Re: Couple questions for evolution experts

On Wed, 03 Jun 2009 03:22:57 GMT, in talk.origins , William Morse
<wdNOSPAmorse@xxxxxxxxxxxxxxxx> in
<l0mVl.2424$9L2.1113@xxxxxxxxxxxxxxxxxxxx> wrote:

On Sun, 31 May 2009 20:48:50 -0700, rnorman@xxxxxxxxx wrote:

On May 31, 11:21 pm, Matt Silberstein
<RemoveThisPrefixmatts2nos...@xxxxxxxxxxxxx> wrote:
On Sun, 31 May 2009 14:57:48 -0700, in talk.origins , Phatty Boombatty
<pha...@xxxxxxxxxxxxx> in <pav5259pd8gnvmb9hr2sheutan68bob...@xxxxxxx>
wrote:





I've been wondering about a couple of things, hopefully someone here
can answer these questions with well-researched and well-reasoned
responses.

ASSUMPTION: Mankind (homo sapiens sapiens) evolved from early
primates, the same evolutionary line as chimps and apes.

QUESTIONS:

1. Human brain size and therefore cranial size increased as a result
of our evolutionary increase in intelligence. Why, while this long
process of evolution was occuring, did the human female birth canal
not evolve to accomodate this increasing cranial size? Human women
appear to be the only mammals who experience excruciating pain during
childbirth. If it were beneficial for the survival of the species, why
is there so much pain and not a larger birth canal?

There are several good responses to this, I just want to emphasize a
particular point. Evolution does not minimize pain or discomfort. At
best it maximizes reproductive success.  If the pain was so much that
people would not reproduce than, to the extent the pain had a genetic
cause, it would disappear. Instead we have a trade-off: more
intelligent humans seem a bit better at reproducing, bigger heads seems
to occasionally kill the mom during birth. Put these and a few other
factors into a set of equations and you can find the equilibrium
points.

2. Continuing with the theme... it seems that just about every animal
(mammals at least) have evolved a sense of when the female ovulation
cycle is occuring, so that fertility is guaranteed. The male of the
species senses the heat cycle, mates with the female, and a child or
children are conceived. Why is it such a guessing game with humans?
Sure, we can gauge the female cycle with some accuracy, based on her
regularity, but if it were beneficial for the survival of the human
species to "know" when the female was in heat and fertile, why would
we have not evolved this sense, in the same way that most of the
animal kingdom has?

There are answers given here that are reasonable, so let me take
another view again. This is a *great* question! Hidden ovulation, not
tool use or language use or upright walking, is likely the most
significant biological difference between humans and other animals. The
thing about great questions is that the help us explore and understand.
So answering this question, which takes lots of work and we have more
to go, will help us learn. Failure to answer just means we don't know
yet.

3. Considering we evolved from early primates, and all other primates
we know of are virtually covered with hair or fur (in fact, just about
every other land mammal on the planet is covered with hair, fur, or
"armor"), why was it beneficial for the survival of the species for us
to "lose" this hair, thereby exposing our very sensitive skin to the
very same elements as our ancestors?

And this is a *bad* question. Bad in that it rests on a false notion,
that we don't have the hair. If you had asked why it got finer you
would have an average question.

I chime in agreeing that many answers here are good. To be specific, my
recollection (meaning I did not go back to look up and verify whether my
memory is good) is that pain in childbirth is mostly related to the
upright posture combined with the large brain size, as one poster
already pointed out. And the menstrual cycle as opposed to estrus, with
the concealed ovulation, is related to female sexual receptiveness
throughout the cycle and the use of sex as a pair bonding mechanism to
assist in biparental care of the young.

I disagree about #3, the question of hair on several points. First,
I don't think it a "bad" question in the sense that we did lose the
"bulk" of our hair. The actual number of follicles doesn't matter -- we
don't have fur and our situation is commonly referred to as
"hairlessness" no matter how many very fine downy hairs we have. I also
disagree on the reasons usually given -- heat loss. I believe the
modern explanation has now shifted from that one to the better ability
to control skin parasites like fleas and ticks and the like.
Socialization, with numbers of people living closely together, increased
the ability of these parasites to spread but, at the same time, the
development of fire and shelter and the use of furs as clothing allowed
us to become hairless even in cold climates where fur is advantageous.
And, of course, hairlessness is benefecial in warm climates especially
for long-extended periods of strenuous activity like long distance
running in search of prey (or to avoid being prey). Humans really do
have unusual capabilities for enduring running far in excess of just
about everything else. Many animals can outrun us in short distances
but I believe a human can even outrun and track down a horse given
enough time -- usually many days. But on balance, I think the current
thinking is that the parasite story is the dominant one.

That is also my impression. But I have heard of another explanation that
was interesting if not persuasive - that human loss of hairiness was in
response to the common use of fire. The idea is that being very hairy
around a fire was a distinct danger. The fact that so many human
societies use furs as protection from cold argues against the theory, but
I still conjure up the mental picture of proto-humans bursting into
flames and running screaming to dive into the nearest body of water.

Seems to me that when we can come up with half a dozen different
selection based explanations we are in just-so story territory. How
about "we don't know"?

--
Matt Silberstein

Do something today about the Darfur Genocide

http://www.beawitness.org
http://www.darfurgenocide.org
http://www.savedarfur.org

"Darfur: A Genocide We can Stop"

.

Relevant Pages

  • Re: Couple questions for evolution experts
    ... appear to be the only mammals who experience excruciating pain during ... Evolution does not minimize pain or discomfort. ... we know of are virtually covered with hair or fur (in fact, ...
    (talk.origins)
  • Re: Couple questions for evolution experts
    ... did the human female birth canal ... appear to be the only mammals who experience excruciating pain during ... Evolution does not minimize pain or discomfort. ... we know of are virtually covered with hair or fur (in fact, ...
    (talk.origins)
  • Re: Couple questions for evolution experts
    ... process of evolution was occuring, did the human female birth canal ... appear to be the only mammals who experience excruciating pain during ... If it were beneficial for the survival of the species, ... we know of are virtually covered with hair or fur (in fact, ...
    (talk.origins)
  • Re: Couple questions for evolution experts
    ... process of evolution was occuring, did the human female birth canal ... appear to be the only mammals who experience excruciating pain during ... If it were beneficial for the survival of the species, ... we know of are virtually covered with hair or fur (in fact, ...
    (talk.origins)
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