Collapse_ How Societies Choose to Fail or Succeed - Jared Diamond [74]
Of those three habitable islands of Southeast Polynesia, the one capable of supporting by far the largest human population, and most abundantly endowed with natural resources important to humans, was Mangareva. It consists of a large lagoon 15 miles in diameter, sheltered by an outer reef, and containing two dozen extinct volcanic islands and a few coral atolls with a total land area of 10 square miles. The lagoon, its reefs, and the ocean outside the lagoon teem with fish and shellfish. Especially valuable among the species of shellfish is the black-lipped pearl oyster, a very large oyster of which the lagoon offered virtually inexhaustible quantities to Polynesian settlers, and which is the species used today to raise the famous black cultured pearls. In addition to the oyster itself being edible, its thick shell, up to eight inches long, was an ideal raw material that Polynesians carved into fishhooks, vegetable peelers and graters, and ornaments.
The higher islands of Mangareva’s lagoon received enough rain to have springs and intermittent streams, and were originally forested. In the narrow band of flat land around the coasts, the Polynesian colonists built their settlements. On the slopes behind the villages they grew crops such as sweet potato and yams; terraced slopes and flats below the springs were planted in taro, irrigated by spring water; and higher elevations were planted in tree crops such as breadfruit and bananas. In this way, farming and fishing and gathering of shellfish would have been able to support a human population of several thousand on Mangareva, more than 10 times the likely combined populations of Pitcairn and Henderson in ancient Polynesian times.
From a Polynesian perspective, Mangareva’s most significant drawback was its lack of high-quality stone for making adzes and other stone tools. (That’s as if the United States contained all important natural resources except high-grade iron deposits.) The coral atolls in Mangareva lagoon had no good raw stone at all, and even the volcanic islands offered only relatively coarse-grained basalt. That was adequate for building houses and garden walls, using as oven stones, and fashioning into canoe anchors and food pounders and other crude tools, but coarse-grained basalt yielded only inferior adzes.
Fortunately, that deficiency was spectacularly remedied on Pitcairn, the much smaller (2½ square miles) and steeper extinct volcanic island lying 300 miles southeast of Mangareva. Imagine the excitement when the first canoeload of Mangarevans discovered Pitcairn after several days’ travel on open ocean, landed at its only feasible beach, scrambled up the steep slopes, and came upon Down Rope Quarry, Southeast Polynesia’s sole useable lode of volcanic glass, whose flakes could serve as sharp tools for fine cutting tasks—the Polynesian equivalent of scissors and scalpels. Their excitement would have turned to ecstasy when, barely a mile farther west along the cost, they discovered the Tautama lode of fine-grained basalt, which became Southeast Polynesia’s biggest quarry for making adzes.
In other respects, Pitcairn offered much more limited opportunities than did Mangareva. It did have intermittent streams, and its forests included trees large enough to fashion into hulls of outrigger canoes. But Pitcairn’s steepness and small total area meant that the area of level plateau suitable for agriculture was very small. An equally serious drawback is that Pitcairn’s coastline lacks a reef, and the surrounding sea bottom falls off steeply, with the result that fishing and the search for shellfish are much less rewarding than on Mangareva. In particular, Pitcairn has no beds of those black-lipped pearl oysters so useful for eating and tool-making. Hence the total