Phyletic gradualism

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Phyletic gradualism, top, would consist of steady evolutionary change in small steps, in contrast to punctuated equilibrium Punctuated-equilibrium.svg
Phyletic gradualism, top, would consist of steady evolutionary change in small steps, in contrast to punctuated equilibrium
Apparently sudden changes can be explained either by macromutation or by relatively rapid episodes of gradual evolution, since 10,000 years barely registers in the fossil record. Punctuated Equilibrium.svg
Apparently sudden changes can be explained either by macromutation or by relatively rapid episodes of gradual evolution, since 10,000 years barely registers in the fossil record.

Phyletic gradualism is a model of evolution which theorizes that most speciation is slow, uniform and gradual. [1] When evolution occurs in this mode, it is usually by the steady transformation of a whole species into a new one (through a process called anagenesis). In this view no clear line of demarcation exists between an ancestral species and a descendant species, unless splitting occurs. The theory is contrasted with punctuated equilibrium.

Evolution Change in the heritable characteristics of biological populations over successive generations

Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes that are passed on from parent to offspring during reproduction. Different characteristics tend to exist within any given population as a result of mutation, genetic recombination and other sources of genetic variation. Evolution occurs when evolutionary processes such as natural selection and genetic drift act on this variation, resulting in certain characteristics becoming more common or rare within a population. It is this process of evolution that has given rise to biodiversity at every level of biological organisation, including the levels of species, individual organisms and molecules.

Speciation The evolutionary process by which populations evolve to become distinct species

Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within lineages. Charles Darwin was the first to describe the role of natural selection in speciation in his 1859 book The Origin of Species. He also identified sexual selection as a likely mechanism, but found it problematic.

In biology, a species ( ) is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, morphology, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. While these definitions may seem adequate, when looked at more closely they represent problematic species concepts. For example, the boundaries between closely related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, and in a ring species. Also, among organisms that reproduce only asexually, the concept of a reproductive species breaks down, and each clone is potentially a microspecies.

Contents

History

The word phyletic derives from the Greek φυλετικός phūletikos, which conveys the meaning of a line of descent. [2] Phyletic gradualism contrasts with the theory of punctuated equilibrium, which proposes that most evolution occurs isolated in rare episodes of rapid evolution, when a single species splits into two distinct species, followed by a long period of stasis or non-change. These models both contrast with variable-speed evolution ("variable speedism"), which maintains that different species evolve at different rates, and that there is no reason to stress one rate of change over another. [3] [4]

Greek language language spoken in Greece, Cyprus and Southern Albania

Greek is an independent branch of the Indo-European family of languages, native to Greece, Cyprus and other parts of the Eastern Mediterranean and the Black Sea. It has the longest documented history of any living Indo-European language, spanning more than 3000 years of written records. Its writing system has been the Greek alphabet for the major part of its history; other systems, such as Linear B and the Cypriot syllabary, were used previously. The alphabet arose from the Phoenician script and was in turn the basis of the Latin, Cyrillic, Armenian, Coptic, Gothic, and many other writing systems.

Punctuated equilibrium theory in evolutionary biology

Punctuated equilibrium is a theory in evolutionary biology which proposes that once species appear in the fossil record the population will become stable, showing little evolutionary change for most of its geological history. This state of little or no morphological change is called stasis. When significant evolutionary change occurs, the theory proposes that it is generally restricted to rare and geologically rapid events of branching speciation called cladogenesis. Cladogenesis is the process by which a species splits into two distinct species, rather than one species gradually transforming into another.

Evolutionary biologist Richard Dawkins argues that constant-rate gradualism is not present in the professional literature, thereby the term serves only as a straw-man for punctuated-equilibrium advocates. In his book The Blind Watchmaker , Dawkins observes that Charles Darwin himself was not a constant-rate gradualist, as suggested by Niles Eldredge and Stephen Jay Gould. In the first edition of On the Origin of Species , Darwin stated that "Species of different genera and classes have not changed at the same rate, or in the same degree. In the oldest tertiary beds a few living shells may still be found in the midst of a multitude of extinct forms... The Silurian Lingula differs but little from the living species of this genus". [5]

Richard Dawkins English ethologist, evolutionary biologist and author

Clinton Richard Dawkins, is an English ethologist, evolutionary biologist, and author. He is an emeritus fellow of New College, Oxford, and was the University of Oxford's Professor for Public Understanding of Science from 1995 until 2008.

