Re: Man & wife -- why oh why?

On Wednesday 27 June 2007 21:12, Cory Albrecht wrote:

Niels wrote, On 2007/06/27 05:16:
On Wednesday 27 June 2007 00:35, Cory Albrecht wrote:
Niels wrote, On 2007/06/26 04:53:
On Monday 25 June 2007 21:15, Andrew Arensburger wrote:
Niels <name@xxxxxxxxxxx> wrote:
But usually, even within small
societies and groups, people tend to find together in twos, not
threes or twelves. The question is why.
Because the more partners you have, the more wet spots on the
bed you have to avoid after sex?
I get your point, but if this is what guides humans to form pairs
("groups of two"), then why doesn't it work like that for chimpanzees?
Chimpanzees don't sleep in beds, therefore they don't have to worry
about avoiding the wet spot. :-)

But seriously, I think you're wrongly confusing Andrew's use of game
theory with the idea that monogamy is the only good mating strategy. IN
truth, it's merely one out of many.

Good point.


If monogamy were truly the objective best strategy, the we would see
that all species had evolved towards it (or it didn't evolve away from
it) after the first metazoans finally evolved sexual reproduction. But
in the animal kingdom as a whole, it's relatively rare.

No, we'd see monogamy for species that where like us.

There is a difference between "monogamy is the objective best strategy"
and "monogamy is the objective best strategy for primates". I said the
first one, without a limiting qualifier, and therefore I was referring
to all species, not just primates.


As for what guides humans into favouring monogamy, look at our
offspring. Reproductive strategies can be divided into two groups -
"high K and "low K". The variable K is how much (or how little) energy
the parent(s) invest in each individual offspring. Fish are usually low
K because the have lots of fry at once and give each one almost no care.
Gorillas, chimps and humans are high K because they have (usually) one
baby at a time and take years to raise them, humans being obviously the
highest of the high Ks.

But other individuals than the parents help with the upbringing, at least
for the more social animals. So it's not quite so clear cut.

I apologize if I didn't make it clear, but I was intending to convey
that "high K" and "low K" are two ends on the K spectrum - not two
separate states with nothing in between.

Since we are high K species - each individual offspring requires a large
investment - it is advantageous to the male to be monogamous as high
investment from him means more surviving descendants. Anythings that
distracts him too often for too long, reducing his investment, is
detrimental to his reproductive success.

Chimps and gorillas, which aren't quite as high K as humans though still
taking a couple years to raise an individual baby, "solved" this problem
in different ways. Gorillas practice polygyny and deny sexual access to
non-troop leaders. Chimps are polygamous and females in estrus mate with
all local males and the males mate with each female as they cycle.

So why are humans a higher K species? Because of our larger brains and
more complex societies?

Like I said, K is how much "energy" the species invests in each
individual offspring. Pretend that every species has a fixed budget of
1000 units of offspring care to spend in every round of reproduction.
Now a species can produce 1000 offspring and invest 1 unit in each, or
50 offspring and invest 20 units each, 4 offspring at 250 units each or
just one offspring and give all 1000 units to it. Now this "energy" can
be many different things. It can be something as simple as the amount of
food provided or as complex as time spent teaching the offspring how to
do things. How much energy the parent invests in each individual
offspring is directly relevant to the offsprings' rate of survival - if
you don't invest much in your young you want to produce a whole lot of
them so that at least a few will survive to reproductive maturity.

Thus it is not our larger brains which makes us high-K, it is the fact
that we have relatively few and we spend so much time taking care of
their needs before they become independent.


All in all, I think this is a pretty good explanation. In modern societies,
we see few children per parent, partly because of social norms and economic
pressure. Social norms also shape the way we treat our children, leading to
high Ks, in general. This makes monogamy more attractive for both parents,
although infidelity occurs regularly.

I find it hard to imagine that this would change a lot, even if our
societies were to change into some sort of wonderfully free and open minded
Utopia. As long as infant mortality rates are (extremely) low, it doesn't
seem likely that women would start having 12 children each, or even 5.

Thanks,
Niels

.

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