"and another ... In order to act as raw material only , variation must walk a tightrope between two unacceptable alternatives . first and foremost , variation must exist in sufficient amounts , for natural selection can make nothing , and must rely upon bounty thus provided ; but variation must not be too florid or showy either , lest it become the creative agent of change itself . Variation , in short , must be copious , small in extent , and undirected ."
"And as far as we know , they are undirected . Evidence to the contrary ?"
"In order to act as raw material only , variation must walk a tightrope"
"they are undirected . Evidence to the contrary ?"