Adaptation and Natural Selection
Encyclopedia
Adaptation and Natural Selection: A Critique of Some Current Evolutionary Thought is a 1966
book by the American
evolutionary biologist George C. Williams
. Williams, in what is now considered a classic
by evolutionary biologists, outlines a gene-centered view of evolution
, disputes notions of evolutionary progress, and criticizes contemporary models of group selection, including the theories of Alfred Emerson, A. H. Sturtevant, and to a smaller extent, the work of V. C. Wynne-Edwards. The book takes its title from a lecture by George Gaylord Simpson
in January 1947 at the University of Princeton. Aspects of Williams' book were popularised by Richard Dawkins
' in his 1976 book The Selfish Gene
.
The aim of the book is to "clarify certain issues in the study of adaptation
and the underlying evolutionary processes." Though more technical than a popular science
book, its target audience is not specialists but biologist
s in general and the more advanced students of the topic. It was mostly written in the summer of 1963 when Williams utilized the University of California, Berkeley
's library.
Assuming that the trait has a genetic component, over time the mean will move in the direction of the positive effect, and away from the negative effect.
The shape of the distribution may change depending on a number of factors.
With each generation, individuals that carry deleterious forms of the trait are likely to produce fewer off-spring than those that do not. Over a number of generations, the frequency of organisms with the disadvantageous trait will decrease. This process is known as directed selection.
Why is it that the more genes that determine a trait, the more continuous is the distribution of that trait in a population? Does directed selection ever stop? That is, does the mean ever stop changing?
Conservative selection: Another possibility is that individuals with traits at either end of the population distribution are at a reproductive disadvantage compared with organisms that are closer to the mean. With each generation, the contribution of these "outliers" to the next generation will be reduced. The distribution mean will remain constant, but the standard deviation will decrease.The stronger the disadvantage the outliers face, the narrower the distribution will become. In the end, the size of the standard deviation will reflect the rate at which new variation enters the population.
Disruptive selection: A third possibility is that the organisms with traits at the extremes of the population distribution actually have a reproductive advantage over those nearer the mean. This type of behavior would tend to expand the population distribution, while mating between organisms at the extremes would tend to bring the population distribution back to the original state. If organisms at the extremes preferred to mate with organisms with the same form of the trait, the population would split into two.
In the first chapter Williams introduces some of his main arguments. Adaptation
is "a special and onerous concept that should not be used unnecessarily". He writes that something should not be assigned a function
unless it is uncontroversially the result of design rather than chance. For instance he considers mutation
s to be errors only, not a process that has persisted to provide variation and evolutionary potential. If something is considered (after critical appraisal) to be an adaptation, then we should assume the unit of selection
in the process was as simple as possible, provided it is compatible with the evidence. For example selection between individuals should be preferred to group selection
as an explanation if both seem plausible. Finally, Williams writes that the only way adaptations can come into existence or persist is by natural selection
.
The next chapter deals with the idea of evolutionary progress. Firstly, it is argued that for natural selection to work, there have to be "certain quantitative relationships among sampling error
s, selection coefficient
s, and rates of random change
." It is put forward that Mendelian selection of allele
s (alternative versions of a gene
) is the only kind of selection
imaginable that satisfies these requirements. Elaborating on the nature of selection, he writes that it only works on the basis of whether alleles are better or worse than others in the population, in terms of their immediate fitness
effects. Survival of the population
is beside the point, e.g. populations don't take any measures to avoid impending extinction
. Finally he evaluates various ideas about progress in evolution, denying that selection will bring about the kind of progress that some have suggested. The author concludes that his view on the topic is similar to that of most of his colleagues, but worries that it is misrepresented to the public "when biologists become self-consciously philosophical".
1966 in literature
The year 1966 in literature involved some significant events and new books.-Events:*February 14 - Dissident writers Yuli Daniel and Andrei Sinyavsky are sentenced to hard labour for "anti-Soviet activity"....
book by the American
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
evolutionary biologist George C. Williams
George C. Williams
Professor George Christopher Williams was an American evolutionary biologist.Williams was a professor emeritus of biology at the State University of New York at Stony Brook. He was best known for his vigorous critique of group selection. The work of Williams in this area, along with W. D...
