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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.
Punctuated gradualism is considered to be a variation of these models, lying somewhere in between the phyletic gradualism model and the punctuated equilibrium model. It states that speciation is not needed for a lineage to rapidly evolve from one equilibrium to another but may show rapid transitions between long-stable states.
In 1983, Malmgren and colleagues published a paper called "Evidence for punctuated gradualism in the late Neogene Globorotalia tumida lineage of planktonic foraminifera." [1] This paper studied the lineage of planktonic foraminifera, specifically the evolutionary transition from G. plesiotumida to G. tumida across the Miocene/Pliocene boundary. [1] The study found that the G. tumida lineage, while remaining in relative stasis over a considerable part of its total duration underwent periodic, relatively rapid, morphologic change that did not lead to lineage branching. [1] Based on these findings, Malmgren and colleagues introduced a new mode of evolution and proposed to call it "punctuated gradualism." [1] There is strong evidence supporting both gradual evolution of a species over time and rapid events of species evolution separated by periods of little evolutionary change. Organisms have a great propensity to adapt and evolve depending on the circumstances.
Studies use evidence to predict how organisms evolved in the past and apply this evidence to the present. Both models of evolution can not only be seen between species, but also within a species. This is shown in a study done on the body size evolution in the radiolarian Pseudocubus vema. [2] This study presents evidence of a species exhibiting punctuated and gradual evolution, while also having periods of relative stasis. [2] Another study also used body size and looked at both micro-evolutionary patterns and fossil records. [3] The study uses quantitative data to make conclusions and is an example of another study using body size as an indicator of evolution. [3]
One study focuses on how efforts to apply only one mode of evolution to a phenomenon can be inaccurate. [4] It supports how difficult it can be to show that only one mode of evolution is at play at any given time. [4] Another study also displays the importance of considering both models. The study supports that there can always be both models at play at any time. [5] Another related study focuses on the extent of undefined area when trying to compare the two modes of evolution making it difficult to isolate one model. [6]
There will always be variance in environments. Some environments present challenges that require quick adaptation for survival, while others are relatively stable. In addition, organisms differ in the amount of traits upon which selection can act. These factors along with replication time can create barriers when working to prove a single mode of evolution as being accurate. A study expresses the importance of defining the clear objectives before research is done. The study directly challenges phyletic gradualism and punctuated equilibrium. It shows how many factors can come into play when comparing the two modes of evolution. [7]
Other evidence for the inclusion of both styles of evolution is the consideration of how organisms relate and may interact. Two species that diverged from each other over time may both still possess a characteristic that only one still uses. The species that doesn't use the characteristic might begin to use it for an alternate function, causing difficulty when trying to track evolution. [8] Fossils do not always show the evolution of function.
Another avenue in which evolutionary characteristics are studied is within cancer research. There are studies on many types of cancer where similarities and differences have been identified. One study compares phenotypic characteristics to genotypic characteristics. [9] The study concludes that genomic analysis supports both models and highlights the importance of studying the genotype, phenotype, and the relationship between the two. [9] One study looked at pancreatic cancer. [10] Pancreatic cancer is a rapidly progressing cancer. This study examines the punctuated genomic change that results in the rapid progression of this cancer. [10] Cancer studies are compared to analyze modes of evolution.
A similar study also looks at cancer to describe evolutionary change. This study challenges old conclusions and supports both models using more modern techniques providing current evidence for interpretation. [11] A study looks at breast cancer. This study focuses on genome analysis that some of the previous studies expressed the importance of doing. [12] The study highlights how dynamic the body can be during the progression of cancer. [12] The changes can be seen in cancer cells as they can show patters of punctuation, gradualism, and relative stasis. [12]
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. For the Social democratics, the socialist society is achieved through gradualism.
In evolutionary biology, punctuated equilibrium is a theory that proposes that once a species appears 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.
Stephen Jay Gould 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 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, after which he divided his time teaching between there and Harvard.
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 On the Origin of Species. He also identified sexual selection as a likely mechanism, but found it problematic.
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 bradytelic, horotelic, and tachytelic.
