''Tempo and Mode in Evolution'' (1944) was George Gaylord Simpson's seminal contribution to the

evolutionary synthesis Modern synthesis or modern evolutionary synthesis refers to several perspectives on evolutionary biology, namely: * Modern synthesis (20th century), the term coined by Julian Huxley in 1942 to denote the synthesis between Mendelian genetics and s ...

, which integrated the facts of paleontology with those of

genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar wor ...

and

natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charle ...

. Simpson argued that the

microevolution Microevolution is the change in allele frequencies that occurs over time within a population. This change is due to four different processes: mutation, selection (natural and artificial), gene flow and genetic drift. This change happens over a r ...

population genetics Population genetics is a subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and pop ...

was sufficient in itself to explain the patterns of

macroevolution Macroevolution usually means the evolution of large-scale structures and traits that go significantly beyond the intraspecific variation found in microevolution (including speciation). In other words, macroevolution is the evolution of taxa abov ...

observed by

paleontology Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

. 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: * Evolution's tempo can impart information about its mode. * Multiple tempos can be found in the fossil record: horotelic (medium tempo), bradytelic (slow tempo), and tachytelic (rapid tempo). * The facts of paleontology are consistent with the genetical theory of natural selection. Moreover, theories such as

orthogenesis Orthogenesis, also known as orthogenetic evolution, progressive evolution, evolutionary progress, or progressionism, is an obsolete biological hypothesis that organisms have an innate tendency to evolve in a definite direction towards some go ...

Lamarckism Lamarckism, also known as Lamarckian inheritance or neo-Lamarckism, is the notion that an organism can pass on to its offspring physical characteristics that the parent organism acquired through use or disuse during its lifetime. It is also calle ...

, mutation pressures, and macromutations either are false or play little to no role. * Most evolution—"nine-tenths"—occurs by the steady phyletic transformation of whole lineages (

anagenesis Anagenesis is the gradual evolution of a species that continues to exist as an interbreeding population. This contrasts with cladogenesis, which occurs when there is branching or splitting, leading to two or more lineages and resulting in separate ...

). This contrasts with Ernst Mayr's interpretation of speciation by splitting, particularly

allopatric Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...

and peripatric 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, second, as a consequence of

quantum evolution Quantum evolution is a component of George Gaylord Simpson's multi-tempoed theory of evolution proposed to explain the rapid emergence of higher taxonomic groups In biology, taxonomy () is the scientific study of naming, defining ( circumscr ...

(which is responsible for "the origin of taxonomic units of relatively high rank, such as families, orders, and classes"). Quantum evolution built upon Sewall Wright's theory of

random genetic drift Genetic drift, also known as allelic drift or the Wright effect, is the change in the frequency of an existing gene variant (allele) in a population due to random chance. Genetic drift may cause gene variants to disappear completely and there ...

. ''Tempo and Mode'' earned Simpson the

Daniel Giraud Elliot Medal The Daniel Giraud Elliot Medal is awarded by the U.S. United States National Academy of Sciences, National Academy of Sciences "for meritorious work in zoology or paleontology study published in a three- to five-year period." Named after Daniel Gir ...

from the

National Academy of Sciences The National Academy of Sciences (NAS) is a United States nonprofit, non-governmental organization. NAS is part of the National Academies of Sciences, Engineering, and Medicine, along with the National Academy of Engineering (NAE) and the Nati ...

in 1944. Fifty years after its publication, the

commissioned a book entitled ''Tempo and Mode in Evolution: Genetics and Paleontology 50 Years After Simpson'' edited by

Walter M. Fitch Walter Monroe Fitch (May 21, 1929 – March 10, 2011) was a pioneering American researcher in molecular evolution. Education and career Fitch attended University of California, Berkeley, where he graduated with an A.B. in chemistry in 1953 and a ...

and

Francisco J. Ayala Francisco José Ayala Pereda (born March 12, 1934) is a Spanish-American evolutionary biologist, philosopher, and former Catholic priest who was a longtime faculty member at the University of California, Irvine and University of California, Dav ...

. It includes contributions by Ayala,

Stephen Jay Gould Stephen Jay Gould (; September 10, 1941 – May 20, 2002) was an American paleontologist, evolutionary biologist, and historian of science. He was one of the most influential and widely read authors of popular science of his generation. Gould sp ...

, and W. Ford Doolittle.

References

{{Reflist * Eldredge, N. (1995) ''Reinventing Darwin''. New York: John Wiley & Sons. pp. 20–26. * Fitch, W. M. and F. J. Ayala (1995)
Tempo and Mode in Evolution: Genetics and Paleontology 50 Years After Simpson
'. New York: National Academies Press. * Gould, S. J. (1980) "G. G. Simpson, Paleontology and the Modern Synthesis." In E. Mayr and W. B. Provine, eds., ''The Evolutionary Synthesis''. Cambridge MA: Harvard University Press, pp. 153–172. * Gould, S. J. (1983
"The hardening of the Modern Synthesis"
In Marjorie Grene, ed., ''Dimensions of Darwinism''. Cambridge UK: Cambridge University Press, pp. 71–93. * Gould, S. J. (1994
"Tempo and mode in the macroevolutionary reconstruction on Darwinism"
''PNAS USA'' 91(15):6764-71. * Gould, S. J. (2002) ''

The Structure of Evolutionary Theory ''The Structure of Evolutionary Theory'' (2002) is Harvard paleontologist Stephen Jay Gould's technical book on macroevolution and the historical development of evolutionary theory. The book was twenty years in the making, published just two mon ...

''. Cambridge MA: Belknap Press. pp. 529–31. * Mayr, E. (1976) ''Evolution and the Diversity of Life''. Cambridge MA: Belknap Press. p. 206. * Mayr, E. (1982) ''

The Growth of Biological Thought ''The Growth of Biological Thought'' (992 pages, Belknap Press, ) is a book written by Ernst Mayr, first published in 1982. It is subtitled Diversity, Evolution, and Inheritance, and is as much a book of philosophy and history as it is of bi ...

''. Cambridge MA: Belknap Press. pp. 555, 609–10. * Simpson, G. G. (1944) ''Tempo and Mode in Evolution''. New York: Columbia Univ. Press.

External links

George Gaylord Simpson: Natural Selection and the Fossil Record
1944 non-fiction books Books about evolution Modern synthesis (20th century)