What do people do with social networking sites?
The biggest discovery: pictures. “People just love to look at pictures,” says Piskorski. “That’s the killer app of all online social networks. Seventy percent of all actions are related to viewing pictures or viewing other people’s profiles.” […]
Piskorski has also found deep gender differences in the use of sites. The biggest usage categories are men looking at women they don’t know, followed by men looking at women they do know. Women look at other women they know. Overall, women receive two-thirds of all page views.
This is because on the savanna it was very important for men to be familiar with what strange women looked like in case of a chance encounter while out hunting for gazelle.