Richard Lewontin (1929–2021) was an American evolutionary biologist, mathematician, and geneticist who significantly shaped 20th-century scientific thought. He pioneered population genetics, advancing its mathematical foundations. Beyond his laboratory work, Lewontin also became a prominent public intellectual, challenging scientific and societal assumptions. His contributions extended into the philosophy of science, where he critically examined the influences of broader ideologies on scientific inquiry.
Uncovering Genetic Variation
Before the mid-1960s, a significant debate existed in evolutionary genetics concerning the extent of genetic diversity within natural populations. This involved two main perspectives: the “classical” view, which proposed that most individuals were genetically uniform with rare mutations, and the “balance” view, suggesting that populations maintained high levels of genetic variation due to various forms of selection. There was no direct method to measure this variation at the molecular level, leaving the debate largely theoretical.
Richard Lewontin, in collaboration with John L. Hubby, revolutionized this field with their 1966 papers published in the journal Genetics. They applied gel electrophoresis to study genetic variation in natural populations of fruit flies, specifically Drosophila pseudoobscura. This method allowed them to separate proteins based on their electrical charge, revealing differences in protein sequences that indicated underlying genetic variation.
Their work demonstrated that natural populations harbored a surprising and substantial amount of genetic variation, far more than previously thought. For the first time, researchers could quantify genetic heterozygosity at specific gene loci across an organism’s genome. This empirical evidence revealed that a significant proportion of gene loci in fruit flies were polymorphic, meaning multiple forms of a gene existed within the population.
The findings from Lewontin and Hubby’s research provided strong support for the “balance” hypothesis, confirming that abundant genetic diversity serves as the raw material upon which evolutionary forces, like natural selection, can act. Their innovative approach established the foundation for molecular evolution, paving the way for subsequent studies that explored genetic variation across diverse species.
The Apportionment of Human Diversity
Richard Lewontin further extended his work on genetic variation to human populations, publishing his influential 1972 paper, “The Apportionment of Human Diversity.” In this study, he analyzed genetic diversity across different human groups using data from 17 indirect genetic markers, such as blood group proteins. His aim was to determine how human genetic variation is distributed within and between conventionally defined racial categories.
Lewontin employed an analysis of variance to partition the total human genetic variation. His findings were striking: approximately 85.4% of all human genetic variation exists within local populations. Another 8.3% of the variation was found between populations within larger “racial” groups, such as continental groupings.
Only about 6.3% of total human genetic variation could be attributed to differences between the major continental “racial” classifications. From these data, Lewontin concluded that conventional racial categories have no genetic or taxonomic significance. He argued that since most human genetic differences occur within, rather than between, these groups, biological race is not a meaningful scientific concept.
While Lewontin’s statistical apportionment is widely accepted and has been confirmed by later studies using modern DNA sequencing, its interpretation has generated discussion. A common counterargument, sometimes referred to as “Lewontin’s Fallacy,” points out that even a small percentage of variation between groups, when combined across many genetic markers, can still contain enough information to identify an individual’s ancestral geographic origins. This highlights the distinction between overall genetic diversity and patterns of genetic differentiation.
A Critique of Adaptationism
Richard Lewontin, along with paleontologist Stephen Jay Gould, made a theoretical contribution to evolutionary biology with their 1979 paper, “The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme.” This paper challenged “adaptationism.” Adaptationism is the view that nearly every biological trait an organism possesses is a direct product of natural selection, serving a specific adaptive purpose.
Gould and Lewontin argued that this approach often led to “just-so stories,” where biologists would invent speculative adaptive explanations for every observed trait without sufficient evidence. They contended that such explanations overlooked other factors in evolution. Their critique was framed using the architectural metaphor of “spandrels.”
Spandrels are the triangular spaces that are necessarily formed when a dome is placed on top of rounded arches. In the Basilica of San Marco in Venice, these spandrels are elaborately decorated with mosaics. Gould and Lewontin used this example to illustrate that while the mosaics are beautiful and appear purposeful, the spandrels themselves are not designed for the mosaics; rather, they are unavoidable architectural byproducts of the structural design. The decorations are then added to these existing spaces.
Applying this analogy to biology, they proposed that many biological traits might not be direct adaptations but rather “spandrels”—byproducts of other evolutionary changes, developmental constraints, or historical contingencies. A trait might arise as an incidental consequence of selection acting on a different feature, or it could be a leftover from an earlier evolutionary stage. This perspective encouraged biologists to consider a broader range of explanations for the origin and existence of traits, moving beyond direct adaptation by natural selection.
The Dialectical Biologist
Beyond his empirical and theoretical contributions to genetics, Richard Lewontin also developed a philosophical and political framework that underpinned his scientific critiques. This framework is evident in his co-authored books, “Not in Our Genes: Biology, Ideology, and Human Nature” (1984) and “The Dialectical Biologist” (1985). These works articulated his opposition to genetic determinism and sociobiology.
Lewontin, along with his co-authors, viewed genetic determinism—the idea that genes alone dictate an organism’s traits, behaviors, and social structures—as an oversimplification. They argued that such perspectives were often ideologically driven, justifying social inequalities by attributing them to inherent biological differences. He saw sociobiology, a field that seeks to explain animal and human behavior through evolutionary principles, as susceptible to these deterministic pitfalls.
Lewontin’s analysis was informed by a Marxist perspective, which provided a lens through which he examined the relationship between science and society. He believed that scientific inquiry is not a neutral but is embedded within, and influenced by, prevailing social and economic ideologies. From this viewpoint, scientific concepts can sometimes be shaped by societal values and then, in turn, used to legitimize existing social hierarchies.
His “dialectical” approach emphasized the interconnectedness and reciprocal influence between genes, organisms, and their environments, rather than a one-way determination from genes to traits. This perspective highlighted the dynamic interactions that shape biological reality, challenging reductionist explanations that sought to isolate and simplify biological phenomena. He argued for a science that acknowledges its social context and remains vigilant against its potential misuse for political ends.
Lewontin’s Enduring Influence
Richard Lewontin’s impact on biology and the public understanding of science continues to resonate. He compelled evolutionary biologists to adopt a more rigorous and self-critical approach to their explanations, particularly regarding claims of adaptation. His work fostered awareness of the complexities involved in discerning the origins and functions of biological traits, urging a consideration of non-adaptive factors and developmental constraints.
His statistical findings on human genetic diversity, published in 1972, remain a foundational element in population genetics. The finding that most human genetic variation exists within, rather than between, conventionally defined racial groups continues to inform discussions about human unity and the biological meaninglessness of race. Even as interpretations are debated, the core data from his work stands.
Lewontin’s critiques of genetic determinism and sociobiology also left a lasting mark, encouraging a nuanced understanding of the interplay between genes, environment, and societal factors in shaping human characteristics. He transformed how scientists and the public engage with discussions about genes, evolution, and their implications for society.