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Richard Lewontin (1929-2021) |
Molecular evolution pioneer Richard Lewontin died at 92. His
ground-breaking publication was
The Genetic Basis of Evolutionary Change (1974). In 1979 he wrote
together with Steven Jay Gould the famous article
"The Spandrels of San Marco and the Panglossian Paradigm: A Critique of
the Adaptationist Programme". He was also known for his Marxist writings criticizing genetic
determinism, social inequality and racism: Not in Our Genes (1984,
together with Steven Rose and Leon Kamin);
Biology as Ideology: The Doctrine of DNA (1993);
The Triple Helix. Gene, Organism, and Environment (2000); and
It Ain't Necessarily So. The dream of the human genome and other
illusions
(2001).
To understand what was so revolutionary about Lewontin's contribution to
evolutionary biology, we need to go back to the time before DNA
sequencing. Today we see thousands of SARS-CoV-2 sequences being published
almost on a daily basis. We can follow the spontaneous origin, spread or
disappearance of new variants over the planet. Variation is the
cornerstone for Darwin's theory. But the only variation available to
Darwin was
morphological variation. When Lewontin started his research in the mid sixties certain
variations of proteins were detectable by a technique called
electrophoresis. This technique could detect protein size differences and
differences in electrical charge. Lewontin applied this technique to
detect mutations in natural populations of Drosophila. That is, mutations
that changed the size or electrical charge of a protein compared to the
wildtype protein. In this way he could measure the degree of
heterozygosity. Heterozygous refers to having inherited different forms of
a particular gene (or protein) from each parent. Lewontin and Hubby found
to their surprise that an average individual was heterozygous at 12% of
its genes. The other 88% is homozygous (two identical copies of a
gene).
Why is this so important for evolution? Suppose there was no genetic
variation in natural populations. All individuals are homozygous, as if
they were clones. Or identical twins. Then natural selection could do
nothing. No evolution. But as soon one of the two copies of a gene has
mutated, natural selection could favour one over the other. Textbooks say:
"variation is the raw material for evolution." Darwin was right about
that.
This study was soon followed by many others. The results were always:
every individual in a population is genetically unique because there are
potentially hundreds to thousands of variants of each gene and each
individual harbours different combinations of all those gene variants.
That was big news at the time. It transformed the way scientists think
about evolution.
Researchers wondered why all those variant forms were not eliminated? Why don't we see only the wildtype? Are they random variations with no effect on fitness? Why did natural selection not eliminate them? In other words scientists at the time worried there was too much variation. Natural selection is a costly process ('the cost of natural selection problem'). Selection requires differential survival or reproduction. Later these questions led Kimura to propose his now famous 'The neutral theory of molecular evolution'.
Still later protein and DNA sequencing revealed far more differences
between individuals. The first study of genetic variation using DNA
sequences was published in 1983. That is 30 years after Watson and Crick
published the structure of DNA. The rest is history. Today the study of
evolution is the study of variation at the DNA level.
The popular science books I mentioned above are within a different category. Difficult to summarize. These books are a mix of political activism, science criticism, and popular science. Often written from a political perspective or highly critical to mainstream scientific views on adaptation, genetic determinism, development, and the role of the environment. Undoubtedly, the most famous is the article he wrote with Steven Jay Gould: 'The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptationist programme' (1979).
See also an obituary of Lewontin in Nature: Richard C. Lewontin (1929–2021). Pioneer of molecular evolution who campaigned against biological racism.
What the textbooks say about Lewontin
- Douglas Futuyma (2005) Evolution. Lewontin is not in the index, but present in Literature list and a good discussion of the importance of his work can be found in the paragraph 'Genetic variations in proteins', page 203.
-
Stephen Stearns, Rolf Hoekstra (2005)
Evolution: an introduction. Lewontin is not in the index, not in
the Literature cited, but he is mentioned on page 31: "... Lewontin and
Ayala, for gene products detectable by electrophoresis, ... have shown
that a great deal of genetic variation is present in natural populations
for many types of trait and organism." (page 31).
- Freeman and Herron (2007) Evolutionary Analysis, 4th Edition. Lewontin is in index and discussed in paragraph 5.4 'Measuring genetic variation in natural populations'.
- Nicholas Barton et al (2007) Evolution. Lewontin is in the index and S. J. Gould, Lewontin (1979) is discussed in the text.
- 'Strickberger's Evolution' (2008). Lewontin is not in the index but in Literature cited. I could not find him in the text.
- Carl Bergstrom, Lee Alan Dugatkin (2012) Evolution. Lewontin is discussed in 8.5 'The Neutral Theory of Molecular Evolution', page 276. They consider the work of Lewontin as a prelude to The Neutral Theory of Molecular Evolution.
-
Carl Zimmer, Douglas Emlen (2013)
Evolution. Making Sense of Life. They have replaced Lewontin with
modern day examples of genetic variation in populations.
