Developmental Denialism
“Nature is probably quite indifferent to the aesthetic preferences of mathematicians.”
― Alfred North Whitehead
The tendency to assume that we can understand how complex processes work with an equation, or even a single number, is seductive. Heritability is such a seduction because at first glance it seems to measure the intuitive, that traits run in families. However, common sense is an awful guide for scientific investigation, especially developmental science. In developing organisms many non-intuitive factors play critical causal roles in the development of specific traits. One such example is that baby chicks require the experience of seeing their toes to learn to peck and consume mealworms (Wallman, 1979). In such cases, it is highly unlikely that a prior and targeted hypotheses would be able to pinpoint all the necessary and sufficient factors for the development of that trait. Studying development is hard, it involves lots of longitudinal observations, persistence, grit, trial-and-error, and a fair amount of luck. Those willing to spend the time observing organisms across development can be handsomely rewarded, often by discovering never-before-seen factors in the development of behavior that can then be investigated using targeted experimental approaches. 
Faced with the difficulties of researching development, it is tempting to go a simpler route, by ignoring the details of individual development and assuming that traits are exchanged between generations in “units” of information—genes that bias organisms towards acquiring some traits and not others. Behavioral and population geneticists often never directly measure genetic contributions, but estimate them by measuring how variation in traits across individuals is predicted by sharing genes with others (comparing related individuals or monozygotic twins) or sharing environments with others. By separating the variance in terms of genetic and environmental components they can calculate a single number that shows how much genes control the development of a trait. A heritability estimate of 0.0 means that a trait is entirely controlled by the environment and a heritability estimate of 1.0 means that a trait is entirely controlled by genes.
Heritability tries to calculate the genetic contributions underlying traits in a population by reducing the complex process of individual development. It does this by assuming that all traits have an independent genetic and environmental component (and sometimes and interactions between the two) during development. In cases such as animal breeding where husbandry conditions carefully control many aspects of the developmental environment heritability estimates have some utility, although even in these conditions they do not tell you anything about the actual processes underlying the ontogeny of traits of interest. For example, one could easily calculate heritability estimates on early responses to mealworms in chicks, but it would never tell you that chicks need to see their own feet to develop the ability to peck and eat mealworms.
Developmental denialism occurs when heritability is treated as a causal mechanism governing the developmental reoccurrence of traits across generations in individuals. Such an approach thwarts true developmental science by assuming a priori which mechanisms are causal in the development of specific traits. Opposition to heritability as a causal explanation is not new. Zing-yang Kuo was arguing for the abolishment of heritability in psychology in the 1920s, and afterward American comparative psychologists lead by T.C. Schneirla, Gilbert Gottlieb, Ethel Tobach argued for a developmental approach to the reoccurrence of traits.
Why is developmental denialism a problem? Because understanding development is the only way to really understand where differences and similarities between individuals come from, it is the best way to identify causal factors shaping the emergence of differences, and design interventions to correct differences that lead to disadvantages. Assuming that highly heritable traits are “mostly genetic” thwarts research into understanding the actual mechanisms governing the emergence of traits, it creates black boxes in lieu of understanding how genes and environments shape development and provides just enough empirical clout to be misused by those with nefarious political aims. In particular, three major issues with using heritability to deny development should be further elaborated.
Issues with using heritability as a replacement for development:
- Genetic and Environment influences are never independent
- Analysis of variance can not uncover causal developmental processes
- The organism is negated
It often surprises people when I say that I believe everything is genetic, because genes are a continually present factor shaping organisms throughout their development, and without them, there could be no developmental at all. But the same could be said for a wide range of different developmental resources. Try developing without mitochondria, gravity, light, water, food, or interactions with other individuals. All these factors are essential for an organism to maintain and perpetuate itself. Furthermore, variation in these factors influence variation in phenotypes. But genes do not occupy a privileged, centralized role in development, they do not direct, control, or guide development any more than other factors. This is because the information in genes is always relational, they are never independent of other factors, and do not have a direct, isolated, or linear influence on organisms. For example, the gene for FoxP2 protein plays a role in vocal learning in the brain, liver function, and even cancer based on differences in where, and how, the gene is used by the organism during development. The information in genes is dependent on the state of the organisms, its behavior, its environment, its developmental stage. Thus a core assumption of hereditarianism, that organisms can be partitioned off into separate, independent environmental and genetic influences denies the reality of how development actually works.
Using analysis of variance to understand the causal process is also difficult. Moore (2006) discussed this in his paper on the heritability of IQ, and I will repeat his argument here. Snow only occurs when temperature and moisture are at the correct levels. If one was to use an analysis of variance to look at the causal factors underlying the presence of snow in montane tropical environments and Antarctica you would get very different results. In Antarctica, where the temperature is always low enough for snow to occur, only variation in humidity that would correspond with the presence of snow, thus humidity would seem to “cause" snow. In montane tropical forests where humidity is always high it would be differences in temperature that lead to the presence of snow, thus temperature would seem to “cause" snow. Using heritability estimates to uncover independent causal processes is misguided, as multiple factors can shape variation in traits across individuals in the population, and the heritability estimates will never be able to uncover the processes that generate such variation across individuals.
Another problem of this approach is that traits that don't vary across individuals are always environmental. For instance, the ability to use language is a uniquely human ability. Since linguistic ability is ubiquitous across all human populations and thus does not vary, by calculating a heritability estimate of linguistic ability you will come to the conclusion that it is entirely environmental. A more reasonable assumption that universal aspects of human neural physiology, involving key genetic influences, allow humans to develop linguistic abilities.
My largest issue with hereditarianism is that it negates its own object of study, the organism itself. By treating organisms as bundles of independent traits each separated into independent genetic and environmental influences, it ignores the fact that the organism is a whole integrated system that continually interacts and changes its proximal environment throughout its life. The organism is a nexus where genes and environment interact, it is an irreducible common reference point for all of biology and psychology. The behavior of the organism can feedback into shaping both the environment it experiences and the expression and functionality of the genome across ontogeny. When taking the development of the organism seriously it quickly becomes apparent that causality is bidirectional going from genes-to-organism-to-environment as easily as it can go from environments-to-organism-to-genes. Key reference point for understanding the function of both the genes and the environment.
Wallman, J. (1979). A minimal visual restriction experiment: Preventing chicks from seeing their feet affects later responses to mealworms. Developmental Psychobiology: The Journal of the International Society for Developmental Psychobiology, 12, 391-397.
Moore, D. S. (2006). A very little bit of knowledge: Re-evaluating the meaning of the heritability of IQ. Human Development, 49, 347–353.
