After looking at the list of leaders of nations that were women, its hard not to think this is true. Sure there are exceptions (Mrs. May in the UK comes to mind), but overall, there were some very effective women on this list. Its worth a look. From the trailblazers like Indira Gandhi, and Golda Meir to the women who rule today. Another striking detail was the number of women who served as caretaker heads of state.
Hard to run a double blind study on this. In any case, I would guess that capabilities and performances overlap between males and females.
Say, mammalian sexual reproduction requires different chromosomes between the sexes. Are we sure that men and women are the same species or are two closely related species in a symbiotic relationship?