From: Kevin Freels (megaquark@hotmail.com)
Date: Wed Sep 03 2003 - 22:56:26 MDT
> Not so -- K-selection vs. R-selection will apply selection pressure
> particularly if the "elders" of a group contribute significantly
> to the survival of their children, grand-children, etc. This seems
> likely to be true in humans, elephants and whales -- though there
> is still a fair amount of academic debate on this topic.
Yes, I see your point here. I hadn't considered that. I keep forgetting that
"social" aspect of our nature. Maybe because I'm reclusive. :-)
Still, I have to wonder what, if any, contribution "elders" would have that
were significant enough to increase the likelihood of grand-children
surviving to reproductive age in the early hunter-gatherer tribes of modern
humans. The only thing I can think of is to help raise and educate the young
while the parents were away hunting and gathering. But it is my
understanding that the sharing of food was an early development in hominid
evolution and that by the time modern humans arose, the women were most
likely staying "home with the kids". I may be wrong here and maybe someone
will accuse me of being a sexist, but that's just what I remember when I was
researching it years ago. Also, given the social nature of (most)human
beings, one would think that if a grandparent dies, the rest of the "tribe"
would pitch in and help raise and protect the child.
In order for this scenario to work, the death of an "elder" via prostate
cancer at age 60 would have to have enough impact on a "family" to cause the
death of a grand-child before they were able to reproduce. This would have
to happen in the majority or nearly all cases at which time the mutation
that causes prostate cancer would eventually disappear. If it happened
occasionally, I don't think it would have enough impact on the mutation to
make a difference.
I am under the impression that the average human life span was only 40-50
years during this time. The most likely causes of death were from diseases,
not cancers. If this is the case and most cancers occur later in life, then
it would onlyhave been after the life expantancy of humans began to increase
when selection pressures would start taking affect on that particular
mutation. If the mutation that caused that cancer 40-50 thousand years ago,
it would be well distributed throughout the population before these
selection pressures began to apply themselves. In the last few hundred
years, life expectancy has increased by about 25 years which means that it
would only be during this period when the mutation should start working its
way out of the population. Today, grandparents rarely play a necessary part
in the survival of the grandchild except in the death of the parents or such
similar events. So once again, this mutation should continue to make its way
through the population. Maybe if parents had children but grandparent raised
them, we could naturally weed this out in a few tens of thousands of years,
but for the most part, we try to take care of everyone, even if their
caretaker passes away.
Again, it would be very interesting if we could tie these cancers to
specific mutations and date them.
The scary part is the intermixing of people. History has shown that people
breed wherever and whenever possible. Everyone is a hodgepodge of DNA with
the same mitochondrial DNA dating back to mitochondrial "Eve". Given enough
time, you would think that most people will carry most of the mutations that
cause most of the cancers. All humans will be big cancer bags unless we do
something about it at the genetic level to rid ourselves of these things.
Also, as human life-spans increase, new ones will undoubtably crop up that
remained hidden, being secretly passed along to offspring for thousands of
years, until we reached the age where it started to cause problems.
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