Should humans practice survival of the fittest?

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Not that I believe it should be done, but I often wonder if this is the reason for overpopulation, global warming etc. I mean, if we allowed the weaker of the species to pass on or fail, would we better off? (again I don't support this)If we allowed the physically ill, mentally challenged, the "stupid" people to pass on, would the species be better off? Isn't this practiced by other animals? They seem to be better off, eventually after the food supply grows short, the ones who don't have access to it die off and the species becomes stronger. Does this seem like an idea that could be possible for humans, or do our emotions get the best of us? Or is survival of the fittest already practiced? (Finally, I do not support this! Just a question!)