The planet Kinsoro, in a star system on the edge of the Bracket nebula, had a strange climate marked by long alternating periods of wonderful and terrible climates. Each phase of the climatic cycle (whose origins were mysterious) lasted approximately 120 Earth years. The strange climate had given rise to an equally strange ecology early in the planet’s history: The more complex species were all polymorphic, typically existing in two forms adapted to the two regimes (and occasionally as many as six, adapted to minor climate epicycles). The dominant species, the Kinsorans, existed in two adult forms, which Kinsoran biologists called the S-type and the I-type. The two types had clear but minor physical differences, but more importantly, dramatically different behavioral and cognitive dispositions. While both types could survive both climates, the S-type flourished in the wonderful half-cycles, while the I-types flourished during the terrible half-cycles.
Kinsoran biologists calculated that the environmental variation ought to lead to a slow 240-year limit cycle in the S/I ratio between 80:20 and 20:80, but in practice the ratio showed much more extreme variation: swinging between 99:1 to 1:99. The reason was not hard to discover; during each half-cycle, the dominant type would violent repress and slaughter the subordinate type to near-extinction.
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