American Scientist

To the Editors:

We find it difficult to take seriously the article "Rethinking the Fall of Easter Island" (September-October) in which Terry L. Hunt concludes that rats, not humans, were the main cause of the island's deforestation. We strongly believe that the archaeological and botanical data do point clearly to a scenario of human overexploitation of resources.

Dr. Hunt advocates the theory that colonists arrived relatively late, around 1200 A.D. He supports this with carbon dating of charcoal from a site called Anakena, where the base deposit is clay soil with stratified sand on top. We assert that this finding is weak: There is no "natural" stratified layer below the lowest cultural one. How do we know that there were not other sandy layers that blew or washed away before the ones Dr. Hunt investigated were deposited? In addition, if this was the site of the first settlement, why is there evidence that there were other people at two other locations at the same date?

It seems likely that the charcoal Dr. Hunt identified was from the palm tree Jubaea chilensis. This tree lives for about 2,000 years. There is only evidence that rats ate the fruits of the trees, so if the rats did not arrive until 1200, and were mostly responsible for deforestation, there should still be lots of palms left.

The date of deforestation based on pollen is not easily dismissed. The deforestation at Rano Kau was shown by two dates to be virtually complete by 1000. These dates were shown by sediment analysis to be unlikely to be contaminated by inwashed older sediment.

Dr. Hunt also denies that any overpopulation-induced internal warfare took place on Rapa Nui. There is abundant evidence that obsidian spearheads proliferated after the deforestation, and there is skeletal material that shows severe wounds.

We have not proved that there was ecological disaster, but we have shown it could well have happened and in fact probably did so.

John Flenley
Massey University
Palmerston North, New Zealand

Paul Bahn
Hull, England

Dr. Hunt responds:

Recent research from the Hawaiian Islands demonstrates that the Pacific rat, carried by Polynesian colonists, exploded into the millions and spread over the islands faster than people, consuming seeds of native plants. In the absence of fire, felling or direct human presence, rats deforested much of the Hawaiian Islands. Why would their relative impact on Rapa Nui be any less?

The earliest human presence at Anakena is about 1200 A.D. We found the oldest artifacts, charcoal and bones of introduced rats embedded in the ancient soil horizon of the lowest clay layer. Directly beneath these finds are palm root molds, proof of the layer's undisturbed state. Our carbon dates also confirm a consistent chronology of deposition from the bottom to the top of the sand dune's layers. But nothing would stop early colonists from venturing further from this site. Carbon dates contemporary (that is, typically within 50 to 100 years) with those at Anakena would merely reflect expansion across the island.

The question of the extinct palm's lifespan is relevant, but it is a unique species or even distinct genus from the native palms growing in Chile. Estimating its lifespan by comparison with different species or genera is dubious. In any case, the equable climate of Rapa Nui differs significantly from Chile's, raising doubts about inferring growth rates or lifespan.

The claim of complete deforestation by 1000 A.D. is many centuries earlier than the chronology established by multiple independent research teams reporting more than 65 radiocarbon dates. These teams detail a consistent chronology for deforestation that begins about 1250-1300 A.D., with signs of forest surviving into historic times.

Finally, some warfare may have taken place on Rapa Nui. But evidence for it remains ambiguous. We have analyzed hundreds of the artifacts Drs. Flenley and Bahn label "obsidian spearheads" (mata'a), and only a minute fraction have anything resembling a point. Studies of use-wear indicate these tools were used in cutting and scraping plant materials. Published analysis of hundreds of Rapa Nui skeletons has revealed that violent injury was minimal, with signs of any fatal assaults even more rare.

Nowhere do I suggest that rats were the sole agent of deforestation and Rapa Nui's downfall. I raise the question of their relative impact. If the extinct palms of Rapa Nui did have a great lifespan, felling and fire may have finished what rats started. Importantly, these relative impacts have not yet been adequately researched.