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Understanding the Link Between Human Health and Biodiversity
March 3, 2009
by Eric Chivian, M.D., Director of the Center for Health and the Global Environment at Harvard Medical School Everything we do that damages the environment -- from degrading forests and coral reefs, to increasing greenhouse gases in the atmosphere, to releasing pollutants into soils and aquatic systems -- ultimately ends up affecting living things. And there is nothing more important that we understand than how these effects threaten our health and our lives. That is why more than a hundred leading scientists from around the world wrote Sustaining Life: How Human Health Depends on Biodiversity, published by Oxford University Press in June 2008. Let me give some examples from the book that illustrate our dependency on Nature. Like all hibernating bears, polar bears don't lose bone mass during their several months of immobility, as do all other mammals including ourselves. They also don't become ill during this period, even though they don't urinate the entire time. And while polar bears become massively obese prior to hibernation, they don't develop Type II diabetes, as we humans tend to do when we become obese. If polar bears become extinct in the wild by the end of this century, as is predicted, they may take with them the secrets for treating, and possibly even preventing, osteoporosis, kidney failure, and obesity-related Type II Diabetes -- that together kill some 400,000 people in the United States each year.
The Pacific Yew -- a small, misshapen tree in Pacific Northwest old growth forests -- was routinely burned until the compound Taxol was found in its bark. This discovery led to an entirely new class of medicines that have become some of the most effective agents known for ovarian, breast, lung, and other malignant cancers, and that have also been used to coat arterial stents so that newly opened vessels do not close up again. With deforestation, how many other potential wonder drugs are we losing before we even realize they exist? Or consider Lyme Disease, where it has been shown that we are at increased risk of getting Lyme when forest fragmentation reduces the diversity of vertebrate species living in these forests. This is so because in diverse populations of vertebrates, many are poor hosts that do not keep the tick-borne Lyme infection cycle going, while others keep the populations of the best hosts down by competing with them for food or by eating them. In tropical forests, deforestation increases the risk of other infectious diseases, for example, by tending to favor those mosquito species that are better vectors for malaria, and those snail species that are better hosts for schistosomiasis. With the loss of plant, animal, and microbial species, we lose not only new medicines and critically important models for medical research, we may also lose the contributions these species make to ecosystems in ways we barely understand, disrupting these interdependent webs of life that pollinate our crops, make soils fertile, break down wastes and dead organisms, and perform a host of other essential services that keep us and all over organisms on Earth alive. It is a dangerous delusion to believe that we have a choice about whether we protect the natural world or not. We have no choice, for our health and our lives depend on it.
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