Evolution of traits related to population density in a heterogeneous metapopulation: an application of the "cornucopia principle" to changes in human political propensities by Charles N.W. Keckler Human Evolutionary Ecology Program University of New Mexico

Vegetation of the Old World (National Geographic, 1997)

Current Population Density -Asia Source: CIESEN

Selection in Metapopulations If a species is present in multiple environments, and the selective force acting on a trait differs across these environments, net selection will depend (all else equal) on the proportion of the population in each habitat. The population proportion will be determined by (a) the frequency with which a habitat is utilized (b) the relative population of utilized habitats

The “Cornucopia Principle” For the same frequency distribution or "landscape" of environments, the selective forces of those environments that support larger populations will have a disproportionate impact on the traits of future generations. Therefore: With equivalent intensity of selection, "good" environments (with higher than average densities and growth) form the main selective background of a multi-environment species.

Variability in Foragers Source: Binford (1980)

Time-Averaged Distribution of Habitable Zones -- Old World (Source: Atlas of Paleovegetation, Adams and Faure)

Estimates of Population Usage of Different Ecozones EcoZonePopulation Densities /mi 2 Arctic*0.178 Tropical Forest0.554 Tropical Desert0.168 Temperate Forest2.8 Temperate Desert0.058 Boreal Forest0.08 (Derived from Keeley 1988, Kelly 1995)

Estimated Average Population Distribution of Old World Foragers

Distribution of Social Types Derived from foragers in Outline of World Cultures (1981) Average size of Egalitarian Population – 3576 Average size of Inegalitarian Population

Strategies Under Varying Selection in Different Forager Environments (H) allele -- the willingness to exploit (e.g. through contest competition) advantages in competitive ability in order extract further selective gain ("pressing your luck"). Strategic expression conditional on status (h) allele -- at minimum, an unwillingness to act in this manner given the opportunity

Simulation Conditions Environment 1 (Good) Selective Effects Environment 2 (Poor) Selective Effects Dominants(H) + A Dominants(H) -C Dominants(h) -A * D * P(H) P(h) * (1-D) Dominants(h) Normal Subordinate(H) -A * D * P(H) P(h) * (1-D) Subordinate(H) Normal Subordinate(h) -A * D * P(H) P(h) * (1-D) Subordinate(h) Normal D = proportion “dominants,” A= advantage of exploitation, C= cost of punishment, P(H) = freq of allele H (initially set to 1)

Fixation of Alleles in Different Environments

Parameter Sensitivity

Source-Sink Metapopulation Dynamics Marginal Populations Exposed to Extinction and Replacement

Differential Colonization of Favorable Habitats

Effect of Genetic Influx

Preliminary Conclusions Under realistic assumptions, there have been substantial numbers of inegalitarian foragers. These populations can provide a powerful counterweight against negative selection for “hierarchical” behavior in “standard” foragers. Persistence of “special design” for egalitarianism, or of genetic change in political propensity, is doubtful. More plausibly, egalitarianism is a consequence of a flexible general trait capable of tracking socioecology, assisted by social learning (culture).

Source: Atlas of Paleovegetation (Adams & Faure)