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13.8 Late 20th Century

– Gene-centred view

In the mid-1960s, George C. Williams strongly critiqued explanations of adaptations worded in terms of “survival of the species”. Such explanations were largely replaced by a gene-centred view of evolution, epitomized by the kin selection arguments of W. D. Hamilton, George R. Price and John Maynard Smith. This viewpoint would be summarized and popularized in the influential 1976 book “The Selfish Gene by Richard Dawkins”. Models of the period showed that group selection was severely limited in its strength; though newer models do admit the possibility of significant multi-level selection.

In 1973, Leigh Van Valen proposed the term “Red Queen” to describe a scenario where a species involved in one or more evolutionary arms races would have to constantly change just to keep pace with the species with which it was co-evolving. Hamilton, Williams and others suggested that this idea might explain the evolution of sexual reproduction. The gene-centric view has also led to an increased interest in Darwin’s old idea of sexual selection, and more recently in topics such as sexual conflict and intragenomic conflict.

– Sociobiology

W. D. Hamilton’s work on kin selection contributed to the emergence of the discipline of sociobiology. The existence of altruistic behaviours has been a difficult problem for evolutionary theorists from the beginning. Significant progress was made in 1964 when Hamilton formulated the inequality in kin selection known as Hamilton’s rule. Other theories followed, some derived from game theory, such as reciprocal altruism. In 1975, E.O. Wilson published the influential and highly controversial book “Sociobiology: The New Synthesis” which claimed evolutionary theory could help explain many aspects of animal, including human, behaviour. Critics claimed that the theories of sociobiologists often reflected their own ideological biases.

– Evolutionary paths and processes

One of the most prominent debates arising during the 1970s was over the theory of punctuated equilibrium. Niles Eldredge and Stephen Jay Gould proposed that there was a pattern of fossil species that remained largely unchanged for long periods, interspersed with relatively brief periods of rapid change during speciation. Improvements in sequencing methods resulted in a large increase of sequenced genomes, allowing the testing and refining of evolutionary theories using this huge amount of genome data. Comparisons between these genomes provide insights into the molecular mechanisms of speciation and adaptation. Advances in computational hardware and software allow the testing and extrapolation of increasingly advanced evolutionary models and the development of the field of systems biology. One of the results has been an exchange of ideas between theories of biological evolution and the field of computer science known as evolutionary computation. Discoveries in biotechnology now allow the modification of entire genomes, advancing evolutionary studies to the level where future experiments may involve the creation of entirely synthetic organisms.

– Microbiology and horizontal gene transfer

Microbiology was largely ignored by early evolutionary theory. Now, evolutionary researchers are taking advantage of their improved understanding of microbial physiology and ecology, produced by the comparative ease of microbial genomics, to explore the taxonomy and evolution of these organisms. These studies are revealing unanticipated levels of diversity amongst microbes.

One particularly important outcome from studies on microbial evolution was the discovery in Japan of horizontal gene transfer in 1959. This transfer of genetic material between different species of bacteria was first recognized since it played a major role in the spread of antibiotic resistance. More recently, as knowledge of genomes has continued to expand, it has been suggested that lateral transfer of genetic material has played an important role in the evolution of all organisms. These high levels of horizontal gene transfer have led to suggestions that the family tree of today’s organisms, the so-called “tree of life”, is more similar to an interconnected web or net.

– Evolutionary developmental biology

The evolutionary biologist Stephen Jay Gould revived earlier ideas of heterochrony, alterations in the relative rates of developmental processes over the course of evolution, to account for the generation of novel forms. The evolutionary biologist Richard Lewontin wrote an influential paper in 1979 suggesting that a change in one biological structure, or even a structural novelty, could arise incidentally as an accidental result of selection on another structure, rather than through direct selection for that particular adaptation. They called such incidental structural changes “spandrels” after an architectural feature.

Molecular data regarding the mechanisms underlying development accumulated rapidly during the 1980s and ’90s. It became clear that the diversity of animal morphology was not the result of different sets of proteins regulating the development of different animals, but from changes in the deployment of a small set of proteins that were common to all animals. These proteins became known as the “developmental toolkit“.

More recent work in this field by Mary Jane West-Eberhard has emphasized phenotypic and developmental plasticity. It has been suggested, for example, that the rapid emergence of basic animal body plans in the Cambrian explosion was due in part to changes in the environment acting on inherent material properties of cell aggregates, such as differential cell adhesion and biochemical oscillation. The resulting forms were later stabilized by natural selection.