title: Atavisms: medical, genetic, and evolutionary implications.
abstract: Traits expected to be lost in the evolutionary history of a species occasionally reappear apparently out of the blue. Such traits as extra nipples or tails in humans, hind limbs in whales, teeth in birds, or wings in wingless stick insects remind us that certain genetic information is not completely lost, but can be reactivated. Atavisms seem to violate one of the central evolutionary principles, known as Dollo's law, that "an organism is unable to return, even partially, to a previous stage already realized in the ranks of its ancestors." Although it is still not clear what triggers and controls the reactivation of dormant traits, atavisms are a challenge to evolutionary biologists and geneticists. This article presents some of the more striking examples of atavisms, discusses some of the currently controversial issues like human quadrupedalism, and reviews the progress made in explaining some of the mechanisms that can lead to atavistic features.
authors.affiliation: Hospital Universitario de Canarias-Unidád Mixta de Investigación, Facultad de Medicina, Campus de Ofra, Santa Cruz de Tenerife, Spain.
authors.forename: Nenad
authors.initials: N
authors.lastname: Tomić
authors.forename: Victor Benno
authors.initials: VB
authors.lastname: Meyer-Rochow
mesh_terms: D000818:Animals; D005075:Biological Evolution; D019521:Body Patterning; D044127:Epigenesis, Genetic; D005260:Female; D018507:Gene Expression Regulation, Developmental; D053263:Gene Regulatory Networks; D005809:Genes, Regulator; D006801:Humans; D008297:Male; D009154:Mutation; D010641:Phenotype; D010802:Phylogeny; D012641:Selection, Genetic; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D014157:Transcription Factors