Men who think that size really matters should probably not think too hard about the Y chromosome. This bundle of genes is the ultimate determinant of manliness, and it happens to be a degenerate runt.  Over a few hundred million years, it has shrunk considerably, jettisoning around 97% of its original genes. Where it was once a large library of genes, now it’s more a struggling independent bookstore. This loss of information defined the youth of the Y chromosome but nowadays, things are different. Renovation is the order of the day.

This drastic remodelling contradicts the current view of Y evolution, which suggests that the chromosome has stagnated. It has lost so many of its genes that some scientists thought it