How Much is in the Genes?

Scott Sumner writes: In “Babies by Design,” Ronald Green claims:

Studies of identical twins reared together or apart indicate that much obesity may be caused by hereditary factors. In technical terms, the heritability of obesity, the percentage of observed variation among people that is attributed to genes, is very high, somewhere between 50 and 80 percent.

There is also a kindness gene:

People with a certain gene trait are known to be more kind and caring than people without it, and strangers can quickly tell the difference, according to US research published on Monday.

The variation is linked to the body’s receptor gene of oxytocin, sometimes called the “love hormone” because it often manifests during sex and promotes bonding, empathy and other social behaviors.

Happiness is also genetic, according to an article in The Economist:

Serotonin is involved in mood regulation. Serotonin transporters are crucial to this job. The serotonin-transporter gene comes in two functional variants—long and short. The long one produces more transporter-protein molecules than the short one. People have two versions (known as alleles) of each gene, one from each parent. So some have two short alleles, some have two long ones, and the rest have one of each.

The adolescents in Dr. De Neve’s study were asked to grade themselves from very satisfied to very dissatisfied. Dr. De Neve found that those with one long allele were 8% more likely than those with none to describe themselves as very satisfied; those with two long alleles were 17% more likely.

So is empathy:

People who have two copies of the G allele are generally judged as more empathetic, trusting and loving.

Those with AG or AA genotypes tend to say they feel less positive overall, and feel less parental sensitivity. Previous research has shown they also may have a higher risk of autism.

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