Image: Clare Flemming COLLECTING TUSKS. MacPhee lugs a mammoth tusk he found in a creek bed on Wrangel Island, north of Siberia.

SA: So, in your opinion, even if the first Americans were highly skilled hunters, could their population sizes and the population sizes of these animals have been such that overkill would even be plausible?

RM: The answer is no, by any scenario. I don¿t care how early you want people to get into the New World, there¿s absolutely no evidence of a positive sort that they were there in huge numbers. In fact, it has to be the opposite, whereas the animals, in some cases, had distributions that were continent wide. Some of the ground sloths, for example, are known from as far south as Mexico and from as far north as the Yukon. The notion that people in whatever numbers and with whatever intent could have come in and slaughtered enough sloths in every possible habitat where they lived in numbers sufficient to cause their extinction¿this is unbelievable to me.

Archaeologists say in looking at Clovis sites and similar ones in Monte Verde in South America that there¿s nothing at these sites that suggests anything other than band-level organization. What we know from modern ethnographic examples is that the individual family groups that compose a band tend to cooperate only for very specific objectives. As soon as that economic objective is met, it¿s over¿they don¿t keep a high level of organization once there¿s no need. So if we¿re talking about Clovis people being at essentially the band level economically, how can it be that they would stay together for common purposes at the level necessary to cause these extinctions? You¿d have to be killing things all the time, and you¿d have to be doing it for some purpose, even if the purpose was just to kill. And it¿s just unimaginable to me that the people concerned would be interested merely in killing, especially large, dangerous animals like mammoths. You take out the one or two a year that you need, and then you go off gathering roots and tubers, which is in fact how most of these outfits keep going¿it¿s not by direct hunting. You can¿t look at the first Americans as being basically people like us who didn¿t wear suits¿that their objectives would be similar, that their worldview would be similar, and all the rest of it. In fact, most assuredly they were not, if ethnographic comparisons mean anything.

SA: Enter hyperdisease.

RM: Hyperdisease has its own extremely large explanatory defects. But the notions that you can¿t get cross-species infections, or that you can¿t get huge mortalities that might lead to extinction, are not among them. In fact, there are such examples. There is a group of birds native to Hawaii called the Hawaiian honeycreepers, several species of which have gone extinct probably within the last 100 years. Whereas when Europeans were first going to Hawaii at the beginning of the 19th century, honeycreepers were known at lower elevations. Nowadays, however, the surviving populations all live at high altitude. Why should this be? Researchers figured out in the 1960s that the distribution of the surviving birds is mediated by how far up in altitude avian malaria-carrying mosquitoes can go. The mosquitoes that we¿re talking about, representing a species of Culex, were introduced from tropical North America probably in the 1850s or 1860s. And in all probability what happened was that some boat going from San Francisco or Mexico over to Honolulu had freshwater in its bilge and female mosquitoes were laying eggs there. Some of the larvae survived after the bilge was dumped, they started biting the native birds, and some of the larvae had the [malaria-causing] protozoan Plasmodium in their system, so they inoculated the birds, and the birds died in droves. To repeat the experiment and thereby document what happened, what the researchers did was take some of these individuals from surviving populations up on the high mountains, bring them down to the lab at sea level, and then introduce them to Culex individuals that were known to be carrying avian malaria. The exposed birds died without exception¿100 percent mortality.

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