Re: Culture may depend on numbers; warfare and altruism



Dave Smith wrote:
On 10 June, 19:17, Lance <LanceG...@xxxxxxxxx> wrote:
Warfare, culture and human evolution
Blood and treasure

Jun 4th 2009
From The Economist print edition
People are altruistic because they are militaristic, and cultured
because they are common. At least that is the message of a couple of
new studies

TWO of the oddest things about people are morality and culture.
Neither is unique to humans, but Homo sapiens has both in an abundance
missing from other species. Indeed, that abundance—of concern for the
well-being of others, (even unrelated others), and of finely crafted
material objects both useful and ornamental—is seen by many as the
mark of man, as what distinguishes humanity from mere beasts.

How these human traits evolved is controversial. But two papers in
this week’s Science may throw light on the process. In one, Samuel
Bowles of the Santa Fe Institute in New Mexico fleshes out his
paradoxical theory that much of human virtue was forged in the
crucible of war. Comrades in arms, he believes, become comrades in
other things, too.

In the other paper, Mark Thomas and his colleagues at University
College, London, suggest that cultural sophistication depends on more
than just the evolution of intelligence. It also requires a dense
population. If correct, this would explain some puzzling features of
the archaeological record that have hitherto been put down to the
arbitrary nature of what has survived to the present and what has not.

Dr Bowles’s argument starts in an obscure cranny of evolutionary
theory called group selection. This suggests that groups of
collaborative individuals will often do better than groups of selfish
ones, and thus prosper at their expense. It is therefore no surprise,
according to group-selectionists, that individuals might be
genetically predisposed to act in self-sacrificial ways.

This good-of-the-group argument was widely believed until the 1960s,
when it was subject to rigorous scrutiny and found wanting. The new
theory does not pitch groups against groups, or even individuals
against individuals, but genes against genes. It does not disallow
altruistic behaviour, but requires that this evolve in a way that
promotes the interest of a particular gene—for example by helping
close relatives who might also harbour the gene in question. The
“selfish gene” analysis, so called after a book by Richard Dawkins,
makes good-of-the-group outcomes almost impossible to achieve.
War and peace

A few researchers, of whom Dr Bowles is one, have been unwilling to
give up on group selection completely. They note the word “almost” in
the argument above and contend that humans, with their high
intelligence and possession of language, and their tendency to live in
small, tightly knit groups, might be exceptional. They also think
people could be subject to a form of group selection that is
genetically selfish.

Dr Bowles has focused the argument on war, since it is both highly
collaborative and often genetically terminal for the losers. In his
latest paper he puts some numbers on the idea. He looks at the data,
plugs them into a mathematical model of his devising and finds a
pleasing outcome.

To gather his data, Dr Bowles trawled through ethnographic and
archaeological evidence about warfare between groups of hunter-
gatherers. This is rarely war in the modern sense of planned
campaigns. It is more a matter of raids, ambushes and fights between
groups who have met accidentally. It is, nevertheless, quite lethal.
Dr Bowles identified eight ethnographic and 15 archaeological studies
that met his criteria of reliability and abundance of data. They
suggest that 12-16% of mortality is the result of such low-level
warfare. This is a figure much higher than, for example, the mortality
caused in Europe by two world wars, and is certainly enough to drive
evolution. But the question remained of whether it could drive group
selection.

It was to test that idea that Dr Bowles devised his model. Although it
pitches group against group, it is strictly based on the idea of
selfish genes. It looks at the benefit to a notional gene that
promotes self-sacrifice. The question is, does such a gene do well if
individuals having it belong to a group that takes over the territory
and resources of a similar, neighbouring group, but at the risk of
some of those individuals losing their life in the process? What is
the maximum self-sacrificial cost that can evolve in these
circumstances?

In the absence of war, a gene imposing a self-sacrificial cost of as
little as 3% in forgone reproduction would drop from 90% to 10% of the
population in 150 generations. Dr Bowles’s model, however, predicts
that much higher levels of self-sacrifice—up to 13% in one case—could
be sustained if warfare were brought into the equation. This, he
contends, allows the evolution of collaborative, altruistic traits
that would not otherwise be possible. Moreover, although warfare is an
extreme example, other, less martial forms of self sacrifice may have
similar group-strengthening virtues.

Dr Thomas and his colleagues also rely on a mathematical model. They
are trying to explain the pattern of apparent false-starts to modern
human culture. The species is now believed to have emerged
150,000-200,000 years ago in Africa and to have begun spreading to the
rest of the world about 60,000 years ago. But signs of modern culture,
such as shell beads for necklaces, the use of pigments and delicate,
sophisticated tools like bone harpoons, do not appear until 90,000
years ago. They then disappear, before popping up again (and also
sometimes disappearing), until they really get going around 35,000
years ago in Europe.

The team drew on an earlier insight that it requires a certain number
of people to maintain skills and knowledge in a population. Below this
level, random effects can be important. The probability of useful
inventions being made is low and if only a few have the skills to
fabricate the new inventions, they may die without having passed on
their knowledge.

In their model, Dr Thomas and his colleagues divided a simulated world
into regions with different densities of human groups. Individuals in
these groups had certain “skills”, each with an associated degree of
complexity. Such skills could be passed on, more or less faithfully,
thus yielding an average level of skills that could vary over time.
The groups could also exchange skills.

The model suggested that once more than about 50 groups were in
contact with one another, the complexity of skills that could be
maintained did not increase as the number of groups increased. Rather,
it was population density that turned out to be the key to cultural
sophistication. The more people there were, the more exchange there
was between groups and the richer the culture of each group became.

Dr Thomas therefore suggests that the reason there is so little sign
of culture until 90,000 years ago is that there were not enough people
to support it. It is at this point that a couple of places in Africa—
one in the southernmost tip of the continent and one in eastern Congo—
yield signs of jewellery, art and modern weapons. But then they go
away again. That, Dr Thomas suggests, corresponds with a period when
human numbers shrank. Climate data provides evidence this shrinkage
did happen.

According to Dr Thomas, therefore, culture was not invented once, when
people had become clever enough, and then gradually built up into the
edifice it is today. Rather, it came and went as the population waxed
and waned. Since the invention of agriculture, of course, the
population has done nothing but wax. The consequences are all around
you.

http://www.economist.com/science/displaystory.cfm?story_id=13776964


I don't find the claim about warfare and altruism convincing. If it's
a matter of one group taking the resources and territory of another
group, then presumably there would mainly be selection for traits
such as strength, aggression and intelligence. As Sober and Wilson
argued at length in 'Unto Others', I think co-operation between
individuals within a group might provide a selective advantage over
other groups, regardless of the need to fight with other groups.

Dave Smith

I think a lot turns on the claim that inter-tribal conflict accounted
for between 12-16% of mortality. If that figure is real then selection
pressure to band together and cooperate would have been very great,
and it would indeed have been the result of war. So can you find
reason to dispute that figure?

Lance
.

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