Advances in genetics, personalized genomics, and gene therapy are getting a lot of attention. The hope—some say fear—is that we will ultimately be able to use medical technology to reshape the genomes of patients, curing ailments by changing somatic genes (thus affecting the life of an individual). Some even hope that we will be able to modify our species for the better by introducing changes into our germline (thus affecting not only an individual, but also all of his or her progeny).
Ethicists hotly debate this topic, arguing the case for, or against, “perfection.” Some question whether we have the right to develop technologies that would allow us to change the human genome. Others say this is not only a right, but actually a duty. After all, if we could develop a genetically based treatment for patients with sickle cell disease, cystic fibrosis, or diabetes, who could object? And who would not want to see farther or live longer?
But overlooked in this debate are the ways in which—just possibly— medical advances may already be changing our genes, at the population level.
It used to be thought that our genes were historically immutable and that it was not possible to imagine a conversation between culture and genetics. It was thought that we as a species evolved over a timescale far too long to be influenced by human actions. But evidence has been mounting for the past decade that we as a species are evolving genetically in real time, under the pressure of discernable social and historical forces.
The best example so far is the evolution of lactose tolerance in adults. The ability of adults to digest lactose confers evolutionary advantages only when a stable supply of milk is available, such as after milk-producing animals (sheep, cattle, goats) have been domesticated. The advantages are several, ranging from a source of valuable energy to a source of necessary hydration during times of water shortage or spoilage.
Amazingly, several adaptive mutations have occurred in widely separated populations in Africa and Europe just over the past 3,000 to 9,000 years, all conferring the ability to digest lactose. These mutations are principally seen in populations of people who are herders and not in nearby populations who have retained a hunter-gatherer lifestyle. This trait is sufficiently advantageous that those with the trait may have many more descendants than those without.
A similar story can be told about relatively recent mutations that confer advantages in terms of surviving epidemic diseases, such as typhoid in Europe. Since these diseases were made more likely when the density of human settlement increased and far-flung trade became possible, here we have another example of how cultural change may affect our genes.
Of course, our biology and our culture have always been in conversation. For example, rising socioeconomic status with industrial development resulted in people becoming taller (a biological effect of a cultural development), and taller people required a change in architecture (a cultural effect of a biological development). Anyone marveling at the small size of beds in medieval houses knows this first hand. But it seems that it is also possible for specifically genetic change to take place over similarly short time periods.
Why does this matter to medicine? Because many of the things we are already doing may be modifying our genes. Maybe we are all more myopic as a result of medieval lens grinders. Maybe our bones are weaker since we have had bone-setting technology for thousands of years. Maybe the changes in survival of patients receiving treatment for all sorts of conditions that are wholly or partly attributable to single or multiple genes (ranging from sickle cell disease to type 1 diabetes) are resulting in changes in the human genome. Maybe the introduction of penicillin and childhood immunization has changed our genes. Some have noted that the number of children with Down’s syndrome is falling in many industrialized societies as a result of selective abortion. With the onset of personal genetics, it is not hard to imagine this being taken a step further. Medical technology might change our genes indeed.
Advances in medical technology are not the only things doing this in ways relevant to health and wellbeing. There may be genetic variants that favor survival in cities, or that confer a preference for complicated social networks, or that foster altruistic behavior consistent with living in a more democratic society. Maybe even the more complex world we live in nowadays really is making us smarter.
Unfortunately, this also means that particular ways of living and particular medical technologies could create advantages for some but not all members of our species. Certain groups might acquire (admittedly, over centuries) certain advantages. The idea that the application of medical technology can modify what kind of offspring we have is thus as troubling as it is amazing.
Realizing the ways in which we humans may have been inadvertently changing our genes for millennia provides a way for us to begin to think about the inevitable genetic revolution in medicine that is going to allow us to advertently change our genes over centuries and even decades.
Nicholas A. Christakis, is Professor of Medicine and of Medical Sociology at Harvard Medical School, Professor of Sociology at the Harvard Faculty of Arts and Sciences and the House Master of Pforzheimer House.