A parasite‐driven wedge: infectious diseases may explain language and other biodiversity

The benefits of out-group interactions include gains through intergroup trade, new and better ideas and technology, and diversified and larger social networks for marriage and other social alliances.

“The benefits of out-group interactions include gains through intergroup trade, new and better ideas and technology, and diversified and larger social networks for marriage and other social alliances”

Individuals who experience relatively high levels of parasite-stress show greater in-group assortative sociality than those who experience relatively lower levels of parasite-stress.

“Individuals who experience relatively high levels of parasite-stress show greater ingroup assortative sociality than those who experience relatively lower levels of parasite-stress”

High parasite-stress is associated with high collectivism (low individualism), and low infectious disease risk with low collectivism (high individualism).

“High parasite-stress is associated with high collectivism (low individualism), and low infectious disease risk with low collectivism (high individualism).”

Across many countries of the world, the unidimension of collectivism-individualism is predicted strongly by infectious disease prevalence.

“Fincher et al. (2008) showed that the unidimension of collectivism-individualism across many countries of the world is predicted strongly by infectious disease prevalence.”

In-group assortative sociality is an example of adaptive phenotypic plasticity, that is, of a conditional strategy with multiple contingent tactics.

“In-group assortative sociality is an example, we argue, of adaptive phenotypic plasticity, that is, of a conditional strategy with multiple contingent tactics”

Culture-gene coevolution may produce genetically differentiated cross-cultural variation in the values and behaviors of assortative sociality.

“Culture-gene coevolution may produce genetically differentiated cross-cultural variation in the values and behaviors of assortative sociality.”

Conservatism-liberalism overlaps considerably with the well-studied cross-cultural value system referred to as collectivism-individualism.

“conservatism-liberalism overlaps considerably with the well-studied cross-cultural value system referred to as 'collectivism-individualism'”

Collectivism includes strong family ties and preferential assortment with in-group members outside the extended family.

“it also includes preferential assortment with in-group members outside the extended family (Fincher et al. 2008; Gelfand et al. 2004; Hofstede 2001; Thornhill et al. 2009; Triandis 1995).”

The findings cross-nationally and across the USA that strong family ties was correlated with parasite-stress complement earlier work linking collectivism-individualism with parasite-stress.

“The findings cross-nationally and across the USA that strong family ties was correlated with parasite-stress complement our earlier work that linked collectivismindividualism with parasite-stress (Fincher et al. 2008; Thornhill et al. 2010).”

The strong positive correlation between Vandello and Cohen's measure of collectivism and parasite-stress within the United States complements cross-national findings of the same relationship.

“Our finding of the strong positive correlation between Vandello and Cohen's measure of collectivism and parasite-stress within the United States is also an important complement to the cross-national findings of the same relationship reported in Fincher et al. (2008) and Thornhill et al. (2010).”

Gladden et al. suggested their findings were consistent with the fact that pathogen-stress and collectivism were positively related.

“Gladden et al. suggested their findings were consistent with the fact that pathogen-stress and collectivism were positively related (Fincher et al. 2008), presumably because much of moral intuitions taps into cognition about pathogens (Oaten et al. 2009).”