The concept of neoteny- Why humans are forever young

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In the 1860s Auguste Duméril made an astonishing discovery. He had received a shipment of strange amphibians from Mexico. Scientists knew that the animal – the axolotl – grew into a peculiar aquatic species: what Duméril discovered was that if the animal was forced to live in drier environments it metamorphosed into something much more like a salamander, with lungs instead of gills. Duméril’s work was a step towards recognizing an important factor at play in evolution.

Auguste Duméril // 1812–۱۸۷۰

Almost at the same time that Duméril was performing his experiments, Edward Drinker Cope was considering the role that accelerated or arrested development might play in the origin of new species. Organisms can change their appearance drastically as they grow to sexual maturity. Perhaps, suggested Cope, some new species might evolve simply by random shifts in this pace of development. Charles Darwin read Cope’s essay on this concept and was clearly impressed. He folded the idea into his sixth and final edition of On the Origin of Species, published in 1872.

A decade later Julius Kollmann recognized that Duméril’s work on the axolotl provided a concrete example of Cope’s concept in action. Duméril had helped to show that the axolotl seems to become stuck in a state of arrested development if it spends its entire life in water: it retains gills and other juvenile features even as a sexually mature adult. Kollmann called this retention of juvenile characters into adulthood the concept of neoteny. Today, many biologists recognize that neoteny has played a key role in the evolution of species – probably including our own.

Raise the axolotl in water and it will retain the features of a juvenile amphibian even into old age.

Biologists often use humans as a classic example of neoteny. Our nearest living relatives, the chimpanzees and bonobos, produce babies that look relatively similar to human babies. However, as chimps and bonobos grow they develop additional features: they gain more hair, a large jaw and long muscular arms, for instance. As humans grow they retain many “babyish” features: little hair, a small and weak jaw, relatively short arms, and so on. Humans certainly grow old, but in a peculiar way we look forever young.

Evolution isn’t always about the appearance of brand new characteristics.

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Sometimes it’s simply about slowing (or speeding up) the rate that existing features develop.

   

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