Two toddlers are at play: Timmy hands his truck to his friend, “Here you can play with it.”

But Ricky hangs on to that truck for dear life. “No it is mine!”

Is the difference genetic?

In an Israeli study reported in the Wall Street Journal, researchers found that kids who didn’t share had a gene variation in common. The gene, AVPRIA, regulates a hormone in the brain associated with social behaviors like sharing. The noted genetic variation was associated with an unwillingness to share.

But don’t get too worried by this finding because altruism, or sharing, seems to be more controlled by environment. Positive reinforcement of sharing and altruistic behavior brings out those behaviors in children.  Generosity can be habit forming and learned. It engages the reward circuits of the brain and releases feel good transmitters.

The researchers also discovered that generosity increases as children grow and mature and develop stronger ideas of morality and fairness.

So if you want to encourage less selfishness in your child, praise his or her character when he or she shares.

Try these five suggestions:

1) Encourage sharing and activities that benefit others

2) Talk about how people feel in order to teach empathy

3) Praise a child’s character when he or she shows signs of goodness

4) Discuss consequences of behavior when a child is selfish–how the other person may feel

5) Model sharing and concern for others