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Ärende: Dom World
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http://www.biolbull.org/cgi/content/full/202/3/283 
P.S. Rest of article at website

Biol. Bull.  202: 283-288. (June 2002)
© 2002 Marine Biological Laboratory 
Self-Organization and Natural Selection in the Evolution of Complex
Despotic Societies 
C. K. Hemelrijk 
Department of Information Technology and Anthropological Institute and
Museum, University of Zurich, Switzerland 
   
Abstract
 
Differences between related species are usually explained as separate
adaptations produced by individual selection. I discuss in this paper
how related species, which differ in many respects, may evolve by a
combination of individual selection, self-organization, and
group-selection, requiring an evolutionary adaptation of only a single
trait. In line with the supposed evolution of despotic species of
macaques, we take as a starting point an ancestral species that is
egalitarian and mildly aggressive. We suppose it to live in an
environment with abundant food and we put the case that, if food becomes
scarce and more clumped, natural selection at the level of the
individual will favor individuals with a more intense aggression
(implying, for instance, biting and fierce fighting). 

Using an individual-centered model, called DomWorld, I show what happens
when the intensity of aggression increases. In DomWorld, group life is
represented by artificial individuals that live in a homogeneous world.
Individuals are extremely simple: all they do is flock together and,
upon meeting one another, they may perform dominance interactions in
which the effects of winning and losing are self-reinforcing. When the
intensity of aggression in the model is increased, a complex feedback
between the hierarchy and spatial structure results; via
self-organization, this feedback causes the egalitarian society to
change into a despotic one. The many differences between the two types
of artificial society closely correspond to those between despotic and
egalitarian macaques in the real world. Given that, in the model, the
organization changes as a side effect of the change of one single trait
proper to an egalitarian society, in the real world a despotic society
may also have arisen as a side effect of the mutation of a single trait
of an egalitarian species. 

If groups with different intensities of aggression evolve in this way,
they will also have different gradients of hierarchy. When food is
scarce, groups with the steepest hierarchy may have the best chance to
survive, because at least a small number of individuals in such a group
may succeed in producing offspring, whereas in egalitarian societies
every individual is at risk of being insufficiently fed to reproduce.
Therefore, intrademic group selection (selection within an interbreeding
group) may have contributed to the evolution of despotic societies.



Discussion

Changing only one trait—intensity of aggression—in the model leads
to a great number of phenotypic differences at the level of the
individual and of the group. Thus, by changing the intensity of
aggression in DomWorld, as suggested by the hypothesis for egalitarian
and despotic macaques (McKenna, 1979; Thierry, 1985a, b, 1990), we may
switch from an egalitarian society to a despotic one. Intensity of
aggression is not the only variable, however, that can produce such a
cascade of effects. If we increase cohesion under one and the same level
of intensity of aggression (which must lie somewhere between medium and
high values), the society becomes more despotic in all its
characteristics (Hemelrijk, 1999a). The question of whether stronger
cohesion of groups is also accompanied by greater despotism in real
primates must be studied empirically. 

Thus, the model shows how self-organization causes nonlinearity in the
connection between the behavioral rules and the observed behavior (which
respectively correspond to the genotype and the phenotype). These
results of DomWorld may also be relevant to results of a selection
experiment with fish by Ruzzante and Doyle (1991, 1993). After two
generations of selection for speed of growth, an increase in growth
speed among fish fed on clumped food (leading to intense competition)
was accompanied by three effects: a decrease in aggressiveness, an
increase in density of schooling, and an increase in social tolerance.
According to the authors, selection for fast growth results in a high
threshold for aggression, and this threshold also genetically influences
the other two features of social behavior—cohesion and social
tolerance. These findings resemble those from DomWorld; but in DomWorld
only the intensity of aggression is changed "genetically," and all other
changes of social behavior are mere side effects. Such parsimonious
explanations may be relevant to many species of despotic animals that
have been studied and possibly even to plants, where a kind of despotism
is also described (for a study on a hemiparasite, see Prati et al.,
1997). 

Groups with different degrees of intensity of aggression may be liable
to group selection similar to that suggested for spiders by Ulbrich et
al. (1996). Group selection has always been a controversial issue. The
only studies in which any evidence has been produced (Bradley, 1999)
concern invertebrates (namely, a species of virus, social spider, and
ant). However, designating group selection as a useful explanation for
behavior of (nonhuman) primates is usually avoided (Bradley, 1999). Yet,
primates utter alarm calls that, though they are at the expense of the
fitness of the individual that uses them, may serve to protect group
members (both kin and non-kin). When alarm-calls are more beneficial for
the group than they are costly for the individual, they will evolve by
group selection, as explained by differential selection among groups for
the same trait—so-called intrademic group selection (Wilson, 2001).
Computer models show how such an intrademic group selection favors
altruistic traits, particularly under harsh conditions (Mitteldorf and
Wilson, 2000; Pepper and Smuts, 2000).  

Similarly, I suggest that group selection may operate on a
non-altruistic trait, namely intensity of aggression, in primate
societies in which there is sharp contest competition for food (during
harsh conditions). Such stronger competition leads to a more
asymmetrical distribution of food intake, and by guaranteeing that at
least some individuals of a group reproduce, aids group survival (of the
core group of the resident sex). 

Note that in the other transition, from despotic societies to
egalitarian ones (see Fig. 4), progressively milder aggression would be
favored by selection on the level of the individual and the group,
because less energy is wasted on conflicts. In this case, selection at
the level of the group and the individual will be weak, and
self-organization will not be operative. Thus, a different number of
processes are at work depending on the direction of the transition
between egalitarian and despotic societies. 

The different ways in which selection may act (namely, on self-organized
patterns, and on the level of the individual and the group) illustrate
how we may envision a multiple-level selection theory for the creation
of a despotic society. Although, for the sake of clarity in the sketch I
have given above, I have made individual selection, self-organization,
and group selection function one after the other, in reality they
operate mostly simultaneously in different proportions (Lewontin, 1970). 

   Acknowledgments 
 
I thank Rolf Pfeifer and Bob Martin for continuous support. I am
grateful to Scott Camazine for inviting me to the workshop on "The
Limits to Self-organization in Biological Systems," and to Bernard
Schmidt and Jens Krause for making me aware of similarities between
DomWorld and plant and fish communities. This work is partly supported
by a grant from the A. H. Schultz foundation.

"It's uncertain whether intelligence has any long term survival value.
Bacteria do quite well without it."
 Stephen Hawking
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