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The Genetic Basis of Evolutionary Change
The Genetic Basis of Evolutionary Change [Jul 01, 1974] Lewontin, Richard C.
- GenresScience
352 pages, Hardcover
Published January 1, 1974
89 people want to read
About the author
Richard C. Lewontin
44 books98 followersRichard Charles "Dick" Lewontin is an American evolutionary biologist, mathematician, geneticist, and social commentator.
A leader in developing the mathematical basis of population genetics and evolutionary theory, he pioneered the application of techniques from molecular biology, such as gel electrophoresis, to questions of genetic variation and evolution.
In a pair of seminal 1966 papers co-authored with J. L. Hubby in the journal Genetics, Lewontin helped set the stage for the modern field of molecular evolution. In 1979 he and Stephen Jay Gould introduced the term "spandrel" into evolutionary theory. From 1973 to 1998, he held an endowed chair in zoology and biology at Harvard University, and from 2003 until his death in 2021 had been a research professor there.
A leader in developing the mathematical basis of population genetics and evolutionary theory, he pioneered the application of techniques from molecular biology, such as gel electrophoresis, to questions of genetic variation and evolution.
In a pair of seminal 1966 papers co-authored with J. L. Hubby in the journal Genetics, Lewontin helped set the stage for the modern field of molecular evolution. In 1979 he and Stephen Jay Gould introduced the term "spandrel" into evolutionary theory. From 1973 to 1998, he held an endowed chair in zoology and biology at Harvard University, and from 2003 until his death in 2021 had been a research professor there.
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May 3, 2025
This is Lewontin's technical work on population genetics basis of evolution. He provides a framework to explain the constancy of inheritance and variation using genetics down to genome level. His approach features a wealth of lab work and the statistical study of population genotypic frequencies of drosophilia or fruit flies, but also involves studies in other living organisms.
After describing the set up of his approach of the problem, the second part of the book examines the genotypic facts revealed. A first challenge is to measure genetic variation. There is an epistemological paradox of what needs to be studied and what can be studied. The Mendelian approach suggests the frequencies of genotypes as the appropriate genetic description of a population. The enumeration of genotypes requires that the effects of allelic substitutions be so large to offer an unambigious assignment of individuals to genotypes. On the other hand the substance of evolutionary change at the phenotypic level makes only slight difference as compared with variation produced by genetic background and environment, making what can be studied in genetic variation difficult. In genetic statistics, there are 3 theories offering interpretation of the facts, the classical, balanced, and neoclassical. In the classical theory, it is assumed that every locus for every individual is homozygous for a wild type gene while in balanced theory suggest individuals from sex producing population cross breeding population is heterozygus for every one of their loci. Which interpretation you use affects how one treats the genetic variation experimental results.
Then Lewontin suggests one useful method to treat genetic variation in natural populations by looking at the molecular genetics, namely, by considering any substitution, deletion, or addition of the amnio acid of a protein which reflects clearly any change in a DNA molecule. The tracking of amnio acids offers clear changes in allelic substitutions for the focus coding in the polypetide. Lewontin discusses the popular experimental method, gel electrophoresis, to separate proteins for identifying the allelic forms of genes. This method uses coloured gel on proteins and electric field separation. The book offers many experimental results of this method for various drosophilia species.
The third important genotypic fact to consider is speciation in the evolutionary process. At the time when the book was written, there was still no quantitative analysis of genetic change in speciation. Experts were not able to make a determination of how many generations it takes for allelic frequency to change from one to another. Nor did they establish the connection between the genotypic differences among populations or species with their phenotypic differences. Speciation occurs by natural selection pressure and population isolation. In the third stage of speciation when phyletic or original lineage changes occurs independent of the sister species can one see divergence. The rate of divergence depends on morphological changes while sister species can differ from 10 to 50 % of their genomes.
Lewontin then devotes a chapter on paradoxes of variation. Genetic distribution is subjected to many factors that acts separately or interactively to increase, decrease, or stabilizes variation. He offers a survey of them. Variation of population is introduced by mutation or immigration of genes by other populations with different alleles. Variation may increase from introgression of alleles from subspecies or species if reproductive isolation breaks down in the zone of contact contributing to recombination. Variation can also increase or stabilise due to natural selection if the allele is favoured by the new environment or more fit. Variation can also be stabilised by balanced selection which is the condition that heterozygotes are much more fit than homozygotes creating a over dominance of fitness. Variation may also be removed from random and deterministic forces. A population eventually loses variation because it is limited in size. Random allelic frequency may eventually stabilise in one frequency if unopposed by new allelic frequency. The strongest force against variation is selection against recessive or partly dominant deleterious genes. If there is one wild type over the population, that wild type is uniform over the whole population. The paradox of variation bears on the neoclassical theory of interpreting variation. The theory suggests many mutations are subject to natural selection but are almost deleterious and are removed from the population. Rare favourable mutation is fixed by natural selection for adaptive advantages.
