Clyde Hertzman and Tom Boyce published an excellent article, How Experience Gets Under the Skin to Create Gradients in Developmental Health, in the 2010 Annual Review of Public Health. I am going to cover their concepts of biological embedding and social causation, both of which are relevant to neuroanthropology. And then we get some great media from both authors at the end.
Here is the abstract:
Social environments and experiences get under the skin early in life in ways that affect the course of human development. Because most factors associated with early child development are a function of socio-economic status, differences in early child development form a socio-economic gradient. We are now learning how, when, and by what means early experiences influence key biological systems over the long term to produce gradients: a process known as biological embedding.
Opportunities for biological embedding are tethered closely to sensitive periods in the development of neural circuitry. Epigenetic regulation is the best example of operating principles relevant to biological embedding. We are now in a position to ask how early childhood environments work together with genetic variation and epigenetic regulation to generate socially partitioned developmental trajectories with impact on health across the life course.
Hertzman and Boyce describe biological embedding in the following way:
Biological embedding occurs when experience gets under the skin and alters human biological processes; systematic differences in experience in a socially partitioned environment lead to different bio-developmental states; the difference are stable and long-term; and these differences influence health, well-being, learning, and/or behavior over the life course (330).
In the article, they do not apply biological embedding in an indiscriminate fashion, rather stating that “not only must experience have biological effects, but also these effects must, in turn, influence long-term human developmental outcomes and the expression of gradients in human development (336).”
They identify candidate systems that meet four basic characteristics for biological embedding: the system can be influenced by daily experience, and responds to experience over the lifecourse; its functioning (or dysfunction) has significant impacts on health, learning, and/or behavior, and the differences in outcome can derive in part from early experience.
Their four candidate systems are: (1) the hypothalamic-pituitary-adrenal (HPA) axis and accompanying secretion of cortisol; (2) the autonomic nervous system and epinephrine and norepinephrine; (3) the prefontal cortex and memory, attention and other executive functions; and (4) systems for social affiliation involving connections between the amygdala and locus coeruleus and higher-order cerebral connections, which are mediated by serotonin and other hormones. They focus on the HPA axis in their review, given that it’s the best researched system
I would add a fifth system, the mesolimbic dopamine system which mediates behavioral engagement, reward learning, seeking, and the allocation of attention, and is mediated by dopamine and glutamate. It meets the basic criteria: shaped by daily experience, including early experience, and with significant impacts on learning and behavior, including addition and other behavioral health problems.
So, how are these systems affected by daily experience? Here their description of social causation proves useful. What I also find remarkable about their summary here is that it represents a direct move away from older ideas of linear cause-effect cause into a realm much closer to how anthropologists think about social causation.
Social causation is:
- Non-linear, where exposure to social conditions can have unpredictable and dynamic relationships to outcomes of interest, related to the accumulation of exposures over time and complex interactions between causal factors
- Non-specific, related more to generalized susceptibility rather than links between singular causes and singular outcomes – “adverse social conditions yield broad, pluripotential pathogenicity rather than focal, specific mordibities, whereas as salutary social environments tend to diminish liabilities to multiple diseases (331)”
- Iterative and recursive, relying on repeated exposures over time that can be self-amplifying and involve chains of contingent causation, for example, marital conflict leading to divorce and then moving homes and loss of social relationships, so that over time individuals can find themselves in “intensely negative and stressful social contexts (331)” and experience “the cumulative wear and tear of life conditions (331)”
- Involves largely mundane exposures, rather than exceptional events, so that cumulative wear and tear “become[s] embedded in neural circuitry and produce[s] the vulnerabilities of adult life (331)”
- Involves symbolic or semiotic processes. “The psychosocial determinants of disease uniquely traffic in the meaning and affective valences of life experience (331).”
I want to quote at length their description of racial and socioeconomic discrimination and accelerated aging as a vivid example of the last type of social causation:
It is thus the meaning of such encounters, and their implications for assessments of self-worth, social position, and respectability, that drives the downstream, biological effects of racism and other discriminatory social interactions. The shortening of chromosomal teleomeres offers a novel biological marker of such aging acceleration, reflecting not so much the individual’s encounters with physical hardships, but more so the meanings that signify positions of burden, disregard, and subordination (331).
