Implications of New Research on Horizontal Gene Transfer
Humans have been modifying the genomes of plants and animals for millennia with techniques ranging from cross-breeding to irradiation. But these methods and their products do not seem to raise the same level of public outcry as transgenesis, which is the ability to directly move genes between organisms without sexual reproduction. An explanation for the unequal opposition to such genetically modified organisms (GMOs) is the idea that transgenesis is more “unnatural” (Pivetti 2007). Splicing genes from a flounder into a tomato (Hightower et al. 1991) or from a bacterium into rice (Tang et al. 2015) is seen as posing unspecified risks beyond those of conventional breeding because, while plant and even some animal hybrids exist in nature (Zhang et al. 2014), cross-kingdom hybrids do not. Surveys suggest the more “dissimilar” the organisms whose genes are being shared (Dragojlovic and Einsiedel 2013), and the more artificial the methods used to move the genes (Kronberger et al. 2014), the more unnatural the food will appear and the more reluctant consumers will be to eat it, especially if one of the organisms is an animal (Frewer et al. 2013).
Some of this fear is supported by concepts taught in secondary school– and college-level biology textbooks (Zeigler 2011; Alberts et al. 2013). Among animals, cross-species breed ing is taught to generally fail or produce infertile hybrids such as mules; among plants, it only works for closely related organisms (Morris et al. 2013). Horizontal gene transfer (HGT), or the natural movement of genes from one organism to another without sexual reproduction (sound familiar?), is taught as being “rare among eukaryotes [animals, plants, fungi, and protists] but common among bacteria” (Alberts et al. 2013). When HGT between domains of life is taught, it is often limited to the ancient, onetime transfers of mitochondrial and chloroplast genes from bacteria to eukaryotes (Reece et al. 2012; Morris et al. 2013). Even when HGT among eukaryotes is noted, the emphasis is still on unicellular organisms (Fitzpatrick 2012). The assumption is that the evolution of separate, distinct sex cells in multicellular life posed unambiguous restrictions on HGT (Doolittle 2000). Both laypersons and many scientists thus believe that the sharing of genes over large phylogenetic distances, especially between animals, is rare or even impossible and that HGT is purely in the domain of unicellular life. Since genetic engineering is artificial HGT between two organisms of seemingly any evolutionary distance, it is accordingly seen as an unnatural violation of these laws: the creation of something that could not arise naturally even in theory.