What controversial theory in evolutionary biology proposes that most sexually reproducing species will experience little or no evolutionary change and remain in an extended state called stasis?
"disciplines. Defend the extended synthesis Criticism of the extended synthesis Extended evolutionary synthesis The extended evolutionary synthesis consists of a set of theoretical concepts more comprehensive than the earlier modern synthesis of evolutionary biology that took place between 1918 and 1942. The extended evolutionary synthesis was called for in the 1950s by C. H. Waddington, argued for on the basis of punctuated equilibrium by Stephen Jay Gould and Niles Eldredge in the 1980s, and was reconceptualized in 2007 by Massimo Pigliucci and Gerd B. Müller. The extended evolutionary synthesis revisits the relative importance of different factors at play, examining several"
"very little evolutionary change, for a large proportion of the species' lifespan. This would result in increased cases of speciation through cladogenesis and true extinction, with fewer cases of Pseudoextinction. Nearly all species undergo true extinction under the model of punctuated equilibrium. Charles Darwin proposed the idea of stasis in his book, ""On the Origin of Species"". He suggested that species spend the majority of their evolutionary lifespan in the same form, having undergone very little morphological or genetic change. Another concept of species on the tree of life is the composite species concept. It sees one species as occupying"
"by the nature of subdivided populations, normalizing clade selection, and koinophilia. Evidence for the existence of stasis has also been corroborated from the genetics of sibling species, species which are morphologically indistinguishable, but whose proteins have diverged sufficiently to suggest they have been separated for millions of years. According to Gould, ""stasis may emerge as the theory's most important contribution to evolutionary science."" Philosopher Kim Sterelny in clarifying the meaning of stasis adds, ""In claiming that species typically undergo no further evolutionary change once speciation is complete, they are not claiming that there is no change at all between one"
"relied upon ordinary speciation, particularly Ernst Mayr's concept of allopatric speciation. Lastly, and perhaps most significantly, quantum evolution took no position on the issue of stasis. Although Simpson acknowledged the existence of stasis in what he called the bradytelic mode, he considered it (along with rapid evolution) to be unimportant in the larger scope of evolution. In his ""Major Features of Evolution"" Simpson stated, ""Evolutionary change is so nearly the universal rule that a state of motion is, figuratively, normal in evolving populations. The state of rest, as in bradytely, is the exception and it seems that some restraint or"
"Nevertheless, similar but distinct species have sometimes been isolated for a long time without evolving differences, a phenomenon called ""morphological stasis"". As an examples, the Amazonian frog ""Pristimantis ockendeni"" is actually at least three different species that diverged over 5 million years ago. Stabilizing selection has been invoked as a force maintaining similarity in species complexes, especially when adaptation to special environments, such as a host in the case of symbionts, or extreme environments, constrains possible directions of evolution: In such cases, strongly divergent selection is not to be expected. Also, asexual reproduction, such as through apomixis in plants, may"
"studies on speciation patterns in the fossil record showed that 71% of species exhibited stasis, and 63% were associated with punctuated patterns of evolutionary change. According to Michael Benton, ""it seems clear then that stasis is common, and that had not been predicted from modern genetic studies."" A paramount example of evolutionary stasis is the fern ""Osmunda claytoniana"". Based on paleontological evidence it has remained unchanged, even at the level of fossilized nuclei and chromosomes, for at least 180 million years. When Eldredge and Gould published their 1972 paper, allopatric speciation was considered the ""standard"" model of speciation. This model"
"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. Punctuated"
"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. 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"
"they should arise on a chromosome with deleterious genes. Supporters of these theories respond to the balance argument that the individuals produced by sexual and asexual reproduction may differ in other respects too – which may influence the persistence of sexuality. For example, in the heterogamous water fleas of the genus ""Cladocera"", sexual offspring form eggs which are better able to survive the winter versus those the fleas produce asexually. One of the most widely discussed theories to explain the persistence of sex is that it is maintained to assist sexual individuals in resisting parasites, also known as the Red"
