Eugenics and the Modern Synthesis, Part I

For the Legacies of Eugenics series, Jessica Riskin explores how the neo-Darwinian idea of ‘modern synthesis’ tried to fuse eugenics, genetics, and evolution as three aspects of the same science.

By Jessica RiskinMarch 23, 2026

• Science & Technology

• History

• Politics

This is the first part of the 14th installment in the Legacies of Eugenics series, which features essays by leading thinkers devoted to exploring the history of eugenics and the ways it shapes our present. The series is organized by Osagie K. Obasogie in collaboration with the Los Angeles Review of Books, and supported by the Center for Genetics and Society, the Othering & Belonging Institute, and Berkeley Public Health.

¤

THIS STORY BEGINS on a train. It is May 8, 1900, and we’re traveling from Cambridge to London. In one of the seats, we spy a slender, youngish man with a thatch of wavy brown hair, broad forehead, long nose and moustache. He is William Bateson, 38 years old, a biologist at St. John’s College, on his way to deliver a lecture at the Royal Botanical Society. As the train rattles along, he opens an old report from the proceedings of an obscure society for natural sciences that, although published 34 years ago, has only just begun to receive attention (while its author, poor man, has been dead for 16 years). We observe our fellow passenger’s mounting excitement as he turns the pages of the article. Suddenly, he pulls out another text and begins to edit it hurriedly, crossing out sentences and scribbling in additions. Bateson’s wife will later describe how her husband’s life changed in an instant on this train ride, beginning with his spontaneous rewriting of the lecture he was about to give.

The article in Bateson’s hands was “Experiments on Plant-Hybridisation,” by a Moravian monk named Gregor Mendel, in which he reported on the inheritance of various traits in pea plants in his monastery’s garden, such as the shape and color of the seeds and pods. Mendel here introduced the concept of inheritance “factors” in each reproductive cell—egg or pollen—corresponding with these traits, and he also divided the traits into the now-familiar categories of “dominant”—those he thought required only a single copy of the corresponding factor to appear in the plant—and “recessive”—those that required two copies, one from each parent. From the moment of his train ride to London, Bateson dedicated his professional life to establishing a new science inspired by Mendel. He clearly felt this to be a mission: half-jokingly, he said he’d thought of calling a book of his writings on Mendel “Scientific Calvinism,” a biological version of the Calvinist doctrine of predestination, that people are fated to be saved or damned.

In this regard, Bateson saw eye to eye with his friend Francis Galton, Charless Darwin’s first cousin, who was also a Scientific Calvinist predestinarian, persuaded that people’s destinies were indelibly inscribed in them by the biological mechanism of inheritance. “[P]retensions of natural equality,” Galton said, were morality tales for children. Innate “mental capacity” followed “the law of deviation from an average”: “the range of mental power between—I will not say the highest Caucasian and the lowest savage—but between the greatest and least of English intellects, is enormous.” Galton coined the term “eugenic” to designate the scientific “cultivation of race,” composing the name from Greek roots meaning “good in stock, hereditarily endowed with noble qualities.” He developed some of the fundamental concepts of statistics, including correlation, deviation, and regression, to provide a mathematical basis for this new “science of improving stock.” Bateson, too, became keenly interested in eugenics, as we will see.

Bateson’s encounter with Mendel’s paper launched a process that would lead, over the subsequent decades, to what Julian Huxley would name “the modern synthesis”: a marriage of neo-Darwinian theory with Mendelian genetics that has served as the central paradigm of evolutionary biology ever since. At the time of Bateson’s momentous train journey, Huxley—the grandson of T. H. Huxley, an evolutionist and friend of Charles Darwin—was not quite 13 years old, but he would grow up to become a biologist like his grandfather, a neo-Darwinist and also a eugenicist. The other architects of the modern synthesis, too, like Bateson and Huxley, were fervent believers in eugenics. Their eugenic logic and ideology are built into the deep structure of the neo-Darwinian interpretation of evolutionary biology, tightly connected to the principle that all organisms, including humans, are the passive objects of their genetic fate.

¤

After Bateson stepped off the train with a new sense of direction and made his way to the Royal Botanical Society’s lecture hall, he delivered a lecture that featured both Galton and—with its hastily composed new ending—Mendel. Bateson praised Galton for having been the first to enunciate a law of heredity. Galton had announced, after studying the coats of basset hounds over several generations, that the average “ancestral contribution” of the progenitors to the offspring halved with each successive generation, diminishing geometrically but never disappearing: the grandparents have half the contribution of the parents, the great-grandparents one-fourth, the great-great-grandparents one-eighth, and so on.