More broadly, subjective experience, through recurring encounters with discrimination and unequal power, can have direct biological effects on the systems described above. As they write:
Findings on the health correlates of subjective social status and peer group subordination suggest that the health disparities associated with SES may be at least partially attributable to differences in individuals’ sense of identity, respect, and position within societies, small or large, marked by nonegalitarian structures and values (332).
The Power of Neighborhoods
Hertzman and Boyce outline one major study they have undertaken in British Columbia on early child development, including physical, social, emotional, language/cognitive and communication domains, and measured through the early development instrument (EDI), given to kindergarten teachers to assess children in these different domains. These rankings are then linked to neighborhood socioeconomic characteristics. What is striking, especially given how social causation is described, is that these neighborhood characteristics have general explanatory power, even if in specific domains the linkage can be less.
More than 40% of the variance for vulnerability on one or more scales can be explained by neighborhood socioeconomic characteristics, which clearly demonstrates the strength of the emerging gradient in basic developmental competencies (334).
Link to Hertzman & Boyce’s How Experience Gets Under the Skin to Create Gradients in Developmental Health,
Expansion through Social Media
W. Thomas Boyce is Professor of Interdisciplinary Studies and Pediatrics at the University of British Columbia. In the 2010 American Association for the Advancement of Science meeting, he was part of the panel The Long Reach of Early Childhood Poverty: Pathways and Impacts. Here’s the video of his contribution:
Clyde Hertzman is Director of the Human Early Learning Partnership at the University of British Columbia. His website offers a selection of talks, including a powerpoint that covers some of the same areas I’ve written about here, including many more graphics and much greater detail on the British Columbia example. The talk is Early Human Development as a Social Determinant of Health (direct link to the powerpoint).
The striking image at the top of this post comes from Hertzman’s opening slide; I took the liberty of also adding in Tom Boyce’s name. I also want to include one other graphic from the lecture. The image below is a great representation of how to get from social causation (e.g., recurrent abuse) to the mediating biological candidate systems (e.g., the mid-brain, prefrontal cortices, and HPA axis) to biological embedding that then causes developmental gradients and health problems (e.g., mental health and chronic disease). In other words, it captures well the argument of their paper.
Where does neuroanthropology work in comparison to this approach? In a broad sense, we are in large agreement – social causation, human development, daily experience, and neurobiological systems come together in important ways that lend insight into the human lifecourse, health and development, and our behavior. I like their attention to linking social causation, biological systems, and outcomes, and advocate that people interested in neuroanthropology pay close attention to that style of reasoning.
The differences are more in the conceptualization of specific problems. Addiction is not just a behavioral health outcome, it is something that is neuroanthropological in itself, involving subjective experience, social contexts, and biological systems. I undertake a similar sort analysis in my post, The Insidious, Elusive Becoming: Addiction in Four Steps. Similarly, concepts like stress and executive function are areas ripe for neuroanthropological analysis. Greg has already done extensive work on balance in this area.
I also see a role for neuroanthropology in doing certain things that Hertzman & Boyce’s more population level approach does not do. Neuroanthropology can characterize daily experience and neighborhood characteristics both locally and cross-culturally that get at what these experiences and characteristics are actually like for the people on the ground. Neuroanthropology can also focus more on how social causation actually works on the ground, helping to characterize what is meant by mundane and iterative causes.
Finally, neuroanthropology can add the concept of cultural causation to get at the issues of meaning and identity that Hertzman and Boyce identify as a crucial starting point for how experience gets under the skin. The concept of cultural inequality is one way to do that; Greg’s use of plasticity and enculturation of balance, including the cunning balance of capoiera, is another.
Finally, neuroanthropology brings a critical perspective that can help us ask, Why do the sorts of developmental gradients that Hertzman and Boyce exist in the first place? It’s not just because poverty poisons the brain. We can also ask critical questions, where we focus more on the poverty side than the brain side. Here our work on social and cultural causation can put us in a position to get at those things that do the poisoning in the first place.