The Y ™s genealogical chart is vast and while the finer branches are just now being discovered, the major limbs already tell the stories of Y chromosome variants that arose tens of thousands of years ago in different parts of the world. The scientists looked for evidence of chromosomes containing this particular deletion, and found this type of Y amidst others on 14 different branches of the chromosome ™s family tree, including one where every single Y chromosome had the deletion. The scientists traced the geographical origin of this particular branch to Japan and discovered that 30 percent of all Japanese men have this chromosomal type.

On the one hand, we have evidence that this deletion is being weeded out, somewhat slowly, but being weeded out nonetheless, because on average, the men with this deletion are at greater risk of having sperm production problems, Rozen observes. But on the other hand, we have a case where a branch with this particular deletion has gone to a very high frequency in one population. It ™s contradictory and we don ™t know how to resolve the contradiction.

The scientists hope they won ™t be stumped for long. The next step of their work will involve further analysis of this new deletion to unlock more secrets of this family tree.