Apart from reproduction it also applies to survival. And feeling good is clearly on the side of supporting survival. Take tails for example, it does not provide

Apart from reproduction it also applies to survival. And feeling good is clearly on the side of supporting survival. Take tails for example, it does not provide any reproductive support (i believe) and it was unnecessary since we started walking on ground instead of trees so it eventually went away. Same for gills. All i am saying is that if it had good enough use, it would have made some development in the regard however small or trivial it may be. Also my first question was regarding its side effects, evolution is just something i used to support my question, but my question in general still remains unanswered..