Peripatric speciation

From Wikipedia, the free encyclopedia

Figure 1: Peripatric speciation

 

Figure 2: Centrifugal speciation

 

Diagrams representing the process of peripatric and centrifugal speciation. In peripatry, a small population becomes isolated on the periphery of the central population evolving reproductive isolation (blue) due to reduced gene flow. In centrifugal speciation, an original population (green) range expands and contracts, leaving an isolated fragment population behind. The central population (changed to blue) evolves reproductive isolation in contrast to peripatry.

 

Peripatric speciation is a mode of speciation in which a new species is formed from an isolated peripheral population. Since peripatric speciation resembles allopatric speciation, in that populations are isolated and prevented from exchanging genes, it can often be difficult to distinguish between them. Nevertheless, the primary characteristic of peripatric speciation proposes that one of the populations is much smaller than the other. The terms peripatric and peripatry are often used in biogeography, referring to organisms whose ranges are closely adjacent but do not overlap, being separated where these organisms do not occur—for example on an oceanic island compared to the mainland. Such organisms are usually closely related (e.g. sister species); their distribution being the result of peripatric speciation.

The concept of peripatric speciation was first outlined by the evolutionary biologist Ernst Mayr in 1954. Since then, other alternative models have been developed such as centrifugal speciation, that posits that a species' population experiences periods of geographic range expansion followed by shrinking periods, leaving behind small isolated populations on the periphery of the main population. Other models have involved the effects of sexual selection on limited population sizes. Other related models of peripherally isolated populations based on chromosomal rearrangements have been developed such as budding speciation and quantum speciation.

The existence of peripatric speciation is supported by observational evidence and laboratory experiments. Scientists observing the patterns of a species biogeographic distribution and its phylogenetic relationships are able to reconstruct the historical process by which they diverged. Further, oceanic islands are often the subject of peripatric speciation research due to their isolated habitats—with the Hawaiian Islands widely represented in much of the scientific literature.

History

Peripatric speciation was originally proposed by Ernst Mayr in 1954, and fully theoretically modeled in 1982. It is related to the founder effect, where small living populations may undergo selection bottlenecks. The founder effect is based on models that suggest peripatric speciation can occur by the interaction of selection and genetic drift, which may play a significant role. Mayr first conceived of the idea by his observations of kingfisher populations in New Guinea and its surrounding islands. Tanysiptera galatea was largely uniform in morphology on the mainland, but the populations on the surrounding islands differed significantly—referring to this pattern as "peripatric". This same pattern was observed by many of Mayr's contemporaries at the time such as by E. B. Ford's studies of Maniola jurtina. Around the same time, the botanist Verne Grant developed a model of quantum speciation very similar to Mayr's model in the context of plants.

In what has been called Mayr's genetic revolutions, he postulated that genetic drift played the primary role that resulted in this pattern. Seeing that a species cohesion is maintained by conservative forces such as epistasis and the slow pace of the spread of favorable alleles in a large population (based heavily on J. B. S. Haldane's calculations), he reasoned that speciation could only take place in which a population bottleneck occurred. A small, isolated, founder population could be established on an island for example. Containing less genetic variation from the main population, shifts in allele frequencies may occur from different selection pressures. This to further changes in the network of linked loci, driving a cascade of genetic change, or a "genetic revolution"—a large-scale reorganization of the entire genome of the peripheral population. Mayr did recognize that the chances of success were incredibly low and that extinction was likely; though noting that some examples of successful founder populations existed at the time.

Shortly after Mayr, William Louis Brown, Jr. proposed an alternative model of peripatric speciation in 1957 called centrifugal speciation. In 1976 and 1980, the Kaneshiro model of peripatric speciation was developed by Kenneth Y. Kaneshiro which focused on sexual selection as a driver for speciation during population bottlenecks.

Models

Peripatric

Peripatric speciation models are identical to models of vicariance (allopatric speciation). Requiring both geographic separation and time, speciation can result as a predictable byproduct. Peripatry can be distinguished from allopatric speciation by three key features:

• The size of the isolated population
• Strong selection caused by the dispersal and colonization of novel environments,
• The effects of genetic drift on small populations.

The size of a population is important because individuals colonizing a new habitat likely contain only a small sample of the genetic variation of the original population. This promotes divergence due to strong selective pressures, leading to the rapid fixation of an allele within the descendant population. This gives rise to the potential for genetic incompatibilities to evolve. These incompatibilities cause reproductive isolation, giving rise to—sometimes rapid—speciation events. Furthermore, two important predictions are invoked, namely that geological or climactic changes cause populations to become locally fragmented (or regionally when considering allopatric speciation), and that an isolated population's reproductive traits evolve enough as to prevent interbreeding upon potential secondary contact.