"generally reproduce asexually by budding, though sexual reproduction does occur in some groups. The scientific validity of the term ""coelenterate"" is currently disputed, as the Cnidaria and Ctenophora have less in common than previously assumed. Coelentera may only be monophyletic if both Placozoa and Bilateria are included. In particular, the phylogenetic position of Ctenophora is controversial; it was first considered a sub-group of coelenterata but Hyman regarded it as a separate phylum. Some researchers suggest that Coelenterata is not monophyletic, and therefore any group containing Cnidaria and Ctenophora but excluding other phyla would be paraphyletic. However, some genomic studies have"
"Hypothesis. In natural populations of ""C. elegans"", self-fertilization is the predominant mode of reproduction, but infrequent out-crossing events occur at a rate of about 1%. Critics of the Red Queen hypothesis question whether the constantly changing environment of hosts and parasites is sufficiently common to explain the evolution of sex. In particular, Otto and Nuismer presented results showing that species interactions (e.g. host vs parasite interactions) typically select against sex. They concluded that, although the Red Queen hypothesis favors sex under certain circumstances, it alone does not account for the ubiquity of sex. Otto and Gerstein further stated that “it"
"down to the present day."" John Wilkins and Gareth Nelson have argued that French architect Pierre Trémaux proposed an ""anticipation of the theory of punctuated equilibrium of Gould and Eldredge."" The fossil record includes well documented examples of both phyletic gradualism and punctuational evolution. As such, much debate persists over the prominence of stasis in the fossil record. Before punctuated equilibrium, most evolutionists considered stasis to be rare or unimportant. The paleontologist George Gaylord Simpson, for example, believed that phyletic gradual evolution (called ""horotely"" in his terminology) comprised 90% of evolution. More modern studies, including a meta-analysis examining 58 published"
"(parthenogenetic) reproduction for millions of years, the longest period known for any insect. In the grass thrips genus ""Aptinothrips"" there have been several transitions to asexuality, likely due to different causes. Asexual reproduction Asexual reproduction is a type of reproduction by which offspring arise from a single organism, and inherit the genes of that parent only; it does not involve the fusion of gametes, and almost never changes the number of chromosomes. Asexual reproduction is the primary form of reproduction for single-celled organisms such as archaea and bacteria. Many plants and fungi sometimes reproduce asexually. While all prokaryotes reproduce without"
"splitting occurs. 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 palaeontology, the phylogenetic model, states 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"
"against phyletic gradualism, the idea that evolution generally occurs uniformly and by the steady and gradual transformation of whole lineages (called anagenesis). In this view, evolution is seen as generally smooth and continuous. In 1972, paleontologists Niles Eldredge and Stephen Jay Gould published a landmark paper developing their theory and called it ""punctuated equilibria"". Their paper built upon Ernst Mayr's model of geographic speciation, I. Michael Lerner's theories of developmental and genetic homeostasis, and their own empirical research. Eldredge and Gould proposed that the degree of gradualism commonly attributed to Charles Darwin is virtually nonexistent in the fossil record, and"
"the gene-centered view (which held selection as the predominant cause of evolution) and the neutral theory (which made genetic drift a key factor) spawned perennial debates over the proper balance of adaptationism and contingency in evolutionary theory. In the 1970s Stephen Jay Gould and Niles Eldredge proposed the theory of punctuated equilibrium which holds that stasis is the most prominent feature of the fossil record, and that most evolutionary changes occur rapidly over relatively short periods of time. In 1980 Luis Alvarez and Walter Alvarez proposed the hypothesis that an impact event was responsible for the Cretaceous–Paleogene extinction event. Also"
"and Niles Eldredge to contrast with their model of punctuated equilibrium, which is gradualist itself, but argues that most evolution is marked by long periods of evolutionary stability (called stasis), which is punctuated by rare instances of branching evolution. 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 (through a process called anagenesis). In this view no clear line of demarcation exists between an ancestral species and a descendant species, unless"
