Why Not Friend Match?

Bryan Caplan recently pointed out to a few of us that while many dating web sites offer to help you find matching romantic mates, there are far fewer friend finding helpers.  We tend to collect friends informally, by liking the people we meet for other reasons, and especially friends of friends. But for mating purposes we are more willing to choose folks based on a list of their interests, an intro paragraph, a picture, etc.  Why the difference?

The explanation that occurs to me is:  We need mates more for their simple surface features, while we need friends more to serve as social allies in our existing social network.  Since we need friends in substantial part to serve as allies in our social world, supporting us against opposing coalitions, it makes sense to draw our friends from our existing social world.  And since we need mates more for their personal quality, e.g., good genes, youth, wealth, smarts, mood, etc., it makes sense to pick them more via such features.

Now if the personal qualities we sought in mates were difficult to discern and describe, dating web sites wouldn’t be very useful; we’d more want to rely on personal experience and on folks who know us well recommending others who they thought would match us well.  And we do like to think that our mate (and friend) preferences are complex and subtle, not easily captured in a few match website entries. But in fact, I suspect, the truth is that we are more mating simpletons than we care to admit; we can actually find much of what we need to know about potential mates in a few simple items, especially the picture.

Added 1p: Many suggest the explanation is that friends are worth much less than mates because we can have many friends.  But I value top friends similarly to top mates – am I unusual?

Added 15Aug: Al Roth weighs in.

Added 12Nov 2013: Now there is at least one friend match site: bigfriendo