Atavistic

Atavistic is an adjective describing a reversion to an ancestral type or characteristic that was present in distant evolutionary ancestors but is not typical of the current lineage. The term is used across biology, anthropology, and related fields to indicate a phenotype that resembles traits seen in earlier forms of a lineage.

In genetics and developmental biology, atavism refers to the reappearance of ancestral traits due to the reactivation of dormant genetic pathways or alterations in regulatory networks. Such traits are typically latent across generations and may become expressed under certain genetic or environmental conditions. Examples cited in discussions of atavism are usually rare and describe features that resemble earlier species, such as vestigial or rudimentary structures.

In humans, discussions of atavism have historically been linked to claims of primitive physical features. While some congenital conditions can produce brief reappearances of ancestral traits, modern genetics emphasizes that these events usually involve complex gene expression rather than simple, direct reversions to ancient states. Consequently, the concept is considered of historical interest rather than a primary framework in contemporary medicine.

In criminology, the idea of atavistic criminals—proposed by Cesare Lombroso in the 19th century—posited that certain individuals bear primitive, biological traits linked to criminality. This theory has been criticized and largely rejected by modern science for its methodological shortcomings and oversimplified view of behavior.

Etymology: from Italian atavismo, from atavus, ancestor. See also vestigial, paedomorphosis, evolutionary throwback.