Tremblay, WORLD ORCHID CONFERENCE - MIAMI Friday, September 7, 2007, PAGE 1 Re-evaluation of evolutionary processes in orchids. Didn’t Darwin explain it all? Raymond L. Tremblay 1,2 James D. Ackerman 2 1 Department of Biology, 100 carr. 908, University of Puerto Rico-Humacao, Humacao, Puerto Rico 00971-4300 2 Department of Biology, PO Box 23360, University of Puerto Rico-Rio Piedras, San Juan, Puerto Rico, 00931-3360 Early in the history of evolutionary biology, orchids had a prominent role in providing evidence for natural selection. The unusual pollination mechanisms attracted the attention of Darwin (1877) who had argued that orchids offer strong evidence for natural selection and for the advantages of cross pollination. Since then, much effort has been devoted to describing pollination mechanisms (van der Pijl & Dodson, 1966; van der Cingel, 1995). These reports contribute to Darwin’s arguments, although it is not often stated explicitly. Most agree that there is a link between orchid pollination systems and orchid diversity but the distinction between cause and effect is often not clear. Darwin (1877) produced the first treatise on orchid pollination to corroborate his thesis that sexual reproduction, and cross-pollination in particular, are fundamental to organic evolution. He thoroughly described the functional floral morphology of a number of orchids and these essays served as indirect evidence of selection for flower characteristics that enhance the probability of cross-pollination. Darwin recognised