Stretch Genes

“This book contains the first attempt to trace development all the way from genes through the mind to culture.” The authors’ illusion that this is so is owing at least in part to their neglect or ignorance of the thought of many others who have attempted to arrive at a conception of human heredity that brings in minds and culture as well as genes.

Although Herbert Spencer groped his way toward the notion, I believe that Thomas Hunt Morgan,1 the most influential geneticist since Mendel, was the first to realize that in addition to an ordinary genetic evolution in the Darwinian mode, human beings also enjoy an “exogenetic” evolution in the Lamarckian mode: the latter is mediated not through chromosomes but through indoctrination and learning, example and imitation (“aping”)—a form of evolutionary change written about in addition by J.S. Huxley, C.H. Waddington, and myself.

T.H. Morgan’s formulation is so unfamiliar that it is worth quoting in full, especially since it is a model of clear thinking and writing.

While biologists have come to reject the theory of the inheritance of acquired characters by means of the germ-cells, nevertheless they recognize the fact that the human race has succeeded in another way in transmitting certain traits acquired in one generation to the next. There are, then, in man two processes of inheritance: one through the physical continuity of the germ-cells; and the other through the transmission of the experiences of one generation to the next by means of example and by spoken and written language. It is his ability to communicate with his fellows and train his offspring that has probably been the chief agency in the rapid social evolution of man. In the animal kingdom we find many cases in which the young are protected and cared for by their parents. Such beginnings furnish the background out of which has evolved the more complex relation of parents and offspring in the human race, where a prolonged period of childhood furnishes exceptional opportunities for the transmission of tradition and experience.2

“Cultural evolution” is not a very good description because it could be taken to connote evolution of culture instead of an evolution mediated through culture, so perhaps Julian Huxley’s “psychosocial evolution” is better, though I myself prefer the wholly neutral “exogenetic” or (A. J. Lotka’s term) “exosomatic” evolution. Because of the crucial importance of the cultural nexus between one generation and the next, S. A. Barnett has thought to replace Homo sapiens or Homo faber by Homo docens (teaching man) as the specific designation of man. The trouble with Homo sapiens is the temptation it offers to the cynic to contrast man’s titular wisdom with his actual lack of it.

The most important differences between the ordinary and exogenetic evolution are that the latter is reversible and that the knowledge, skills, and manners acquired in one generation can be transmitted to the next (for this reason it is said to be an evolution “in the Lamarckian…

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