Bateson and others received Galton’s law with enormous enthusiasm, seemingly undimmed by their equally great confusion. For one thing, Galton himself stated his law in two different ways that were mathematically inconsistent with one another (one in terms of the average contribution of each generation of ancestors to the offspring, the other in terms of the deviation of each generation from a mean). For another thing, what did Galton mean by “contribution”? How did one measure it from observations of dogs? Still, Bateson celebrated Galton as a pioneer in the science of inheritance and Mendel as its Messiah.

As for himself, Bateson assumed the role of Saint Paul the Apostle. The Second Coming of Mendel had been “a moment of rejoicing,” he wrote, “and they who had heard the news hastened to spread them and take the instant way.” Alas, not everyone was ready to receive the Truth: “[E]very gospel must be preached to all alike. It will be heard by the Scribes, by the Pharisees, by Demetrius the Silversmith, and the rest.” Demetrius, who wanted to keep selling his silver idols and worshipping Artemis, and so incited a riot against Paul, was in this case Raphael Weldon, an invertebrate zoologist at Oxford. Weldon had reservations about the teachings of Mendel as preached by Bateson. For instance, Weldon said Mendel’s categories were ambiguous: “‘[G]reen’ and ‘yellow’ are not quantitatively definite terms; each includes a considerable range of recognisably different colours.” In general, Weldon argued that Mendel’s paper didn’t provide a reliable basis for generalizing about inheritance. A bitter quarrel between Bateson and Weldon ended only when Weldon died unexpectedly in April 1906 at the age of 46 from acute pneumonia.

Three months later, at the Third International Conference on Plant Hybridization, Bateson proposed a new Mendelian science of heredity to be called “genetics” (the term’s derivation will become clear presently). The proposal was received with such enthusiasm that the conference immediately renamed itself; its published proceedings have the historically revisionist title of “Third Annual Conference on Genetics.”

The following year, Galton and a fellow eugenicist named Sybil Neville-Rolfe founded the Eugenics Society. Genetics and eugenics were born as conjoined twins. When Bateson delivered the annual Galton Lecture to the Eugenics Society in 1919—his lecture was entitled “Common-Sense in Racial Problems”—he explained the connection. Anyone interested in genetics must necessarily be sympathetic to eugenics: the nature of the parents obviously determines the nature of their offspring, and by now surely no one “would venture to assert that men are born equal,” although probably “few realise how unequal they are.”

Among other things, Bateson recommended that the “feeble-minded” not be allowed to “interbreed,” and he criticized promoters of mass education for regarding “mankind as a homogeneous plastic substance which can be modelled to taste.” He concluded on an ominous note. “Equality of political power has been bestowed on the lowest elements of our population,” he warned, and he prophesied darkly that his and his audience’s children and grandchildren would “learn something of the consequences of un-applied biology. […] The truth has been recognised too late.”

¤

Mendel was not the first to suggest there might be some sort of atoms of inheritance that carry traits from parents into offspring. The idea existed in various versions during the second half of the 19th century. One was Darwin’s tentative theory of inheritance, which he called “pangenesis,” in which he tried to explain how organisms might pass on to their offspring the changes they underwent during their lifetimes. He hypothesized that each part of an organism threw off particles he called “gemmules,” which served as the mechanism of inheritance. Darwin’s gemmules were importantly different from the later idea of genes. He imagined that gemmules were modified by the organism’s use or disuse of the corresponding parts, and that they shared a “mutual affinity” for one another, leading them to gather in the reproductive organs, whence they transmitted qualities to the offspring. Soon after his death, Darwin’s followers rejected his idea that any hypothetical mechanism of inheritance must be able to explain what he called “the inherited effects of use and disuse,” and this rejection marks the transition from Darwinian to neo-Darwinian evolutionary theory.

The turning point came during the late 1880s when a German zoologist named August Weismann conducted a series of spurious and rather cruel experiments on mice, amputating their tails in order to show that their offspring were normally tailed. Weismann’s purpose was to disprove what he called the “transmission of acquired characters” and establish what came to be known as the “Weismann barrier,” a strict separation of germ cells from body cells such that no change taking place in body cells could ever be inherited. The mouse experiments were spurious because amputations were not the sort of acquired change that Darwin had described as inherited. Darwin did believe that by using a limb or body part, animals strengthened it, or by declining to use it, they weakened it, and then passed on the changes to their offspring. He adopted this idea from the French naturalist Jean-Baptiste Lamarck, author of the field of biology—he coined the term “biologie” in 1802—and of the first theory of evolution.

