men adopt twice as often as women

But among men who adopt, they generally do so through adopting the children of a second spouse, or in same-sex relationships.  Women in same-sex relationships are capable of having their own children. 

Despite cultural trends toward adoption by gay men, men who have never been married are far less likely to have adopted a child than are currently or formerly married men.

And here's another interesting statistic: Men who adopt are more likely to have fathered a child than men who do not adopt. For the other sex, it's the other way around: Women who have never had a child are more likely to adopt than are those who have given birth. (full article)