A brave new world where the human race stagnates in cloned similarity or a genetically engineered master race ruling mankind are terrifying images of what we might become. But fear of the possibilities should not prevent us from moving forward when we are no longer progressing. Science is our last hope to reach our limits.
In 1859, Charles Darwin published one of the most important works of the 19th century, “The Origin of Species.” Although not the first to introduce a theory of evolution to explain changes within species over time, Darwin’s concept of natural selection became vindicated in the 20th century, as it was coupled with genetic theory.
Before I dig too deeply into the theory of evolution and its impact, I must beg the indulgence of some of my readers. I am not trying to pick a fight with Creationists, defending scientific theory over religious dogma. If you want to deny evolution and maintain that God created all the species of Earth just the way that He wanted them, be my guest. I am, however, assuming that the modern synthesis of evolutionary theory and genetics is the correct, or at least close to correct, description of the way the world works. The origins of life and the development of all species fit into an evolutionary framework. If you don’t believe that, humor me or flip to the Network section now.
Evolution can be simply defined as a change in the gene pool of a population over time. Take a human physical trait like handedness. Your dominant hand is determined, in a simplified model, by the presence of a certain gene at a certain position on your chromosomes. Since I am right-handed, I have the R-gene at that spot; a left-handed person would have the L-gene in the same place.
A biologist will look at the entire human genetic pool, the collection of each person’s genetic makeup, and determine that 11 percent of handedness genes are of the L-type right now. Jump ahead 50 years, and a biologist might survey the pool again, discovering that the percentage of L-genes has fallen to 9 percent. And that’s it. Evolution has taken place — the gene pool has changed over time.
So what’s all the debate about? Evolution looks uncontroversial. The exciting part is in trying to figure out the mechanisms that bring about these changes in the genetic pool, not the evolution itself.
The three most important mechanisms for bringing about evolutionary change are natural selection, genetic drift and mutation.
Natural selection, often confused with evolution itself, is crudely summarized in the maxim, “Survival of the fittest.” Within a species, some particular trait will afford a slight advantage to those individuals who possess it. This will lead to increased reproduction on the part of the advantaged individuals and, hence, the passing on of the genetic trait to its more abundant offspring. Over many generations, this imbalance, no matter how slight, leads to the trait becoming widespread throughout the species.
The case of the English moth, Biston betularia, is a common example of natural selection at work. In 1848 H.B.D. Kettlewell observed that in the naturally occurring population of the moth, only 2 percent had a dark coloration. However by 1898, the population in urban areas was 95 percent dark. Since the second half of the 19th century was the time of England’s industrial revolution, the birch trees around urban areas had become stained with soot from factories. The dark colored moths were able to blend in with trees better than the light colored ones, thereby avoiding predators. The increased life span, and subsequent increased reproductive rate, of the dark-colored moths led to the domination of the gene for dark coloredness in the gene pool.
Similarly, among humans, we find that over the past millennia, our height has increased, body hair has decreased, etc. Each change occurred in response to some environmental factor or to make us more attractive to members of the opposite sex.
The second mechanism, genetic drift, is responsible for gradual changes in the population through random breeding. Over time the average expected change in the frequency of a gene is zero since an increase or decrease is equally probable from one generation to the next. However, in rare cases, one gene may come to dominate another because of random increases in its frequency over several generations.
Think of it as a coin toss. If it comes up heads, the frequency of the L-gene will increase ever so slightly in the next generation because of random sampling; tails and it will decrease. Over several tosses, an equal number of heads and tails should come up, but it is possible that we might get five heads in a row. Then, over those five generations, the L-gene will become more common in the genetic pool. In this way, over a long time, the L-gene could eventually be more populous in the pool than the R-gene, and a change in the species as a whole will occur.
Both natural selection and genetic drift only eliminate or amplify genetic traits already present in the pool. The third means of change, mutation, increases genetic variation.
At rare moments, genes become mutated, differing from all other genes in the pool. One of the English moths might have had a mutated gene that made it purple instead of light or dark. If this new gene provided a beneficial trait it might have become popular in the genetic pool through natural selection or, if it is lucky, through genetic drift. Most mutations are detrimental to the species and therefore are bred out quickly, but the rare beneficial trait can arise in this way
Where does this leave the human race? Humans have evolved over time because we have lived in a state of struggle with the natural world. When we did not know where our next meal was coming from, when there were predators that would devour us, when diseases killed many, when the weather was a threat; at all these times the fittest of humans would live and breed, passing on their genetic advantages.
But now, at the end of the second millennium, there is no longer a struggle. We live in controlled environments, heated when it is too cold, air conditioned when it is too hot. Medicine is rapidly finding cures for diseases that afflict us. Predators no longer stalk us. Our next meal is down the street at the grocery store. Moreover, nearly everyone is able to reproduce. A quick look at the Jerry Springer show indicates that even the most unattractive, unintelligent, immoral specimen of humanity is able to pass on his or her genes to the next generation.
Genetic drift is no longer an issue either. As our population has boomed and the birthrate per individual declined, the possibility of one gene gaining superiority over others simply by chance is all but eliminated. Drift is effective only in small communities, but the global village precludes this.
Even mutation is not a problem. We are able to detect detrimental mutations and eliminate them quickly. When they cannot be quickly removed from the genetic pool, science creates accommodations for them, nullifying any benefit or detriment that may have resulted.
Humans are no longer evolving.
Science has changed the world to make it fit our needs. We no longer need to adapt to a hostile environment. The humans of the future will have no reason to evolve. Telepaths will not be walking down the street. Super strong, highly intelligent humans will not inherit the Earth. The same genes will continue to be passed on from us to our children, to our children’s children … The future of mankind is in the mirror.
Although rationally we know that there is no teleological goal for mankind as a species. There is no end toward which evolution is driving us. But emotionally we all feel that there are better and worse traits to have. Being physically fit is rarely a drawback. Being immune to disease is certainly a benefit. Higher IQs can only better our species as a whole. But to reach these ends, we will have to do it ourselves.
Mother Nature will no longer help us along through evolution. Science must drive changes in our species, leading to any improvements. Genetic engineering will bring about any changes in the genetic pool. Computer implants and mechanical enhancements will someday be added to our biological bodies. Of course this path is not without hazard, but careful planning and control can lead mankind into a post-evolutionary age.
Chris Trejbal’s column appears every Tuesday. He welcomes comments at [email protected]