The Spread of Inequality Deborah S. Rogers, Omkar Deshpande, Marcus W. Feldman Sept 21, 2011


The causes of socioeconomic inequality have been debated since the time of Plato. Many reasons for the development of stratification have been proposed, from the need for hierarchical control over large-scale irrigation systems to the accumulation of small differences in wealth over time via inheritance processes. However, none of these explains how unequal societies came to completely displace egalitarian cultural norms over time. Our study models demographic consequences associated with the unequal distribution of resources in stratified societies. Agent-based simulation results show that in constant environments, unequal access to resources can be demographically destabilizing, resulting in the outward migration and spread of such societies even when population size is relatively small. In variable environments, stratified societies spread more and are also better able to survive resource shortages by sequestering mortality in the lower classes. The predictions of our simulation are provided modest support by a range of existing empirical studies. In short, the fact that stratified societies today vastly outnumber egalitarian societies may not be due to the transformation of egalitarian norms and structures, but may instead reflect the more rapid migration of stratified societies and consequent conquest or displacement of egalitarian societies over time.



Meta-analysis of the heritability of human traits based on fifty years of twin studies.


Despite a century of research on complex traits in humans, the relative importance and specific nature of the influences of genes and environment on human traits remain controversial. We report a meta-analysis of twin correlations and reported variance components for 17,804 traits from 2,748 publications including 14,558,903 partly dependent twin pairs, virtually all published twin studies of complex traits. Estimates of heritability cluster strongly within functional domains, and across all traits the reported heritability is 49%. For a majority (69%) of traits, the observed twin correlations are consistent with a simple and parsimonious model where twin resemblance is solely due to additive genetic variation. The data are inconsistent with substantial influences from shared environment or non-additive genetic variation. This study provides the most comprehensive analysis of the causes of individual differences in human traits thus far and will guide future gene-mapping efforts. All the results can be visualized using the MaTCH webtool.

Women live longer than men even during severe famines and epidemics


Women in almost all modern populations live longer than men. Research to date provides evidence for both biological and social factors influencing this gender gap. Conditions when both men and women experience extremely high levels of mortality risk are unexplored sources of information. We investigate the survival of both sexes in seven populations under extreme conditions from famines, epidemics, and slavery. Women survived better than men: In all populations, they had lower mortality across almost all ages, and, with the exception of one slave population, they lived longer on average than men. Gender differences in infant mortality contributed the most to the gender gap in life expectancy, indicating that newborn girls were able to survive extreme mortality hazards better than newborn boys. Our results confirm the ubiquity of a female survival advantage even when mortality is extraordinarily high. The hypothesis that the survival advantage of women has fundamental biological underpinnings is supported by the fact that under very harsh conditions females survive better than males even at infant ages when behavioral and social differences may be minimal or favor males. Our findings also indicate that the female advantage differs across environments and is modulated by social factors.


A Meta-Analytic Review of Treatment of Homosexuality

This paper examined and synthesized studies of treatment of individuals identified as homosexual using meta-analytic technique. A large number of studies (146) evaluating treatment efficacy were identified, most published prior to 1975 and 14 of which met inclusion criteria and provided statistics that could be used in a meta-analysis. These 14 outcome studies were published between 1969 and 1982 and used primarily behavioral interventions. Analysis indicated that treatment for homosexuality was significantly more effective than alternative treatments or control groups for homosexuality (ES = .72), and significant differences were found across pre- to postanalysis (ES = .89). In other words, the average patient receiving treatment was better off than 79% of those in the alternative treatments or as compared to pretreatment scores on the several outcome measures. This meta-analysis of 14 studies provides empirical support for a group of 146 studies which have narratively suggested that treatment for homosexuality is effective. Variables related to treatment efficacy are examined.