<i>The Blind Watchmaker</i> Book by Richard Dawkins

The Blind Watchmaker: Why the Evidence of Evolution Reveals a Universe without Design is a 1986 book by Richard Dawkins, in which the author presents an explanation of, and argument for, the theory of evolution by means of natural selection. He also presents arguments to refute certain criticisms made on his first book, The Selfish Gene. An unabridged audiobook edition was released in 2011, narrated by Richard Dawkins and Lalla Ward.

Charles Darwin British naturalist, author of "On the origin of species, by means of natural selection"

Charles Robert Darwin, was an English naturalist, geologist and biologist, best known for his contributions to the science of evolution. His proposition that all species of life have descended over time from common ancestors is now widely accepted, and considered a foundational concept in science. In a joint publication with Alfred Russel Wallace, he introduced his scientific theory that this branching pattern of evolution resulted from a process that he called natural selection, in which the struggle for existence has a similar effect to the artificial selection involved in selective breeding.

Lingula is among the few brachiopods surviving today but also known from fossils over 500 million years old. In the fifth edition of The Origin of Species, Darwin wrote that "the periods during which species have undergone modification, though long as measured in years, have probably been short in comparison with the periods during which they retain the same form". [6]

See also

Punctuated gradualism

Punctuated gradualism is a microevolutionary hypothesis that refers to a species that has "relative stasis over a considerable part of its total duration [and] underwent periodic, relatively rapid, morphologic change that did not lead to lineage branching". It is one of the three common models of evolution. While the traditional model of paleontology, the phylogenetic model, posits that features evolved slowly without any direct association with speciation, the relatively newer and more controversial idea of punctuated equilibrium claims that major evolutionary changes don't happen over a gradual period but in localized, rare, rapid events of branching speciation.

Quantum evolution Evolution where transitional forms are particularly unstable and do not last long

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 the fossil record. According to Simpson, evolutionary rates differ from group to group and even among closely related lineages. These different rates of evolutionary change were designated by Simpson as horotelic, bradytelic, and tachytelic.

Related Research Articles

Gradualism, from the Latin gradus ("step"), is a hypothesis, a theory or a tenet assuming that change comes about gradually or that variation is gradual in nature and happens over time as opposed to in large steps. Uniformitarianism, incrementalism, and reformism are similar concepts.

Stephen Jay Gould American evolutionary biologist and historian of science

Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read authors of popular science of his generation. Gould spent most of his career teaching at Harvard University and working at the American Museum of Natural History in New York. In 1996, Gould was hired as the Vincent Astor Visiting Research Professor of Biology at New York University, where he divided his time teaching there and at Harvard.

Milford Howell Wolpoff is a paleoanthropologist working as a professor of anthropology and adjunct associate research scientist, Museum of Anthropology, at the University of Michigan. He was born in 1942 to Ruth (Silver) and Ben Wolpoff, in Chicago. He is the leading proponent of the multiregional evolution hypothesis that attempts to explain the evolution of Homo sapiens as a consequence of evolutionary processes within a single species. He is the author of Paleoanthropology and the co-author of Race and Human Evolution: A Fatal Attraction, which reviews the scientific evidence and conflicting theories about how human evolution has been interpreted, and how its interpretation is related to views about race.

The Beak of the Finch: A Story of Evolution in Our Time (ISBN 0-679-40003-6) is a 1994 nonfiction book about evolutionary biology, written by Jonathan Weiner. It won the 1995 Pulitzer Prize for General Non-Fiction. In 2014, a substantially unchanged 20th-anniversary edition e-book was issued with a preface by the author.

