Annals of morphology. Atavisms: Phylogenetic lazarus?

Abstract

Dedication: with highest respect and affection to Prof. Giovanni Neri on the eve of his official administrative retirement as Chair of the Institute of Medical Genetics of the Università Cattolica of Rome for leadership in medical genetics and medical science and friendship for decades. The concept “atavism,” reversion, throwback, Rückschlag remains an epistemological challenge in biology; unwise or implausible over‐interpretation of a given structure as such has led some to almost total skepticism as to its existence. Originating in botany in the 18th century it became applied to zoology (and humans) with increasing frequency over the last two centuries such that the very concept became widely discredited. Presently, atavisms have acquired a new life and reconsideration given certain reasonable criteria, including: Homology of structure of the postulated atavism to that of ancestral fossils or collateral species with plausible soft tissue reconstructions taking into account relationships of parts, obvious sites of origin and insertion of muscles, vascular channels, etc. Most parsimonious, plausible phylogenetic assumptions. Evident rudimentary or vestigial anatomical state in prior generations or in morphogenesis of a given organism. Developmental instability in prior generations, that is, some closely related species facultatively with or without the trait. Genetic identity or phylogenomic similarity inferred in ancestors and corroborated in more or less closely related species. Fluctuating asymmetry may be the basis for the striking evolutionary diversification and common atavisms in limbs; however, strong selection and developmental constraints would make atavisms in, for example, cardiac or CNS development less likely.Thus, purported atavisms must be examined critically in light of the above criteria. © 2013 Wiley Periodicals, Inc.

Differential regulation of myc homologs by Wnt/β‐Catenin signaling in the early metazoan Hydra

“…Intriguingly, natural occurring tumors have been observed in Hydra , presumably resulting from differentiation‐arrested female gametes , a cell type in which myc2 is expressed at high levels . The occurrence of tumors in this early diverging organism is actually in line with the atavistic cancer model, in which the biological origin of malignant growth is traced back to the transition between unicellularity to multicellularity . This theory was recently supported by molecular analyses of multiple sets of genes with common phylogenetic origin (phylostrata) in solid human tumors.…”

Exploring Anatomic Variants to Enhance Anatomy Teaching: Musculus Sternalis

“…Phylogenetic analysis ( Figure 4 ) shows that M sternalis is unlikely to be an “atavism” (see Table 1 ) failing most of the criteria proposed by Zanni and Opitz [ 35 ]. Since M sternalis usually appears in the absence of underlying skeletal or other connective-tissue abnormalities as it did in our lab, its presence is more likely due to local environmental influences on muscle development [ 6 , 20 ].…”

“…For students of human anatomy, the phylogenetic pattern illustrates the history of anatomic changes that the earliest humans inherited from populations of their ancestors and that are used as a basis for the anatomic specializations that define our species. Zanni and Opitz lay out a general approach to analyzing the evolutionary components of usual and unusual anatomic features [ 35 ].…”

“…Among the primates, there are two patterns of ventral muscles worth noting. First, the R abdominis generally tends to attach more cephalad than is typical in humans [ 35 , 36 ], often on the manubrium [ 40 , 43 , 44 ] or as high as the first rib [ 44 ]. The naming of additional muscle bodies that are described as cephalad extensions of the aponeurosis of the R abdominis varies to include the names found in the older literature (discussed above).…”

Genetics of Atavism

“…According Wilhelm Roux, the term "atavism" in biology defines the revival of a biological structure that was lost in ancestors during evolution (Correns et al, 1912). The term "atavism," coined in 1766 by French botanist Duchenne, comes from the Latin atavis, which roughly corresponds to the word "precursor" (Hall, 2010;Zanni and Opitz, 2013). We know several atavisms in humans: color blindness, extra nipples, enlarged teeth, an elongated coccyx ("tail"), excess hair, etc.…”