For some reason - at least in my experience and in my observations - women seem to be more open to the idea of 'sharing' than guys are. Whether this is conditioning or something genetic or both, I don't know, but it is something I've observed.
Whether or not that comes in the form of being the willing mono partner to a poly man or being the poly one in the group seems to depend more on the relationship dyamics than the person, oddly enough. Think about that for a while before flaming me for it - it's a pattern I've observed repeatedly. Women seem more comfortable with sharing a relationship in general - be that sharing their parter with others, or sharing themselves with other partners, or both.
I have often wondered if it relates to the gay/straight/bi debate. FAR more women are bisexual than men, at least everywhere I've EVER lived. Not counting the "party bi" chicks. But guys seem to settle in as gay or straight very quickly, and really bisexual or even bi curious males seem far less common. Women on the other hand - I know two or three in my whole life that count as "truly straight" - the number is down from 10 or 12 as more and more of them finally admit tht under the right circumstances or with the right woman, they'd willingly and even excitedly try it.
As for men and poly - that's also a different can of worms, and a complex one, and I'll post about it later 'cuz I'm distracted right now, lol.