Caution, overload: The troubled past of genetic load

PREOCCUPATION with “genetic load” seems to be on the rise again, fueled by the new opportunities that full human genome sequencing provides (e.g., Simons et al. 2014; Lynch 2016a; Stewart et al. 2017; Verduijn et al. 2017). The fear of the ultimately devastating effect that the accumulation of deleterious mutations would have on the future of humanity was articulated nearly 70 years ago by Hermann J. Muller in a 1950 seminal paper, Our Load of Mutations. Four decades later, in his 50 Years of Genetic Load: An Odyssey, Bruce Wallace (1991) recounted how the concept of genetic load had evolved in the twentieth century, and traced its origins further back to J. B. S. Haldane’s 1937, The Effect of Variation on Fitness. This paper by Haldane, wrote Wallace, “marks the origin of the genetic load concept.” Both points of departure, however—Muller (1950) as well as Haldane (1937)—furnish a history of the concept “genetic load” that utterly ignores its eugenic roots, manifested most clearly in the concept’s German predecessor: erbliche Belastung. To properly assess the meaning and complexities of the concept of genetic load, as well as its potential social implications, it is vital that we acknowledge these scientific and cultural origins, some of whose trajectories are still pertinent today.