Neither Lamarck nor Darwin ever suggested that amputations would be transmitted, but Weismann’s experimental pseudo-refutation nevertheless carried the day. In Weismann’s new, revised version of Darwin’s theory, he eradicated all traces of Lamarckian inheritance. Lamarck and Darwin had seemed to usurp God’s monopoly on creation, reassigning it to mortal living beings, whereas Weismann left room for what he called a “Universal Cause” operating “behind” the mechanism of the universe. Weismann wasn’t sure exactly what the hereditary atoms were, but he called them “determinants.” These were units of inheritance like Darwin’s gemmules, but they had a crucial difference. While Darwin’s gemmules traveled from all throughout the body to the reproductive organs, bearing marks of any changes undergone by the various body parts, Weismann’s determinants were absolutely separate from body cells and isolated from all bodily transformations. Lamarckism became, in the words of the Harvard entomologist William Morton Wheeler, “the ninth mortal sin” in biology. Weismann’s revision rendered living beings once again the passive objects of outside forces, just as they had been according to the doctrine of direct divine creation.

Others continued to propose different models for the hypothetical units or particles that they thought carried traits from parents into offspring. From Weismann onwards, these models incorporated his ban on evolutionary agency for organisms and his insistence that nothing they did could influence the course of evolution. Hugo de Vries, a botanist at the University of Amsterdam, praised Weismann for having “shattered” the belief in Lamarckian inheritance, and he rejected Darwin’s idea that the gemmules traveled from all over the body to the reproductive organs bearing marks of bodily changes. But he still thought Darwin had gotten something right in the notion that there must be material particles of inheritance that carried combinations of characteristics into organisms in a “mosaic-like” way. Instead of imagining that these particles traveled throughout the body, he proposed that copies of them existed in every cell, but each was only active in certain cells. He called his particles “pangens,” or “pangenes” (which was where Bateson got the name “genetics”).

Mendel’s unknown inheritance “factors” got their current name in 1909, when the Danish botanist Wilhelm Johannsen coined the term “gene” to replace Darwin’s gemmules and De Vries’s pangenes, both of which had predated Mendel, or at least Mendel’s Second Coming. The word “gene,” Johannsen said, was new and neutral and would “prejudice nothing”: it was simply “a very applicable little word, easily combined with others.” Johannsen didn’t pretend to know just what a gene was, but he knew from Mendel that it must be something. And it corresponded nicely with Bateson’s “genetics.” But of course, the term “gene,” like all terms, certainly did carry implications. For instance, it carried the implication that individual organisms can’t possibly influence their offspring by means of their “personal qualities,” but only through their “sexual substances”; that “Mendelism” was defeating “Lamarckism”; and that these facts were foundational to “the modern view of heredity.”

Genes remain foundational to the modern view of heredity, and yet they also remain as hypothetical as they were in 1909. When Francis Crick, Rosalind Franklin, James Watson and Maurice Wilkins identified the DNA molecule’s structure in 1953, it didn’t help clarify what a gene was. On the contrary, their discovery rendered the question murkier yet. How do DNA molecules, made up of long chains of nucleotides, correspond to the idea of a “gene”? When we say “gene,” do we mean a section of DNA that encodes the information for making a protein? Or do we mean a heritable factor that determines a specific characteristic? These are different things, yet various versions of each appear as standard definitions of “gene” in biology textbooks, often both within the same textbook, implying that they’re the same. In fact, rather than converging, these two conceptions of “gene” have diverged over time. Research has shown that most traits correspond with more than one section of DNA, and even those that correspond with only a single section are not determined by it but depend on other developmental processes in the organism.

In short, the word “gene” continues to imply something mostly fictional: that there are atoms of inheritance tightly correlated with phenotypic traits. The fact that we still use the word represents a mismatch between the dominant way of thinking about inheritance, even among scientists, and the much more complicated physiological situation. The presiding fiction has its roots in Saint William’s Calvinist science of genetics. The eradication of Lamarckian inheritance and the idea that living beings were the passive objects of their “determinants” were founding principles of neo-Darwinism, eugenics and genetics alike. “No inheritance of acquired characteristics” became the defining slogan of evolutionary biology and the core doctrine of the modern synthesis. The doctrine holds that organisms are strictly passive in the evolutionary process, able only to vary randomly and be acted upon by natural selection, either favored or disfavored in the struggle for survival. In intimate conjunction with this principle of the passivity of organisms arose a eugenic tradition devoted to the idea of imposing a new form on the human race by controlling reproduction.

¤

This essay is an adapted excerpt from Jessica Riskin’s book The Power of Life: The Invention of Biology and the Revolutionary Science of Jean-Baptiste Lamarck, on sale this week. Part II of the excerpt will also be published tomorrow.

¤

Featured image: From the cover of The Power of Life: The Invention of Biology and the Revolutionary Science of Jean-Baptiste Lamarck, 2026, by Jessica Riskin.