Actually, there may be parallels as necropsies on SuperSpiders show defects to GI and lungs
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You misunderstand the “survival of the fittest” concept. Yes, in their wild environment, the wild-type has a genetic advantage. However, in captivity, the wild-type has a very clear genetic disadvantage because it is the phenotype that is most strongly selected against
“Fitness” is determined by which animal is more likely to breed under a given environment. Change the environment, change the selective pressure, and you change the genetic advantage