Guest author Amir Teicher discusses how the concept of “genetic load” traces its roots back to eugenic thinking, as described in his recent Perspectives article in GENETICS.

The possibilities opened up by advances in genome sequencing have recently spurred discussions on the burden, or cost, that mutations pose to organisms and populations. Does the relaxation of selection pressure, especially among humans in modern, industrial society, mean deleterious mutations will keep on cropping up and accumulating, ultimately leading to a catastrophic genetic price that later generations would be forced to pay?

Hermann J Muller—the Nobel laureate who discovered in 1927 that radiation causes mutation—thought so. It was he who introduced the term “genetic load”, in a 1950 paper called Our Load of Mutations. Radiation anxiety following World War II seemed to justify Muller’s concern over the accumulation of mutations in human populations. His ideas were eagerly taken up by geneticists during the following three decades. In reality, however, Muller’s concept did not originate solely from his concerns over the hazards of nuclear energy or the overuse of X-rays in medicine, but had much earlier roots in eugenic thinking.

In fact, the term “genetic load” itself was far from novel. In Germany, discussions on erbliche Belastung—literally, hereditary burden, or load—were common from the late nineteenth century onwards, especially among psychiatrists (Muller spoke fluent German and was acquainted with these discussions). In most cases, the term was used to designate the pathological endowment that the mentally ill transfer to their family members. Practically speaking, anyone with a mentally ill relative was considered, to some degree, ‘hereditarily burdened’.

During the 1920s, studies on these alleged hereditary burdens became statistically more sophisticated, absorbing Mendelian concepts and providing robust proof on the heritability of mental diseases and neurological disorders. After the Nazis seized power, talk of the burden that the mentally ill posed was omnipresent and led to the mass sterilization, and later annihilation, of people with mental and physical disabilities. The ambiguity of the term was found useful: it conveyed simultaneously a hereditary burden, a social, and an economic one.

Muller was a vehement anti-Nazi, but he was also a devoted eugenicist. Using the fear of radiation as a pretext, he introduced into population genetics a concept whose roots lay in eugenic thinking, and whose implications were eugenic, too. This fact was recognized by some of his colleagues (and opponents) at the time. Some not only argued against the mathematical implications of the concept, but also advocated changing the terminology itself, which they saw as impregnated with eugenic connotations.

As recent works on genetic load indicate, not only did the term remain in force; some of its own related assumptions are still with us, too. Discussion of genetic load can easily lead to suggestions for top-down management of reproduction, in the name of future generations, wherein those with lesser genetic value would be politely requested to limit their procreation, for the common good. Awareness of the history of this scientific concept therefore might not be a mere curiosity, but an important reminder for the range of meanings that accompany it – indeed, for the kind of load that it, too, carries along.

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