Strange Adventures Vol. 1 (1950-1973) #8

Plot

Scientist Ralph Gain invents a machine that can evolve animal subjects. His hoodlum friend, Johnny Farrel, accidentally kills him and uses the machine on himself, running up the evolutionary ladder until he finds himself devolved into a gorilla's form. He tries to convinced authorities that he is Gain but he slowly loses his mind and becomes a gorilla in thought as well as form.