Some leaves are smooth, some wrinkled. Some plants are dark green, some light green. Some plants contain more protein or oil than others. Some have the male sterility characteristic. Some leaves are waxed, some are not.
Some plants mature early, some late.
Some genetic strains don't even produce ears of corn. These plants are not monstrosities. Some of these strains go back to the first part of the century. Many of them occurred spontaneously in nature. Others were induced experimentally.