That’s how one complex adaptation can jump-start a new complex adaptation. Complexity can also accrete incrementally, starting from a single mutation. First comes some gene A which is simple, but at least a little useful on its own, so that A increases to universality in the gene pool. Now along comes gene B, which is only useful in the presence of A, but A is reliably present in the gene pool, so there’s a reliable selection pressure in favor of B. Now a modified version of A* arises, which depends on B, but doesn’t break B’s dependency on A∕A*. Then along comes C, which depends on A* and B,
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