ABSTRACT
Darwinists have recognized that resemblances caused by a basic plan are preferable to common evolutionary origin, so that the concept of homology has come to refer to commonality of ancestry. The selective advantage, or biological function, of leaf-turning behavior is yet more difficult to assess, because finding and following variant individuals without the behavior is nearly impossible under natural conditions. Three bits of information can then be communicated with a statement such as “the character pair shows common ancestry and appearance but not common function.” A criterion of efficiency, derived from the mathematical theory of information, has been presented and difficulties attendant to its application have been discussed. The difference between the camps is that the structurists want to omit mention of phylogeny by sticking to Owne’s pre-Darwinian criteria for “homolog,” whereas the phylogenists want to utilize the same comparison in an evolutionary setting.
