“Rapid Evolution” Method Found in Eyeless Fish

And chemicals like thalidomide can suppress fetal development of different parts (arms, etc) and several organism show an evolutionary history of interrupted development becoming 'normal' -- such as:Axolotl (Ambystoma mexicanum) – Our Wild World

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Although ‘water monster’ is pretty harsh, axolotls are funny looking creatures. This is because axolotls are not fully developed salamanders. Much like frogs, salamanders are born in the water and then must undergo metamorphosis to start their adult lives on land. But this doesn’t happen in the axolotl; instead they spend their entire lives in water, and never grow up (much like Peter Pan, but in a less endearing way).

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Axolotls retain the characteristics of youthful salamanders, including external gills and a fin on its back. This sort of arrested development is known as neoteny. Neoteny is often seen in domesticated animals, most obviously dogs (shorter snouts, floppy ears and playful attitudes are all characteristics of puppies). For the axolotl, staying in this immature state makes sense, since the waters in which they live have very little food. Metamorphosis in salamanders is triggered by thyroid stimulating hormone, which is derived from iodine. Iodine in particular is lacking in the axolotl’s habitat, causing neoteny. But this might also help the salamanders survive; neotenous animals are smaller and require much less food, and in an uncertain environment like that of the axolotl, this might be the best way to live.

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If organisms reach sexual maturity before some parts are fully developed then neoteny can be propagated.Note that humans exhibit neotony as well ... that is one of the reasons humans appear hairless compared to apes, the vellus hair (short, light\blond) is retained (especially in women) rather than being replaced by mature hair (longer, darker), and also why the human skull is 'frozen' in a juvenile form compared to other apes.Certainly eyes are part of the development in a mature fish, but are not fully formed in early fetal development.EnjoyEdited by RAZD, : punctuation