homoplasy

Evolution sometimes arrives at the same design by entirely different roads: wings in birds and bats, for instance, are not inherited from one winged ancestor but assembled separately from ancient forelimbs. British zoologist Ray Lankester coined homoplasy in 1870 by joining Greek ὁμός, “alike,” to πλάσσω, “to mold.” The second root is a sculptor’s word, so the image is wonderfully physical: nature keeps pressing similar shapes out of different lumps of biological clay. That makes homoplasy a useful rival to homology, whose resemblance is explained by common ancestry; the two can look like twins while having different family histories. The same Greek shaping family gives us plastic, plasma, and dysplasia—words that preserve the notion of something formed, re-formed, or formed badly. Remember homoplasy as “same shape, separate workshops”: resemblance does not always mean shared origin.