Simple answer: mammals have fur, reptiles and fish have scales, and birds have feathers. All three are simple variants of maturation in skin cells: if the cells just get thick, then you get scales....
Because some don't have the ability. That's true for individuals, As a species, all multi-celluar animals must mate or else become extinct.
Some drug are legal and some not because legal drugs help your body (not including Alcohol and Tobacco. Illegal drugs affect your body in bad ways.
Because there is a difference between eccentric and insane. It's often hard to distinguish between the two.
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