Everyone knows genes determine your blood type. Now it appears genes may determine whether you're the type who gives blood.

Researchers in Canada and Great Britain have been comparing sets of twins -- identical and fraternal -- to determine whether altruism and other traits are inherited or learned.

They found that identical twins are similar to each other in tests of atruism, empathy and nurturance, and that fraternal twins are quite different, Psychology Today reports.

Identical twins have identical genes; fraternal twins don't. So the finding indicates that genes play a larger role than the home environment in determining altruism and the other qualities.

The 573 pairs of twins in the study, done at the University of Western Ontario, were aged 19 to 70.

Empathy was measured by whether the subjects answered "yes" or "no" to statements such as "I like to watch people open presents." Nurturance was measured by responses to true/false statements such as "I often take young people under my wing."

Altruism was measured by various behaviors, including giving directions to strangers and donating blood.

"Less than 2 percent of altruistic behavior can be attributed to the home environment that the twins shared as children," says researcher J. Philippe Rushton.