Cold War in Eastern Island

Why did the inhabitants of Easter Island (Rapa Nui) spend enormous human resources carving, transporting and erecting the legendary moai (giant statues carved from volcanic rock) that are such a distinctive feature of the island’s man-made landscape? Over 800 statues have been identified, with an average height of around 4 metres and an average weight of around 10 tons; the largest weighs 87 tons, and it appears that the average size of moai erected increased substantially over time. Although nearly half of the statues identified still lie in the quarry at Rano Raraku where they were carved, those that were erected (probably between 1200 and 1600 CE) required the building of platforms (ahu) that weighed around 20 times as much as the statues themselves. It has been estimated that during the 300 or so years of peak construction activity, the work of constructing the statues and their platforms “added about 25 per cent to the food requirements of Easter’s population” (Diamond, 2005, p. 102).

Little attention has been given to why the moai were built. Diamond (2005) writes that “the clans competed peacefully by seeking to outdo each other in building platforms and statues, but eventually their competition took the form of ferocious fighting” (p. 94). He adds “I cannot resist the thought that they were produced as a show of one-upmanship” (p. 98), but does not explain why the one-upmanship took such a costly and elaborate form.

The theory of costly signaling suggests an answer to all of these questions: the cost of this status competition was both justified and limited by the need for the islanders to signal their military strength, and the purpose of signaling military strength was to be able to divide valuable resources among groups without fighting for them, which would have been even more costly.

The idea of costly signaling has been familiar to economists since the work of Spence (1974), and to biologists since the work of Zahavi (1975). It explains the cost of certain activities (e.g., having a long, cumbersome tail, if you are a peacock) as being part of their point. The cost of the activities is what makes them credible signals of the possession of certain characteristics (being resistant to parasites, in the case of peacocks). The cost of a signal is the cost that an individual truly possessing the characteristic has to pay in order just to dissuade a rival who does not possess the characteristic from falsely claiming to do so. For this to be possible the signal has to be some activity that the true possessor of the characteristic can afford to undertake more easily than a rival who does not possess it. In Easter Island, the characteristic was strength: which increases your possibility of winning a military confrontation, and also diminishes the cost of building moai.

References:

Diamond, Jared (2005):  Collapse: How Societies Choose to Fail or Survive, London: Allen Lane.

Spence, Michael (1974):  Market Signaling: Informational Transfer in Hiring and Related Screening Processes, Cambridge, MA: Harvard University Press.

Zahavi, Amotz (1975) “Mate Sleection: A Selection for a Handicap,” Journal of Theoretical Biology, 53: 205-214.