Instead of smelly T-shirts, Chaix and colleague Peter Donnelly of the University of Oxford studied previously gathered genetic data on 30 Caucasian couples from Utah and 30 Yoruba couples from Nigeria. The researchers analysed about 9000 genetic differences within the MHC genes, as well as more than 3 million differences dotted across the rest of their genomes.

This suggests that the American couples are selecting mates, in large part, based on MHC genes.

Not so for Yoruba couples, who seemed to pick mates with MHC genes no more different than would be expected for any two people picked at random from the population.
One explanation for the different findings could be diversity. Overall, Yoruba people had more differences in their MHC genes than Americans, so there could be less evolutionary pressure to find a mate with new genes.

I wouldn't let my jeans pick a mate for me. Oh sure my jeans fit me nice at first but then they start to bag and sag after I wear them for a while. No, my jeans let me down personally, I certainly wouldn't trust them to find a perfect fitting mate for me.