Nature Nurture

The fathers ate sour grapes and the children's teeth were set on edge.” Ezekial

What might this biblical quote have to say to us regarding the increasingly popular topic of population health? Stay with me for just a bit, we are about to take a deep dive and bring a number of threads together.

Our story begins with this man

The man who ultimately brought us graph paper (Cartesian coordinates), Rene Descartes. But he is important to our tale because he was the first to suggest tha… the body works like a machine, that it has material properties. The mind (or soul), on the other hand, was described as a nonmaterial and does not follow the laws of nature. Descartes argued that the mind interacts with the body at the pineal gland.

Clearly the wrong organ, but as it turns out his conceptualization may also have been flawed. Dualism, the mind-body problem that originates with Descartes has provided the intellectual means for understanding our biological and increasingly our psychological behavior. It has been an enormous intellectual tool; but it caused a disruption in seeing our holistic nature. Two other strands of thought arise from Descartes thought. Its secular form goes by nature versus nurture and was popularized by the half-cousin of Charles Darwin, this man: 

Francis Galton.

A heftier version of the duality can be found in the religious discussion of free will and determinism. Determinism holds that only one course of events, those ‘foreordained” by God, are possible. Free will holds that we can break the “causal chain of events” and that our lives have choice. The debate between these polar opposites reverberates throughout society and our politics. Isn’t the argument around the ‘welfare state’ versus ‘self-reliance’ and ‘compassionate conservatism’ a variation on free will and determinism?

But for all dualism’s power to craft our thought, it turns out to be not quite true and that nature/nurture and freewill/determinism are locked together at a much deeper biological level. Enter epigenics, which shows how are genes are controlled, in part, by our behavior and environment.

RACHEL YEHUDA: We're just starting to understand that just because you're born with a certain set of genes, you're not in a biologic prison as a result of those genes. That changes can be made to how those genes function that can help. The idea is a very simple idea. And you hear it from people all the time. People say, when something cataclysmic happens to them, “I'm not the same person. I've been changed. I am not the same person that I was.” And epigenetics gives us the language and the science to be able to start unpacking that.

Are you still with me? Great! Let me digress into understanding the social role of genes in this wonderful article first published in Pacific Standard (coincidentally the origin of the threads of this newsletter). Beginning with African Killer bees and moving on to fish, lonely people and our immune system this is an easy review of the science that is beginning to close the mind body duality. The article will help you bridge the next jump in my thoughts. If you do not have the time then be satisfied with this quote

Your DNA is not a blueprint. Day by day, week-by-week, your genes are in a conversation with your surroundings. Your neighbors, your family, your feelings of loneliness: They don't just get under your skin, they get into the control rooms of your cells.  … Cole often puts it differently at the end of his talks about this line of work. “Your experiences today will influence the molecular composition of your body for the next two to three months,” he tells his audience, “or, perhaps, for the rest of your life. Plan your day accordingly.”

OK, we are in the home stretch. Darwin’s survival of the fittest, his theory of evolution, is based upon a very long timeframes, eons. Epigenetics has a time frame that is a quantum smaller, days, weeks, and years. I suppose it is in an evolutionary sense like our current thinking about our thinking, that there is a rapid, intuitive mechanism and a slower, analytic mechanism.

MS. TIPPETT: … we would think about biological change between generations as being evolutionary, as something that would take time. But what you're learning is that epigenetics — it's a mechanism for short-term adaptation,

 DR. YEHUDA: ...the purpose of epigenetic changes, I think, is simply to increase the repertoire of possible responses. I don't think it's meant to damage or not damage people. It just, it expands the range of biologic responses, and that can be a very positive thing when that's needed. ….  So let's say, for some reason, your parents transmitted to you biologic changes that are very appropriate to starvation, but you don't live in a culture where food is not plentiful.


DR. YEHUDA: You're just not optimized…

Consider two major population health problems, obesity and hypertension; and yes, I understand there underlying physiologic connection to one another. There is a large body of evidence that obesity can be found in family and neighborhood clusters or even transmitted through social networks

In the social network study if a randomly selected person in the study has obese friends, it’s 45% more likely (Red dots are normal weight individuals, Yellow are obese individuals) for that person to be obese as well.

It is also a well-known fact that there is a greater incidence of hypertension in black rather than white Americans

The higher prevalence of hypertension in blacks living in the United States instead of Africa demonstrates that environmental and behavioral characteristics are the more likely reasons for the higher prevalence in blacks living in the United States. They could act directly or by triggering mechanisms of blood pressure increase that are dormant in blacks living in Africa.

The implications of epigenetics to population health are significant.

First, by acknowledging the bridge between the environment and our behavior with our genetic responses we open up two areas for therapy. Perhaps obesity is more a response to socioeconomic stress fueled by a poor dietary environment and choices? Perhaps hypertension is a real heritage of slavery-transmitted trans-generationally through epigenetic markers because of environment and behavior? It certainly puts the fight over the ‘Stars and Bars’ in a different perspective.  

Second, epigenetics accelerates the merging of social care (think discharge planning, visiting nurses, Meals on Wheels, reliable public transportation) and health care.

Third, as with all great power comes great responsibility (Peter Parker) and humility. Humans and our society are complex, non-linear systems; simple causation does not consider individual responses. Small changes in input can have small or large consequences in these systems.

I think that what throws us off and why these ideas are often challenged is because there isn't a uniform response to stress or trauma. And it throws things off when the world isn't that ordered. … It throws things off when people respond differently to events. So, it's very hard to have somebody say, “this event derailed me,” when somebody else who experienced the same event wasn't derailed by the event. We have to appreciate that there is quite a lot of variability and diversity in the way that we respond.

 Fourth, it shifts the time frame for changes. Epigenic changes are relatively quick, trans generational. We must be careful not to dismiss environmental/behavioral/dietary changes as ineffective because our therapeutic time from is too short.

 A society grows great when old men plant trees whose shade they know they shall never sit in.

As Dr. Yehuda states

So how we behave towards one another individually and in society, I think can really make a very big difference in — honestly, the effects of environmental events on our molecular biology...

 Thanks, once again to Krista Tippett’s podcast On Being who provided the ‘Aha moment’ that allow these threads collected over 2 years to be knit together.