“The only way out of this cul-de-sac seems to be to substitute for genetic atomism, which has so drastically broken down, the concept of the genetic micro-hierarchy, with its own built-in rules, that permit a great amount of variation, but only in limited directions on a limited number of themes. This really amounts to the revival of an ancient idea which goes back to Goethe-and even further to Plato. The point is worth a short historical digression-which may make it clear why the concept of homology has such great importance not only for the biologist, but also for the philosopher.”