Tempo and Mode in Evolution
Encyclopedia
Tempo and Mode in Evolution (1944) was George Gaylord Simpson's
seminal contribution to the evolutionary synthesis
, which integrated the facts of paleontology with those of genetics
and natural selection
.
Simpson argued that the microevolution
of population genetics
was sufficient in itself to explain the patterns of macroevolution
observed by paleontology
. Simpson also highlighted the distinction between tempo and mode. "Tempo" encompasses "evolutionary rates . . . their acceleration and deceleration, the conditions of exceptionally slow or rapid evolutions, and phenomena suggestive of inertia and momentum." While "mode" embraces "the study of the way, manner, or pattern of evolution, a study in which tempo is a basic factor, but which embraces considerably more than tempo."
Simpson's Tempo and Mode attempted to draw out several distinct generalizations:
Tempo and Mode earned Simpson the Daniel Giraud Elliot Medal
from the National Academy of Sciences
in 1944. Fifty years after its publication, the National Academy of Sciences
commissioned a book entitled Tempo and Mode in Evolution: Genetics and Paleontology 50 Years After Simpson edited by Walter M. Fitch
and Francisco J. Ayala
. It includes contributions by Ayala, Stephen Jay Gould
, and W. Ford Doolittle.
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...
seminal contribution to the evolutionary synthesis
Modern evolutionary synthesis
The modern evolutionary synthesis is a union of ideas from several biological specialties which provides a widely accepted account of evolution...
, which integrated the facts of paleontology with those of genetics
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
and 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....
.
Simpson argued that the microevolution
Microevolution
Microevolution is the changes in allele frequencies that occur over time within a population. This change is due to four different processes: mutation, selection , gene flow, and genetic drift....
of population genetics
Population genetics
Population genetics is the study of allele frequency distribution and change under the influence of the four main evolutionary processes: natural selection, genetic drift, mutation and gene flow. It also takes into account the factors of recombination, population subdivision and population...
was sufficient in itself to explain the patterns of macroevolution
Macroevolution
Macroevolution is evolution on a scale of separated gene pools. Macroevolutionary studies focus on change that occurs at or above the level of species, in contrast with microevolution, which refers to smaller evolutionary changes within a species or population.The process of speciation may fall...
observed by paleontology
Paleontology
Paleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...
. Simpson also highlighted the distinction between tempo and mode. "Tempo" encompasses "evolutionary rates . . . their acceleration and deceleration, the conditions of exceptionally slow or rapid evolutions, and phenomena suggestive of inertia and momentum." While "mode" embraces "the study of the way, manner, or pattern of evolution, a study in which tempo is a basic factor, but which embraces considerably more than tempo."
Simpson's Tempo and Mode attempted to draw out several distinct generalizations:
- That evolution's tempo can impart information about its mode.
- That multiple tempos can be found in the fossil record (bradytelic, tachytelic, horotelic).
- That the facts of paleontology are consistent with the genetical theory of natural selectionNeo-DarwinismNeo-Darwinism is the 'modern synthesis' of Darwinian evolution through natural selection with Mendelian genetics, the latter being a set of primary tenets specifying that evolution involves the transmission of characteristics from parent to child through the mechanism of genetic transfer, rather...
. Moreover, that theories such as orthogenesisOrthogenesisOrthogenesis, orthogenetic evolution, progressive evolution or autogenesis, is the hypothesis that life has an innate tendency to evolve in a unilinear fashion due to some internal or external "driving force". The hypothesis is based on essentialism and cosmic teleology and proposes an intrinsic...
, LamarckismLamarckismLamarckism is the idea that an organism can pass on characteristics that it acquired during its lifetime to its offspring . It is named after the French biologist Jean-Baptiste Lamarck , who incorporated the action of soft inheritance into his evolutionary theories...
, mutation pressures, and macromutations are either false or play little to no role. - Most evolution—"nine-tenths"—occurs by the steady phyletic transformation of whole lineages (anagenesis). In contrast to Ernst Mayr'sErnst MayrErnst Walter Mayr was one of the 20th century's leading evolutionary biologists. He was also a renowned taxonomist, tropical explorer, ornithologist, historian of science, and naturalist...
interpretation of speciation by splitting, particularly allopatricAllopatric speciationAllopatric speciation or geographic speciation is speciation that occurs when biological populations of the same species become isolated due to geographical changes such as mountain building or social changes such as emigration...
and peripatricPeripatric speciationPeripatric and peripatry are terms from biogeography, referring to organisms whose ranges are closely adjacent but do not overlap, being separated where these organisms do not occur – for example a wide river or a mountain range. Such organisms are usually closely related Peripatric and...
speciation. - The lack of evidence for evolutionary transitions in the fossil record is best accounted for, first, by the poorness of the geological record, and secondly as a consequence of quantum evolutionQuantum evolutionQuantum evolution is a component of George Gaylord Simpson's multi-tempoed theory of evolutionary change, proposed to explain the rapid emergence of higher taxonomic groups. According to Simpson, evolutionary rates differ from group to group and even among closely related lineages...
(which is responsible for "the origin taxonomic units of relatively high rank, such as families, orders, and classes."). Quantum evolution built upon Sewall Wright'sSewall WrightSewall Green Wright was an American geneticist known for his influential work on evolutionary theory and also for his work on path analysis. With R. A. Fisher and J.B.S. Haldane, he was a founder of theoretical population genetics. He is the discoverer of the inbreeding coefficient and of...
theory of random genetic driftGenetic driftGenetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...
.
Tempo and Mode earned Simpson the Daniel Giraud Elliot Medal
Daniel Giraud Elliot Medal
The Daniel Giraud Elliot Medal is awarded by the U.S. National Academy of Sciences "for meritorious work in zoology or paleontology published in a three- to five-year period." Named after Daniel Giraud Elliot, it was first awarded in 1917....
from the National Academy of Sciences
United States National Academy of Sciences
The National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...
in 1944. Fifty years after its publication, the National Academy of Sciences
United States National Academy of Sciences
The National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...
commissioned a book entitled Tempo and Mode in Evolution: Genetics and Paleontology 50 Years After Simpson edited by Walter M. Fitch
Walter M. Fitch
Walter M. Fitch . Until his death he was professor of molecular evolution at the University of California, Irvine. He was also a member of the National Academy of Sciences, the American Philosophical Society, and the American Association for the Advancement of Science, and was a Foreign Member of...
and Francisco J. Ayala
Francisco J. Ayala
Francisco José Ayala Pereda is a Spanish-American biologist and philosopher at the University of California, Irvine. He is a former Dominican priest, ordained in 1960, but left the priesthood that same year. After graduating from the University of Salamanca, he moved to the US in 1961 to study for...
. It includes contributions by Ayala, Stephen Jay Gould
Stephen Jay Gould
Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation....
, and W. Ford Doolittle.