Parasites are thought to diversify with their host species, but the theory has rarely been tested. Kevin Johnson at the University of Illinois and his colleagues sequenced the genomes of 46 species of lice that parasitise birds or mammals, and two non-parasitic bark lice, and constructed an evolutionary tree. They estimated that parasitic lice first emerged between 90 and 100 million years ago, but didn’t begin to diversify until 66 million years ago – around the time of the dinosaurs’ extinction.

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