Coeffecient of relatedness and predictions of complex genetic influences The coefficient of relatedness (r) between two individuals is defined as the percentage of genes that those two individuals share by common descent. MZ twins = 1.0 DZ twins = 0.5 Siblings = 0.5 Parents & offspring = 0.5 Grandparents & grand children =0.25 If a behavioral trait is under complete genetic control would we predict that r =total variability in the trait?

Environmental hypothesis

Two major approaches used by behavior geneticists to study relative contributions of genes & environment in the development of behavior Hold genetic make-up constant to study effects of the environment alone (VT=VE) cross-fostering experiments & twin studies Hold environment constant & explore effects of genes alone (VT=VG) selective breeding experiments use of genetic “knock-outs” Keep in mind: Genetic effects are usually complex, involving Pleiotropic and Polygenic effects Environmental effects are complex involving multiple environmental factors Complex genetic and environmental effects will be further complicated by gene/environment interactions. Taken from Personality and Individual Differences, Vol. 23, No. 1 (July 1997), pp

A measure of how strongly a phenotype is influenced by genetics Total phenotypic variation=VT=VG+VE+VI where: VT= total phenotypic variation observed in a (behavioral) trait VG= variation in population due to genotype VE =variation in population due to environment VI = variation in population due to interaction of VG with VE (i.e. VGxVE) Heritability: Heritability (H 2 ) H 2 =VG/(VG+VE+VI) = VG/VT Characteristics of H2 Heritability is standardized variance ranging from Indicates what fraction of the total variance in a trait is due to variation in genes: H2=0: None of the variance in the trait is influenced by genes H2=1: All of the variance in the trait is determined by genes Taken from Personality and Individual Differences, Vol. 23, No. 1 (July 1997), pp

RushtonPhillip Psychology 1/19 / Primary research interest is altruism and social learning of generosity More controversial is on race differences Philippe Rushton

Heritability (H 2 ) of IQ = 0.70 Average IQ by Ethnic group: African Americans 85 Latino 89 White 103 Asian 106 Jewish Americans 115 Correlation between IQ and head/brain size = 0.40 (MRI normal adults) 0.24 (MRI clinical adults) Taken from Personality and Individual Differences, Vol. 23, No. 1 (July 1997), pp

Brain size and race Brain size and SES Men Unskilled 1,324cc Professional 1,468cc Women Unskilled1256cc Professional 1264cc Brain size and sex Men1325g Women1144g ***However no difference in IQ ??? Brain size Taken from Personality and Individual Differences, Vol. 23, No. 1 (July 1997), pp

1 of 6 warbler species that regularly winter in the British Isles, 4 of which are migratory Chiffchaff, Blackcap, Firecrest and Goldcrest winter Atlas , estimates 3,000 Blackcaps

Quantifying intended flight direction