We study gender differences in altruism by examining a modified dictator ga
me with varying incomes and prices. Our results indicate that the question
"which is the fair sex?" has a complicated answer-when altruism is expensiv
e, women are kinder, but when it is cheap, men are more altruistic. That is
, we find that the male and female "demand curves for altruism" cross, and
that men are more responsive to price changes. Furthermore, men are more li
kely to be either perfectly selfish or perfectly selfless, whereas women te
nd to be "equalitarians" who prefer to share evenly.