Foraminifera are single-celled organisms, members of a phylum or class of Rhizarian protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly an external shell of diverse forms and materials. Tests of chitin are believed to be the most primitive type. Most foraminifera are marine, the majority of which live on or within the seafloor sediment, while a smaller number float in the water column at various depths, which belong to the suborder Globigerinina. Fewer are known from freshwater or brackish conditions, and some very few (nonaquatic) soil species have been identified through molecular analysis of small subunit ribosomal DNA.
Cladogenesis is an evolutionary splitting of a parent species into two distinct species, forming a clade.
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 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.
Phyletic gradualism is a model of evolution which theorizes that most speciation is slow, uniform and gradual. When evolution occurs in this mode, it is usually by the steady transformation of a whole species into a new one. 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.
In biology, saltation is a sudden and large mutational change from one generation to the next, potentially causing single-step speciation. This was historically offered as an alternative to Darwinism. Some forms of mutationism were effectively saltationist, implying large discontinuous jumps.
Rapid modes of evolution have been proposed by several notable biologists after Charles Darwin proposed his theory of evolutionary descent by natural selection. In his book On the Origin of Species (1859), Darwin stressed the gradual nature of descent, writing:
Punctuated equilibrium in social theory is a conceptual framework for understanding the process of change in complex social systems. The approach studies the evolution of policy change, including the evolution of conflicts. The theory posits that most social systems exist in an extended period of stasis, which may be punctuated by sudden shifts leading to radical change. The theory was largely inspired by the evolutionary biology theory of punctuated equilibrium developed by paleontologists Niles Eldredge and Stephen Jay Gould.
Oxyrrhis is a genus of heterotrophic dinoflagellate, the only genus in the family Oxyrrhinaceae. It inhabits a range of marine environments worldwide and is important in the food web dynamics of these ecosystems. It has the potential to be considered a model organism for the study of other protists. Oxyrrhis is an early-branching lineage and has long been described in literature as a monospecific genus, containing only Oxyrrhis marina. Some recent molecular phylogenetic studies argue that Oxyrrhis comprises O. marina and O. maritima as distinct species, while other publications state that the two are genetically diverse lineages of the same species. The genus has previously been suggested to contain O. parasitica as a separate species, however the current consensus appears to exclude this, with Oxyrrhis being monospecific and containing O. marina and O. maritima as separate lineages of the type species. The genus is characterised by its elongated body which is anteriorly prolonged to a point, its complex flagellar apparatuses which attach to the ventral side of the cell, and the unique features of its nucleus.
Reticulate evolution, or network evolution is the origination of a lineage through the partial merging of two ancestor lineages, leading to relationships better described by a phylogenetic network than a bifurcating tree. Reticulate patterns can be found in the phylogenetic reconstructions of biodiversity lineages obtained by comparing the characteristics of organisms. Reticulation processes can potentially be convergent and divergent at the same time. Reticulate evolution indicates the lack of independence between two evolutionary lineages. Reticulation affects survival, fitness and speciation rates of species.
The rate of evolution is quantified as the speed of genetic or morphological change in a lineage over a period of time. The speed at which a molecular entity evolves is of considerable interest in evolutionary biology since determining the evolutionary rate is the first step in characterizing its evolution. Calculating rates of evolutionary change is also useful when studying phenotypic changes in phylogenetic comparative biology. In either case, it can be beneficial to consider and compare both genomic data and paleontological data, especially in regards to estimating the timing of divergence events and establishing geological time scales.
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.
This glossary of genetics and evolutionary biology is a list of definitions of terms and concepts used in the study of genetics and evolutionary biology, as well as sub-disciplines and related fields, with an emphasis on classical genetics, quantitative genetics, population biology, phylogenetics, speciation, and systematics. It has been designed as a companion to Glossary of cellular and molecular biology, which contains many overlapping and related terms; other related glossaries include Glossary of biology and Glossary of ecology.
The sloshing bucket model of evolution is a theory in evolutionary biology that describes how environmental disturbances varying in magnitude will affect the species present. The theory emphasizes the causal relationship between environmental factors that impinge and affect genealogical systems, providing an overarching view that determines the relationship between the variety of biological systems.
Henry HQ Heng is a professor of molecular medicine and genetics and of pathology at the Wayne State University School of Medicine. Heng first received his PhD from the University of Toronto Hospital for Sick Children in 1994, mentored by Lap-Chee Tsui. He then completed his post-doc under Peter Moens at York University, before joining the Wayne State University School of Medicine faculty.