. Williams, in what is now considered a classic
Classic book
A classic book is a book accepted as being exemplary or noteworthy, either through an imprimatur such as being listed in any of the Western canons or through a reader's own personal opinion. The term itself is closely related to Western Canon and to various college/university Senior Comprehensive...
by evolutionary biologists, outlines a gene-centered view of evolution
Gene-centered view of evolution
The gene-centered view of evolution, gene selection theory or selfish gene theory holds that evolution occurs through the differential survival of competing genes, increasing the frequency of those alleles whose phenotypic effects successfully promote their own propagation, with gene defined as...
, disputes notions of evolutionary progress, and criticizes contemporary models of group selection, including the theories of Alfred Emerson, A. H. Sturtevant, and to a smaller extent, the work of V. C. Wynne-Edwards. The book takes its title from a lecture by George Gaylord Simpson
George Gaylord Simpson
George Gaylord Simpson was an American paleontologist. Simpson was perhaps the most influential paleontologist of the twentieth century, and a major participant in the modern evolutionary synthesis, contributing Tempo and mode in evolution , The meaning of evolution and The major features of...
in January 1947 at the University of Princeton. Aspects of Williams' book were popularised by Richard Dawkins
Richard Dawkins
Clinton Richard Dawkins, FRS, FRSL , known as Richard Dawkins, is a British ethologist, evolutionary biologist and author...
' in his 1976 book The Selfish Gene
The Selfish Gene
The Selfish Gene is a book on evolution by Richard Dawkins, published in 1976. It builds upon the principal theory of George C. Williams's first book Adaptation and Natural Selection. Dawkins coined the term "selfish gene" as a way of expressing the gene-centred view of evolution as opposed to the...
.
The aim of the book is to "clarify certain issues in the study of adaptation
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
and the underlying evolutionary processes." Though more technical than a popular science
Popular science
Popular science, sometimes called literature of science, is interpretation of science intended for a general audience. While science journalism focuses on recent scientific developments, popular science is broad-ranging, often written by scientists as well as journalists, and is presented in many...
book, its target audience is not specialists but biologist
Biologist
A biologist is a scientist devoted to and producing results in biology through the study of life. Typically biologists study organisms and their relationship to their environment. Biologists involved in basic research attempt to discover underlying mechanisms that govern how organisms work...
s in general and the more advanced students of the topic. It was mostly written in the summer of 1963 when Williams utilized the University of California, Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
's library.
Adaption and Selection
Directed selection: What happens when certain values of a trait positively impact survival while values at the other extreme negatively impact survival?Assuming that the trait has a genetic component, over time the mean will move in the direction of the positive effect, and away from the negative effect.
The shape of the distribution may change depending on a number of factors.
With each generation, individuals that carry deleterious forms of the trait are likely to produce fewer off-spring than those that do not. Over a number of generations, the frequency of organisms with the disadvantageous trait will decrease. This process is known as directed selection.
Why is it that the more genes that determine a trait, the more continuous is the distribution of that trait in a population? Does directed selection ever stop? That is, does the mean ever stop changing?
Conservative selection: Another possibility is that individuals with traits at either end of the population distribution are at a reproductive disadvantage compared with organisms that are closer to the mean. With each generation, the contribution of these "outliers" to the next generation will be reduced. The distribution mean will remain constant, but the standard deviation will decrease.The stronger the disadvantage the outliers face, the narrower the distribution will become. In the end, the size of the standard deviation will reflect the rate at which new variation enters the population.
Disruptive selection: A third possibility is that the organisms with traits at the extremes of the population distribution actually have a reproductive advantage over those nearer the mean. This type of behavior would tend to expand the population distribution, while mating between organisms at the extremes would tend to bring the population distribution back to the original state. If organisms at the extremes preferred to mate with organisms with the same form of the trait, the population would split into two.
