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> A cave fish in Germany shows the adaptations that can occur in short periods. It is still the same species but changed:
> 
> https://www.newscientist.com/article/2126523-first-ever-cavefish-discovered-in-europe-evolved-super-fast/
> 
> "The pale-coloured loach, shown above, is thought to have diverged from surface fish as glaciers from the last ice age receded some 16,000 to 20,000 years ago.
> 
> “'Our first genetic studies, plus knowledge of the geological history of the region, suggest the cave loach population is amazingly young, certainly not older than 20,000 years,” says Jasminca Behrmann-Godel at the University of Konstanz in Germany, who led the team that analysed the fish. “Despite this short time span, the fish show trademark adaptions to cave life compared with loaches from surface locations nearby, including a pale body colouration, much smaller eyes, plus larger nostrils and barbels.”
> 
> "It shows that adaptation to these subterranean habitats can be fast, and just a few thousand years might be enough for a fish to adapt to cave life, says Behrmann-Godel. “Cavefish could exist virtually everywhere in principle, and there’s no good reason to expect long evolution times for them to adapt to cave environments,” she says.
> 
> ***
> 
> "knowledge of local geology enabled the birth of the new lineage to be dated. The cave system had been sealed for hundreds of thousands of years, but an opening called the Aach spring made it accessible when Alpine glaciers retreated northward around 16,000 to 20,000 years ago. This allowed surface loaches to enter the system for the first time, and they have followed their own evolutionary trajectory since.
> 
> "The cavefish’s eyes are about 10 per cent smaller than those of surface loaches, and their barbels are longer. They also lack scales. Most obviously, they have lost the dark brown blotches typical of surface loaches.
> 
> “'The barbels are enlarged in what seems to be a possible adaption to tactile sensing in the dark,” says Roi Holzman of Tel Aviv University in Israel, who studies how cavefish navigate. “In other cavefish species, barbels are also equipped with chemosensors to help them identify food in sediment, so these fish will need to be further studied to figure these mechanisms out.'”
> 
> Comment: this shows how rapidly epigenetic adaptations can occur to changes in environment. Reznick's guppies took only two years.