The peripatric model results in, what have been called, progenitor-derivative species pairs, whereby the derivative species (the peripherally isolated population)—geographically and genetically isolated from the progenitor species—diverges. A specific phylogenetic signature results from this mode of speciation: the geographically widespread progenitor species becomes paraphyletic (thereby becoming a paraspecies), with respect to the derivative species (the peripheral isolate). The concept of a paraspecies is therefore a logical consequence of the evolutionary species concept, by which one species gives rise to a daughter species. It is thought that the character traits of the peripherally isolated species become apomorphic, while the central population remains pleisomorphic.

Modern cladistic methods have developed definitions that have incidentally removed derivative species by defining clades in a way that assumes that when a speciation event occurs, the original species no longer exists, while two new species arise; this is not the case in peripatric speciation. Mayr warned against this, as it causes a species to lose their classification status. Loren H. Rieseberg and Luc Brouillet recognized the same dilemma in plant classification.

Quantum and budding speciation

The botanist Verne Grant proposed the term quantum speciation that combined the ideas of J. T. Gulick (his observation of the variation of species in semi-isolation), Sewall Wright (his models of genetic drift), Mayr (both his peripatric and genetic revolution models), and George Gaylord Simpson (his development of the idea of quantum evolution). Quantum speciation is a rapid process with large genotypic or phenotypic effects, whereby a new, cross-fertilizing plant species buds off from a larger population as a semi-isolated peripheral population. Interbreeding and genetic drift takes place due to the reduced population size, driving changes to the genome that would most likely result in extinction (due to low adaptive value). In rare instances, chromosomal traits with adaptive value may arise, resulting in the origin of a new, derivative species. Evidence for the occurrence of this type of speciation has been found in several plant species pairs: Layia discoidea and L. glandulosa, Clarkia lingulata and C. biloba, and Stephanomeria malheurensis and S. exigua ssp. coronaria.

A closely related model of peripatric speciation is called budding speciation—largely applied in the context of plant speciation. The budding process, where a new species originates at the margins of an ancestral range, is thought to be common in plants—especially in progenitor-derivative species pairs.

Centrifugal speciation

William Louis Brown, Jr. proposed an alternative model of peripatric speciation in 1957 called centrifugal speciation. This model contrasts with peripatric speciation by virtue of the origin of the genetic novelty that leads to reproductive isolation. A population of a species experiences periods of geographic range expansion followed by periods of contraction. During the contraction phase, fragments of the population become isolated as small refugial populations on the periphery of the central population. Because of the large size and potentially greater genetic variation within the central population, mutations arise more readily. These mutations are left in the isolated peripheral populations, whereby, promoting reproductive isolation. Consequently, Brown suggested that during another expansion phase, the central population would overwhelm the peripheral populations, hindering speciation. However, if the species finds a specialized ecological niche, the two may coexist. The phylogenetic signature of this model is that the central population becomes derived, while the peripheral isolates stay pleisomorphic—the reverse of the general model. In contrast to centrifugal speciation, peripatric speciation has sometimes been referred to as centripetal speciation (see figures 1 and 2 for a contrast). Centrifugal speciation has been largely ignored in the scientific literature, often dominated by the traditional model of peripatric speciation. Despite this, Brown cited a wealth of evidence to support his model, of which has not yet been refuted.

Peromyscus polionotus and P. melanotis (the peripherally isolated species from the central population of P. maniculatus) arose via the centrifugal speciation model. Centrifugal speciation may have taken place in tree kangaroos, South American frogs (Ceratophrys), shrews (Crocidura), and primates (Presbytis melalophos). John C. Briggs associates centrifugal speciation with centers of origin, contending that the centrifugal model is better supported by the data, citing species patterns from the proposed 'center of origin' within the Indo-West Pacific.

Kaneshiro model

In the Kaneshiro model, a sample of a larger population results in an isolated population with less males containing attractive traits. Over time, choosy females are selected against as the population increases. Sexual selection drives new traits to arise (green), reproductively isolating the new population from the old one (blue).

 

When a sexual species experiences a population bottleneck—that is, when the genetic variation is reduced due to small population size—mating discrimination among females may be altered by the decrease in courtship behaviors of males. Sexual selection pressures may become weakened by this in an isolated peripheral population, and as a by-product of the altered mating recognition system, secondary sexual traits may appear. Eventually, a growth in population size paired with novel female mate preferences will give rise to reproductive isolation from the main population-thereby completing the peripatric speciation process. Support for this model comes from experiments and observation of species that exhibit asymmetric mating patterns such as the Hawaiian Drosophila species or the Hawaiian cricket Laupala. However, this model has not been entirely supported by experiments, and therefore, it may not represent a plausible process of peripatric speciation that takes place in nature.

