W. Ford Doolittle (Dalhousie University)
Although molecular biology’s “central dogma” (DNA → RNA → protein; Crick 1958) emphasized the causal primacy of genes, many molecular biologists held to a naïve, organism-centered panadaptationism until the publication in 1976 of The Selfish Gene (Dawkins 1976). This widely-read book argued that a gene’s phenotypic benefit to its bearers should be seen as nothing more than a mechanism by which its own spread and maintenance are ensured, a means but not an end. The 1980 “selfish DNA” papers (Doolittle and Sapienza 1980; Orgel and Crick 1980) went what their authors considered to be one step further, pointing out that regions of DNA with the ability to replicate within genomes (what were then called “jumping genes”) need confer no phenotypic benefit. They argued that both the insertion sequences and transposons then being investigated as endogenous mutagenic agents in bacteria and repetitive DNA in eukaryotes (comprising half our own genome, for example) are best understood as such “selfish DNA” elements, with no necessary individual phenotypic expression (hence not “selfish genes”), and possibly in sum detrimental. Both “selfish DNA” papers aimed to counter claims that such elements, because they might someday prove useful, were retained “for the good of the species”. Indeed as Hickey (1982) soon pointed out, even individual elements that reduce fitness by up to 50% will spread in a sexually-reproducing lineage.
Reactions to this proposal are of four sorts, each still vigorously defended by a part of the community of practicing biologists. (1) What I will call the panadaptationist response, while now more openly gene-centric, holds that most of our genome is “functional’ (expressed in phenotypes under selection, and not “junk”). Many genomic researchers are in this camp. (2) Dawkins himself considers selfish DNA as but a minor tweaking of the genes-eye view promoted in The Selfish Gene. (3) Hierarchists, following Gould (1983), see in “selfish DNA” (as distinct from “selfish genes”) a compelling argument for multilevel selection theory. (4) Future-directed researchers imagine (as they did in the 1970s) that such elements are not selfish, but retained in anticipation of future use. There are some justifications for each of these positions: here I will try to come up with a balanced view, not simply pluralistic, but in line with “spatial tool” approach of Godfrey-Smith (2009).