The book ends with a discussion of the genome as a unit of selection. Lewontin suggests that a genome cannot have its selection effects considered in isolation. A sufficient description of changes in the frequency of an allele in one locus involves the frequencies of other alleles in other loci so that a total genetic description of a population is an enumeration of all its diplpid genotypes. A evolutionary study by genomes is an interactive study in a global picture of the organism genotypes.
After describing the set up of his approach of the problem, the second part of the book examines the genotypic facts revealed. A first challenge is to measure genetic variation. There is an epistemological paradox of what needs to be studied and what can be studied. The Mendelian approach suggests the frequencies of genotypes as the appropriate genetic description of a population. The enumeration of genotypes requires that the effects of allelic substitutions be so large to offer an unambigious assignment of individuals to genotypes. On the other hand the substance of evolutionary change at the phenotypic level makes only slight difference as compared with variation produced by genetic background and environment, making what can be studied in genetic variation difficult. In genetic statistics, there are 3 theories offering interpretation of the facts, the classical, balanced, and neoclassical. In the classical theory, it is assumed that every locus for every individual is homozygous for a wild type gene while in balanced theory suggest individuals from sex producing population cross breeding population is heterozygus for every one of their loci. Which interpretation you use affects how one treats the genetic variation experimental results.
Then Lewontin suggests one useful method to treat genetic variation in natural populations by looking at the molecular genetics, namely, by considering any substitution, deletion, or addition of the amnio acid of a protein which reflects clearly any change in a DNA molecule. The tracking of amnio acids offers clear changes in allelic substitutions for the focus coding in the polypetide. Lewontin discusses the popular experimental method, gel electrophoresis, to separate proteins for identifying the allelic forms of genes. This method uses coloured gel on proteins and electric field separation. The book offers many experimental results of this method for various drosophilia species.
The third important genotypic fact to consider is speciation in the evolutionary process. At the time when the book was written, there was still no quantitative analysis of genetic change in speciation. Experts were not able to make a determination of how many generations it takes for allelic frequency to change from one to another. Nor did they establish the connection between the genotypic differences among populations or species with their phenotypic differences. Speciation occurs by natural selection pressure and population isolation. In the third stage of speciation when phyletic or original lineage changes occurs independent of the sister species can one see divergence. The rate of divergence depends on morphological changes while sister species can differ from 10 to 50 % of their genomes.
Lewontin then devotes a chapter on paradoxes of variation. Genetic distribution is subjected to many factors that acts separately or interactively to increase, decrease, or stabilizes variation. He offers a survey of them. Variation of population is introduced by mutation or immigration of genes by other populations with different alleles. Variation may increase from introgression of alleles from subspecies or species if reproductive isolation breaks down in the zone of contact contributing to recombination. Variation can also increase or stabilise due to natural selection if the allele is favoured by the new environment or more fit. Variation can also be stabilised by balanced selection which is the condition that heterozygotes are much more fit than homozygotes creating a over dominance of fitness. Variation may also be removed from random and deterministic forces. A population eventually loses variation because it is limited in size. Random allelic frequency may eventually stabilise in one frequency if unopposed by new allelic frequency. The strongest force against variation is selection against recessive or partly dominant deleterious genes. If there is one wild type over the population, that wild type is uniform over the whole population. The paradox of variation bears on the neoclassical theory of interpreting variation. The theory suggests many mutations are subject to natural selection but are almost deleterious and are removed from the population. Rare favourable mutation is fixed by natural selection for adaptive advantages.
The book ends with a discussion of the genome as a unit of selection. Lewontin suggests that a genome cannot have its selection effects considered in isolation. A sufficient description of changes in the frequency of an allele in one locus involves the frequencies of other alleles in other loci so that a total genetic description of a population is an enumeration of all its diplpid genotypes. A evolutionary study by genomes is an interactive study in a global picture of the organism genotypes.
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