"The grooming behavior displayed by primates is due to less rational behavior than often thought. According to a computer model, one basic rule explains all possible grooming patterns: individuals will groom others if they're afraid they'll lose from them in a fight."
...um, so I've gone ahead and read the actual article to this one because I needed to figure out if I was missing something deeper in the text that would explain how this assertion isn't very misguided. In summary, I didn't find anything.
Firstly, their model is based entirely on macaque data... no new world monkeys, no apes, certainly no baboons. This isn't inherently broken, but it simply is not satisfying when one considers that social grooming is ubiquitous in primates, and a crucial device.
Second, I've seen baboons violate this rule on many an occasion. Since males and females do groom each other, and the model does not appear to exclude such behavior, I have a bit of an issue.
Intergender grooming is a bit problem for this model. It happens. It doesn't follow these rules. Let us stipulate that a fully adult male can beat any female in a fight. This is a fact. On many occasions, I've seen a male, even the alpha male. Plop his shaggy form down next to some female who is sitting, minding her own business. If there is any behavior which say "groom me," its this. Yet, a lot of the time the female will just walk away.
This alone would not be enough to discount their findings. However, on several occasions, after his failed attempt to solicit grooming, the male will follow after the female and begin grooming her. Sometimes its a different female. However, the key is that by all accounts, he has initiated the grooming behavior, not the female. He is not afraid of losing to her in a fight.
So why does he groom her? Well, this paper is trying to discount much of the complex social jockeying and diplomacy that researchers believe grooming to be crucial to. Diplomacy is a damn good reason to groom. I'm not at all convinced of the authors' conclusions. Maybe in some monkeys, this is the case, but saying "all primates" is pushing the boundaries... a lot.