Sexual selection in hermaphrodites: where did our ideas come from?

Interpretations of hermaphroditism have been influenced by the old idea that organisms can be arranged in a series from lower to higher, with human beings at the top, leading toward the angels and God (the scala naturae). The consequent notion that hermaphroditism is a primitive condition is still with us. Such issues need to be addressed empirically, in a phylogenetic context. Darwin's theory of sexual selection provided the key to understanding sex switches, but it was not invoked until 1969 when it was conjoined with ideas about relative size influenced by the work of Bernhard Rensch. In principle the problem could have been solved a century earlier, and genetics was misleading rather than helpful. What really helped was an appreciation of Darwin's nonteleological way of thinking.