Genes, epigenes and best-laid plans
Published on -12/30/2013, 8:03 AM
Evolution imposes a sort of genetic screening upon populations of living beings. The vast process of natural selection weeds certain genes out of the group, while preserving others.
Evolution occurs on a scale that might seem imperceptible, but like X-rays and viruses, it still can be detected with appropriate techniques.
Genes aren't "good" or "bad" -- but when genes are turned on, or "expressed," their consequences can favorably or unfavorably influence the survival and reproduction of the gene-carriers. We humans are such gene-carriers.
Our species, like others, is a product of the millions of years and countless generations invested in trial-and-error-based development and change.
Natural variation and selection proceed without purpose or compassion. When Nature culls the herd, it's ugly -- violence, disease and starvation.
But evolution is not entirely inexorable. In the past few centuries, we've done something no other species has ever done, so far. We have altered the course of our own evolution.
With few exceptions, these man-made alterations have occurred inadvertently, unplanned and often unappreciated, even by the people who instigate them.
Soon, we will be technologically capable of genetically enhancing our species. We might eradicate our counterproductive genes by substituting healthy ones, reducing the burden of genetic diseases or predispositions to disease. We could even remodel the standard human being to grow gills or armor, to expand our habitable habitats. Some might worry in doing so, we'd be "playing god."
There certainly would be hazards with such genome tinkering, and it should proceed with utmost caution. But just as eye doctors routinely override god's flawed design by removing cloudy eye lenses and implanting artificial ones, we could do the same with cloudy genes.
Meanwhile, the pursuit of unintended consequences proceeds apace. I can offer a couple examples from my own professional practice.
Gestational diabetes occurs when non-diabetic women get pregnant, and then begin to manifest characteristics of diabetes. This can be catastrophic for mother and child. Mothers are prone to diabetic complications, including runaway weight gain. Babies are more susceptible to stillbirth and gain too much weight too soon. Arrested labor can lead to C-sections. Oxygen deprivation during birth, or metabolic instability as a neonate, can compromise a child's neurologic development.
Nowadays, with proper medical management, mothers with GDM can survive and have additional successful pregnancies. Previously, a predisposition to GDM could doom mothers and their babies, bringing their gene-lines to an abrupt halt. In nature, GDM genes simply kill off their carriers, keeping the GDM trait-bearing population small.
A byproduct of our compassionate medical care, in this case, is an expansion of the GDM-carrying population. GDM rates are rising -- an "unnatural" natural consequence of our medical interventions.
Many Native American groups are experiencing skyrocketing rates of obesity, and the diabetes obesity often triggers. Some researchers have postulated the involvement of a so-called "thrifty gene."
Pre-Columbian Indians, both sedentary hunter-gardeners and nomadic hunter-gatherers, were vulnerable to food shortages during periods of drought or prolonged bad weather. This feast/famine existence encouraged a hereditary trait, the ability to put on weight efficiently during times of plenty. During lush summer months, people, like their horses, grew fat. During lean winter months, those with large and accessible body-fat reserves were more likely to survive famine conditions. It worked pretty well for thrifty-gene carriers.
Today, there is no famine. It's all feast.
Among impoverished peoples in America, frank hunger is often less problematic than a horrible diet. The paleo diet of nomads -- lean meat, fruits and veggies, no refined carbs -- was generally a healthy diet. Today, the least expensive calories come as junk foods (known on the Rez as "commodities") -- chips and Cokes and fatty ground meats. A limited budget encourages hi-cal purchases, while more expensive lean meats and fresh produce are (or appear to be) out of reach.
The thrifty gene keeps on working as it always has, but now body fat just builds and builds, since there's no Starving Time to trim it back into balance. With unconstrained weight gain, the genes that favor diabetes "switch on." Obesity and diabetes are burgeoning among nearly all Americans, not just American Indians. Lots of us might harbor a thrifty gene.
A better diet relies both on adequate funds and the knowledge to understand what makes food "healthy" or not; I'm all in favor of correcting deficiencies in both areas. I'm not suggesting we quit treating mothers with GDM, of course.
But we need to realize the unintended consequences of well-intentioned behaviors. As our medical prowess expands, we must incorporate principles of Evolutionary Theory into our public health planning.
Complicating matters is a new field called "epigenetics." Small chemical structures, methyl groups, sit "on top" of the DNA genes. These groups function as "switches" which turn genes or gene complexes on and off. The remarkable thing is these can convert individual life experiences, our internal and external environments, into heritable traits.
Our own starvation or over-eating can program our epigenes to tweak genes in our grandkids that incline them to be overweight. Smoking is another "experience" that can cause epigenetic damage in subsequent generations, even when they aren't personally exposed to smoke.
"Know thyself," wrote Plato. Today, we cannot know ourselves without understanding the genetic, epigenetic and evolutionary determinants of our species' history.
Today is history, too.
Jon Hauxwell, MD, is a retired family
physician who grew up in Stockton and now lives outside Hays.