January 07, 2005
Twins Study Shows About Half Of Altruism Is Genetic

Male altruism is more heavily genetically determined than female altruism.

A paper showing a strong genetic contribution to social responsibility was published in the December 22 issue of Proceedings of the Royal Society: Biological Sciences, 271, 2583-2585, entitled "Genetic and environmental contributions to pro-social attitudes: a twin study of social responsibility."

The study compared identical twins with non-identical twins to see how much they agreed on 22 questions, such as "I am a person people can count on," "It is important to finish anything you have started," and "Cheating on income tax is as bad as stealing," using a scale from 1 (strongly disagree) to 5 (strongly agree). Answers are known to predict real-life behavior such as whether a person votes in elections or volunteers to help others.

The twins came from the University of London Twin Register. There were 174 pairs of monozygotic (identical twins, who share all their genes) and 148 pairs of dizygotic (non-identical twins, who share only half their genes). If monozygotic twins agree more than dizygotic twins it suggests that morality has a biological basis and is part of our evolved psychology.

The answers of the identical twins were almost twice as alike as those of the non-identical twins. The results showed that genes account for 42% of the individual differences in attitudes, growing up in the same home for 23%, and differences within the same home for the rest.

The study also found that genes had a stronger influence on males than females (50% vs. 40%) and that home upbringing had a stronger influence on females (40% vs. 0%). This suggests parents may watch over the behavior of daughters more carefully than they do for their sons.

In previous research Rushton has shown that genes influence people's levels of altruism and aggression--including feelings of empathy like enjoying watching people open presents and acts of violence such as fighting with a weapon. Rushton has also demonstrated that the male sex hormone testosterone sets the levels of aggression and altruism.

When asked about his findings Prof. Rushton noted, "They join a host of recent research in showing that both genes and upbringing influence almost every human behavior. It is especially interesting to see that this applies to moral attitudes." He said that he agreed with George Eliot's sentiment: "What do we live for, if it is not to make life less difficult for each other?"

If your reaction is that identical twins share more social environment keep in mind that a great many of twins studies have been done, including on twins reared apart. My impression from reading on twins studies and comparison across these studies is that the common experiences of identical twins as compared to non-identical twins and non-twin siblings do not end up counting for that much. So Rushton's use of this data to draw the conclusions he reaches about hereditability is sound in my opinion.

What is most important about this result? When something is genetic then it becomes manipulable using genetic technologies. Once people can control what genetic variations their offspring can have will they choose genetic variations that make their children more or less altruistic, more or less empathetic, more or less desirous to see justice done (with different levels of brain rewards for carrying out altruistic punishment), or more or less prone to being aggressive?

Once genetic variations for behavior and cognition become choosable by parents they will make choices that differ from what would happen from chance combination of their genes to produce offspring. So human offspring will change somehow as a result. The question is how?

My guess is that in different cultures the average decision made will be different. So cultures will become more unalike as humans make average different decisions about behavioral characteristics in their offspring.

The abstract:

Abstract: Although 51 twin and adoption studies have been performed on the genetic architecture of antisocial behaviour, only four previous studies have examined a genetic contribution to pro-social behaviour. Earlier work by the author with the University of London Institute of Psychiatry Adult Twin Register found that genes contributed approximately half of the variance to measures of self-report altruism, empathy, nurturance and aggression, including acts of violence. The present study extends those results by using a 22-item Social Responsibility Questionnaire with 174 pairs of monozygotic twins and 148 pairs of dizygotic twins. Forty-two per cent of the reliable variance was due to the twins' genes, 23% to the twins' common environment and the remainder to the twins' non-shared environment.

Paid access to the full article can be made here.

Share |      Randall Parker, 2005 January 07 01:55 PM  Brain Altruism

Dan Goodman said at January 7, 2005 2:45 PM:

Considering the researcher, I'm more skeptical than usual. J. Philippe Rushton is best known for his studies showing definite racial differences in intelligence. There are people who consider those studies badly flawed, to put it mildly.

Which doesn't mean there's a problem with this particular study. But I don't give him as much credence as I would, say, a study by a pharmaceutical company showing that its latest product does wonderful things.

Fly said at January 8, 2005 10:23 AM:

“When something is genetic then it becomes manipulable using genetic technologies.”

Discovering that a gene influences a trait is also a major step to understanding the biological mechanisms behind that trait. That can lead to drug or nutritional therapies.

toot said at January 8, 2005 11:18 AM:

Steven Pinker's book "The Blank Slate" discusses issues of heritability of various traits and the tendency there has been to downplay it.
Is Fly suggesting that the government genetically engineer people to make them more (or less?) altruistic. I would assume that it would be more, as that seems to be the direction that government favors. I suspect that if the government had the power, it would like to breed a kind of population in which there is a "tax drive" that operates much in the manner that the "sex drive" does. Wouldn't it be great to be able to get your jollies by looking at the federal tax deduction line of your pay stub? Unfortunately, the red states, inhabited by people who dislike paying taxes, seem to be out-breeding the blue states, where the people who claim to like to pay taxes are more prevalent. But I suspect this is only because the blue states are holding back for altruistic reasons, or maybe it's because they get sufficient gratification by looking at their pay stubs.

Bob Badour said at January 8, 2005 8:23 PM:

Hi Dan,

What were the flaws in Rushton's earlier work?

NuSapiens said at January 9, 2005 4:44 PM:

These studies that find strong genetic sex linkage on the male line might suggest that the Y chromosome plays a key role in such traits. Other traits that vary across gender lines, such as IQ (which has a much higher standard deviation amongst males than amongst females), are good contenders for Y chromosomal influence. This could help explain the emphasis placed on male lineages in Northern Hemisphere (European and Asian) agricultural and pastoral societies.

toot said at January 10, 2005 4:47 PM:


Actually, the effects you cited are usually interpreted as indicating that the gene responsible is located on the X chromosome. The Y chromosome has very few genes on it, while the X chromosome has a goodly number. A defect of one of the genes on the X chromosome will likely have little or no effect on a woman, who has a second X chromosome to substitute for the defective gene, but a defective gene on the X chromosome of a male, who has no second X chromosome to back up the first, will result in an effect on the phenotype.

Invisible Scientist said at January 11, 2005 7:39 AM:

This article makes a lot of sense, but unfortunately this is why I am often an easy prey: during the Great Depression,
my father dropped out of high school because his relatives in New York were in danger of starving, and this is why he
wanted to start working immediately in order to send his salary to them. He immediately went to Belgium to work in his
uncle's shop, and started sending money to New York, and my father even had some malnutrition as a result. In his family,
the philosophy was "one for all, all for one."

ANYWAY, in the year 2001, when I was at Berkeley, as street person said "Please give me a dollar so that I
can buy some beer, because I want to lower my IQ to that of George Bush." At that time I did not know that
Bush's IQ was over 120, and I was so impressed by this street person's sense of humor that I gave him $20 instead of $1.

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