Evidence

Observational evidence and laboratory experiments support the occurrence of peripatric speciation. Islands and archipelagos are often the subject of speciation studies in that they represent isolated populations of organisms. Island species provide direct evidence of speciation occurring peripatrically in such that, "the presence of endemic species on oceanic islands whose closest relatives inhabit a nearby continent" must have originated by a colonization event. Comparative phylogeography of oceanic archipelagos shows consistent patterns of sequential colonization and speciation along island chains, most notably on the Azores islands, Canary Islands, Society Islands, Marquesas Islands, Galápagos Islands, Austral Islands, and the Hawaiian Islands—all of which express geological patterns of spatial isolation and, in some cases, linear arrangement. Peripatric speciation also occurs on continents, as isolation of small populations can occur through various geographic and dispersion events. Laboratory studies have been conducted where populations of Drosophila, for example, are separated from one another and evolve in reproductive isolation.

Hawaiian archipelago

Colonization events of species from the genus Cyanea (green) and species from the genus Drosophila (blue) on the Hawaiian island chain. Islands age from left to right, (Kauai being the oldest and Hawaii being the youngest). Speciation arises peripatrically as they spatiotemporally colonize new islands along the chain. Lighter blue and green indicate colonization in the reverse direction from young-to-old.

 

A map of the Hawaiian archipelago showing the colonization routes of Theridion grallator superimposed. Purple lines indicate colonization occurring in conjunction with island age where light purple indicates backwards colonization. T. grallator is not present on Kauai or Niihau so colonization may have occurred from there, or the nearest continent.

 

The sequential colonization and speciation of the ‘Elepaio subspecies along the Hawaiian island chain.

 

Drosophila species on the Hawaiian archipelago have helped researchers understand speciation processes in great detail. It is well established that Drosophila has undergone an adaptive radiation into hundreds of endemic species on the Hawaiian island chain; originating from a single common ancestor (supported from molecular analysis). Studies consistently find that colonization of each island occurred from older to younger islands, and in Drosophila, speciating peripatrically at least fifty percent of the time. In conjunction with Drosophila, Hawaiian lobeliads (Cyanea) have also undergone an adaptive radiation, with upwards of twenty-seven percent of extant species arising after new island colonization—exemplifying peripatric speciation—once again, occurring in the old-to-young island direction.

Other endemic species in Hawaii also provide evidence of peripatric speciation such as the endemic flightless crickets (Laupala). It has been estimated that, "17 species out of 36 well-studied cases of [Laupala] speciation were peripatric". Plant species in genera's such as Dubautia, Wilkesia, and Argyroxiphium have also radiated along the archipelago. Other animals besides insects show this same pattern such as the Hawaiian amber snail (Succinea caduca), and ‘Elepaio flycatchers.

Tetragnatha spiders have also speciated peripatrically on the Hawaiian islands, Numerous arthropods have been documented existing in patterns consistent with the geologic evolution of the island chain, in such that, phylogenetic reconstructions find younger species inhabiting the geologically younger islands and older species inhabiting the older islands (or in some cases, ancestors date back to when islands currently below sea level were exposed). Spiders such as those from the genus Orsonwelles exhibit patterns compatible with the old-to-young geology. Other endemic genera such as Argyrodes have been shown to have speciated along the island chain. Pagiopalus, Pedinopistha, and part of the family Thomisidae have adaptively radiated along the island chain, as well as the wolf spider family, Lycosidae.

A host of other Hawaiian endemic arthropod species and genera have had their speciation and phylogeographical patterns studied: the Drosophila grimshawi species complex, damselflies (Megalagrion xanthomelas and Megalagrion pacificum), Doryonychus raptor, Littorophiloscia hawaiiensis, Anax strenuus, Nesogonia blackburni, Theridion grallator, Vanessa tameamea, Hyalopeplus pellucidus, Coleotichus blackburniae, Labula, Hawaiioscia, Banza (in the family Tettigoniidae), Caconemobius, Eupethicea, Ptycta, Megalagrion, Prognathogryllus, Nesosydne, Cephalops, Trupanea, and the tribe Platynini—all suggesting repeated radiations among the islands.

Other islands

Phylogenetic studies of a species of crab spider (Misumenops rapaensis) in the genus Thomisidae located on the Austral Islands have established the, "sequential colonization of [the] lineage down the Austral archipelago toward younger islands". M. rapaensis has been traditionally thought of as a single species; whereas this particular study found distinct genetic differences corresponding to the sequential age of the islands. The figwart plant species Scrophularia lowei is thought to have arisen through a peripatric speciation event, with the more widespread mainland species, Scrophularia arguta dispersing to the Macaronesian islands. Other members of the same genus have also arisen by single colonization events between the islands.

