[ExI] Human evolution model (was Iranian riots)

hkhenson hkhenson at rogers.com
Mon Jul 13 16:03:23 UTC 2009

At 05:00 AM 7/13/2009, Stathis Papaioannou wrote:


>They are making changes tending towards greater secularisation, which
>is the historical trend over the centuries. There may be temporary
>setbacks but ultimately religion is doomed, or at least doomed to be
>watered down until it's inoffensive.

This depends on what model you have for why humans have religions at 
all and the trends of the driving forces if you consider religion to 
be an intermediate outcome instead of being a primary factor.

Given the mortality associated with religions and the near universal 
tendency of humans to be vulnerable to them, basic evolutionary 
biology will cause you to suspect that the psychological trait behind 
religions evolved in the EEA and increased the reproductive success 
of those who had it.

How does getting yourself killed help the reproductive success of 
your genes?  It depends on the alternatives.  And you absolutely must 
understand inclusive fitness for the rest of this to make any 

"Thus a gene causing altruistic behavior towards brothers and sisters will
be selected only if the behavior and the circumstances are generally such
that the gain is more than twice the loss; for half-brothers it must be more
than four times the loss; and so on. To put the matter more vividly, an ani-
mal acting on this principle would sacrifice its life if it could thereby save
more than two brothers, but not for less. Some similar illustrations were
given by Haldane (1955)."

As some of you know, my view of religions is that they are xenophobic 
memes.  The human trait to host and be influence by these memes is a 
variable depending on the economic outlook.  It is modulated up when 
the economic outlook is bleak (effectively a behavioral switch when 
the gain in a group goes over one).  Today it would be measured in 
income per capita, in the stone age it was the ability of the 
ecosystem (game and berries) to feed the population.

In the Stone Age such memes synchronized a tribe's warriors for an 
attempt to kill neighbors for resources.   What we need to show is 
that going to war, for all its costs, is an evolutionary stable 
strategy (EES) in some recurring situations.

Of course "war" can range from raids that kill a few of the other 
tribe (and perhaps steal some of their women) to total defeat such as 
is described the Book of Numbers, Chapter 31

Simple model assumptions.  Humans trip into war mode (after a delay 
for xenophobic memes to build up) at some subjective probability that 
hard times a-coming will starve them.  This ranges from zero of them 
dying (being wrong) to the whole tribe starving.  Just to put a 
number on it, say the average event will cost the tribe half its 
members (and gene copies) if they do nothing.  This is the case we 
have to beat by going to war.

For the model I am going to say that on average the men who went off 
to a stone age war had 6 children (since that's about the number 
needed for a couple to raise two to adulthood in hunter gatherer 
societies) and one brother plus enough cousins to make up the equal 
of another brother (sisters were traded away for unrelated 
wives).  That's 8x!/2 (Hamilton's relatedness factor).

The cost of raids is relatively low, but so are the rewards.  The 
gene selection model will assume the extreme (once in a lifetime) 
case--which probably caused most of the selection.  For this simple 
model we will say that a tribe that goes to war loses none of the 
men's genes if it wins and all of the men's genes if it loses, plus 
the genes of all the male children but none of the female children 
who are taken as booty.  The additional resources captured removes 
the threat of starvation for the winners even though they incorporate 
the losing tribe's young females.

Genes of winners come out as 4, losers at 1.5 (three female children 
x 1/2).  Since the chance of winning is 50%, you average the numbers, 
giving 2.75.  That's the average gene survival for making a choice to 
go to war with a 50% chance of winning.

Genes numbers for not going to war at a 50% starvation rate come out at 2.


2.75/2 is 1.375, a 37% advantage.  In per generation evolutionary 
terms that's a *big* number (intense selection).  Of course, going to 
war when the tribe didn't face starvation was 4/2.75 or a 
disadvantage of about 45% so the selection is even stronger for not 
going to war when you didn't see bad times a-coming.  The mental 
detector for making an accurate forecast was also under intense 
selection since the genetic consequences of making a wrong decision 
were so serious.

Back to what Stathis wrote

"They are making changes tending towards greater secularisation, which
is the historical trend over the centuries. There may be temporary
setbacks but ultimately religion is doomed, or at least doomed to be
watered down until it's inoffensive."

The model indicates that a positive future outlook, i.e., good 
economic prospects for you and your children will turn off the switch 
to pass around and be strongly influenced by religious (xenophobic) 
memes.  The current world situation, especially the energy situation, 
leads me to predict that religions (and wars or related social 
disruptions) will be a major problem in the coming decades unless we 
solve the energy problem.  Of course since the detector is tripped on 
per capita, low or negative population growth helps a great deal.  To 
keep humans out of going to war, delta income/population must be 
positive or at least not negative for all segments of the population.



A more complicated model of human stone age evolution could be built, 
but my bet is that it will come to the same general conclusions as 
this simple one.

It looks like the psychological traits for war (and religion) would 
not have evolved if it were not for the practice of incorporating the 
young women of the losers into the winning tribe.

More information about the extropy-chat mailing list