The heritability of these qualities is a matter of debate but estimates are that IQ is about 80% heritable, and the big five personality factors are about 50% heritable. For the above reasons, genetic sexual attraction is presumed to occur as a consequence of genetic relatives meeting as adults, typically as a consequence of adoption.Although this is a rare consequence of adoptive reunions, the large number of adoptive reunions in recent years means that a larger number of people are affected.
People tend to select mates that are like themselves, which is known as assortative mating.This holds both for physical appearances and mental traits.People commonly rank faces similar to their own as more attractive, trustworthy, etc. However, Bereczkei (2004) attributes this in part to childhood imprinting on the opposite-sex parent.As for mental traits, one study found a correlation of 0.403 between husbands and wives, with husbands averaging about 2 IQ points higher.It is hypothesized that this effect evolved to prevent inbreeding.
A brother and sister couple in Germany, Patrick Stübing and Susan Karolewski, fought their country's anti-incest laws.
They grew up separately, met in 2000 when he was 23 and she was 15.
The study also reported a correlation of 0.233 for extraversion and 0.235 for inconsistency (using Eysenck's Personality Inventory).
A review of many previous studies found these numbers to be quite common.
Heredity produces substantial physical and mental similarity between close relatives.
Shared interests and personality traits are commonly considered desirable in a mate.