Species patterns on continents

The southern chestnut-tailed antbird, Sciaphylax hemimelaena

 

Satellite image of the Noel Kempff Mercado National Park (outlined in green) in Bolivia, South America. The white arrow indicates the location of the isolated forest fragment.

 

The occurrence of peripatry on continents is more difficult to detect due to the possibility of vicariant explanations being equally likely. However, studies concerning the Californian plant species Clarkia biloba and C. lingulata strongly suggest a peripatric origin. In addition, a great deal of research has been conducted on several species of land snails involving chirality that suggests peripatry (with some authors noting other possible interpretations).

The chestnut-tailed antbird (Sciaphylax hemimelaena) is located within the Noel Kempff Mercado National Park (Serrania de Huanchaca) in Bolivia. Within this region exists a forest fragment estimated to have been isolated for 1000–3000 years. The population of S. hemimelaena antbirds that reside in the isolated patch express significant song divergence; thought to be an "early step" in the process of peripatric speciation. Further, peripheral isolation "may partly explain the dramatic diversification of suboscines in Amazonia".

The montane spiny throated reed frog species complex (genus: Hyperolius) originated through occurrences of peripatric speciation events. Lucinda P. Lawson maintains that the species' geographic ranges within the Eastern Afromontane Biodiversity Hotspot support a peripatric model that is driving speciation; suggesting that this mode of speciation may play a significant role in "highly fragmented ecosystems".

In a study of the phylogeny and biogeography of the land snail genus Monacha, the species M. ciscaucasica is thought to have speciated peripatrically from a population of M. roseni. In addition, M. claussi consists of a small population located on the peripheral of the much larger range of M. subcarthusiana suggesting that it also arose by peripatric speciation.

Foliage and cones of Picea mariana

 

Foliage and cones of Picea rubens

 

Red spruce (Picea rubens) has arisen from an isolated population of black spruce (Picea mariana). During the Pleistocene, a population of black spruce became geographically isolated, likely due to glaciation. The geographic range of the black spruce is much larger than the red spruce. The red spruce has significantly lower genetic diversity in both its DNA and its mitochondrial DNA than the black spruce. Furthermore, the genetic variation of the red spruce has no unique mitochondrial haplotypes, only subsets of those in the black spruce; suggesting that the red spruce speciated peripatrically from the black spruce population. It is thought that the entire genus Picea in North America has diversified by the process of peripatric speciation, as numerous pairs of closely related species in the genus have smaller southern population ranges; and those with overlapping ranges often exhibit weak reproductive isolation.

Using a phylogeographic approach paired with ecological niche models (i.e. prediction and identification of expansion and contraction species ranges into suitable habitats based on current ecological niches, correlated with fossil and molecular data), researchers found that the prairie dog species Cynomys mexicanus speciated peripatrically from Cynomys ludovicianus approximately 230,000 years ago. North American glacial cycles promoted range expansion and contraction of the prairie dogs, leading to the isolation of a relic population in a refugium located in the present day Coahuila, Mexico. This distribution and paleobiogeographic pattern correlates with other species expressing similar biographic range patterns such as with the Sorex cinereus complex.

Laboratory experiments

Species	Replicates	Year
Drosophila adiastola	1	1979
Drosophila silvestris	1	1980
Drosophila pseudoobscura	8	1985
Drosophila simulans	8	1985
Musca domestica	6	1991
Drosophila pseudoobscura	42	1993
Drosophila melanogaster	50	1998
Drosophila melanogaster	19; 19	1999
Drosophila grimshawi	1	N/A

Peripatric speciation has been researched in both laboratory studies and nature. Jerry Coyne and H. Allen Orr in Speciation suggest that most laboratory studies of allopatric speciation are also examples of peripatric speciation due to their small population sizes and the inevitable divergent selection that they undergo. Much of the laboratory research concerning peripatry is inextricably linked to founder effect research. Coyne and Orr conclude that selection's role in speciation is well established, whereas genetic drift's role is unsupported by experimental and field data—suggesting that founder-effect speciation does not occur. Nevertheless, a great deal of research has been conducted on the matter, and one study conducted involving bottleneck populations of Drosophila pseudoobscura found evidence of isolation after a single bottleneck.

The table is a non-exhaustive table of laboratory experiments focused explicitly on peripatric speciation. Most of the studies also conducted experiments on vicariant speciation as well. The "replicates" column signifies the number of lines used in the experiment—that is, how many independent populations were used (not the population size or the number of generations performed).

