A few years ago, one of the world’s largest sperm banks started turning away donations from many people with a rare, harmless genetic variant. The bank’s director said at the time that there just wasn't much demand for it, though there was an exception: In Ireland, the samples were selling “like hot cakes.”

The variant that many people were avoiding was of the MC1R gene, which is strongly associated with having red hair and fair skin. The director speculated that demand was low because parents-to-be preferred characteristics similar to their own.

It's unlikely that the sperm market has changed much since then, but demand for redheads is currently high elsewhere: a recent analysis found that 11 percent of the actors who appeared in primetime TV ads were redheads. The most common estimate is that two to six percent of the U.S. population has red hair, which means redheads are more common to see on TV than on the street.*

The report, put out by the media analysis firm Upstream Analysis, monitored more than 1,700 ads that aired on ABC, CBS, Fox, and NBC between 8:00 p.m. and 11:00 p.m. on five different evenings earlier this year. Of those ads, about a third featured redheads, and more than half of the ads featuring redheads cast them as main characters.