As good as it gets?
The human race muddles along
By KRISTA CONGER
In October of 1925, the Rollins family traveled nearly 300 miles from San Antonio to Dallas to enter the Texas State Fair’s second annual Fitter Families Contest. Competition was fierce: More than 50 families flocked to a building next to the cattle pens to be judged on their physical, mental and moral qualifications. Comparisons with livestock breeding were unavoidable and intentional. They were also met with unbridled enthusiasm.
“I consider the Fitter Family Exhibit at the fair the most important feature of this year’s exposition,” family patriarch O. B. Rollins, an agricultural agent, told the Dallas Morning News at that time. “For years I have been interested in better livestock in our state and in the betterment of plants. And now I am interested in the betterment of the men and women of the state.” Rollins no doubt found his vote of confidence and the long trip worthwhile when his family of seven took top honors in the competition.
The contests, which were held at various state fairs nationwide in the early ’20s, were a bid by the fledgling American Eugenics Society to encourage those marriages they considered most likely to generate physically and mentally fit children. For a time, members of the society even toyed with the idea of “certifying” families and encouraging marriage only between people of equal status. Like modern-day Mendels, they thought that careful breeding of select individuals, coupled with forced sterilization of the feeble-minded and shiftless, would eventually yield a superior class of Americans capable of advancing both the country and the human race.
Such hubris seems both laughable and alarming now. Studies of human genetics and evolution have taught us that many favorable qualities — intelligence, physical fitness and mental health, for example — are outward manifestations of complex interactions between many genes and their environment. Even without the very real ethical concerns that go hand-in-hand with the value judgments implicit in such a program, simply landing an attractive, healthy mate doesn’t guarantee superior offspring.
Where angels fear to tread
Why bother to try to improve ourselves, anyway? Aren’t we already at the top of our game? After all, like other species, modern humans have been evolving for hundreds of thousands of years in an intricate dance of adaptation and selection. The complexity of some of the steps is breathtaking. Sickle cell anemia has been endemic in African populations for about 3,000 years because the genetic culprit, when present in just one copy, also confers protection against an even more deadly regional foe: malaria.
It’s difficult to imagine that we could have choreographed such a delicate trade-off. Maybe we should leave well enough alone and let the natural forces continue to pound away at us like an enthusiastic physical trainer.
On the other hand, we’re now more able than ever to isolate ourselves from the selective forces that got us this far. We cure ourselves of formerly fatal diseases, we twist the thermostat dials in our houses up and down according to our whims, and, instead of running from predators on the savannah, we watch them on cable. From this perspective, it seems that the evolutionary tango as we know it has stopped. No wonder the Rollins family cast their lot with those who felt our species’ future was better off in human hands.
Maybe they were right. Recent advances in medical technology have made attainable many things that our grandparents would have thought impossible. Sperm banks provide a wide array of choices for women who favor nature over nurture, prenatal testing for disease is commonplace, and couples undergoing in vitro fertilization can be choosy as to which of several embryos they implant. If these changes seem revolutionary, however, we should brace ourselves for the biggest upset of all: our coming ability to modify our own and our children’s genomes in ways that will persist for generations.
So, what does it all mean? Have we finally taken control of our evolutionary destiny? Or are we just flattering ourselves? It depends on who you ask, and how far into the future you’re willing to peer.
Culture clash
“This is not the first time humans have directed their own evolution,” says evolutionary biologist Marcus Feldman, PhD, the Burnet C. and Mildred Finley Wohlford Professor in Stanford’s School of Humanities and Sciences. “Inventions of agriculture and cities caused new food allergies and infections, respectively, which had biological reactions whose strength depended on genes. Our cultural evolution overtook human biological evolution thousands of years ago.” In other words, truly natural selective forces were supplanted by those of our own making long ago.
Of course, one could argue that those very inventions were caused by evolutionary changes that made humans stronger, smarter or more able to work together — a kind of chicken-and-egg conundrum. For example, recent research at the University of Chicago suggests that two human genes controlling brain size have undergone natural selection. Although any associations are purely speculative, the two genes seem to have originated at seminal times in human history, one about 40,000 years ago when humans began to exhibit symbolic behavior, such as painting and beadwork, and the other a mere 5,800 years ago when the earliest Near Eastern cities were formed.
Although there’s no way of knowing exactly what biological and technological advances will be available in the coming decades, there are some obvious candidates that have already proven their mettle in yeast or mammals. Introducing genetic modifications into the egg and sperm, for example, called germline modification, ensures that every cell of the subsequent fetus will carry the newly introduced change, as will every one of that child’s progeny. Alternatively, an artificial chromosome or two could carry a payload of advantageous genes into future generations. Applied across the board, modifications that increase life span or physical endurance could theoretically impact human evolution in ways that make mere city building seem puny.