Ronald Fisher (modern evolutionary synthesis)

From Wikipedia, the free encyclopedia

Sir Ronald Fisher FRS
Fisher in 1913
Born	Ronald Aylmer Fisher 17 February 1890 East Finchley, London, England, United Kingdom
Died	29 July 1962 (aged 72) Adelaide, South Australia, Australia
Residence	United Kingdom and Australia
Nationality	British
Education	Harrow School
Alma mater	University of Cambridge
Known for	Fisher's principle Fisher information
Awards	Weldon Memorial Prize (1930) Royal Medal (1938) Guy Medal (1946) Copley Medal (1955)
Scientific career
Fields	Statistics, Genetics, and Evolutionary biology
Institutions	Rothamsted Experimental Station University College London University of Cambridge University of Adelaide Commonwealth Scientific and Industrial Research Organisation
Academic advisors	James Hopwood Jeans F. J. M. Stratton[citation needed]
Doctoral students	Walter Bodmer D. J. Finney Mary F. Lyon C. R. Rao

Sir Ronald Aylmer Fisher FRS (17 February 1890 – 29 July 1962) was a British statistician and geneticist. For his work in statistics, he has been described as "a genius who almost single-handedly created the foundations for modern statistical science" and "the single most important figure in 20th century statistics". In genetics, his work used mathematics to combine Mendelian genetics and natural selection; this contributed to the revival of Darwinism in the early 20th-century revision of the theory of evolution known as the modern synthesis. For his contributions to biology, Fisher has been called "the greatest of Darwin’s successors".

From 1919 onward, he worked at the Rothamsted Experimental Station for 14 years; there, he analysed its immense data from crop experiments since the 1840s, and developed the analysis of variance (ANOVA). He established his reputation there in the following years as a biostatistician.

He is known as one of the three principal founders of population genetics. He outlined Fisher's principle, the Fisherian runaway and sexy son hypothesis theories of sexual selection. His contributions to statistics include the maximum likelihood, fiducial inference, the derivation of various sampling distributions, founding principles of the design of experiments, and much more.

Fisher held strong views on race. Throughout his life, he was a prominent supporter of eugenics, an interest which led to his work on statistics and genetics. Notably, he was a dissenting voice in UNESCO's statement The Race Question, insisting on racial differences.

Early life and education

As a child

 

Inverforth House North End Way NW3, where Fisher lived from 1896 to 1904

 

Fisher was born in East Finchley in London, England, into a middle-class household; his father, George, was a successful partner in Robinson & Fisher, auctioneers and fine art dealers. He was one of twins, with the other twin being still-born and grew up the youngest, with three sisters and one brother. From 1896 until 1904 they lived at Inverforth House in London, where English Heritage installed a blue plaque in 2002, before moving to Streatham. His mother, Kate, died from acute peritonitis when he was 14, and his father lost his business 18 months later.

Lifelong poor eyesight caused his rejection by the British Army for World War I, but also developed his ability to visualize problems in geometrical terms, not in writing mathematical solutions, or proofs. He entered Harrow School age 14 and won the school's Neeld Medal in mathematics. In 1909, he won a scholarship to study Mathematics at Gonville and Caius College, Cambridge. In 1912, he gained a First in Astronomy. In 1915 he published a paper The evolution of sexual preference on sexual selection and mate choice.

Career

During 1913–1919, Fisher worked for six years as a statistician in the City of London and taught physics and maths at a sequence of public schools, at the Thames Nautical Training College, and at Bradfield College. There he settled with his new bride, Eileen Guinness, with whom he had two sons and six daughters.

In 1918 he published "The Correlation Between Relatives on the Supposition of Mendelian Inheritance", in which he introduced the term variance and proposed its formal analysis. He put forward a genetics conceptual model showing that continuous variation amongst phenotypic traits measured by biostatisticians could be produced by the combined action of many discrete genes and thus be the result of Mendelian inheritance. This was the first step towards establishing population genetics and quantitative genetics, which demonstrated that natural selection could change allele frequencies in a population, resulting in reconciling its discontinuous nature with gradual evolution. Joan Box, Fisher's biographer and daughter says that Fisher had resolved this problem already in 1911.

Rothamsted Experimental Station, 1919–1933

In 1919, he began working at the Rothamsted Experimental Station for 14 years, where he analysed its immense data from crop experiments since the 1840s, and developed the analysis of variance (ANOVA). In 1919, he was offered a position at the Galton Laboratory in University College London led by Karl Pearson, but instead accepted a temporary job at Rothamsted in Harpenden to investigate the possibility of analysing the vast amount of crop data accumulated since 1842 from the "Classical Field Experiments". He analysed the data recorded over many years and in 1921, published Studies in Crop Variation, and his first application of the analysis of variance ANOVA. In 1928, Joseph Oscar Irwin began a three-year stint at Rothamsted and became one of the first people to master Fisher's innovations. Between 1912 and 1922 Fisher recommended, analyzed (with flawed attempts at proofs) and vastly popularized Maximum likelihood.

