I've seen a few papers directed at this exact question, but they've all come to the opposite conclusion. To be fair, these are Economics papers so some level of bias may be in effect, but I believe that at least one of the linked papers goes on to conclude that this is not the case based on experimental trials which showed that while Economics freshmen kept more than people in the Dictator game, seniors in Economics were in line with seniors of other majors and that both gave away more than their freshmen counterparts. I'll see if I can access more of the linked papers later, but it seems like he cites a lot of papers but only actually mentions their conclusions when they agree with his point.