Lab report

Christopher Columbus may have brought syphilis to Europe after all. EO Wilson changes his mind on group selection. Plus, climate lessons from 90m years ago—or not
February 29, 2008
Where did syphilis originate?

Blaming America for the woes of the world is an old European habit. Barely three decades after Columbus's crew returned from the new world, a Spanish doctor accused them of bringing back the new disease that was haunting Europe: syphilis. All social strata were afflicted: kings, cardinals and popes suffered from it alongside soldiers. Treatments were fierce and of limited value—inhalations of mercury vapour, for instance, had side effects as bad as the symptoms.

But during the 20th century it became fashionable to doubt the new-world origin of syphilis: perhaps the disease was a dormant European one that acquired new virulence during the Renaissance? The bacterial spirochete that causes syphilis, Treponema pallidum (subspecies pallidum), is closely related to other "treponemal" pathogens, such as the one that causes yaws in hot, humid regions like the Congo and Indonesia. Most of these diseases leave marks on the skeleton and so can be identified in human remains. They are seen widely in new-world populations dating back thousands of years, but reported cases of syphilis-like lesions in old-world remains before Columbus have been ambiguous.

Now a team of scientists in Atlanta has analysed the genetics of many different strains of treponemal bacteria to construct an evolutionary tree that not only identifies how venereal syphilis emerged but shows where its nearest genetic relatives are found. This kind of "molecular phylogenetics," which builds family trees by comparing gene sequences, has revolutionised palaeontology, and it works as well for viruses and bacteria as it does for hominids and dinosaurs. The upshot is that T pallidum subsp. pallidum is more closely related to a new-world subspecies than it is to old-world strains. So it looks as though the syphilis spirochete did indeed mutate from an American progenitor. But it's also possible that Columbus's sailors carried a non-venereal form of syphilis that mutated into the sexually transmitted disease on its arrival. Given that syphilis was reported within two years of Columbus's landing in Spain, that would have been a quick change.

EO Wilson and group selection

Having helped to bury the notion of group selection in the 1970s, Harvard biologist EO Wilson is now attempting to resurrect it. He has a tough job on his hands; most evolutionary biologists have firmly rejected this explanation for altruism. Richard Dawkins has called Wilson's new support for group selection a "weird infatuation" that is "unfortunate in a biologist who is so justly influential."

The argument is about why we are (occasionally) nice to one another, rather than battling, red in tooth and claw, for limited resources. The old view of group selection simply held that survival prospects may improve if organisms act collectively rather than individually. Human altruism, with its framework of moral and social imperatives, is murky territory for such questions, but co-operation is common enough in the wild, particularly in "eusocial" insects—with reproductive division of labour—such as ants and bees. Since the mid-20th century, such behaviour has been explained not by vague group selection but via kin selection: by helping those genetically related to us, we propagate our genes. Game theory now offers versions of altruism that don't demand kinship—co-operation of non-relatives can also be to mutual benefit—but kin selection remains the dominant explanation for eusociality.

That was the position advocated by Wilson in Sociobiology (1975). But in a forthcoming book, The Superorganism, and a recent paper, he reverses this claim and says that kin selection may not be all that important. What matters, he says, is that a population possesses genes that predispose organisms to flexible behavioural choices, permitting a switch from competitive to co-operative action in "one single leap" when circumstances make it potentially beneficial.

Wilson cites a lack of direct, quantitative evidence for kin selection, although others have disputed that criticism. In the end the devil is in the details—specifically in the mathematics of how much genetic common ground a group needs to make self-sacrifice pay—and it's not clear that either camp yet has the numbers to make an airtight case.

When crocodiles swam in the Arctic

The discovery that there were ice sheets half the size of today's Antarctic ice cap during the "super-greenhouse" climate of the Turonian stage, 93.5-89.3m years ago, seems to imply that we need not fret about polar melting today. The Turonian—with greenhouse gas levels three to ten times higher than now, ocean temperatures around 5oC warmer and crocodiles swimming in the Arctic—sounds like the IPCC's worst nightmare. But comparisons are difficult to make. More intense circulation of water in the atmosphere could have left thick glaciers on the high mountains and plateaus of Antarctica. In any event, a particular set of climatic circumstances seems to have been at play—the glaciation does not persist throughout the warm Cretaceous period. And it's important to remember that with climate, where you end up tends to depend on where you started from.