What Is Atavism?

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Atavism in biology is an evolutionary throwback such as traits that reappear which have disappeared generations before. Atavisms can occur in several ways; one way is when genes from previously existing phenotypical features are preserved in DNA and these becomes expressed through mutation that either knocks out the overriding genes for the new traits or makes the old traits override the new ones. As a result of prolongation or shortening of the fetal development of a trait (neoteny), there’s a number of traits that can vary. A shift in the time a trait in such a case, is allowed to develop before it’s fixed, can lead to it bringing forth an ancestral phenotype.

Atavism also describes a cultural tendency for reversion in the social sciences. Take for example, the people in the modern era going back to the ways of acting and thinking of a former time. The Latin term atavus is known to be from where the word atavism is derived. An atavus is basically an ancestor or a great-great-great-great-grandfather.

In Culture

Roughly around the mid-1800’s to the early 1900’s, during the interval between the rise of the modern understanding of genetics and the acceptance of evolution, the reappearance in an individual of a trait that was absent for several generations was explained by atavism. They called sometimes called such individuals a “throwback”. The idea that atavisms could somehow be made to accumulate by breeding back or selective breeding is what led to the creation of breeds such as the Heck cattle. In an attempt to revive the extinct species called aurochs, breeding had been done from antient landraces with selective primitive traits.

Social Darwinists used the notion of atavism frequently to claim that the races that displayed atavistic traits were inferior and represented more primitive traits compared to their own race. Ernst Haeckel’s recapitulation theory and the notion of atavism, both are related to development towards greater complexity and superior ability, and to evolution as progress.

In addition, the notion of atavism was popularised by the Italian criminologist Cesare Lomboso in the 1870’s as a part of an individualistic explanation of the causes of criminal deviance. He tried to say that the physical characteristics that are common to criminals were atavistic, and were “throwback” traits that he classified as primitive criminal behaviour. All of his closely related ideas of eugenics and statistical evidence have long since been forsaken by the scientific community, still the idea that physical traits could affect the likelihood of unethical or criminal behaviour in an individual, still does have some scientific support.

In Biology

Atavism occurs due to the way genes behave throughout the evolutionary process. During the process of natural selection, when phenotypic traits are lost, the genetic information in the DNA that codes for them might not be necessarily lost but instead it might just be inactive, meaning genes can be reactivated. Vestigial structures and atavisms are different. These are phenotypic features that present in all members of a species but due to the organisms’ evolutionary past might have been essential for survival, but are not functional or used in modern individuals There are several examples atavism in biology.

The human tail – There are a lot of scientific instances when a human baby has been born with a tail that contains a vertebrae and cartilage, called as caudal appendage.

A throwback feature of our evolutionary roots as primates is that all human babies grown in the womb with a small prenatal tail. As a result of gene regulation, the genes that control the growth of the tail are switched off and the embryo reabsorbs the tail into its tissues. But however, there are situations where the gene regulation malfunctions and the tail keeps growing beyond the stage of embryonic development.

Chicken with teeth – scientists, after inspecting the beaks of unhatched embryos have discovered many accounts of chicken embryos that show the evidence of tooth formation, and sometimes even embryos with a full set of developing teeth. What is a little strange is that the developing teeth are similar to those found in their closest living relatives – crocodiles.

Around 80 million years ago birds lost their ability to make teeth, however the gene that is responsible for tooth formation, though long since been deactivated is till carried by chickens.

Dolphins with legs – A dolphin was in caught near Japan in 2006, which along with the two front flippers that dolphins have, had a small pair of symmetrical pelvis flippers near its tail. Since the fins are representative of the hind legs that the dolphins had, it seems to be a throwback phenotype from the ancestors of dolphins that could apparently walk on land. A clear example of atavism. Since they are mammals, the cetacean evolutionary lineage can be traced back to land mammals like hippos. Now, the discovery of this dolphin with two extra limbs suggests that the genes that code for limb growth are still present in them.

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