Has Natural Selection Been Selected Against?

2/16/07
Elle Works
Evolution & Story
Professor Grobstein & Dalke
Paper # 1

Has Natural Selection Been Selected Against?

As complicated as the subject of evolution is, there are a few concepts that are more easily understood than others. Among these few concepts is the idea of natural selection. Darwin based his theory of natural selection on five observations and three inferences, which are neatly summarized by the biologist Ernst Mayr in his book What Evolution Is:
(Fact 1) Every population has such high fertility that its size will increase exponentially if not constrained; (Fact 2) The size of populations, except for temporary annual fluctuations, remains stable over time; (Fact 3) The resources available to every species are limited, Inference #1: There is intense competition (struggle for existence) among the members of a species; (Fact 4) No two individuals of a population are exactly the same (population thinking), Inference #2: Individuals of a population differ from each other in the probability of survival (i.e., natural selection); (Fact 5) Many of the differences among the individuals of a population are, at least part, heritable, Inference #3: Natural selection, continued over many generations, results in evolution (Mayr 116).
Darwin's crucial distinctions as to what natural selection is arise in the last two "facts" derived from his observations. It seems that, according to Darwin, each offspring possesses traits, many of which are inherited from its parents, that either help or hurt its ability to survive and reproduce in a competitive environment. This has come to be called the idea of "survival of the fittest," and it is one of the most common ways that we understand evolution. Like any other organism on Earth, humans are subject to the natural laws of evolution and natural selection. However unlike most organisms on Earth, humans have developed extreme control over the environment. As Robert Fogel and Dora L. Costa explain, "...during the last 300 years, particularly during the last century, humans have gained an unprecedented degree of control over their environment - a degree of control so great that it sets them apart not only from all other species, but also from all previous generations of Homo sapiens" (Fogel 49). Of any of the ways in which humans have come to control their environment, the one way with the largest impact on the continuance of evolution and natural selection is the field of medicine. The advances in medical technology in recent years have had visible impacts on human longevity. In short, individuals in the past who would have been selected against because of various diseases or disorders are now surviving into reproductive age and beyond.

One need only to look at the rise in average life expectancy around the globe to understand that something we have done in recent years is impacting our ability to survive longer than our forebears did. Something as simple as the invention and use of eyeglasses would have an effect on the survival of a near-sighted or far-sighted individual. In the past, someone with a vision problem would have been more likely to literally walk into danger or death, not realizing they were doing so. Now, with the aid of eyeglasses or contact lenses, people with vision problems can see the world around them, danger included. Other important medical advances include the creation and implementation of many inoculations and vaccines that protect individuals from previously fatal illnesses like the mumps, measles, small pox, influenza, and countless others. Where in the past breakouts of illnesses like these would have had dramatic and fatal effects, we are now able to adequately control and prevent them from spreading. True, new illnesses like SARS, West Nile Virus, and Avian Bird Flu pose challenges, but with all of the medical resources and technology that we possess cures and preventative transfer methods are being researched and developed each day. However, when it comes to some diseases like cancer, diabetes, and HIV/AIDS there is no clear cure and these diseases continue to claim thousands of lives every year. But treatments for cancer, like intense course of radiation and chemotherapy, are improving the survival rates for individuals diagnosed with cancer. And diabetics have learned over the years to be vigilant about monitoring their blood-sugar levels and insulin injections, thus decreasing the number of diabetes related deaths. However, when it comes to HIV and AIDS, we must take a step back to examine the situation. HIV and AIDS are relatively new diseases caused by viruses which we are still learning about. In the beginning of the HIV/AIDS epidemic, survival was a bleak prospect. But today there are rigorous drug treatments which help to extend the life expectancy of those diagnosed by decades, and make living with the disease bearable.

It would seem that we humans have a decent handle on all or most of the illness and diseases that in the past would have diminished our ability to survive past reproductive age. This then begs the question, what kind of an impact has medical advances, like the ones seen in recent years, had on evolution and natural selection? Have advances slowed evolution? Have we successfully staved off natural selection in most areas where it was once a dominant force in our lives? It is hard to answer the first question about evolution, since it is such a torturously slow process and humans have only been in existence for a mere blink of an eye, in the scheme of things. To say that we have slowed evolution would be quite a claim, but there is little to suggest that we have done so. What is easier to observe and understand is that we seem to have lessened the impact of natural selection on our lives. In their article "Life Span Extension in Humans Is Self-Reinforcing: A General Theory of Longevity," James R. Carey and Debra S. Judge believe that:
In humans the cognitive ability to target innovation to solve specific problems can result in technologies that further improve health and do so much more rapidly than could be accomplished by natural selection on random genetic variation. Better-educated, more-innovative children then increase the rate of those technological advances that contribute to health and longevity and to higher adult survival to older and older ages (Carey 422).
Here, Carey and Judge bring into the picture the importance of "better-educated, more innovative" children. These children may be the offspring of parents who suffer from inherited illnesses or diseases, but they are brought up in a world and society where there are treatments.

Medical advances aren't the only ways in which humans find ways to extend their lifetime and escape the effects of natural selection. In a social society such as ours where children are often raised in and by their extended families, we must take into account the importance of intergenerational exchanges and the impact they have on longevity. Carey points out that:
...While transfers of genetic information and resources from parents to offspring contribute to the evolution of longevity, additional forms and pathways of intergenerational transfer can elaborate and increase the rate of impact on longevity extension... In humans the transmission of longevity-promoting genes and resources is augmented by culturally transmitted information... (Carey 417).
In short, humans are capable of avoiding natural selection and thereby expanding our life expectancies in these two ways: medical advances and intergenerational and social interactions. This is not to say that we are completely immune to forces in the environment we belong to, but we are becoming better equipped as time passes to deal with these issues and to survive them. Evolution is still an enormous machine churning away in the background, but little by little we are finding ways to affect it.