a. Sir Francis Galton: among the first (if not the first) to frame nature and nurture as disjoint domains (1874)28

“The phrase ‘nature and nurture’ is a convenient jingle of words, for it separates under two distinct heads the innumerable elements of which personality is composed. Nature is all that a man brings with himself into the world; nurture is every influence from without that affects him after his birth. The distinction is clear: the one produces the infant such as it actually is, including its latent faculties of growth of body and mind; the other affords the environment amid which the growth takes place, by which natural tendencies may be strengthened or thwarted, or wholly new ones implanted.”(p12)

“When nature and nurture compete for supremacy on equal terms in the sense to be explained, the former proves the stronger. It is needless to insist that neither is self-sufficient; the highest natural endowments may be starved by defective nurture, while no carefulness of nurture can overcome the evil tendencies of an intrinsically bad physique, weak brain, or brutal disposition.”(p12–13)

Insight from Keller (2010)3

“… the assumption already implicit in Francis Galton’s catchy phrase, ‘Nature and Nurture’ (1874) is that there exist two domains, each separate from the other, waiting to be conjoined. Galton was hardly the first to write about nature and nurture as distinguishable concepts, but he may have been the first to treat them as disjoint.”(p11)

b. Lancelot Hogben–R.A. Fisher 1933 exchange over partitioning causation in relation to heredity vs environment: Hogben’s emphasis on their interdependence (as informed by his own experiments with fruit flies under different conditions) versus Fisher’s assertion of their independence.29(p738–739, 749)

Hogben to Fisher: “Suppose you say that 90 percent of the observed variance is due to heredity, do you mean that the variance would be reduced by 10 per cent, if the environment were uniform? Do you mean that the variance would be reduced by 90 per cent, if all genetic differences were eliminated? Perhaps you might think the question silly; but if you could suggest an alternative form of words, it might help.”

Fisher to Hogben: “Dear Hogben, your question is a sound one . . . if each genotype has an equal chance of experiencing with their proper probabilities, each of the available kinds of environments, then the variance is additive, and the statements you have are equivalent.”

Hogben to Fisher: “Dear Fisher, I don’t think you quite got the difficulty I am trying to raise. It concerns an inherent relativity in the concepts of nature and nurture.”

Fisher to Hogben: “You are on a question of non-linear interactions of environment and heredity . . . it would be very difficult to find a case in which this would be of the least use, as exceptional types of interaction are best treated on their merits, and many become additive or nearly so as to cause no trouble when you choose a more appropriate metric.”

Insight from Tabery (2008)29

“R.A. Fisher, one of the founders of population genetics and the creator of statistical analyses of variance, introduced the biometric concept as he attempted to resolve one of the main problems in the biometric tradition of biology – partitioning the relative contribution of nature and nurture responsible for variation in a population. Lancelot Hogben, an experimental embryologist and also a statistician, introduced the developmental concept as he attempted to resolve one of the main problems in the developmental tradition of biology – determining the role that developmental relationships between genotype and environment played in the generation of variation.”(p717)

Insight from Keller (2010)3

“ . . . as the Swiss primatologist Hans Kummer remarked some years ago . . . trying to determine how much of a trait is produced by nurture, or how much by genes and how much by environment, is as useless as asking whether the drumming we hear in the distance is made by the percussionist or his instrument . . . the point is a logical one about which there ought, at least in principle, to be no debate: causes that interact in such ways simply cannot be parsed; it makes no sense to ask how much is due to one and how much to the other.”(p7)

“Questions about differences between groups require a different kind of analysis than do questions about individuals. . . . For group differences, the question we need to ask is, how much of the variation we hear in the sound of drums is due to variation in drummers, and how much is due to variation in drums? And to answer this question, we must turn to the statistical analysis of populations. Which is precisely how Fisher reformulated Galton’s question, and he was clearly aware of the importance of such a shift. Introducing his very first paper on the topic, Fisher warned that while ‘it is desirable on the one hand that elementary ideas . . . should be clearly understood; and easily expressed in ordinary language,’ nonetheless ‘loose phrases about the ‘percentage of causation’ which obscure the essential distinction between the individual and the population, should be carefully avoided’ (1918, 399–400). Perhaps he even had Galton in mind.”(p54)

c. Hogben (1933)1—in which his chapter titled “The interdependence of Nature and Nurture,”(p91) explained the fallacy of equating explaining variation with explaining cause, and argued for an approach to quantify causal impacts akin to the population attributable fraction.

