biology only evolves to a certain limit, then devolves and evolves new traits

cheetahs evolved to run fast in order to hunt gazelle 

gazelles evolved to run fast to avoid being eaten by cheetahs 

but cheetahs won't evolve to run faster 

and gazelle won't evolve to run faster 

not because it's biologically impossible 

but because biology only allows organisms to evolve to a certain limit 

then biology devolves organisms back to normal state 

and organisms evolves other attributes 

which indicates that cheetahs will devolve to loose their speed 

and instead evolve to become slower and stronger like tiger 

or smaller and stealthier like small cats 

and which indicates that gazelles will devolve to loose their speed 

and instead evolve to become slower and stronger like bison  

or smaller and stealthier like mouse-deer 

this is why intelligence is so precious among humans 

because humans instinctively know that if they reproduce wrong for a few generations then the human species will devolve to loose their intelligence and evolve other traits instead 

genetic engineering has been the tool presumed able to avoid human devolution 

but nano machine cybernetics will probably be a more successful tool to avoid human devolution