Lewontin’s paradox: what is it and what does it say about the concept of human races?

Lewontin's paradox is a curious phenomenon related to genetic diversity.

Evolution is the process by which organisms change over time. Heritable spontaneous mutations produce variability in populations of living things, which allows natural selection to "favor" and select those individuals that are best adapted to the environment.

Together with genetic drift and gene flow, natural selection largely explains the evolutionary process: the strongest remain, while the weak do not reproduce and their genes are lost throughout history.

Thus, we can affirm that evolution bases its functioning on genetic inheritance. If a character is not heritable, its variability in the population is of little importance, since it will not condition the phenotype of the following generations. All these bases seem obvious today, but different thinkers have challenged them over the years, in order to reach the point where we are today.

Today we introduce you to the world of population genetics and unresolved questions, at least from a genetic and social point of view. Don't miss the fascinating Lewontin's paradox and how it applies to human existence.

The basis of evolution

Before introducing Lewontin's paradox, it is necessary to lay certain foundations. Humans have 23 pairs of chromosomes in each of our cells, i.e. a total of 46 chromosomes.. These contain genes, which in turn are differentiated into alleles, which are defined as each of the alternative ways in which the same gene can be expressed. Thus, any gene will consist of 2 alleles, A1 and A2, for example.

Of the 46 chromosomes found in the nucleus of our cells, one comes from the mother and one from the father. Thus, if a mother has the alleles (aa) for a gene and a father has the alleles (AA), the only possible frequency in the offspring would be as follows: Aa, one allele from the father (A) and one from the mother (a). The dominant alleles (A) are those that only need one copy in the gene to manifest themselves, while the recessive alleles (a) have to present two copies in the genome to become dominant (aa). The fixed position of this or any other gene on a chromosome is known as Locus.

When the two alleles are the same for the same character, either dominant (AA) or recessive (aa), the individual is said to be homozygous for a gene. When this is not the case, the individual is called heterozygous (Aa), even though only the dominant allele (A) is externally manifested over the recessive allele (a).

With this express class, we understand a little of the mechanisms of evolution: from a theoretical point of view, the more individuals present genomes with genomes with the dominant allele (A) over the recessive allele (a), the more we understand the mechanisms of evolution, the more individuals have genomes with heterozygous traits, the more likely it is that the population will be maintained over time over time, because natural selection will act negatively on some traits, but will be able to select others positively.

In general, the loss of genetic information results in homozygosity, which leads to the long-term extinction of a species.. Processes such as genetic drift or inbreeding favor this situation, but they are beyond our competence at the moment. With these foundations in place, we can dive into Lewontin's paradox.

What is Lewontin's paradox?

Richard Lewontin is an evolutionary biologist, geneticist and philosopher who was born in New York, USA, in March 1921. He is still alive, at the impressive age of 91. This fascinating researcher was one of the pioneers in applying molecular biology techniques, such as gel electrophoresis, which are still essential in science today. He specialized in population genetics, as we will see in the following lines.

Lewontin was an advocate of the hierarchical theory of evolution.. Although it is difficult to find information on this current of thought, it can be summarized in the following lines: in it, natural selection does not act solely on the basis of genes (as we have seen so far), but cells, organisms, species and clades, among other organizations, are also considered evolutionary units.

Transposing this postulation into the world of animal populations, Lewontin's paradox would tell us that Theoretical predictions about the relationship between population size and genetic diversity are not borne out in the real world.. As anecdotal as this may seem, you will see how it carries over to the human collective.

How does Lewontin's paradox apply to humans?

Lewontin's paradox (or "Lewontin's fallacy", for its English translation) has been a great debate in the scientific community, since on its basis it is argued that the conception of the human race does not make any sense. In an article published in 1972, Richard Lewontin postulated that 85% of genetic variation in humans occurs between individuals of the same population and that, failing this, only the remaining 15% is due to differences between ethnic groups..

This means that, broadly speaking, one individual is different from another because of his or her individual condition and not because of his or her ethnic origin or supposed racial heritage. Thus, the theories that circulate around race would be dismantled, and the supposed behavioral differences between individuals could only be explained by cultural constructs, not by genetic bases. If race does not explain variations at the genotypic (genes) or phenotypic (external characteristics) level, its usefulness in the field of taxonomy is nil..

This is where some of the concepts we have explained above come into play. Some researchers (such as Anthony William Fairbank Edwards) have tried to dismantle Lewontin's paradox, as they do not consider the researcher's approach to be correct. While it is true that the frequency of different alleles (AA or aa, for example) at an individual locus does not report a significant difference between ethnic groups, it does when several areas of the genome are taken into account at the same time. We explain.

If allele frequencies at several loci (plural of locus) are factored in at the same timeIf you factor the allele frequencies at several loci (plural of locus) at the same time, this statistical researcher argues that you can classify individuals into an ethnic group with almost 100% reliability. In other words, the frequency of alleles tends to "cluster" in the different ethnic groups, so, if only the alleles are taken into account separately, the population reality of the human being is clearly not being represented in its entirety.

Between support and fallacies

Some renowned biologists, such as Richard Dawkins, agree with Lewontin that individual variability is much more important than ethnic variability. in explaining genotypic and phenotypic differences in human beings. Nevertheless, he does not think that the concept of race or ethnicity is of no taxonomic interest: "however small, if a racial characteristic is linked to another racial characteristic, it is already informative and therefore of taxonomic importance".

The question that remains up in the air, despite the musings, is the following: is a person of one race "more" different genetically compared to a person of another race, or two different individuals of the same race?

Summary and considerations

According to various biologists around the world, and based on articles published relatively recently, "the use of the hotly contested and confusing Biological concept of race in human genetic research is problematic at best and harmful at worst". Undoubtedly, Lewontin's paradox and its ensuing debates are of great biological interest, but we must not forget that we are talking about human beings with diverse feelings and identities, not statistics and expressions of genes.not statistics and expressions of genes.

Today, the concept of human race is considered problematic and offensive and, therefore, there is no need for a scientific basis to support its replacement by other more correct words, such as ethnicity. Science is an outgrowth of society, not vice versa, and so society must adjust to the new social codes as inclusively and permissively as possible. No matter how "scientifically correct" something may be, if it hurts the collective sensibility and closes bridges of dialogue, it does little to further the search for knowledge.

Bibliographical references:

• Depew, D. J. (2018). Richard Lewontin and the Argument from Ethos. Poroi: An Interdisciplinary Journal of Rhetorical Analysis & Invention, 13(2).
• Edwards, A. W. (2003). Human genetic diversity: Lewontin's fallacy. BioEssays, 25(8), 798-801.
• Kaplan, J. M. (2011). ‘Race’: What biology can tell us about a social construct. eLS.
• Lewontin, R. C. (2005). The fallacy of racial medicine: confusions about human races. Genewatch: a bulletin of the Committee for Responsible Genetics, 18(4), 5-7.
• Moore, D. S., & Shenk, D. (2017). The heritability fallacy. Wiley Interdisciplinary Reviews: Cognitive Science, 8(1-2), e1400.
• Okazaki, A., Yamazaki, S., Inoue, I., & Ott, J. (2020). Population genetics: past, present, and future. Human Genetics, 1-10.
• Sober, E. (2020). AWF Edwards on Phylogenetic Inference, Fisher’s Theorem, and Race. The Quarterly Review of Biology, 95(2), 125-129.