Atavism



In biology, an atavism is an evolutionary throwback, such as traits reappearing that had disappeared generations before. Atavisms can occur in several ways. One way is when genes for previously existing phenotypical 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. 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.

In the social sciences, atavism can also describe a cultural 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. An atavus is a great-great-great-grandfather or, more generally, an ancestor.

Biology
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. 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 as well. Babies have been born with a vestigial tail, called "coccygeal process", "coccygeal projection", and "caudal appendage". Atavism can also be seen in humans who possess large teeth, like those of other primates. 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. However, although they are similar, vestigial structures are distinct from atavisms. Atavisms are ancestral traits that reappear in the modern day, but they do not become vestigial organs or body parts. For example, the wings of an ostrich are vestigial structures that no longer serve their original purpose for flight, but they are not the result of a dormant ancestral trait that has reappeared.

Examples of observed atavisms include:
 * Hind legs on whales or snakes
 * Hind fins on dolphins
 * Extra toes on horses, as in archaic horses
 * Reemergence of sexual reproduction in the flowering plant Hieracium pilosella and the Crotoniidae family of mites.
 * Teeth in chickens
 * Supernumerary nipples on higher primates
 * Color blindness in humans.

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. Such an individual was sometimes called a "throw-back". The notion that somehow, atavisms could be made to accumulate by selective breeding, or breeding back, led to breeds such as the Heck cattle. This had been bred from ancient landraces with selected primitive traits, in an attempt of "reviving" the extinct aurochs.

The notion of atavism was used frequently by social Darwinists, who claimed that inferior races displayed atavistic traits, and represented more primitive traits than their own race. Both the notion of atavism, and Ernst Haeckel's recapitulation theory, are related to notions of evolution as progress, as development towards greater complexity and superior ability.

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. 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.

Culture
The term atavism is sometimes also applied in the discussion of culture. Some social scientists describe the return of older, "more primitive" tendencies (e.g. warlike attitudes, "clan identity", anything suggesting the social and political atmosphere of thousands of years ago) as "atavistic". "Resurgent atavism" is a common name for the belief that people in the modern era are beginning to revert to ways of thinking and acting that are throw-backs to a former time. This is especially used by sociologists in reference to violence.

The neo-pagan subculture also uses this same terminology ("atavism" or "resurgent atavism") to describe how modern, Western countries are experiencing both the decline of Christianity and the rise of religious movements inspired by the pagan religions of centuries past. Some cite the rise of environmentalism, scientific inquiry, and liberalization of society as contributing to an increasingly secular society, one in which religious sentiments are more frequently tied with an appreciation of the physical world rather than set against it. The book Lords of Chaos portrays pagan and occult atavism as an inherently destructive thing, stating that a rash of church burnings across Scandinavia is part of this trend, because many of the perpetrators were pagans seeking to overthrow the establishment they deemed to be the result of centuries of religious oppression of native European religion by Christianity.

Atavism is a key 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.