Rapa Nui (Easter Island) is a remote island in the eastern Pacific, scattered with the remains of huge monolithic statues; with a native population whose collective memory of their pre-historic culture has been virtually eliminated by the ravages of their contact with "civilization" over the last 200 years or so, it presents a mystery that many modern researchers have tried to solve. Why did they construct so many of the giant statues ? How did the inhabitants survive for hundreds of years in such a marginal ecological environment - the island has irregular rainfall, no sources of running water, and its volcanic soils are leached of important minerals, and consequently unproductive for many crops that are staple on other Polynesian islands ? Is there in fact a connection between the expenditure of the limited natural resources of the island on building the statues, the current exhausted state of the island's ecosystem, and the virtual collapse of the native population (down to 110 individuals in 1877) in historic times ?
It is this last hypothesis which has been most explicitly espoused by Jared Diamond in his 2005 book "Collapse: How societies choose to fail or succeed". Diamond describes how the reckless use of resources in the quarrying, transportation and erection of the giant statues first denuded the island of its trees, and led to the consequent erosion and mineral impoverishment of its soils; then how rivalry between different clans for the few remaining resources led to intercommunal violence, and the breakdown and final collapse of island society.
The research carried out personally by the present authors leads them to a completely different narrative. Yes, the arrival of the Polynesian colonists in about 1200 AD led to the destruction of the native palm forests. But this was not because they cut the trees down for fuel, or to create sleds to transport the statues and ramps to erect them; it was the Polynesian rats that accompanied the colonists on their canoes - who met no local predators, and whose population grew exponentially - that did the damage. Reflected in the book's title, the authors convincingly demonstrate how megalithic statues weighing many tons could be "walked" along specially prepared pathways without recourse to wooden sleds.
The assumption, that the state of the island's pristine volcanic soils prior to colonization would have made them suitable for producing the usual Polynesian crops, is shown to be mistaken; the volcanic activity that created Rapa Nui was so far in the past, that the island's soils had already been leached of minerals hundreds of thousands of years before any humans arrived on its shores. Although the disappearance of the palm forests did lead to a further deterioration in the soil, the natives were able to deal with that, as they had developed techniques of cultivation for getting the best out of this impoverished environment. All the evidence suggests that a stable population of about 4000 individuals was able to subsist on the island for about 500 years.
It was the arrival and contact with Europeans in the 18th century that led directly to the collapse of island society. Although largely undocumented, because of the sporadic nature of these arrivals, the usual ship born cargo of European diseases - smallpox, syphilis, plague, and other infections to which Europeans had over the centuries developed natural resistance - undoubtedly literally decimated the island's population. The effect of the first and brief contacts by European explorers with other island and New World populations has been well documented; it is estimated, for example, that the first contacts with North American natives resulted in the loss of up to 90% of that population even before the first permanent colony was set up on the eastern seaboard. In the case of Rapa Nui, the unintentional ravages of European diseases were further compounded by the virtual enslavement of this captive population on their own island by rapacious individuals and companies who indentured them into working on the gigantic sheep farm that the island became for about 80 years. It was only in the 1950's, when the Chilean government got rid of these exploiters, that the population had some relief and began to rebound numerically.
The authors' narrative of what happened is very clearly and convincingly presented. What is less successful is their analysis of why - why did the islanders spend so much time and effort in the construction of the gigantic statues. In general terms it is obvious that the statues played some role in Polynesian religion, probably related to ancestor worship; there is evidence of similar types of statuary - though neither so prolific nor so gigantic - on other islands. But the specific explanations they offer lack credibility. The authors have borrowed some textbook explanations from the field of evolutionary psychology, which they slot in here in an attempt to provide their answer to the mystery.
Building the statues was a form of "costly signaling"; like the peacock's tail, conspicuous consumption of resources communicates " better not mess with us, because we mean business; we'll do whatever it takes". According to the authors, this was a strategy used by the Rapanuans to avoid conflict between different groups - families, clans - on the island. Again, they convincingly demonstrate the "what" - that there is no evidence, either in weaponry or in skeletal remains - of large scale intercommunal violence; but their "why" leaves much to be desired.
An additional explanation offered is that "cultural elaboration" - which in this case means building bigger and bigger statues - diverts resources that might otherwise be used in having a greater number of offspring, during periods when the island's marginal and unreliable agriculture might not be able to support a growing population. Although they dutifully explain that individuals do not have to have a deliberate awareness of these strategies for them to have these effects, this explanation also lacks credibility. My understanding of the so-called "bet-hedging" reproductive strategy is that it applies to individuals, not to groups, and that it is essentially a biological response to variations in resources that increases the overall fitness of the individual. Arguing that it can also be a cultural response, which increases the fitness of a group, seems somewhat problematic.
Despite these drawbacks, the book is very worthwhile. Unlike Jared Diamond's a priori thesis, the authors' is based on very thorough empirical research. It certainly unravels at least part of the story of Easter Island even if it does not solve the whole mystery; but, absent the discovery of some Polynesian Rosetta Stone, that may remain a mystery for some time.