The trait value, Z, of an individual has been classically imagined to consist of genotypic (G) and environmental (E) effects and the interactions (G x E) between them. This perspective allows the differences between individuals within a population to be partitioned into the components of owing to genetic and environmental influences. Such partitionings are the underlying basis of the Nature versus Nurture debate, with genotype in the role of nature and environment in the role of nurture. For individuals, the debate concerns the question of whether his/her characteristics were 'fixed at conception' and are therefore 'hardwired' or whether they were caused by the environment in which the individual developed and, consequently, are malleable. This debate has had effects on policy decisions, for example, those regarding the allocation of financial resources to early education. The argument can be expressed simply as follows. If Nurture plays an important role in desirable characteristics of the populace, then scare resources can be allocated to engineer the environment to bring about the desired social change. However, if desirable or undesirable characteristics are determined primarily by Nature, then it is futile to attempt to address them with policy, since no amount of resource investment or environmental engineering can or will change the underlying genes.
Darwin employed a version of these arguments to deduce that some desirable traits, like the muscles of a blacksmith or the knowledge of a scholar, were entirely (or predominantly) environmentally determined, while many undesirable traits, like 'sports,' were predominantly heritable (i.e., genetic). One of the earliest modern coinings of this debate can be found in Francis Galton's (1874) discussion of the origins of a group of ~300 Englishmen who “deserved” to be called “Men of Science.” Galton (1874, p. 227) the following question: “What then are the conditions of nature, and the various circumstances and conditions of life - which I include under the general name of nurture - which have selected that one and left the remainder?”
In recent years, somewhat more attention has been focused on gene-environment interaction, especially in the investigation of complex human diseases like autism, obesity and asthma. Although each disease has been shown to have a genetic component, the rise in incidence within a single generation is too fast to be accounted for by evolutionary change in gene frequency. Thus, the increased incidence cannot be owing to an increase in the frequency of the underlying genetic causes. Conversely, if the increased incidence were entirely owing to environmental change, there would be no genetic signature associated with these diseases. Rapid change in the inducing environments is conspicuous and it is affecting some genotypes more than others; therefore, gene-environment interaction is inferred to be a major causal component of these diseases.
The lecture adds a new dimension to the Nature versus Nurture debate, namely, the Nurturers, the biotic components of the environment. These biotic environments have genes and their existence allows the possibility of the co-evolution of genes and environments. I will discuss maternal effects as examples of co-evolving environments. Maternal effects are ubiquitous and the most important and well-studied representatives of what are now called “indirect” genetic effects. I will also discuss other social contexts in which such genes play an important role and why these genes are of interest to animal breeders interested in improving animal welfare. Wade came to Indiana University in 1998 and has served as Director of the Graduate Program in Evolution, Ecology, and Behavior, as well as Associate Vice Provost for Faculty and Academic Affairs.