Niles Eldredge is a U.S. biologist and paleontologist, who, along with Stephen Jay Gould, proposed the theory of punctuated equilibrium in 1972.

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.

Pseudoextinction

Pseudoextinction of a species occurs when all members of the species are extinct, but members of a daughter species remain alive. The term pseudoextinction refers to the evolution of a species into a new form, with the resultant disappearance of the ancestral form. Pseudoextinction results in the relationship between ancestor and descendant still existing even though the ancestor species no longer exists.

<i>The Structure of Evolutionary Theory</i> book on macroevolutionary theory by Stephen Jay Gould

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 months before Gould's death. Aimed primarily at professionals, the volume is divided into two parts. The first is a historical study of classical evolutionary thought, drawing extensively upon primary documents; the second is a constructive critique of the modern synthesis, and presents a case for an interpretation of biological evolution based largely on hierarchical selection, and the theory of punctuated equilibrium.

Natura non facit saltus has been an important principle of natural philosophy. It appears as an axiom in the works of Gottfried Leibniz, one of the inventors of the infinitesimal calculus. It is also an essential element of Charles Darwin's treatment of natural selection in his Origin of Species. The Latin translation comes from Linnaeus' Philosophia Botanica.

Koinophilia

Koinophilia is an evolutionary hypothesis proposing that during sexual selection, animals preferentially seek mates with a minimum of unusual or mutant features, including functionality, appearance and behavior. Koinophilia intends to explain the clustering of sexual organisms into species and other issues described by Darwin's Dilemma. The term derives from the Greek, koinos, "common", "that which is shared", and philia, "fondness".

<i>Dawkins vs. Gould</i> Book by Kim Sterelny

Dawkins vs. Gould: Survival of the Fittest is a book about the differing views of biologists Richard Dawkins and Stephen Jay Gould by philosopher of biology Kim Sterelny. When first published in 2001 it became an international best-seller. A new edition was published in 2007 to include Gould's The Structure of Evolutionary Theory finished shortly before his death in 2002, and more recent works by Dawkins. The synopsis below is from the 2007 publication.

Introduction to evolution A non-technical explanation of the basic concepts and principles of biological evolution

Evolution is the process of change in all forms of life over generations, and evolutionary biology is the study of how evolution occurs. Biological populations evolve through genetic changes that correspond to changes in the organisms' observable traits. Genetic changes include mutations, which are caused by damage or replication errors in organisms' DNA. As the genetic variation of a population drifts randomly over generations, natural selection gradually leads traits to become more or less common based on the relative reproductive success of organisms with those traits.

The rate of evolution is a variable of considerable interest in evolutionary biology. It concerns the limits of adaptation to natural environments as well as the limits of artificial selection.

<i>Frozen Evolution</i>

Frozen Evolution is a 2008 book written by parasitologist Jaroslav Flegr, which aims to explain modern developments in evolutionary biology. It also contains information boxes which clarify important topics in science like peer review, scientific journals, citation metrics, philosophy of science, paradigm shifts, and Occam's razor. Flegr's previous research in toxoplasmosis is also mentioned.

References

  1. ↑ Eldredge, N. and S. J. Gould (1972). "Punctuated equilibria: an alternative to phyletic gradualism" In T.J.M. Schopf, ed., Models in Paleobiology. San Francisco: Freeman Cooper. p. 84.
  2. ↑ φυλετικός phūletikos originates from φυλέτης phūletēs "one of the same tribe," from φυλή phulē, "clan, race, people", derived from φύεσθαι phuesthai, "to descend, to originate."
  3. ↑ Dawkins, Richard. 1996. The Blind Watchmaker . New York: W. W. Norton & Company. ISBN   0-393-31570-3
  4. ↑ Futuyma, Douglas. 2005. Evolution. Sunderland MA: Sinauer Associates, pp. 86-89
  5. ↑ Charles Darwin, 1859. On the origin of species London: John Murray. 1st edition, p. 313.
  6. ↑ Charles Darwin, 1869. The Origin of Species London: John Murray. 5th edition, p. 551.
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