The Time of Action of Genes, and Its Bearing on some Evolutionary Problems

(1) Genes can be classified according to their time of action. Not only can they act in diploid zygotes, endosperms or gametes carrying them, but their action can be manifested in the following organisms which do not carry them: mothers of zygotes carrying them, and gametes or embryos borne by zygotes carrying them. Their time of action is therefore distributed over more than one life-cycle. (2) It is contended that change in the time of action of genes has been an important factor in evolution, and that some cases of orthogenesis, including degeneration, can be explained by it. (3) In an organism undergoing metamorphosis the adaptive efficiency of a gene depends on the limitation in time of its action.