“The Point of Nipple Erection 2: The Effect of Nipple Erection on Intended and Expected Altruism”, 2021 (; backlinks; similar):
[part 1] This study shows that men are more likely to do things for sexualized women, in this case, women with nipple erection. Women, however, would prefer to avoid women with nipple erection socially. This can have implications for sex and dating strategies, and female interaction in social settings.
Previous research has shown that men perceive nipple erection as signaling more sexually receptive states. This study intended to determine if this perception changed male hypothetical behavior. For example, would men be more willing to assist women with nipple erection as opposed to those without?
Participants were asked to rate pictures of women with and without salient nipple erection (faces were obscured to prevent discerning emotional states).
Men perceived women with nipple erection as more deserving of altruism, especially if that altruism involved greater interaction with the woman, and they expected these same women to behave more altruistically toward them. They also believed the women with erect nipples should be included in their social groups. Women, on the other hand, did not perceive them as deserving of greater altruistic behaviors, did not expect greater altruistic behaviors from them, and did not want to include them into their social groups.