Much of the concern about the commercialization of transgenic crops has focused on the movement of transgenes into populations of wild relatives via pollen flow (Brown et al., 1984; Colwell et al., 1985; Dale, 1992; Ellstrand, 1988; Ellstrand and Prentice, 1995; Goy and Duesing, 1996; Rissler and Mellon, 1993; Tiedje et al., 1989). If these engineered traits confer a selective advantage, introgression and subsequent evolution might lead to more noxious agricultural weeds (Keeler, 1988; Rissler and Mellon, 1993) and even disrupt natural ecosystem balances by enhancing the fitness of wild relatives (Ellstrand and Hoffman, 1990; Raybould and Gray, 1993; Regal, 1988; Rissler and Mellon, 1993). The genes themselves could directly confer a selective advantage, or unique epistatic interactions might arise between engineered and native genes that result in higher fitness (Keeler, 1989; Mooney and Bernardi, 1990; Rissler and Mellon, 1993). Experience with the release of conventionally bred crops could be used as a guide in predicting the likelihood of escape of genes from crops into native populations. Hybridization and introgression have been occurring between cultivated and wild species since humans began agriculture (Anderson, 1949, 1961; DeWet and Harlan, 1975; Hancock, 1992; Harlan, 1965). Harlan (1965) originally described the interaction between cultigens and wild populations of Sorghum Moench., Triticum L. (wheat), and Hordeum L. (barley). More recently, crop–wild hybridization has been documented between a broad array of crops, including wild and domesticated gourds (Cucurbita L.) (Kirkpatrick and Wilson, 1988), rice (Oryza L.) (Chu and Oka, 1970; Langevin et al., 1990), maize (Zea L.) (Doebley, 1990), oil seed rape (Brassica L.) (Jorgensen and Anderson, 1994; Palmer et al., 1983), carrot (Daucus L.) (Wijnheijmer et al., 1989), beet (Beta L.) (Boudry et al., 1993; Santoni and Berville, 1992), foxtail millet (Setaria Beauv.) (Till-Bottrand et al., 1992), pearl millet (Pennisetum Rich.) (Brunken et al., 1977), potato (Solanum L.) (Urgent, 1970), radish (Raphanus L.) (Klinger et al., 1991), raspberries (Rubus L.) (Jennings, 1988; Luby and McNichol, 1995), and wheat (Triticum L.) (Zohary, 1971, 1976). Most geneticists would agree that it is