Are you sharing the last penny with the others or eating only pretzels not to spend money on food? Are you offering flowers to your female workmates on the 8th of March or on their birthdays, or is this a nonsense gesture for you?

It seems that these reactions are genetically wired, as showed by a team led by Dr. Ariel Knafo, of the Psychology Department at the Hebrew University of Jerusalem, in the journal "Genes, Brain and Behavior". Appealing to an on-line task involving the decision of whether to give away money or not, the scientists discovered that those who agreed to give away some or all of their money had a different DNA variant for a specific gene, in comparison to the subjects who did not want to offer their money.

The study involved 203 on-line "players". Each player could keep the allocated sum of $12, or to give all or some of it to an anonymous other player. The subjects were also taken DNA samples, and DNA sequences were compared to their reactions. A specific variant of the gene AVPR1 was associated with the subjects offering on average about 50% more money than those missing the variant.

"The experiment provided the first evidence, to my knowledge, for a relationship between DNA variability and real human altruism", said Knafo.

AVPR1encodes a protein receptor for the hormone called arginine vasopressin on brain cells. Vasopressin has been connected to social bonding. Higher altruism was connected to a type of AVPR1, having a longer promoter (a DNA stretch controlling how much of the protein encoded by a gene will be synthesized). A longer promoter means higher synthesis.

"The findings could help biologists sort out altruism's evolutionary history", wrote the researchers, pointing to its role in the human evolution.

A mutation of AVPR1in voles had already been shown to promote social bonding.