“If we ever fully implement this type of capability,” says Stanford human evolution expert Peter Underhill, PhD, “it would be a huge milestone in the history of our species, but one burdened with societal baggage regarding parity versus disparity of access.”
However, these types of technologies aren’t likely to affect the course of human evolution unless they become available to many more people. Only about one in every 100 children in the United States is conceived via in vitro fertilization, and only a fraction of these undergo disease screening before implantation. Germline modifications are far more technologically challenging. Gregory Stock, director of UCLA’s Program on Medicine, Technology and Society, estimates in his 2003 book, Redesigning Humans, that germline therapy would have to be used at least 100 times more often than the predicted demand to even begin to make a splash in the human gene pool.
But human society is not one big pool. Cultural differences thwart genetic mixing; they could lead to a genetically stratified society. Those who have access to future germline interventions could use them to give their children every available advantage, cocooning themselves and their descendants in a cozy genetic bubble of their own making. If this separation is maintained over thousands of years, or if one single change gives carriers a unique genetic advantage such as a significantly longer life span, it’s possible that we could see a marked separation between population groups.
Most experts think that’s unlikely.
“Throughout the history of medicine, effective innovations have typically become widely diffused across income levels,” says Victor Fuchs, PhD, Stanford’s Henry J. Kaiser Jr. Professor of Economics (Emeritus). “We can see this when we look at patterns of change in mortality and life expectancy in countries like India, where most people can expect to live well into their 60s. For their average income level, we’d expect them to have a life expectancy decades shorter. All of the poorer countries are way above where we would expect them to be if they weren’t benefiting from technologies and ideas developed elsewhere. Particularly in the case of genetic modifications, I don’t think we’re talking about anything that is going to be so clearly effective and yet so expensive that it’s only available to certain subsets of the population. That’s just not in the cards.”
What’s more, increasing globalization will lead to more mixing of genes, not less, to the benefit of all.
“Genes that in the past have been physically separated by oceans are still kept apart by cultural and social norms,” says Underhill. “As these cultural boundaries become more porous, we set the stage for mixing genes at a higher frequency, which may lead to a phenomenon known as hybrid vigor and make all of our descendents more healthy.” Take that, eugenics society!
Choices, choices
But what if human society reached the critical mass of genetically altered offspring needed to change evolutionary course? Will the “designer children” all end up looking and acting the same? Probably not. Although some hypothetical attributes, like foolproof protection against cancer, would probably be universally sought by people with the financial means to design their babies, other traits, such as personality types or physical attributes, would depend largely on a prospective parent’s personal choice. That we see such individual differences in choices even with today’s rudimentary technologies bodes well for our ability to avoid a future filled with überclones, observes Gene Hoyme, MD, a medical geneticist at Lucile Packard Children’s Hospital and director of its biochemical genetics laboratory.
For example, even though sex selection of embryos fertilized in vitro has many people up in arms, there’s no evidence that it’s on track to alter the gender balance in this country: Boys and girls are nearly equally sought after, says Hoyme. And although some parents will terminate a pregnancy if the fetus has a genetic or developmental problem that they feel isn’t compatible with a meaningful life, different families draw this line at dramatically different points in the sand. For some, it’s too much to consider having a child with Down syndrome. For others it’s important to sustain life as long as possible regardless of the severity of the condition. Still others might choose to have a child as similar to them as possible, down to sharing disabilities such as deafness.
“Eugenics is here now,” says Stanford bioethicist David Magnus, PhD. “So what? We allow parents to have virtually unlimited control over what school their child attends, what church they go to and how much exercise they get. All of these things have a much bigger impact on a child’s future than the limited genetic choices available to us now. As long as these are safe and effective, why not give parents this option as well?” A much more pressing problem, according to Magnus, is the varying levels of access to critical health and educational resources experienced by poor and minority populations.
“I just don’t see the whole human genome careening off in some dramatic trajectory due to genetic interventions when we can’t even get everyone vaccinated,” agrees Underhill.
Some experts also warn that parents who choose specific genetic interventions might be disappointed if the child does not live up to their expectations. Prioritizing life goals for an unborn child denies the child his or her “right to an open future,” they believe. Magnus disagrees. Parents are just as likely to be disappointed, he says, if they spend time and money on music lessons for a child who turns out to have a tin ear.
“Parents close doors for their children all the time,” he says. “That’s part of being a parent.” Underhill hypothesizes that genetic modifications could one day be viewed as optional enhancements that parents may or may not choose for their children.
As our technological abilities and knowledge of genetics increase, the only thing we can be sure of is that the temptation to control the nature of our children will grow. Ensuring that no one group attempts to mandate the outcome of these decisions and that as many people as possible have access to the technology might help us to walk that delicate line between improving and irreparably dividing the human race. After all, how can we deny Rollins’ urge to spend at least as much time thinking about our own future as we do the animals and plants at the fairgrounds?
Comments? Contact Stanford Medicine at
Back
To Contents