On graduating from Cambridge University, 1912

 

The peacock tail in flight, the classic example of a Fisherian runaway

 

Rothamsted Research

Fisher's 1924 article On a distribution yielding the error functions of several well known statistics presented Pearson's chi-squared test and William Gosset's Student's t-distribution in the same framework as the Gaussian distribution and is where he developed Fisher's z-distribution a new statistical method, commonly used decades later as the F distribution. He pioneered the principles of the design of experiments and the statistics of small samples and the analysis of real data.

In 1925 he published Statistical Methods for Research Workers, one of the 20th century's most influential books on statistical methods. Fisher's method is a technique for data fusion or "meta-analysis" (analysis of analyses). This book also popularized the p-value, and plays a central role in his approach. Fisher proposes the level p=0.05, or a 1 in 20 chance of being exceeded by chance, as a limit for statistical significance, and applies this to a normal distribution (as a two-tailed test), thus yielding the rule of two standard deviations (on a normal distribution) for statistical significance. The 1.96, the approximate value of the 97.5 percentile point of the normal distribution used in probability and statistics, also originated in this book.

"The value for which P=.05, or 1 in 20, is 1.96 or nearly 2 ; it is convenient to take this point as a limit in judging whether a deviation is to be considered significant or not."

In Table 1 of the work, he gave the more precise value 1.959964.

In 1928, Fisher was the first to use diffusion equations to attempt to calculate the distribution of allele frequencies and the estimation of genetic linkage by maximum likelihood methods among populations.

In 1930, The Genetical Theory of Natural Selection was first published by Clarendon Press and is dedicated to Leonard Darwin. A core work of the neo-Darwinian modern evolutionary synthesis, it helped define population genetics, which Fisher founded alongside Sewall Wright and J. B. S. Haldane, and revived Darwins neglected idea of sexual selection. One of Fisher's favorite aphorisms was "Natural selection is a mechanism for generating an exceedingly high degree of improbability."

Fisher's fame grew and he began to travel and lecture widely. In 1931, he spent six weeks at the Statistical Laboratory at Iowa State College where he gave three lectures per week, and met many American statisticians, including George W. Snedecor. He returned there again in 1936.^{[citation needed]}

University College London, 1933–39

In 1933, Fisher became the head of the Department of Eugenics at University College London. In 1935, he published The Design of Experiments, which was "also fundamental, [and promoted] statistical technique and application... The mathematical justification of the methods was not stressed and proofs were often barely sketched or omitted altogether .... [This] led H.B. Mann to fill the gaps with a rigorous mathematical treatment". In this book Fisher also outlined the Lady tasting tea, now a famous design of a statistical randomized experiment which uses Fisher's exact test and is the original exposition of Fisher's notion of a null hypothesis.

The same year he also published a paper on fiducial inference and applied it to the Behrens–Fisher problem, the solution to which, proposed first by Walter Behrens and a few years later by Fisher, is the Behrens–Fisher distribution. 

In 1936 he introduced the Iris flower data set as an example of discriminant analysis.

In his 1937 paper The wave of advance of advantageous genes he proposed Fisher's equation in the context of population dynamics to describe the spatial spread of an advantageous allele and explored its travelling wave solutions. Out of this also came the Fisher–Kolmogorov equation. In 1937, he visited the Indian Statistical Institute in Calcutta, and its one part-time employee, P. C. Mahalanobis, often returning to encourage its development. He was the guest of honour at its 25th anniversary in 1957, when it had 2000 employees.

In 1938, Fisher and Frank Yates described the Fisher–Yates shuffle in their book Statistical tables for biological, agricultural and medical research. Their description of the algorithm used pencil and paper; a table of random numbers provided the randomness.

University of Cambridge, 1940–1956

In 1943, along with A.S. Corbet and C.B. Williams he published a paper on relative species abundance where he developed the logseries to fit two different abundance data sets In the same year he took the Balfour Chair of Genetics where the Italian researcher Luigi Luca Cavalli-Sforza was recruited in 1948, establishing a one-man unit of bacterial genetics.

In 1936, Fisher used a Pearson's chi-squared test to analyze Mendel's data and concluded that Mendel's results with the predicted ratios were far too perfect, suggesting that adjustments (intentional or unconscious) had been made to the data to make the observations fit the hypothesis. Later authors have claimed Fisher's analysis was flawed, proposing various statistical and botanical explanations for Mendel's numbers. In 1947, Fisher cofounded the journal Heredity with Cyril Darlington and in 1949 he published The Theory of Inbreeding.

