Population genetics

The logarithm of fitness as a function of the number of deleterious mutations. Synergistic epistasis is represented by the red line - each subsequent deleterious mutation has a larger proportionate effect on the organism's fitness. Antagonistic epistasis is in blue. The black line shows the non-epistatic case, where fitness is the product of the contributions from each of its loci.
Drosophila melanogaster
Gene flow is the transfer of alleles from one population to another population through immigration of individuals. In this example, one of the birds from population A immigrates to population B, which has fewer of the dominant alleles, and through mating incorporates its alleles into the other population.
The Great Wall of China is an obstacle to gene flow of some terrestrial species.
Current tree of life showing vertical and horizontal gene transfers.

Subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology.

- Population genetics
The logarithm of fitness as a function of the number of deleterious mutations. Synergistic epistasis is represented by the red line - each subsequent deleterious mutation has a larger proportionate effect on the organism's fitness. Antagonistic epistasis is in blue. The black line shows the non-epistatic case, where fitness is the product of the contributions from each of its loci.

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Alpha

Diagram of a fly from Robert Hooke's innovative Micrographia, 1665

Evolutionary biology

Subfield of biology that studies the evolutionary processes that produced the diversity of life on Earth.

Subfield of biology that studies the evolutionary processes that produced the diversity of life on Earth.

Diagram of a fly from Robert Hooke's innovative Micrographia, 1665

One challenge in studying genetic architecture is that the classical population genetics that catalysed the modern evolutionary synthesis must be updated to take into account modern molecular knowledge.

W. D. Hamilton, 1996

W. D. Hamilton

British evolutionary biologist, recognised as one of the most significant evolutionary theorists of the 20th century.

British evolutionary biologist, recognised as one of the most significant evolutionary theorists of the 20th century.

W. D. Hamilton, 1996

In 1946, he discovered E.B. Ford's New Naturalist book Butterflies, which introduced him to the principles of evolution by natural selection, genetics, and population genetics.

Motoo Kimura

Japanese biologist best known for introducing the neutral theory of molecular evolution in 1968.

Japanese biologist best known for introducing the neutral theory of molecular evolution in 1968.

He became one of the most influential theoretical population geneticists.

The logarithm of fitness as a function of the number of deleterious mutations. Synergistic epistasis is represented by the red line - each subsequent deleterious mutation has a larger proportionate effect on the organism's fitness. Antagonistic epistasis is in blue. The black line shows the non-epistatic case, where fitness is the product of the contributions from each of its loci.

Linkage disequilibrium

The logarithm of fitness as a function of the number of deleterious mutations. Synergistic epistasis is represented by the red line - each subsequent deleterious mutation has a larger proportionate effect on the organism's fitness. Antagonistic epistasis is in blue. The black line shows the non-epistatic case, where fitness is the product of the contributions from each of its loci.

In population genetics, linkage disequilibrium (LD) is the non-random association of alleles at different loci in a given population.

Diagram of a fly from Robert Hooke's innovative Micrographia, 1665

Richard Lewontin

American evolutionary biologist, mathematician, geneticist, and social commentator.

American evolutionary biologist, mathematician, geneticist, and social commentator.

Diagram of a fly from Robert Hooke's innovative Micrographia, 1665

A leader in developing the mathematical basis of population genetics and evolutionary theory, he pioneered the application of techniques from molecular biology, such as gel electrophoresis, to questions of genetic variation and evolution.

Evolutionary progress as a tree of life. Ernst Haeckel, 1866

Orthogenesis

Obsolete biological hypothesis that organisms have an innate tendency to evolve in a definite direction towards some goal due to some internal mechanism or "driving force".

Obsolete biological hypothesis that organisms have an innate tendency to evolve in a definite direction towards some goal due to some internal mechanism or "driving force".

