Does leaning left politically make you a more prosocial person?

It is often assumed that people who hold left-wing political beliefs have stronger prosocial traits and are more altruistic than those who support right-wing parties. This assumption is probably rooted in the fact that parties on the left are more likely to have social welfare and justice issues on their political agenda, such as financial support for the unemployed or a minimum wage. In turn, it is assumed that left-leaning persons themselves have a more prosocial attitude. But is this really the case?