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Science Wednesday: Lessons on Modern Toxicology – How Darwin Saw It Coming.

2009 March 11

Each week we write about the science behind environmental protection. Previous Science Wednesdays.

About the author: Dr. David Reif is a Statistician in the National Center for Computational Toxicology with the EPA’s Office of Research and Development in Research Triangle Park, NC. He holds degrees in Biology, Statistics, and Human Genetics—giving him an abiding appreciation for the lasting impact of Darwin’s theories.

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From an evolutionary perspective, should we be surprised that our bodies sometimes react inappropriately to novel chemicals encountered in the environment? According to the principles of adaptation by natural selection laid out by Darwin, the answer is “not at all.”

Each of us alive today is the product of tens of thousands of years of environmental adaptation. This long evolutionary process allows modern humans to respond appropriately to a remarkable set of naturally-occurring substances.

In contrast, people have had comparatively zero time to figure out how to handle the myriad of man-made chemicals introduced since industrialization. Even at the earliest centers of the Industrial Revolution, we’ve had less than 10 generations to obtain evolutionary solutions to previously unseen combinations of substances. Given that Darwin posited “incomprehensively vast” time periods for natural selection to arrive at workable solutions, he would not be surprised that humans have yet to adapt. Neither should we.

Modern civilization has given us all sorts of incredible tools for fighting diseases, making more efficient use of natural resources, and dealing with identifiably toxic substances. However, along with this progress, we have burdened ourselves with an unquantified volume of synthetic substances to which we are all exposed (to various degrees) on a daily basis. This tension between the needs of modern society versus the volume of new chemicals introduced into the environment puts enormous pressure on our bodies to appropriately respond.

Does that mean we must wait patiently while hoping that natural selection weeds through humanity to settle on appropriate adaptations for continuously shifting environmental conditions? No! Thankfully, a key adaptation of modern society is compassion—meaning that we must explore potential toxic effects of all new chemicals through smart science and careful consideration of relevant ethical, legal, and social consequences. Darwin would be proud.

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action, and EPA does not verify the accuracy or science of the contents of the blog.

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4 Responses leave one →
  1. Susie permalink
    March 11, 2009

    I agree with this blog post right up until the end. I believe all of the unnatural chemicals and synthetic substances in this world expose humans to a threat that we are unable to deal with or quickly adapt to. Before we would even have the chance to become use to a chemical, hundreds of others are produced. In a class I took last semester, my professor said there were currently five hundred unregulated chemicals. Lead is still a significant threat, as our water supply, older homes, and certain materials still contain enough to cause brain damage and other illnesses. Our air quality is tainted by industries and power plants, inducing respiratory conditions and degrading our environment. I wonder if eventually humans will ever be able to overcome harsh environmental conditions, if evolution will cause our immune systems to strengthen and not be phased by common exposure. However, our vey technologies that put us at risk develop faster than we can test for them. The luxuries, services, and speed that our country demands require the use of sparsely tested chemicals just to keep up. At what point to we sacrifice safety for commodity? It is a classic dilemma, should the money and time be spent to protect everyone, even though only a small population is at risk, or should we trust statistics and only go as far as to protect the majority of the population? I think we need to slow down. Commodities and products can wait for the necessary testing to catch up. It may seem like an unnecessary delay, but when human and environmental healths are at stake, the time will not seem so substantial.

  2. David Reif permalink
    March 13, 2009

    First, let me say that I completely agree with the spirit of your comment: There can be no sacrifice of safety for commodity. However, I think that you are using the word “commodity” as a pejorative in implying that all new entities enter into the environment to enhance “luxuries, services, and speed”. This view misses the very important aspect of intent. Products are generally introduced with the intent of improving peoples’ lives. For example, new medicines and hybrid car batteries may contain unseen mixtures of chemicals that pose potential toxic threats, yet those same products may improve aspects of personal and environmental health. In these situations, we need objective science to quantify the positives and negatives of any new product. Eventually, such research might identify superior solutions that reduce or eliminate the negatives (e.g. safe battery materials).

    Again, I agree that we cannot afford to trade safety for luxury. The points you raise are exactly the kind of important ethical questions that we need to address (with the aid of careful science) in finding a balance between delaying the release of beneficial new products and protecting the environment we all share.

  3. Gazelle Rouhani permalink
    March 14, 2009

    As a current University of Miami graduate student taking an environmental health course, my concern is the continual regulation of chemicals that are incorporated in products used by the public. I think you raise an important perceptive with the concept of intent. In the development and manufacturing of products, the intent may be well-suited to benefit our health and it may years before the potential harm is realized. A great example is the introduction of trans-fats into our diets which were initially synthesized with the idea that the addition of hydrogens would make them more compact and perhaps easier to metabolize. By replacing semi-solid fats traditionally found in animal fats, trans-fats were thought to become an attractive ‘fat’ alternative for baking. The use of trans-fats in Crisco replaced use of animal fats, known to be unhealthy, decreased the need for refrigeration, and increased shelf life of baked goods. Less than one hundred years later, we have come to learn the harm of trans-fats and are now attempting to remove them from our diet. I think this clearly delineates modern-day natural selection. Inevitably, some individuals will survive while others will develop the health implications of unhealthy diets. Of course, the central tenet of public health is to identify risks and to develop interventions. Do you think, however, by regulating the introduction of chemicals in use that we are altering the natural course of what should happen? It would be unethical to stand by and allow nature to take its course but what are the potential biological implications of intervening with the dynamics of our selections process?

  4. David Reif permalink
    March 17, 2009

    Your questions have been major points of debate since the publication of Darwin’s theories. The meaning of “should” in your first question (second-to-last sentence of your post) has been twisted in all sorts of directions, from dispassionate survival-of-the-fittest attitudes through horrific Eugenics movements in many countries ( Here, let us assume that what “should” happen is that we do not subject people to selection via human activity (introduction of new products, ecological alterations, etc.).

    Given this goal, it is very difficult to identify what might be altering selection dynamics because, in the strictest sense, only those things affecting reproductive fitness impact the selection process. Natural selection does not necessarily care about things that fail to impact how many offspring can themselves produce offspring. Using your trans-fat example, if trans-fat consumers contribute just as many offspring as non-consumers, we won’t see the traditional evolutionary effect of shifting genotype frequencies. Additionally, scientists are finding that factors such as maternal nutrition can affect epigenetic changes that do not alter DNA sequence (the traditional unit of heredity), making it even more difficult to discern how and when we are creating selective pressure.

    So in summary, I agree with your post that if risk factors can be linked to negative health effects, then we should develop interventions immediately. The subtleties of if/how/when environmental agents truly affect selective processes will take generations to untangle, and the regulatory perspective on “fitness” must be necessarily broad—including concepts such as quality of life.

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