(a) Summary tree of orders forming a soft polytomy at the base of the arachnids, based on References 8, 35, 58, 74, 75, and 78. Dotted lines reflect unstable relationships.

Genetic testing of people who died in Kyrgyzstan eight years before plague reached Europe reveals an ancient strain of the bacterium Yersinia pestis. In the foothills of the Tian Shan mountains in ...