“Clearly we are on safe ground when we speak of a genetic difference between two groups measured in one and the same environment or in speaking of difference due to environment when identical stocks are measured under different conditions of development. Are we on equally safe ground when we speak on the contribution of heredity and environment to the measurement of genetically different individuals or groups measured in different kinds of environments? . . . The question is easily seen to be devoid of a definite meaning.”(p97)

“On the basis of such statements as the previous quotation about stature [by Fisher], it is often argued that the results of legislation directed towards more equitable distribution of medical care must be small, and that in consequence we must look to selection for any noteworthy improvement in a population. . . . The gross nature of the fallacy is easily seen with the help of a parable. Imagine a city after a prolonged siege or blockade ending over a number of years. The available supplies of food containing the necessary vitamins have long since been exhausted in the open market. Young children still growing are stunted in consequence and weigh on average 20 per cent. less than prewar children. One biochemist has a small stock of crystallized vitamins which he has reserved for his family of 4, who grow up normally. There are, let us say, a million stunted children to 4 healthy ones. A party of rabid environmentalists is clamouring for peace. The Government appoints an official inquiry of statisticians. They report that far less than 1 per cent. of the observed variance with respect to body-weight is due to differences in diet, that the improvement produced by change in diet if peace were made would therefore be negligible, and that eugenic selection would solve the problem of how to keep a community alive with vitamins if the war could be prolonged for a few more millennia. It requires no subtlety to see what is wrong with this conclusion. If only 4 in a million and 4 children had sufficient vitamins for normal growth, the effect of differences in the vitamin content of the diet to the observed variance in the population would be a statistically negligible quantity. In spite of this, the mean bodyweight of the population could be increased by 30 per cent. if all children had received a ration with a vitamin content equivalent to the greatest amount available to any child in the same population.”(p116–117)

Related insights from the new field of ecological evolutionary developmental biology (“eco–evo–devo”) about the interdependence of nature and nurture, and the ubiquity of flexible phenotypes.

–From Gilbert and Epel (2015)30

“A quiet biological revolution, driven by new technologies in molecular, cell, and developmental biology and ecology has made the biology of the twenty-first century a different science than that of the twentieth. . . . Some unexpected ideas must be integrated into our new thinking about inheritance, development, evolution, and health. These include the following: Symbiosis. Once thought of as the exception to the rule of life, symbiosis is now recognized as a signature of life, including its development and evolution. We function, develop, and evolve as consortia. Developmental plasticity. Also thought of as an exception to the rules of life, developmental plasticity is also ubiquitous. A single genome can generate numerous phenotypes, depending on environmental conditions. Epialleles, environmentally induced modifications of the genome. Formerly considered impossible, such environmentally modified chromatin not only exists but can be inherited for many generations.”(p.xiii)

“ . . . ‘eco-evo-devo’ seeks to bring into evolutionary biology the rules by which an organism’s genes, environment, and development interact to create the variation and selective pressures needed for evolution.”(p.xiv)

–From Piermsa and van Gils (2011)31

“Bodies ‘express ecology’ by being sufficiently plastic, by taking on different structure, form or composition in different environments,” including “phenotypic plasticity expressed by single reproductively mature organisms throughout their life, phenotypic flexibility – reversible within-individual variation.”(p3)

How big is a python’s gut or heart?—it depends: “Prey capture . . . elicits a burst of physiological activity, with drastic upregulation of many metabolic processes. Immediately, the heart starts to grow. With a doubling of the rate of heartbeat, and as blood is shunted away from the muscles to the gut, blood flow to the gut increases by an order of magnitude. Within two days, the wet mass of the intestine more than doubles.”(p85)

“. . . the older identical twins become, the easier it is to tell them apart! . . . organisms and their particular environments are inseparable: changes in an individual’s shape, size, and capacity will often be direct functions of the ecological demands placed upon them. Bodies express ecology.”(p174)