Its a cornerstone of nature.

The slow, dumb, are simply removed from the genepool thereby increasing the percentage of faster more intelligent of the species. And,, prevents further degradion of the species.

1/2 an hour watching the nature channel shows what happens to the slow and dumb one's.

The only problem is in our species,, the slow dumb can wind up taking out the faster smarter one's on their way out the door. 

In nature the faster smarter one's simple get away from the slow dumb and the gene pool doesn't have collateral damage.

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