Major islands of the world

Story hook

1869. A 26-year-old British naturalist named Alfred Russel Wallace is in the Malay Archipelago, finishing the 8-year voyage that will produce his masterwork The Malay Archipelago. He has already, in 1858, written to Charles Darwin from a fever-bed in Ternate outlining his independent theory of natural selection.

Wallace notices something nobody before him has — an invisible line runs through the islands of Indonesia. West of it (Borneo, Sumatra, Java, Bali) you find Asian fauna — tigers, elephants, rhinos, monkeys. East of it (Sulawesi, Lombok, the Moluccas, New Guinea, Australia) you find Australian fauna — marsupials, cockatoos, no placental mammals. The line passes through the narrow Lombok Strait, just 35 km wide — yet the fauna change completely. He calls it the Wallace Line. It marks where the Sahul Shelf (Australian Plate) meets the Sunda Shelf (Asian Plate) — two ancient continental fragments that never connected even at lowest Ice Age sea levels.

That observation, made by walking and noticing, became the foundation of biogeography. Islands are not just bits of land in water. They are isolated evolutionary experiments, tectonic billboards, and — in the 21st century — the most vulnerable territories of the climate-change age.

Why this matters for UPSC

Syllabus location: GS-I — World Physical Geography (major islands). Asked 2-3 times in Prelims over the last decade — island-country pairings, island chains and strategic significance. Mains uses islands as case studies for biodiversity, geopolitics (Diego Garcia, South China Sea), climate refugees (Tuvalu, Maldives). Solid map zone.