|MadSci Network: Zoology|
Dear Tiago, Your river turtle was very lucky to survive but unlike sea turtles, it was adapted to a changeable water content (its concentration or dilution). The sea was the source of all of our distant ancestors because it has stable chemistry. The concentration of most substances in the marine environment varies only with depth. Most organisms live within 10 metres of the surface, so the environment is so stable that it’s a wonder anything gave up such a safe place to live! The water also supports their bodies.Land animals and probably freshwater animals before them adapted to terrible ”drought” and awesome “flooding” respectively. Their bodies are forever robbed of all water on land and flooded with dilute water in most rivers and lakes. Now you have a problem. As a water animal, the turtle has both the ability to control its water content and a tough outer carapace to help with exposure problems. You may say the octopus is adapted, but never to the freshwater environment. His ancestors only lived among the rocks of the sea. No genetic engineering could provide him with the osmotic control to lose excess water in a river or prevent water loss on land. The ancestral coiled shell, typically Mollusc, could only help if some method of movement could evolve for land . In effect, your proposal hits on two obvious rebuttals—  mutable characteristics in the octopus such as a reversion to its shelled ancestral type (such as the Pearly Nautilus)could not provide any useful adapation to life on land or in rivers  genetic modification of a species is possible only within specified narrow limits. You have to change the genes that are present or introduce one that you know will perform a simple change. The future holds incredible ideas that will change our comprehension of life. I doubt if we can see the octopus changing its behaviour and its muscles.
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