 

In 1950 he published "Gene Frequencies in a Cline Determined by Selection and Diffusion" on the wave of advance of advantageous genes and on clines of gene frequency, being notable as the first application of a computer, the EDSAC, to biology. He developed computational algorithms for analyzing data from his balanced experimental designs, with various editions and translations, becoming a standard reference work for scientists in many disciplines. In ecological genetics he and E. B. Ford showed how the force of natural selection was much stronger than had been assumed, with many ecogenetic situations (such as polymorphism) being maintained by the force of selection.

During this time he also worked on mouse chromosome mapping; breeding the mice in laboratories in his own house.

Fisher publicly spoke out against the 1950 study showing that smoking tobacco causes lung cancer, arguing that correlation does not imply causation. To quote his biographers Yates and Mather, "It has been suggested that the fact that Fisher was employed as consultant by the tobacco firms in this controversy casts doubt on the value of his arguments. This is to misjudge the man. He was not above accepting financial reward for his labours, but the reason for his interest was undoubtedly his dislike and mistrust of puritanical tendencies of all kinds; and perhaps also the personal solace he had always found in tobacco."

He gave the 1953 Croonian lecture on population genetics.

In the winter of 1954–1955 Fisher met Debabrata Basu, the Indian statistician who wrote in 1988, "With his reference set argument, Sir Ronald was trying to find a via media between the two poles of Statistics – Berkeley and Bayes. My efforts to understand this Fisher compromise led me to the likelihood principle".

Adelaide, 1957–1962

Memorial plaque over his mortal remains, lectern-side aisle of St Peter's Cathedral, Adelaide

 

In 1957, a retired Fisher emigrated to Australia, where he spent time as a senior research fellow at the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Adelaide. He died there in 1962, and his remains were interred within St Peter's Cathedral, Adelaide.

Personal life and beliefs

He married Eileen Guinness, with whom he had two sons and six daughters. His marriage disintegrated during World War II, and his oldest son George, an aviator, was killed in combat. His daughter Joan, who wrote a biography of her father, married the noted statistician George E. P. Box.

Stained glass window in the dining hall of Caius College, in Cambridge, commemorating Ronald Fisher and representing a Latin square, discussed by him in The Design of Experiments

 

According to Yates and Mather, "His large family, in particular, reared in conditions of great financial stringency, was a personal expression of his genetic and evolutionary convictions." Fisher was noted for being loyal, and was seen as a patriot, a member of the Church of England, politically conservative, as well as a scientific rationalist. He developed a reputation for carelessness in his dress and was the archetype of the absent-minded professor. H. Allen Orr describes him in the Boston Review as a "deeply devout Anglican who, between founding modern statistics and population genetics, penned articles for church magazines". In a 1955 broadcast on Science and Christianity,^[3] he said:

“

The custom of making abstract dogmatic assertions is not, certainly, derived from the teaching of Jesus, but has been a widespread weakness among religious teachers in subsequent centuries. I do not think that the word for the Christian virtue of faith should be prostituted to mean the credulous acceptance of all such piously intended assertions. Much self-deception in the young believer is needed to convince himself that he knows that of which in reality he knows himself to be ignorant. That surely is hypocrisy, against which we have been most conspicuously warned.

”

Parapsychology

Fisher was involved with the Society for Psychical Research.

Eugenics

As a steward at the First International Eugenics Conference, 1912

 

In 1910 Fisher joined the Eugenics Society (UK) at University of Cambridge, whose members included John Maynard Keynes, R. C. Punnett, and Horace Darwin. He saw eugenics as addressing pressing social and scientific issues that encompassed and drove his interest in both genetics and statistics. During World War I Fisher started writing book reviews for the Eugenic Review and volunteered to undertake all such reviews for the journal, being hired for a part-time position.

The last third of The Genetical Theory of Natural Selection focussed on eugenics, attributing the fall of civilizations to the fertility of their upper classes being diminished, and used British 1911 census data to show an inverse relationship between fertility and social class, partly due, he claimed, to the lower financial costs and hence increasing social status of families with fewer children. He proposed the abolition of extra allowances to large families, with the allowances proportional to the earnings of the father. He served in several official committees to promote eugenics. In 1934, he resigned from the Eugenics Society over a dispute about increasing the power of scientists within the movement.

Race

In 1950, Fisher opposed UNESCO's The Race Question, believing that evidence and everyday experience showed that human groups differ profoundly "in their innate capacity for intellectual and emotional development" and concluded that the "practical international problem is that of learning to share the resources of this planet amicably with persons of materially different nature", and that "this problem is being obscured by entirely well-intentioned efforts to minimize the real differences that exist". The revised statement titled "The Race Concept: Results of an Inquiry" (1951) was accompanied by Fisher's dissenting commentary.

