So, I was especially confused by the claim that "in-group bias is much weaker in men in general." I knew that in fact, when asked to play a job interviewer or evaluator, men punished women more often than other men for trying to negotiate salary, whereas women punished everyone equally.

But I do see other evidence that calling this "in-group bias" gives the wrong idea. Maybe women tend to have a greater belief in 'gender roles,' while disagreeing with men on what those roles require/allow for men specifically. This however seems kind of odd when we see that participants in the first study (both male and female) were less likely to ask for more money from a female evaluator. I guess the women there may have a false picture of men's motives if they think men will punish them more than another women would (I don't know the exact numbers). Except, what can the men be thinking if they know that 1. women would treat them the same as everyone would treat women, and 2. the men would treat themselves more leniently than they would treat women?

ETA: actually, it seems unclear from the abstract if men did behave differently with a female evaluator!