; Puleston; and Michael Gurven, an assistant professor of
anthropology at UCSB, co-authored the study in an effort to understand
why humans don't die when female reproduction ends.
Human ability to scale the so-called "wall of death"-surviving beyond
the reproductive years-has been a center of scientific controversy for
more than 50 years, Puleston said. "The central question is: Why
should a species that stops reproducing by some age stick around
afterward?" he said. "Evolutionary theory predicts that, over time,
harmful mutations that decrease survival will arise in the population
and will remain invisible to natural selection after reproduction
ends." However, in hunter-gatherer societies, which likely represent
early human demographic conditions and mating patterns, one-third of
people live beyond 55 years, past the reproductive lifespan for women.
Furthermore, life expectancy in today's industrialized countries is 75
to 85 years, with mortality increasing gradually, not abruptly,
following female menopause.
Grandmother hypothesis
In 1966, William Hamilton, a British evolutionary biologist, worked
out the mathematics describing the "wall of death." Since then, the
most popular explanation for why humans don't die by age 55 has been
termed the "grandmother hypothesis," which suggests that women enhance
the survival of their children and grandchildren by living long enough
to care for them and "increasing the success of their genes," Puleston
said. However, Hamilton's work has been difficult to express as a
mathematical and genetic argument explaining why people live into old
age.
Unlike previous research on human reproduction, this study-for the
first time-includes data on males, a tweak that allowed the
researchers to begin answering the "wall of death" question by
matching it to human mortality patterns. According to Puleston,
earlier studies looked only at women, because scientists can reproduce
good datasets for humans entirely based on information related to
female fertility and survival rates.
"People don't like to do two-sex models because [it's difficult] to
look at how [men and women] pair up," he said. "But men's fertility is
contingent on women's fertility-you have to figure out how they match
up. We care about reproduction because that is a currency by which
force of selection is counted. If we have not accounted for the entire
pattern of reproduction, we may be missing something that's important
to evolution."
Men and longevity
In the paper, the researchers analyzed "a general two-sex model to
show that selection favors survival for as long as men reproduce." The
scientists presented a "range of data showing that males much older
than 50 years have substantial realized fertility through matings with
younger females, a pattern that was likely typical among early
humans." As a result, Puleston said, older male fertility helps to
select against damaging cell mutations in humans who have passed the
age of female menopause, consequently eliminating the "wall of
death."
"Our analysis shows that old-age male fertility allows evolution to
breach Hamilton's wall of death and predicts a gradual rise in
mortality after the age of female menopause without relying on
'grandmother' effects or economic optimality," the researchers say in
the paper.
The article didn't talk about an interesting but little known fact - we all
know that females over the age of 40 run a greater chance of having a baby
with a chromosonal birth defect. This is due to the fact that the oogcytes
(eggs) are already all manufactured while a fetus and they degenerate or
break down after a time.
However, men over the age of about 45+ run the risk of having children with
birth defects also,(this is why the usual cut off date for a sperm donar is
around 40 years), even if having children with a much younger female. This
is because the spermatocytes (sperm cells) are continously being replicated
(copied). By the time a guy is say 55 his sperm and dna have replicated
thousands of times and there is more chance of a replication error.
Syndromes like Marfan Syndrome, Apert Syndrome and Retinitis Pigmentosa are
believed to be caused by errors in the sperm.
Aus Wendy
.
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