"The time at which these two louse species shared a common ancestor — 3.3 million years ago — is much younger than the time that gorillas and humans last shared a common ancestor — 7 to 9 million years ago," Reed explained. "That means a host switch occurred 3.3 million years ago."
The study also suggests human head lice originated from contact with chimpanzees. Today gorillas suffer from pubic lice, but not head lice, while chimps only have the latter.
Lance Durden, associate professor of biology at Georgia Southern University, said the findings make sense.
"It has long puzzled parasitologists as to why humans are unique...in having two [kinds] of sucking lice," said Durden, referring to the head louse and the body louse. "Through some elaborate molecular phylogenetic detective work, David Reed and his research team have come up with a compelling and parsimonious answer."
Durden thinks it is "entirely feasible that humans acquired lice from gorillas by means other than sexual contact, such as nest sharing — not at the same time, hopefully — or handling gorillas while hunting or feeding on them."
Dale Clayton, a University of Utah biology professor, admits the possibilities are a real, and almost literal, head-scratcher.
Clayton said, "This paper makes one's imagination run wild, giving graphic new meaning to that '800 pound gorilla.'"
