A major empirical achievement of the sociology of science is the evidence of the ubiquity of simultaneous invention. If many scientists are trying variations on the same corpus of current scientific knowledge, and if their trials are being edited by the same stable external reality, then the selected variants are apt to be similar, the same discovery encountered independently by numerous workers. This process is no more mysterious than that all of a set of blind rats, each starting with quite different patterns of initial responses, learn the same maze pattern, under the maze's common editorship of the varied response repertoires. Their learning is actually their independent invention or discovery of the same response pattern.
Sociologists could have just checked with the Patent & Trademark Office, where multiple simultaneous inventions have been a way of life since way before Darwin.
But is Campbell right here about there being no difference between blind rats in a maze and inventors tackling the same problem? Maybe. But doesn't the "pattern of initial responses" matter in terms of how fast a particular rat runs the maze? And if some rats run mazes faster than others, then don't we want to reward those rats?
In fact, the "initial pattern of responses" of an experienced inventor may take on the characteristics we more typically associate with artistic or mathematical genius after a lifetime of inventing. But who will devote a lifetime to inventing without inventions being protectible as property? Rats in a maze indeed.