All rights reserved. Walter E. Lammerts, Ph.D. By reference to beans, roses and corn, variation is shown to be limited and not unlimited as Darwin thought.
Mutations are generally harmful.
This makes them ineffective even in microevolution as means of accumulating the constant features distinguishing species. The giraffe is used to illustrate this fact. Also biological species show remarkable variation in chromosome number and form. Translocations and inversions occur rarely and spontaneously in species populations. Most translocations in the fruit fly, Drosophila, are either invariable when homozygous or cause a reduction in fertility in one or both the sexes.