Legacy

Fisher's former doctoral students include Walter Bodmer, D. J. Finney, Mary F. Lyon, and C. R. Rao.  Although a prominent opponent of Bayesian statistics, Fisher was the first to use the term "Bayesian", in 1950. The 1930 The Genetical Theory of Natural Selection is commonly cited in biology books, and outlines many important concepts, such as:

• Parental investment, is any parental expenditure (time, energy etc.) that benefits one offspring at a cost to parents' ability to invest in other components of fitness,
• Fisherian runaway, explaining how the desire for a phenotypic trait in one sex combined with the trait in the other sex (for example a peacock's tail) creates a runaway development of the trait.
• Fisher's principle, which explains why the sex ratio is mostly 1:1 in nature.
• Reproductive value which implies that sexually reproductive value measures the contribution of an individual of a given age to the future growth of the population.
• Fisher's fundamental theorem of natural selection, which states that "the rate of increase in fitness of any organism at any time is equal to its genetic variance in fitness at that time."
• Fisher's geometric model, an evolutionary model of the effect sizes on fitness of spontaneous mutations proposed by Fisher to explain the distribution of effects of mutations that could contribute to adaptive evolution.
• Sexy son hypothesis, which hypothesizes that females may choose arbitrarily attractive male mates simply because they are attractive, thus increasing the attractiveness of their sons who attract more mates of their own. This is in contrast to theories of female mate choice based on the assumption that females choose attractive males because the attractive traits are markers of male fitness.
• Mimicry, a similarity of one species to another that protects one or both
• Dominance, a relationship between alleles of one gene, in which the effect on phenotype of one allele masks the contribution of a second allele at the same locus.
• Heterozygote advantage which was later found to play a frequent role in genetic polymorphism.
• Demonstrating that the probability of a mutation increasing the fitness of an organism decreases proportionately with the magnitude of the mutation and that larger populations carry more variation so that they have a greater chance of survival.

Fisher is also known for:

• Linear discriminant analysis is a generalization of Fisher's linear discriminant
• Fisher information, see also scoring algorithm also known as Fisher's scoring, and Minimum Fisher information, a variational principle which, when applied with the proper constraints needed to reproduce empirically known expectation values, determines the best probability distribution that characterizes the system.
• F-distribution, arises frequently as the null distribution of a test statistic, most notably in the analysis of variance
• Fisher–Tippett–Gnedenko theorem Fisher's contribution to this was made in 1927
• Fisher–Tippett distribution
• Von Mises–Fisher distribution
• Inverse probability, a term Fisher used in 1922, referring to "the fundamental paradox of inverse probability" as the source of the confusion between statistical terms which refer to the true value to be estimated, with the actual value arrived at by estimation, which is subject to error.
• Fisher's permutation test
• Fisher's inequality
• Sufficient statistic, when a statistic is sufficient with respect to a statistical model and its associated unknown parameter if "no other statistic that can be calculated from the same sample provides any additional information as to the value of the parameter".
• Fisher's noncentral hypergeometric distribution, a generalization of the hypergeometric distribution, where sampling probabilities are modified by weight factors.
• Student's t-distribution, widely used in statistics.

Recognition

Fisher was elected to the Royal Society in 1929. He was made a Knight Bachelor by Queen Elizabeth II in 1952 and awarded the Linnean Society of London Darwin–Wallace Medal in 1958.

He won Copley Medal and the Royal Medal. He was an Invited Speaker of the ICM in 1924 in Toronto and in 1928 in Bologna.

In 1950, Maurice Wilkes and David Wheeler used the Electronic Delay Storage Automatic Calculator to solve a differential equation relating to gene frequencies in a paper by Ronald Fisher. This represents the first use of a computer for a problem in the field of biology. The Kent distribution (also known as the Fisher–Bingham distribution) was named after him and Christopher Bingham in 1982 while Fisher kernel was named after Fisher in 1998.

The R. A. Fisher Lectureship is a North American annual lecture prize, established in 1963. On 28 April 1998 a minor planet, 21451 Fisher, was named after him.

Anders Hald called Fisher "a genius who almost single-handedly created the foundations for modern statistical science", while Richard Dawkins named him "the greatest biologist since Darwin":

Not only was he the most original and constructive of the architects of the neo-Darwinian synthesis, Fisher also was the father of modern statistics and experimental design. He therefore could be said to have provided researchers in biology and medicine with their most important research tools, as well as with the modern version of biology's central theorem.

Geoffrey Miller said of him:

To biologists, he was an architect of the "modern synthesis" that used mathematical models to integrate Mendelian genetics with Darwin's selection theories. To psychologists, Fisher was the inventor of various statistical tests that are still supposed to be used whenever possible in psychology journals. To farmers, Fisher was the founder of experimental agricultural research, saving millions from starvation through rational crop breeding programs.