"George C. Williams, John Maynard Smith and Richard Dawkins. because it is not to the benefit of the individual. Consequently, sexual ""individuals"" would be expected to avoid transmitting mutations to their progeny by avoiding mates with strange or unusual characteristics. Mutations that therefore affect the external appearance and habits of their carriers will seldom be passed on to the next and subsequent generations. They will therefore seldom be tested by natural selection. Evolutionary change in a large population with a wide choice of mates, will, therefore, come to a virtual standstill. The only mutations that can accumulate in a population"
"of eukaryotes and that the genes controlling it have changed very little since then. How sexual reproduction evolved and survived is an unsolved puzzle. The Red Queen hypothesis suggests that sexual reproduction provides protection against parasites, because it is easier for parasites to evolve means of overcoming the defenses of genetically identical clones than those of sexual species that present moving targets, and there is some experimental evidence for this. However, there is still doubt about whether it would explain the survival of sexual species if multiple similar clone species were present, as one of the clones may survive the"
"speciation. There is debate as to the rate at which speciation events occur over geologic time. While some evolutionary biologists claim that speciation events have remained relatively constant and gradual over time (known as ""Phyletic gradualism"" - see diagram), some palaeontologists such as Niles Eldredge and Stephen Jay Gould have argued that species usually remain unchanged over long stretches of time, and that speciation occurs only over relatively brief intervals, a view known as ""punctuated equilibrium"". (See diagram, and .) Evolution can be extremely rapid, as shown in the creation of domesticated animals and plants in a very short geological"
"(see synonymous or silent substitution). Such changes are presumed to have little or no biological effect. A second hypothesis of the neutral theory is that most evolutionary change is the result of genetic drift acting on neutral alleles, rather than for example genetic hitchhiking of a neutral allele due to genetic linkage with non-neutral alleles. After appearing by mutation, a neutral allele may become more common within the population via genetic drift. Usually, it will be lost, or in rare cases it may become fixed, meaning that the new allele becomes standard in the population. This stochastic process is assumed"
"be “almost universal” among sexually reproducing species. Critics proposed that females might be more subject to sexual selection than males, but not in all circumstances. Experimental and statistical criticisms followed. Until approximately a decade ago, critics of Bateman’s model focused on his experimental design. In recent years, they have shifted attention to the actual experimental and statistical calculations Bateman published throughout his trials. Birkhead wrote a 2000 review arguing that since Bateman’s experiments lasted only three to four days, the female fruit fly, ""Drosophila melanogaster"", may not have needed to mate repeatedly, as it can store sperm for up to"
"For this reason, evolution of mutators is generally expected to happen largely in asexual species where recombination cannot disrupt linkage disequilibrium. The neutral theory of molecular evolution assumes that most new mutations are either deleterious (and quickly purged by selection) or else neutral, with very few being adaptive. It also assumes that the behavior of neutral allele frequencies can be described by the mathematics of genetic drift. Genetic hitchhiking has therefore been viewed as a major challenge to neutral theory, and an explanation for why genome-wide versions of the McDonald-Kreitman test appear to indicate a high proportion of mutations becoming"
"Asexual reproduction Asexual reproduction is a type of reproduction by which offspring arise from a single organism, and inherit the genes of that parent only; it does not involve the fusion of gametes, and almost never changes the number of chromosomes. Asexual reproduction is the primary form of reproduction for single-celled organisms such as archaea and bacteria. Many plants and fungi sometimes reproduce asexually. While all prokaryotes reproduce without the formation and fusion of gametes, mechanisms for lateral gene transfer such as conjugation, transformation and transduction can be likened to sexual reproduction in the sense of genetic recombination in meiosis."
