Why do we cum more during a gang bang?

I noticed early on when inviting friends to join us for kinky weekends. When there were 3 or more of us guys we would get off more times in a row, and get hard again faster than if we were just one on one with my Wife. On or own we would only get off a couple of times, and rarely a third later on, but with a few of us it was easy to pop off 5 times in just a couple of hours, and over a night as many as 8 times. Normally after getting off 2 or 3 times it is a chore for her to suck me really hard, and it wilts easy. With the guys there it takes a few loads before I get soft, and almost any sight, or sound of her having sex gives me a instant rock hard dick. It has been the same with my friends, that when we fuck as a group our bodies seem to act differently. We are all straight, and we never got excited by seeing each other naked. A few of the guys have had overnight visits from her, and no matter how much they need sex, or lust for her they just cum 2 or 3 times, and things are pretty tame. When we are in a group with her our dicks seem to get harder than usual, actually narrowing the shaft enough for us to notice, and her to see, so we aren't just imagining having harder and longer lasting erections..Just like in the ads for those pills, only the Rx is partying with friends in my Wife's pussy. I wonder if other guys notice the same thing when sharing their Wives with friends? I think that the woman is a major factor, because some of the guys tried the same thing with other women, but the results weren't the same for the guys. There have been a couple of girls that let us that did have the same effect on our dicks. In the past I thought it might have to do with us guys getting even with the much more multi orgasmic wives. Or getting even for past sexual rejection where us boys gang up on a girl volunteering to let us have our way. I don't think we competed with each other while fucking her, but we did often compete against her, by working as a team to keep her at as high a sexual excitement level, and for long as we could. Some of us make her moan more than others, or our own tricks to get her off, but it wasn't competition..we would joke about our over hung friends competing with an unfair advantage. The focus was getting her just fucked till she was in a daze. I've also thought it has to do with our c***dhoods, back when us little boys would read porn, and jack off while wishing there was a girl we could share, and promised each other that when we grew up we would talk our wives into it. I wonder if the marathon erections, and extra loads of cum are just some ancient breeding instincts kicking in. There are primitive societies where some designated, or volunteer older female will let herself be the pussy party for young horny boys, or single men in the tribe. My Wife has guessed that we stay so hard, and get off more times is because she is putting on a live sex show in the room, when one stops fucking her they become the audience, and if the show is good it will make us horny, and hard again. I'd like to hear some Xhamster's thoughts about all this.