Throughout my life I've heard that men have a higher average of (heterosexual) partners. I've never really thought about it and just accepted it as truth, but after giving it some thought I do not see how it's possible to have any significant difference, now or ever.

Lets use small numbers to illustrate. Say you have 10 couples. 2 of the men sleep with all the ladies and 8 only sleep with their one. The men and women both end up with a 28 sexual partners or a 2.8 partner average.

Because of population differences, birth, and death the numbers will never be exactly even like the example? But they will always be "close enough" to say that men and women have the same average number of sexual partners.

In my example there would be a noticeable difference in the median number of sexual partners, with the women's median being the same as their average and men's median being much lower ( I suspect this is true in real life as well).