Theories on biology/brain differences to explain racial and gender differences were used to promote stereotypes at certain times and have little or no real basis in science. Hormonal differences are fact, however. The biology theory isnt mean to give men a waiver to go ahead and cheat, it's just one of the possible differences between the genders and offers some explanation as to the motivation behind their behavior and why the reasons are often different in men and women. This is a fact - testosterone promotes certain behavior (aggression for example) and the more testosterone one has, the more extreme the behavior. It also increases sex drive. As testosterone decreases with age, so does sex drive. Thats why men and women tend to be mismatched in sex drive at certain ages. It could also be used to argue one reason why you may find more 35 year old men cheating than you will 60 year olds. Women cheat too, but often for different reasons and often are more dissatisfied in their relationships as they age than men are. None of this is set in stone of course, but it is pretty interesting when you look deeper into relationship dynamics and how they are not as clear cut as they seem. As for telling people, that's a loaded debate and many people feel differently about it. I think the most important thing to consider is hat the consequences may be for all the people involved before sharing anything. Sometimes people want to know, but sometimes they really don't - it depends on so many factors besides simple right and wrong. I might confront the cheater, but I'm not sure about rest. I don't think it's necessarily up to me to make that decision for someone else based on my own values.