Genetic variation in some parts of the world is much less than it was 1000 years ago due to the Black Plague and other contagious diseases.

From the article:

"Ancient DNA tends to elevate diversity, because the way DNA is damaged
over time tends to mimic the mutations that lead to diversity," he
said.

The way that DNA degrades after a person's death can make ancient DNA
appear to have more variation than modern DNA, he explained.

Well, that would explain the British royal family. Except for William. He's OK.

Razsk, I'm sure that's true also, but I'm assuming there must have been a discernible difference in the DNA of pre-plague Englanders and those after for it to have been recorded this way. The report said there were multiple controls done to ensure the results were not due to post-mortem changes or DNA contamination. It killed about half the population. (Strike one against genetic variation.)The fact that the plague affected some whole lines of families and others weren't affected makes perfect sense as to why the gene-pool narrowed, (Strike two) but there may be some degradation of DNA here, as well. It could feasibly be a combination of both.