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Early embryos of various species display some ancestral features, like the tail on this human embryo. These features normally disappear in later development, but it may not happen if the animal has an atavism. Tubal Pregnancy with embryo.jpg
Early embryos of various species display some ancestral features, like the tail on this human embryo. These features normally disappear in later development, but it may not happen if the animal has an atavism.

In biology, an atavism is a modification of a biological structure whereby an ancestral genetic trait reappears after having been lost through evolutionary change in previous generations. [3] Atavisms can occur in several ways; [4] one of which is when genes for previously existing phenotypic features are preserved in DNA, and these become expressed through a mutation that either knocks out the overriding genes for the new traits or makes the old traits override the new one. [3] A number of traits can vary as a result of shortening of the fetal development of a trait (neoteny) or by prolongation of the same. In such a case, a shift in the time a trait is allowed to develop before it is fixed can bring forth an ancestral phenotype. [5] Atavisms are often seen as evidence of evolution. [6]


In social sciences, atavism is the tendency of reversion. For example, people in the modern era reverting to the ways of thinking and acting of a former time. The word atavism is derived from the Latin atavus—a great-great-great-grandfather or, more generally, an ancestor.


Evolutionarily traits that have disappeared phenotypically do not necessarily disappear from an organism's DNA. The gene sequence often remains, but is inactive. Such an unused gene may remain in the genome for many generations. [7] [8] As long as the gene remains intact, a fault in the genetic control suppressing the gene can lead to it being expressed again. Sometimes, the expression of dormant genes can be induced by artificial stimulation.

Atavisms have been observed in humans, such as with infants born with vestigial tails (called a "coccygeal process", "coccygeal projection", or "caudal appendage"). [9] Atavism can also be seen in humans who possess large teeth, like those of other primates. [10] In addition, a case of "snake heart", the presence of "coronary circulation and myocardial architecture [which resemble] those of the reptilian heart", has also been reported in medical literature. [11] Atavism has also recently been induced in modern avian dinosaur (bird) foetuses to express dormant ancestral non-avian dinosaur features, including teeth. [12]

Other examples of observed atavisms include:


Atavism is a term in Joseph Schumpeter's explanation of World War I in twentieth-century liberal Europe. He defends the liberal international relations theory that an international society built on commerce will avoid war because of war's destructiveness and comparative cost. His reason for World War I is termed "atavism", in which he asserts that senescent governments in Europe (those of the German Empire, Russian Empire, Ottoman Empire, and Austro-Hungarian Empire) pulled the liberal Europe into war, and that the liberal regimes of the other continental powers did not cause it. He used this idea to say that liberalism and commerce would continue to have a soothing effect in international relations, and that war would not arise between nations which are connected by commercial ties. [32]

University of London professor Guy Standing has identified three distinct sub-groups of the precariat, one of which he refers to as "atavists", who long for what they see as a lost past. [33]

Social Darwinism

During the interval between the acceptance of evolution in the mid-1800s and the rise of the modern understanding of genetics in the early 1900s, atavism was used to account for the reappearance in an individual of a trait after several generations of absence — often called a "throw-back".[ citation needed ] The idea that atavisms could be made to accumulate by selective breeding, or breeding back, led to breeds such as the Heck cattle.[ citation needed ] This had been bred from ancient landraces with selected primitive traits, in an attempt of "reviving" the aurochs, an extinct species of wild cattle.[ citation needed ] The same notions of atavisms were used by social Darwinists, who claimed that inferior races displayed atavistic traits, and represented more primitive traits than other races.[ citation needed ] Both atavism's and Ernst Haeckel's recapitulation theory are related to evolutionary progress, as development towards a greater complexity and a superior ability.[ citation needed ]

In addition, the concept of atavism as part of an individualistic explanation of the causes of criminal deviance was popularised by the Italian criminologist Cesare Lombroso in the 1870s. [34] He attempted to identify physical characteristics common to criminals and labeled those he found as atavistic, 'throw-back' traits that determined 'primitive' criminal behavior. His statistical evidence and the closely related idea of eugenics have long since been abandoned by the scientific community, but the concept that physical traits may affect the likelihood of criminal or unethical behavior in a person still has some scientific support. [35]

See also

Related Research Articles

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

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

Heredity Passing of traits to offspring from the speciess parents or ancestor

Heredity, also called inheritance or biological inheritance, is the passing on of traits from parents to their offspring; either through asexual reproduction or sexual reproduction, the offspring cells or organisms acquire the genetic information of their parents. Through heredity, variations between individuals can accumulate and cause species to evolve by natural selection. The study of heredity in biology is genetics.

Microevolution change in allele frequencies that occurs over time within a population

Microevolution is the change in allele frequencies that occurs over time within a population. This change is due to four different processes: mutation, selection, gene flow and genetic drift. This change happens over a relatively short amount of time compared to the changes termed macroevolution.

Convergent evolution Independent evolution of similar features in species of different lineages which creates analogous structures

Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last common ancestor of those groups. The cladistic term for the same phenomenon is homoplasy. The recurrent evolution of flight is a classic example, as flying insects, birds, pterosaurs, and bats have independently evolved the useful capacity of flight. Functionally similar features that have arisen through convergent evolution are analogous, whereas homologous structures or traits have a common origin but can have dissimilar functions. Bird, bat, and pterosaur wings are analogous structures, but their forelimbs are homologous, sharing an ancestral state despite serving different functions.

Population genetics Study of genetic differences within and between populations including the study of adaptation, speciation, and population structure

Population genetics is a subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and population structure.

Phenylthiocarbamide (PTC), also known as phenylthiourea (PTU), is an organosulfur thiourea containing a phenyl ring.

Dollos law of irreversibility hypothesis proposed by Louis Dollo which states evolution is not reversible

Dollo's law of irreversibility, proposed in 1893 by Belgian paleontologist Louis Dollo states that, "an organism never returns exactly to a former state, even if it finds itself placed in conditions of existence identical to those in which it has previously lived ... it always keeps some trace of the intermediate stages through which it has passed."

Baldwin effect Effect of learned behavior on evolution

In evolutionary biology, the Baldwin effect describes the effect of learned behavior on evolution. James Mark Baldwin and others suggested during the eclipse of Darwinism in the late 19th century that an organism's ability to learn new behaviours will affect its reproductive success and will therefore have an effect on the genetic makeup of its species through natural selection. Though this process appears similar to Lamarckism, that view proposes that living things inherited their parents' acquired characteristics. The Baldwin effect has been independently proposed several times, and today it is generally recognized as part of the modern synthesis.

Domestication of animals mutual relationship between animals with the humans who have influence on their care and reproduction

The domestication of animals is the mutual relationship between animals and the humans who have influence on their care and reproduction. Charles Darwin recognized a small number of traits that made domesticated species different from their wild ancestors. He was also the first to recognize the difference between conscious selective breeding in which humans directly select for desirable traits, and unconscious selection where traits evolve as a by-product of natural selection or from selection on other traits. There is a genetic difference between domestic and wild populations. There is also a genetic difference between the domestication traits that researchers believe to have been essential at the early stages of domestication, and the improvement traits that have appeared since the split between wild and domestic populations. Domestication traits are generally fixed within all domesticates, and were selected during the initial episode of domestication of that animal or plant, whereas improvement traits are present only in a proportion of domesticates, though they may be fixed in individual breeds or regional populations.

Evidence of common descent Evidence that a given group of organisms have a common ancestor, and therefore that evolution has taken place.

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