Summary(of the book)
- Introduction
- Natural Selection, Adaptation, and Progress
- Natural Selection, Ecology and Morphogenesis
- Group Selection
- Adaptations of the Genetic System
- Reproductive Physiology and Behavior
- Social Adaptations
- Other Supposedly Group-Related Adaptations
- The Scientific Study of Adaptation
In the first chapter Williams introduces some of his main arguments. Adaptation
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
is "a special and onerous concept that should not be used unnecessarily". He writes that something should not be assigned a function
Function (biology)
A function is part of an answer to a question about why some object or process occurred in a system that evolved through a process of selection. Thus, function refers forward from the object or process, along some chain of causation, to the goal or success...
unless it is uncontroversially the result of design rather than chance. For instance he considers mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
s to be errors only, not a process that has persisted to provide variation and evolutionary potential. If something is considered (after critical appraisal) to be an adaptation, then we should assume the unit of selection
Unit of selection
A unit of selection is a biological entity within the hierarchy of biological organisation that is subject to natural selection...
in the process was as simple as possible, provided it is compatible with the evidence. For example selection between individuals should be preferred to group selection
Group selection
In evolutionary biology, group selection refers to the idea that alleles can become fixed or spread in a population because of the benefits they bestow on groups, regardless of the alleles' effect on the fitness of individuals within that group....
as an explanation if both seem plausible. Finally, Williams writes that the only way adaptations can come into existence or persist is by natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
.
The next chapter deals with the idea of evolutionary progress. Firstly, it is argued that for natural selection to work, there have to be "certain quantitative relationships among sampling error
Sampling error
-Random sampling:In statistics, sampling error or estimation error is the error caused by observing a sample instead of the whole population. The sampling error can be found by subtracting the value of a parameter from the value of a statistic...
s, selection coefficient
Selection coefficient
In population genetics, the selection coefficient is a measure of the relative fitness of a phenotype. Usually denoted by the letter s, it compares the fitness of a phenotype to another favored phenotype, and is the proportional amount that the considered phenotype is less fit as measured by...
s, and rates of random change
Mutation rate
In genetics, the mutation rate is the chance of a mutation occurring in an organism or gene in each generation...
." It is put forward that Mendelian selection of allele
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
s (alternative versions of a gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
) is the only kind of selection
Selection
In the context of evolution, certain traits or alleles of genes segregating within a population may be subject to selection. Under selection, individuals with advantageous or "adaptive" traits tend to be more successful than their peers reproductively—meaning they contribute more offspring to the...
imaginable that satisfies these requirements. Elaborating on the nature of selection, he writes that it only works on the basis of whether alleles are better or worse than others in the population, in terms of their immediate fitness
Fitness (biology)
Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...
effects. Survival of the population
Population
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
is beside the point, e.g. populations don't take any measures to avoid impending extinction
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
. Finally he evaluates various ideas about progress in evolution, denying that selection will bring about the kind of progress that some have suggested. The author concludes that his view on the topic is similar to that of most of his colleagues, but worries that it is misrepresented to the public "when biologists become self-consciously philosophical".
See also
- EcologyEcologyEcology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
- MorphogenesisMorphogenesisMorphogenesis , is the biological process that causes an organism to develop its shape...
- Reproduction
- Scientific methodScientific methodScientific method refers to a body of techniques for investigating phenomena, acquiring new knowledge, or correcting and integrating previous knowledge. To be termed scientific, a method of inquiry must be based on gathering empirical and measurable evidence subject to specific principles of...
- Social animalSocial animalA social animal is a loosely defined term for an organism that is highly interactive with other members of its species to the point of having a recognizable and distinct society.All mammals are social to the extent that mothers and offspring bond...
External links
- Adaptation and Natural Selection, Princeton University PressPrinceton University Press-Further reading:* "". Artforum International, 2005.-External links:* * * * *...