Reverse engineering parasites (redux)

Just over a year ago, after reading Carl Zimmer's excellent book, Parasite Rex, I wrote rather whimsically:

Charles Darwin famously predicted the existence of a species of Madagascan moth (since aptly named Xanthopan morgani praedicta), based on the shape of the nectaries of a species of orchid (Angraecum sesquipedale). Might it not be possible to take a leaf out of Darwin's book and make similar deductions retrospectively? Could parasitologists not study tetrabothiids and other modern parasites, and make deductions about their extinct ancestral hosts' lifestyles?

It turns out I wasn't being so whimsical after all. A recent New Scientists article (subscribers' only link) described how scientists are studying the DNA of various species to make deductions about the history of associated species—especially humans.

Mice on the Madeira archipelago, for example, have DNA very simlar to Scandinavian mice, indicating that they were probably brought there on Viking ships, hundreds of years before the Portuguese officially discovered the islands in the Fifteenth Century. Similarly, DNA studies of rats on Pacific islands indicate that there were two separate waves of human colonisation, and the unusually high genetic diversity of voles in the Orkney Islands suggests a thriving sea trade with Europe during neolithic times. All that from a few rodents!

And yes, there were even a couple of examples of studying parasites to tell us something about their extinct hosts:

Lice and other parasites that live in close proximity to people can tell us much about our history. For instance, the human pubic louse is most closely related to the body louse of gorillas.

Genetic studies by David Reed of the University of Florida in Gainesville suggest the two diverged just 3 million years ago - much more recently than humans diverged from gorillas. If so, early humans and gorillas must have been in close contact until that time, perhaps sharing caves. "If these data are to be believed, we can put Australopithecus at the same place and the same time as gorillas," says Reed. "That would teach us a lot about gorilla biology 3 million years ago that we have scant other evidence for."

Reed has also found two distinct lineages of modern human head lice, whose genes indicate they diverged more than a million years ago. He concludes that one lineage must have evolved on a different ancestral human species, perhaps Homo erectus, and only relatively recently shifted to Homo sapiens. This suggests that modern humans must have lived side by side with at least one other human species a few tens of thousands of years ago, he says.

Reed has now begun picking lice from ancient Peruvian mummies to extract their DNA. If he can get enough, he hopes to use them to retrace the peopling of the Americas. He also hopes to look at bedbugs and other parasites. "When you have lots of parasites to look at, you'll really get a picture of the evolution of the host," he says.

What a fascinating subject! Perhaps I should be whimsical more often.


Richard Carter, FCD

Writer and photographer Richard Carter, FCD is the founder of the Friends of Charles Darwin. He lives in Hebden Bridge, West Yorkshire.WebsiteNewsletterMastodonetc…

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