THE JOURNAL OF EXPERIMENTAL ZOOLOGY 281:357–358 (1998) Introduction VALENTINE A. LANCE1* AND MARK H. BOGART2 Center for Reproduction of Endangered Species, San Diego, California 92112 2 Mid-Pacific Genetics, Inc., Honolulu, Hawaii 96814 1 “Nothing in biology makes sense except in the light of evolution.” This statement was the title of a lecture presented to an audience of biology teachers in 1972, urging a vigorous stand against the resurgent creationist movement (Dobzhansky, ’73)—a movement that unfortunately is still very much with us today. Dobzhansky gave a number of wellknown examples in biology for which the only logical explanation was evolution. As biologists, we too try to understand our research findings using the logic of evolution. In 1990 the gene on the human and mouse Y chromosome that determines sex (SRY in humans, Sry in mice) was discovered (Gubbay et al., ’90; Sinclair et al., ’90), and this gene is particularly difficult to understand in evolutionary terms. It occurs only in placental mammals, exhibits an extraordinary amount of sequence variability among species (Whitfield et al., ’93), and may not even be required for sex determination, as some mammals undergo normal sex differentiation without any trace of SRY sequence in their genome (Just et al., ’95). Despite an intense research effort in the seven years since its discovery, its mode of action is still unknown. There is no evidence for an SRY gene in egg-laying vertebrates, and SRY clearly evolved from an SRY-like precursor (Graves and Foster, ’95; Graves, ’98), but why and how are still a mystery. Is the evolution of a placenta and viviparity linked to the evolution of SRY? Why can some mammals undergo sex differentiation in the absence of SRY? What does SRY do? This special issue of The Journal of Experimental Zoology is a selection of papers from the First International Symposium on the Biology of Vertebrate Sex Determination held in Honolulu, Hawaii, April 7–11, 1997. This meeting was organized to address the process of sex determination from an evolutionary standpoint. During the past five years or so, interest in this area of research has increased, as reflected in the increased number of international meetings on the topic (Marshall © 1998 WILEY-LISS, INC. Graves, ’93; Short and Balaban, ’94). There have been meetings restricted to sex determination in reptiles (Lance, ’94) and others covering sex determination in some invertebrates and vertebrates (Keystone Symposium, 1995). There has been little interest in amphibians, however, and it has been more than 20 years since a meeting on sex determination in fishes has been held (Reinboth, ’70). No recent meeting has included all the vertebrate classes. This symposium was a small (a total of 62 papers) but extraordinarily successful meeting with registrants from 17 different countries in attendance. There were five plenary lectures and a series of invited papers that covered sex determination from fish to humans. What was soon apparent was that many of the genes now known to be involved in gonadal development in mammals (with the exception of SRY) are also involved in gonadal development in egg-laying vertebrates (Lance, ’97). What was also clear was that the mechanism of sex determination in placental mammals may be quite different from that in the egg-laying vertebrates. It is refreshing for a comparative endocrinologist to see the renewed interest in evolution among cell and molecular biologists. Papers with such titles as “Evolution of gene X: Comparison of mouse and human” are now no longer considered to address evolution. Today we see papers that look at genes from invertebrates to humans in a truly evolutionary manner (Kappen and Ruddle, ’93; Carroll, ’95). It is equally as refreshing to see the study of sex determination in vertebrates couched in an evolutionary context, as presented at this meeting. Perhaps soon we will make sense of the fascinating process of sex determination in the “light of evolution.” Grant sponsors: The March of Dimes Foundation; The Zoological Society of San Diego; The Queens Medical Center, Honolulu, CIBAGEIGY, Basel, Switzerland; Mid-Pacific Genetics, Inc., Honolulu; and Eli Lilly, Indianapolis, Indiana. *Correspondence to: Valentine A. Lance, Center for Reproduction of Endangered Species, P.O. Box 551, San Diego, CA 92112. Received 17 February 1998; Accepted 18 February 1998 358 V.A. LANCE AND M.H. BOGART ACKNOWLEDGMENTS The organizers especially thank Lisa Morici and Robbie Berkstresser for secretarial and organizational help. LITERATURE CITED Dobzhansky, T. (1973) Nothing in biology makes sense except in the light of evolution. Am. Biol. Teach., 35:125–129. Carroll, S.B. (1995) Homeotic genes and the evolution of arthropods and chordates. Nature, 376:479–485. Graves, J.A.M., and J.W. Foster (1994) Evolution of mammalian sex chromosomes and sex determining genes. Int. Rev. Cytol., 154:191–259. Gubbay, J., J. Collignon, P. Koopman, B. Capel, A. Economou, A. Munsterberg, N. Vivian, P.N. Goodfellow, and R. LovellBadge (1990) A gene mapping to the sex-determining region of the mouse Y-chromosome is a member of a novel family of embryonically expressed genes. Nature, 346:245–250. Just, W., W. Rau, W. Vogel, M. Akhverdian, K. Fredga, J.A.M. Graves, and E. Lyapunova (1995) Absence of Sry in species of the vole Elobius. Nature Genet., 11:117–118. Kappen, C., and F.H. Ruddle (1993) Evolution of a regulatory gene family: HOM/HOX genes. Curr. Opin. Genet. Dev., 3:931–938. Lance, V.A. (1994) Introduction: Environmental sex determination in reptiles: Patterns and processes. J. Exp. Zool., 270:1–2. Lance, V.A. (1997) Sex determination in reptiles: An update. Am. Zool., 37:504–513. Reinboth, R. (1970) Intersexuality in fishes. Mem. Soc. Endocrinol., 18:516–543. Short, R.V. and E. Balaban, eds. (1994) The Difference Between the Sexes. Cambridge University Press, Cambridge. Sinclair, A.H., P. Berta, M.S. Palmer, J.R. Hawkins, B.L. Griffiths, M.J. Smith, J.W. Foster, A.M. Frischauf, R. Lovell-Badge, and P.N. Goodfellow (1990) A gene from the human sex-determining region encodes a protein with homology to a conserved DNA-binding motif. Nature (Lond.), 346:240–244. Whitfield, L.S., R. Lovell-Badge, and P.N. Goodfellow (1993) Rapid sequence evolution of the mammalian sex-determining gene SRY. Nature, 364:713–715.