"Initially, Chamisso and Steenstrup described the succession of differently organized generations (sexual and asexual) in animals as ""alternation of generations"", while studying the development of tunicates, cnidarians and trematode animals. This phenomenon is also known as heterogamy. Presently, the term ""alternation of generations"" is almost exclusively associated with the life cycles of plants, specifically with the alternation of haploid gametophytes and diploid sporophytes. Wilhelm Hofmeister demonstrated the morphological alternation of generations in plants, between a spore-bearing generation (sporophyte) and a gamete-bearing generation (gametophyte). By that time, a debate emerged focusing on the origin of the asexual generation of land plants"
"Evolution of sexual reproduction The evolution of sexual reproduction describes how sexually reproducing animals, plants, fungi and protists could have evolved from a common ancestor that was a single celled eukaryotic species. There are a few species which have secondarily lost the ability to reproduce sexually, such as Bdelloidea, and some plants and animals that routinely reproduce asexually (by apomixis and parthenogenesis) without entirely losing sex. The evolution of sex contains two related, yet distinct, themes: its ""origin"" and its ""maintenance"". The maintenance of sexual reproduction in a highly competitive world had long been one of the major mysteries of"
"claytoniana"" is a paramount example of evolutionary stasis. Paleontological evidence indicates it has remained unchanged, even at the level of fossilized nuclei and chromosomes, for at least 180 million years. In eastern North America it occurs in: the Great Lakes region; eastern Canada – in southern Manitoba, Ontario, Quebec (north to tree line); and east to Newfoundland; eastern United States – upper New England south through the Appalachian Mountains and Atlantic seaboard, into the Southeastern United States in Georgia and Alabama; and west across the Southern United States to Mississippi River, and back up the Mississippi embayment through the Midwestern"
"have attempted to answer include: Evolution of sexual reproduction The evolution of sexual reproduction describes how sexually reproducing animals, plants, fungi and protists could have evolved from a common ancestor that was a single celled eukaryotic species. There are a few species which have secondarily lost the ability to reproduce sexually, such as Bdelloidea, and some plants and animals that routinely reproduce asexually (by apomixis and parthenogenesis) without entirely losing sex. The evolution of sex contains two related, yet distinct, themes: its ""origin"" and its ""maintenance"". The maintenance of sexual reproduction in a highly competitive world had long been one"
"has no apparent genetic basis, though its occurrence is common. There are at least 10 million identical human twins and triplets in the world today. Bdelloid rotifers reproduce exclusively asexually, and all individuals in the class Bdelloidea are females. Asexuality evolved in these animals millions of years ago and has persisted since. There is evidence to suggest that asexual reproduction has allowed the animals to evolve new proteins through the Meselson effect that have allowed them to survive better in periods of dehydration. Molecular evidence strongly suggests that several species of the stick insect genus ""Timema"" have used only asexual"
"Red Queen hypothesis The Red Queen hypothesis, also referred to as Red Queen's, Red Queen's race or the Red Queen effect, is an evolutionary hypothesis which proposes that organisms must constantly adapt, evolve, and proliferate not merely to gain reproductive advantage, but also simply to survive while pitted against ever-evolving opposing organisms in a constantly changing environment. The hypothesis intends to explain two different phenomena: the constant extinction rates as observed in the paleontological record caused by co-evolution between competing species, and the advantage of sexual reproduction (as opposed to asexual reproduction) at the level of individuals. Leigh Van Valen"
"evolution seen in that new taxa. This is the main concept of phylogenetic inertia. Richard Dawkins also explained these constraints by likening natural selection to a river in his 1982 book ""The Extended Phenotype"". Birds are the only speciose group of vertebrates that are exclusively oviparous, or egg laying. It has been suggested that birds are phylogenetically constrained, as being derived from reptiles, and likely have not overcome this constraint or diverged far enough away to develop viviparity, or live birth. There have been several studies that have been able to effectively test for phylogenetic inertia when looking into shared"
"equilibria to explain trends, it is infuriating to be quoted again and again by creationists—whether through design or stupidity, I do not know—as admitting that the fossil record includes no transitional forms. Transitional forms are generally lacking at the species level, but they are abundant between larger groups."" Although there exist some debate over how long the punctuations last, supporters of punctuated equilibrium generally place the figure between 50,000 and 100,000 years. Quantum evolution was a controversial hypothesis advanced by Columbia University paleontologist George Gaylord Simpson, who was regarded by Gould as ""the greatest and most biologically astute paleontologist of"
"Extended female sexuality Extended female sexuality is where the female of a species mate despite being infertile. In most species, the female only engages in copulation when she is fertile. However, extended sexuality has been documented in old world primates, pair bonded birds and some insects (such as carrion beetles). Extended sexuality is most prominent in human females who exhibit no change in copulation rate across the ovarian cycle. Although this behaviour incurs costs to females, such as energy and time, many researchers have proposed reasons for its existence. These hypotheses include the male assistance hypothesis, which proposes that females"