Most researchers now agree that personality in our species is also infl uenced by genetic processes, and that genetic differences contribute to a variety of personality profi les and response norms to the various situations life poses. A growing number of molecular, twin and pedigree studies has suggested heritability in personality traits. At present, the variability in personality traits among individuals is well-established (McCrae & Costa, 1987 ) and has a (30 % to 60 % ) heritable component in various population studied (Benjamin et al., 1996 ; Bergeman et al., 1988 ; Cloninger et al., 1993 ; Ebstein et al.; 1996 ; Plomin et al., 1994 ; Tellegen et al., 1988 ). These studies suggest that there are specifi c loci with various alleles infl uencing different (usually opposing) response norms to similar situations (Buss, 1991 ; Lohelin et al., 1998 ; Plomin and Nesselroade, 1990 ; Plomin & Caspi, 1999 ). In this chapter we will not ignore or dismiss the environmental effect of personality variation, but we will especially focus on the genetic aspect of it, and try to answer the following question: Why are there a multitude of different alleles in different loci that infl uence differently the expression of personality traits? Selection is generally understood to favor the most successful traits and eliminate all others given enough time, thus transmitting the single most successful phenotype to the whole population at the expenses (extinction) of all less successful ones (Fisher, 1930 ). Yet, personality traits are highly variable in all populations studied. Most researchers agree that personality traits vary not only because they fail to coalesce into a single successful profi le, but also because there is an inherent permanent presence of a variety of alleles infl uencing all personality traits in different ways (Lohelin & Rowe, 1992 ; Turkheimer, 1998 ). This state of affairs gives rise to a crucial question: Why have millions of years of evolution not eliminated genetic variation in all personality traits, favoring a unique, most adapted one? Penke and colleagues ( 2007 ) examined three possible alternative hypotheses to account for the persistence of a large amount of variation in personality profi les: 1) Neutral selection, 2) Mutation-selection equilibrium and 3) Balanced selection . Accordingly, these authors evaluated the evolutionary dynamics and requirements of all of the hypotheses within a behavioral genetics perspective, and suggested that balanced selection and some of its variants more adequately explained the persistence of a large number of alleles infl uencing personality traits. At a theoretical level, their arguments are convincing. What is yet missing, however, is an empirical test of competing predictions that arise variously from the three contrasting hypotheses.

Testing the evolutionary genetics of personality: Do Balanced Selection and gene flow cause genetically adapted personality differences in Human populations

CAMPERIO CIANI, ANDREA-SIGFRIDO
2011

Abstract

Most researchers now agree that personality in our species is also infl uenced by genetic processes, and that genetic differences contribute to a variety of personality profi les and response norms to the various situations life poses. A growing number of molecular, twin and pedigree studies has suggested heritability in personality traits. At present, the variability in personality traits among individuals is well-established (McCrae & Costa, 1987 ) and has a (30 % to 60 % ) heritable component in various population studied (Benjamin et al., 1996 ; Bergeman et al., 1988 ; Cloninger et al., 1993 ; Ebstein et al.; 1996 ; Plomin et al., 1994 ; Tellegen et al., 1988 ). These studies suggest that there are specifi c loci with various alleles infl uencing different (usually opposing) response norms to similar situations (Buss, 1991 ; Lohelin et al., 1998 ; Plomin and Nesselroade, 1990 ; Plomin & Caspi, 1999 ). In this chapter we will not ignore or dismiss the environmental effect of personality variation, but we will especially focus on the genetic aspect of it, and try to answer the following question: Why are there a multitude of different alleles in different loci that infl uence differently the expression of personality traits? Selection is generally understood to favor the most successful traits and eliminate all others given enough time, thus transmitting the single most successful phenotype to the whole population at the expenses (extinction) of all less successful ones (Fisher, 1930 ). Yet, personality traits are highly variable in all populations studied. Most researchers agree that personality traits vary not only because they fail to coalesce into a single successful profi le, but also because there is an inherent permanent presence of a variety of alleles infl uencing all personality traits in different ways (Lohelin & Rowe, 1992 ; Turkheimer, 1998 ). This state of affairs gives rise to a crucial question: Why have millions of years of evolution not eliminated genetic variation in all personality traits, favoring a unique, most adapted one? Penke and colleagues ( 2007 ) examined three possible alternative hypotheses to account for the persistence of a large amount of variation in personality profi les: 1) Neutral selection, 2) Mutation-selection equilibrium and 3) Balanced selection . Accordingly, these authors evaluated the evolutionary dynamics and requirements of all of the hypotheses within a behavioral genetics perspective, and suggested that balanced selection and some of its variants more adequately explained the persistence of a large number of alleles infl uencing personality traits. At a theoretical level, their arguments are convincing. What is yet missing, however, is an empirical test of competing predictions that arise variously from the three contrasting hypotheses.
2011
The evolution of personality and individual differences
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