Behavioral Genetics

Temperament – that portion of a person’s personality that has an organic, and therefore genetic, basis. It is has been acknowledged for centuries that some portion of the personality has an organic basis, e.g. personality differences between men and women. It is obvious that some of these differences can be attributed to specific proteins, e.g. the hormones testosterone and estrogen.

Chronic and Bipolar Depression Genealogy of a family from the Central Valley of Costa Rica. Deceased persons are marked with a slash.

It has been difficult to identify the specific genes behind bipolar depression because it is a polygenic trait, a trait caused by the joint action of multiple genes.

The midbrain (mesencephalon): center for emotions and sex

Synapses, neurotransmitters, and receptors

Novelty- or Thrill-Seeking, and Addiction Dopamine synthesis

People who psychologists would describe as thrill, or novelty seekers have been shown to have a mutation of the D4DR receptor allele, found on chromosome 11. All addictions involve affecting the release, reuptake, or regulation of dopamine. Reuptake: the transporting of a neurotransmitter back inside a dendrite by means of transporter protein.

Dopamine and addiction

Serotonin and Depression Serotonin – Synthesized from the amino acid tryptophan. Is involved in both relaxation and aggression. Selective Serotonin Reuptake Inhibitors: Zoloft, Prozac.

There is controversy about the role played by the serotonin transporter in chronic depression – whether it is too efficient at transporting serotonin (the majority opinion) or defective in transporting serotonin (Dean Hamer), in which case Prozac and Zoloft should be seen a synthetic serotonin transporter proteins.

IQ and Identical Twins Beginning in the 1970’s, Thomas Bouchard and colleagues at the University of Minnesota began gathering data on monozygotic (identical) twins put up for adoption and raised in separate households (MZA’s). Any similarities shown by the twins would be due to shared genetics, any differences would be due to the environment.

General Outcomes Twin studies have established the overriding influence of genes on Schizophrenia. Male homosexuality (not lesbianism).

Outcomes for IQ Nobody denies that there is a genetic component to IQ. Nobody denies that there is a significant heritability factor to IQ. Everybody agrees that intelligence is polygenic – probably involving hundreds of genes.

IQ and sex differences

IQ and the Achievement Gap The race concept does not have biological validity. In measures of academic achievement in the US there are consistent and persistent differences between average scores of broad ethnic populations. Though it is accepted that it plays some role, socioeconomic status is not held to be the chief cause of this order.

Debate continues to rage about the relative contribution of genes and the environment to this achievement hierarchy.