Ancestry chief Margo Georgiadis touched upon one of the reasons for the company's shrinking sales in her blog post: most early adopters have already entered the category. Another possible reason is that people are becoming more concerned about the privacy implications of taking DNA tests and then sharing their genetic information.

Authorities have started using DNA testing services to solve cold cases in recent years, and interest in the method grew even further after it led to the arrest of the Golden State Killer. It's worth noting, though, that Ancestry tries to protect its customers' privacy -- it even fought a police DNA database search warrant last year and won.

Whatever the reason for the company's sales decline is, Ancestry must now think of new ways to stay in business. As Georgiadis said in her post: