Lasting Biological Effects of Early Influences

PERSPECTIVES IN BIOLOGY AND MEDICINE Volume 12 · Number 4 · Summer 1969 LASTING BIOLOGICAL EFFECTS OF EARLY INFLUENCES RENÉ DUBOS* In his essay "Uses ofGreat Men" Ralph Waldo Emerson wrote a statement that has a direct bearing on the topic I wish to discuss in the present paper: "There are vices and follies incident to whole populations and ages. Men resemble their contemporaries even more than their progenitors." As a moralist, Emerson was primarily concerned with the intellectual and moral attributes of human beings; his aphorism is just as valid tor anatomic and physiological attributes. We resemble our progenitors because we derive from them our genetic endowment; but genes do not really determine the traits by which we know a person. They only govern theresponses thattheperson makes to environmental stimuli. Individuality progressively emerges from these responses. Whereas the genetic pool ofa population remains essentially constant, the environment changes rapidly. We resemble our contemporaries because the phenotypic expression ofthe genetic endowment is determined by the environmental forces that impinge more or less simultaneously on all the members ofa given generation in a given social milieu. Thephenotypeisconstantlybeingmoldedbytheenvironmentthroughout the whole life span. But early influences certainly play the most important role in converting genetic potentialities into phenotypic reality. As commonly used, thephrase "early influences" denotes the conditioning ofbehavior by the experiences ofearly life. Early experiences, however, * The Rockefeller University, New York, New York 10021. Reprinted with permission from the Medical College ofVirginia Quarterly. 479 do more than condition behavioral patterns; they also affect, profoundly and lastingly, other biological characteristics such as initial growth rate, efficiency in the utilization of food, anatomic structures, physiologic attributes , maximum adult size, resistance to infection, response to various forms of stimuli—in brief, almost every phenotypic expression of the adult. A few examples from contemporary life will suffice to illustrate the effects ofearly influences on human populations. Japanese teenagers are now much taller than their parents and differ in behavior from prewar teenagers, not as a result of genetic changes, but because the post-war environment inJapan is very different from what it was in the past. A similar phenomenon is observed in the settlements of Israeli kibbutz. The kibbutz children are given a diet and sanitary conditions as nearly optimum as can be devised. Early in their teens, as a result, they tower over their parents, who originated from crowded and unsanitary ghettos in Central and Eastern Europe. The acceleration ofgrowth inJapan and in the Israeli kibbutz constitutes but a particular case of a constant trend toward earlier maturation of children in Westernized countries. This is evidenced by greater weights andheights ofchildren at each year oflifeandby the earlier age ofthe first menstrual period. In Norway, for example, the mean age ofmenarche has fallen from 17 years in 1850 to 13 in i960; similar findings have been reported from Sweden, Great Britain, the United States, and other affluent countries. Growth is not only being accelerated; the final adult heights and weights are greater aswellas being attained earlier. Some fifty years ago, maximum stature was not being reached, in general, until the age of29; commonly now it is reached about 19 in boys and 17 in girls. With regard to the age of puberty, the change seems to consist in the restoration ofthe developmental timing that had prevailed in the past and that had been greatly retarded by the ways oflife at the beginning ofthe 19th century. The factors responsible for these dramatic changes in the rate of anatomic and sexual maturation are not completely understood. There are good reasons to believe, however, that improvements in nutrition and control ofchildhood infections have played a large part in the acceleration ofdevelopment, and that this change in turn has been responsible for the larger size achieved by adults. 480 .ReMi Dubos · Biological Effects ofEarly Influences Perspectives in Biology and Medicine · Summer 1969 I shall briefly describe experimental models that illustrate the effects of early influences on the development oflaboratory animals. Pioneering investigations on the lasting biological effects ofearly postnatal influences were carried out in England during the 1960's by R. A. McCance and Elsie M. Widdowson of Cambridge University. These investigators compared the growth of rats suckled in small litters (three...