Online dating sites give us an intriguing look at how we meet people now

In the past 20 years, online dating has become the preferred way to find a mate in much of the Western world. In 2000, a few hundred thousand people used the internet to hunt for romantic attachments. Today that figure is well over 300 million.

This change has significant implications for anthropologists who study human mating patterns. In the past, this research has suffered badly from the lack of good data in sizable quantities. But all that has changed with the data from dating websites.

All of a sudden, anthropologists can see who is messaging whom and who replies. That is beginning to provide unprecedented insight into the nature of human mate selection. So what does it show?

This map of the US shows how online daters tend to only message people who live in roughly the same region—which makes sense.

Today we get an answer thanks to Elizabeth Bruch and Mark Newman at the University of Michigan, who have studied the behavior of some 4 million active users from a popular (but unnamed) online dating site. Their analysis reveals much that is expected—men tend to initiate contact, for example. But it also shows curious, unexplained differences in how people date across America.

The researchers collected messages sent between heterosexual individuals during January 2014. They then studied the network that these messages created. In this network, users are nodes, and a link exists between two of them if a message has been sent between them. In particular, the researchers focused on reciprocated messages. “Reciprocal interactions we take to be a signal of a baseline level of mutual interest between potential dating-partners messages,” say Bruch and Newman.

The researchers began their study by looking for communities within this network. These are areas of the network that have a higher density of links than would be expected to occur randomly.

That clearly showed how the dating market is geographically stratified. The communities in the network correspond to regions such as New England, the East Coast, the South, Northern and Southern California, and so on.