Biosocial Worlds. Группа авторов
would be limited to ‘the causal interactions between genes and their products which bring the phenotype into being’ (a subject that Julian Huxley had previously worked on), but broadened his argument very quickly.
Waddington’s position was influenced by the dawning realisation of several researchers of his day that development of the embryo must involve networks of interactions among genes that form a complex integrated system, and that the completely bifurcated subjects of genetics and embryology should be brought closer together, even though many embryologists feared that their field would be completely overtaken by genetics if such a move took place (Waddington 1940). Waddington was trained in both fields; he had worked in Germany with the Nobel Laureate embryologist, Hans Spemann, and with the geneticist Thomas Hunt Morgan in California, and made the very idea of ‘development’ central to his arguments specifically because of its double meaning: the growth of individuals and evolutionary change.
For Waddington, development denotes the set of conditions that enable so-called ‘multi-potent stem cells’ to become differentiated in tissues that develop into cells with specific functions. He insisted that genes are responsible for guiding only ‘the mechanics of development’, and argued that genotypes and environments function together to produce phenotypes. An appreciation of what continues to be recognised as ‘critical periods’ in developmental processes is also embedded in Waddington’s thinking. He adamantly rejected reductionist neo-Darwinianism, and described himself expressly as a Darwinian.
In his book Organisers and Genes, published in 1940, Waddington topologically depicted ‘the epigenetic landscape’ as a symbolic representation of embryonic development. The image is of a ball rolling down an undulating plateau in concert with other balls, in which one of several possible pathways is taken before it eventually comes to rest at a lowest point. In the case of a pathway or ‘creode’ which is deeply carved into the hillside, external disturbance is unlikely to prevent normal development. The balls depict developing eggs and the gradual transformation of their pluripotent cells into tissue types, the process of which is controlled by genes interacting with each other that modulate the manner in which the egg/ball descends the slopes and select specific intersections (Figure 1.1). Waddington’s point was that development is ‘canalised’ – thus ‘buffering’ the outcome of natural selection, understood today as a measure of the ability of a population to produce replicable phenotypes regardless of variability in genotypes or the environment.
Waddington’s intention was to demonstrate that there is no straightforward relationship between a gene and its phenotypic effects, and furthermore that, should a mutation arise, its effects may well be moderated or buffered by other genes – a process he termed ‘genetic assimilation’ that he explicitly linked to Darwinian thinking. Waddington was emphatic that genetic variation and phenotypic expression are not coupled. He acknowledges that change can be random, but at the same time he argued that evolution occurs primarily as a result of mutations that affect developmental anatomy. His theorising influenced debates of his day about both embryology and evolution. See Petryna, this volume, for influences on Waddington’s thinking by the Scottish biologist and mathematician, D’Arcy Thompson.
Waddington was clear that the metaphor of the epigenetic landscape had limitations (Waddington 1940, 92); nevertheless, this image is usually taken as the starting point for a genealogy of epigenetics. His argument that synchronic processes, both among genes and in the larger intra-cellular environment, must be incorporated into and modify linear unidirectional accounts of developmental processes and evolutionary change was in effect a paradigmatic shift. In the preface to the first edition of his book, Waddington notes that his greatest debt goes to the biochemist Joseph Needham, also an extraordinarily influential sinologist best known for his monumental seven-volume work on the history of science in China. It is reasonable to assume that the image of the epigenetic landscape was influenced to some extent by discussions with Needham who, in the 1940s, was teaching himself Chinese, and would have been well acquainted with classical understanding of disease causation in China in which inductive thinking is dominant, and bodies are embedded in encapsulating spheres of the individual, society, environment and cosmos. This type of thinking persists in modified form to the present day in the practice of traditional Chinese medicine (Farquhar 1994). Waddington was also well acquainted with Alexandrian Gnostics and the so-called Arabic alchemists, philosophers whose ideas may have contributed to his writing (Waddington 1975).
Although the majority of epigenetic researchers from Waddington’s time to the present day acknowledge that social, political and economic variables contribute to the epigenetic changes that they are investigating, nevertheless they set these variables to one side and create environments that are deliberately ‘miniaturised’ for the purposes of research. But such miniaturisation, although it facilitates controlled scientific investigation, is problematic when it comes to seeking out other than proximal explanations for epigenetic changes. Exposures to environments external to individuals can have profound, lasting effects on wellbeing that, if ignored, may well result in inappropriate victim blaming, as we will see in what follows.
Jablonka and Lamb, both geneticists and epigeneticists, note that Waddington’s work essentially languished for the first three decades of its existence and one or two scientists argued that it should be abandoned, but it nevertheless survived to become molecularised in form. In the post-genomic era, from the early years of the twenty-first century, the field has been thoroughly revitalised and focuses on ‘alternative developmental pathways, on developmental networks underlying stability and flexibility, and on the influence of environmental conditions on what happens in cells and organisms’ (Jablonka and Lamb 2002, 89) – at both individual and population levels, one might add.
Epigenetics has expanded into an enormous field of inquiry that includes stem cell biology, cancer biology, investigations into genome instability, DNA repair, epigenetic epidemiology, and so on. The concept of environment, having been rendered essentially of no importance in hard-line deterministic genetics, is resuscitated in the post-genomic era to take on singular importance in the formation of reactive genomes and hence with DNA activity and cell functioning. It follows that delineating environment is crucial to understanding the biological embedding of individuals, their families and communities in specific contexts (Hertzman 1999). Of greatest interest to anthropologists is the sub-field of environmental epigenetics, a term used to cover investigations into topics as wide ranging as toxic exposures, malnutrition and abuse.
Disagreements among practitioners of this sub-discipline are evident, and the presumption that one or more teams of researchers represent the entire field would be a mistake (Landecker and Panofsky 2013; Lock 2015).
The embodiment of trauma
An article published in the mid-1990s by the epigeneticist Michael Meaney and colleagues has become iconic in the field of epigenetics. This research made use of a model of maternal deprivation created in rats by removing young pups from their mothers shortly after birth, thus terminating maternal licking and grooming crucial to their development. The deprivation altered the expression of genes that regulate behavioural and endocrine responses to stress, and hence, indirectly, hippocampal synaptic development (Meaney et al. 1996). It was found that these changes could be reversed if pups were returned in a matter of days to their mothers.
Furthermore, when the birth mother was a poor nurturer, placement of her deprived pups with a surrogate mother who licks and grooms them enabled the pups to flourish. Crucially, it was shown that pups or foster pups left to mature with low-licking mothers not only exhibited a chronically increased stress response but also passed on to their own pups this heightened sensitivity to stress. Hence, variation in maternal behaviour results in biological pathways causing significantly different infant phenotypes that can persist into adulthood, and are potentially transmitted to the next generation.