It might be tempting to think that the human ability to alter phenotypic frequencies in populations of other species has been contingent on some knowledge of the physical nature of genomes. However, thousands of years of evolution indicate such to be untrue. The history of agricultural activity and, much more recently, the origin of dog breeds, reveal that humans understood heritability—the concept that individuals tend to share traits with their parents, and thus that much of observed variation can be explained by inherited genetic factors—long before any notion of genomes or DNA emerged.
Agriculture: The history of teosinte, the ancestor of cultivated maize (corn), offers a glimpse at phenotype alteration resulting from human preference in the pre-genome era. As early as 9,000 years ago, humans living in Mexico were able to alter teosinte to achieve better taste, yield, and overall manageability, simply through preferential breeding of high-quality cultivars as food crops. In 2018, using whole-genome data, Logan Kistler and colleagues examined both the geographic history of maize as a domesticate and the genetic changes that have occurred through its transition from wild to cultivated crop. They presented results in “Multiproxy Evidence Highlights a Complex Evolutionary Legacy of Maize in South America.” In “Rethinking the Corny History of Maize,” Brigit Katz offers a summary of the same findings that would be highly accessible for high school biology students. The National Science Foundation also provides an account of this study, “Scientists Trace Corn Ancestry from Ancient Grass to Modern Crop,” on its website.
Dog Breeds: Much more recently, but again operating without knowledge of the specific genetic mechanisms encoding specific traits, human preference has resulted in the emergence of specific dog breeds, commonly defined as genetically closed populations with distinct traits. Dogs are hypothesized to have diverged from ancestral wolves through their use of energy that emerged as increasingly stationary human populations produced “dumps’” containing food waste, inducing strong selection favoring individuals able to persist in the presence of humans, as discussed, for example, by Erik Axelsson and colleagues in “The Genomic Signature of Dog Domestication Reveals Adaptation to a Starch-Rich Diet.” The emergence of specific phenotypes we commonly associate with dog breeds—for example, the short stature of corgis and the curly hair of poodles—are inferred to have arisen much later through human preference for breeding based on certain traits. Instructors and students seeking a history of this instance of human alteration of the genetics of a species, absent any concept of the genome, will appreciate The Invention of the Modern Dog: Breed and Blood in Victorian Britain, by Michael Worboys. In recent years, the wide availability of whole-genome sequencing has enabled examination of the genomic changes that underlie the rapid emergence of conspicuous phenotypic differences among dog breeds. A study by Kathleen Morrill et al., “Ancestry-Inclusive Dog Genomics Challenges Popular Breed Stereotypes,” offers a genomic perspective on many of the phenotypes highlighted by Worboys, and The New York Times published a highly accessible summary of that study written by James Gorman, “They’re All Good Dogs, and It Has Nothing to Do with Their Breed.”
