Hereditary regression

Atavism
Evolutionary degeneration

Nature

Hereditary reappearance of features, usually physical, absent from parents and recent ancestors. Such features may be characteristic of more distant ancestors, or they may constitute a return to characteristics not typical of the species or race at all, but found in allied species or races having a common evolutionary ancestry (as in the case of strongly pronounced canine teeth in humans).

Incidence

Hereditary regression, characterized by the reappearance of ancestral traits or the loss of recently acquired genetic adaptations, has been documented in various populations worldwide. Its incidence is particularly notable in isolated communities where genetic bottlenecks and inbreeding increase the likelihood of regressive traits manifesting. Such occurrences can have significant implications for public health, biodiversity, and the long-term viability of affected populations, making hereditary regression a matter of global concern.
In 2021, researchers in the Faroe Islands reported a resurgence of a rare hereditary neurological disorder, previously thought to be nearly eradicated. Genetic analysis revealed the disorder’s re-emergence was linked to hereditary regression within the island’s small, isolated population.

Counter-claim

Atavism does not necessarily represent a deterioration. It may be the re-emergence of valuable genetic characteristics of less-specialized progenitors. Many phenomena have been labelled atavisms which admit of other interpretations such as the consequences of arrested development due to malnutrition, a qualitative variation in some vestigial organ, or the predictable consequences of hybridization.