Evolutionary progress as a tree of life. Ernst Haeckel, 1866
Lamarck's two-factor theory involves 1) a complexifying force that drives animal body plans towards higher levels (orthogenesis) creating a ladder of phyla, and 2) an adaptive force that causes animals with a given body plan to adapt to circumstances (use and disuse, inheritance of acquired characteristics), creating a diversity of species and genera. Popular views of Lamarckism only consider an aspect of the adaptive force.
Theodor Eimer
The mediaeval great chain of being as a staircase, implying the possibility of progress: Ramon Lull's Ladder of Ascent and Descent of the Mind, 1305
Reviewing Darwin's Origin of Species, Karl Ernst von Baer argued for a directed force guiding evolution.
Henry Fairfield Osborn's 1934 version of orthogenesis, aristogenesis, argued that aristogenes, not mutation or natural selection, created all novelty. Osborn supposed that the horns of Titanotheres evolved into a baroque form, way beyond the adaptive optimum.
Multiple explanations have been offered since the 19th century for how evolution took place, given that many scientists initially had objections to natural selection. Many of these theories led (solid blue arrows) to some form of orthogenesis, with or without invoking divine control (dotted blue arrows) directly or indirectly. For example, evolutionists like Edward Drinker Cope believed in a combination of theistic evolution, Lamarckism, vitalism, and orthogenesis, represented by a sequence of arrows on the left of the diagram. The development of modern Darwinism is indicated by dashed orange arrows.
A satirical opinion of Ernst Haeckel's 1874 The modern theory of the descent of man, showing a linear sequence of forms leading up to 'Man'. Illustration by G. Avery for Scientific American, 11 March 1876
Ernst Mayr considered orthogenesis effectively taboo in 1948.
The frontispiece to Thomas Henry Huxley's 1863 Evidence as to Man's Place in Nature was intended to compare the skeletons of apes and humans, but unintentionally created a durable meme of supposed "monkey-to-man" progress.
Man is But a Worm by Edward Linley Sambourne, Punch's Almanack for 1882
One of many versions of the progressionist meme: Astronomy Evolution 2 artwork by Giuseppe Donatiello, 2016

"There it remained frozen, for nearly another hundred years", until mathematicians such as Fisher provided "both models and status", enabling evolutionary biologists to construct the modern synthesis of the 1930s and 1940s.

A population bottleneck can result in a loss of heterozygosity. In this hypothetical population, an allele has become fixed after the population repeatedly dropped from 10 to 3.

Population structure (genetics)

Presence of a systematic difference in allele frequencies between subpopulations.

Presence of a systematic difference in allele frequencies between subpopulations.

A population bottleneck can result in a loss of heterozygosity. In this hypothetical population, an allele has become fixed after the population repeatedly dropped from 10 to 3.
A map of the locations of genetic samples of several African populations (left) and principal components 1 and 2 of the data superimposed on the map (right). The principal coordinate plane has been rotated 16.11° to align with the map. It corresponds to the east-west and north-south distributions of the populations.

Population structure is an important aspect of evolutionary and population genetics.

Duplication of part of a chromosome

Microevolution

Change in allele frequencies that occurs over time within a population.

Change in allele frequencies that occurs over time within a population.

Duplication of part of a chromosome
Natural selection of a population for dark coloration.
Ten simulations of random genetic drift of a single given allele with an initial frequency distribution 0.5 measured over the course of 50 generations, repeated in three reproductively synchronous populations of different sizes. In general, alleles drift to loss or fixation (frequency of 0.0 or 1.0) significantly faster in smaller populations.

Population genetics is the branch of biology that provides the mathematical structure for the study of the process of microevolution.

Genetic diversity

Total number of genetic characteristics in the genetic makeup of a species, it ranges widely from the number of species to differences within species and can be attributed to the span of survival for a species.

Total number of genetic characteristics in the genetic makeup of a species, it ranges widely from the number of species to differences within species and can be attributed to the span of survival for a species.

A graphical representation of the typical human karyotype.
Varieties of maize in the office of the Russian plant geneticist Nikolai Vavilov
Photomontage of planktonic organisms.
A Tanzanian cheetah.

The academic field of population genetics includes several hypotheses and theories regarding genetic diversity.

Provine in 2008

William B. Provine

Provine in 2008

William Ball Provine (February 19, 1942 – September 1, 2015) was an American historian of science and of evolutionary biology and population genetics.