Robert Plomin is a psychologist and behavioral geneticist at King’s College London and the president of the international Behavioural Genetics Association. He is one of the world’s leading experts in how genes affect human personalities.

Plomin’s new book ‘Blueprint’ explains in fine (but admirably clear and digestible) detail the most up to date research findings in the field of behavioral genetics. Among the many fascinating concepts discussed in the book is the Nature of Nurture finding.

Genetic Differnces Cause Differences in Personality Traits

‘Blueprint’ deals with personality and explores the extent to which psychological differences between individual humans are due to genetic differences.

99% of the information contained in each human’s genome is uniform. This is the information that codes for species-wide traits such as bipedalism, front-facing eyes, and the brain’s core fight, freeze or freeze response to threatening stimuli.

The remaining 1% of each person’s genome contains the variable and always somewhat unique information that makes each of us distinct, one-off individuals.

The 99% makes us human (instead of, say, iguana or bonobo). The 1% makes you you (instead of, say, Mel Gibson, Jesus Christ or your classmate Simon).

Massive twin and adoption studies (with sample sizes reaching into the hundreds of thousands) have now conclusively demonstrated that genetic differences are the single largest systematic factor affecting personality differences between individuals.

What is ‘Heritability’?

‘Heritability’ refers to the extent to which individual differences in a trait are heritable. In other words, are inherited biologically; passed from parent to offspring in the form of genetic information. It measures how much of the differing levels of traits found between individuals can be attributed to genetic differences. Heritability is measured as a percentage of the entire detectable difference.

Heritability of psychological traits has been decisively shown to be, on average, 50%. This means that 50% of the difference in psychological traits between individuals is due to their genes. This is a massive influence! It dwarfs any other influence ever detected in psychological research. (Up until now the largest influences affecting differences in psychological traits have been able to account for between 1 and 5%, with 5% being considered very large!).

This makes genetics far and away the biggest single factor dictating differences in personality traits between individuals.

There is No ‘Gene For X’

A crucial point to understand is that there is no single gene for any trait. There is no gene for shyness, anxiety, happiness, aggression. There is no gene for baldness, weight gain, muscularity, or shoe size.

This “gene for x” canard has been used to distort the complex ...