Toward Confirmation of the Hypotheses

Abstract

This book is about two main hypotheses, and, although they are related, it is important to distinguish between them. The first is the concept that embryonic and larval forms have occasionally been transferred between distinct evolutionary lineages, and the second is the suggestion that such transfers have resulted from cross-fertilizations. Distinction should be made between the series of postulated historical events, which is the subject of the first hypothesis, and the mechanism that, it is suggested, was responsible for these events and forms the subject of the second. As I have pointed out elsewhere (Williamson, 1988a), it is generally accepted that dinosaurs are extinct (a postulated historical event) although there is no general acceptance of the mechanism that brought about their extinction. (Birds probably evolved from dinosaurian ancestors, but these ancestors are as extinct as the rest of the dinosaurs.) I am not trying to draw comparisons between the strength of the evidence for larval transfer and that for extinct dinosaurs. I merely use the extinction of dinosaurs as a familiar biological example in which cause and effect are seldom confused.

Distinction between theories (1) that larval transfers have taken place, (2) that transfers have resulted from cross-fertilizations—Suggested tests of first theory from fossils, electrophoresis of enzymes, DNA annealing and immunotaxonomy—Suggested tests of second theory from chromosomes, nuclear DNA, ribosomal RNA and experimental cross-fertilizations—Results of two experimental cross-fertilizations, one in literature, one in progress