Over 250 million years ago, cataclysmic volcanic activity wiped out nearly all life on earth. 65 million years ago, a meteor impact in the Yucatán drove the dinosaurs to extinction. In the past 540 million years of earth’s history, paleontologists have identified five mass extinction events in which over 75% of Earth’s species have died during a relatively short period of time . Unfortunately, it seems that the disappearance of the dinosaurs may not be Earth’s final experience with mass extinctions.
“We,” said associate director Dr. Aaron Bernstein of Harvard University’s Center for Health and the Global Environment, “Are living through the sixth great extinction event.” 
And this one cannot be wholly attributed to natural disasters. Poaching, consumption of natural resources, habitat destruction, and intentional or accidental introduction of invasive species into non-native habitats are among the human contributions to increasing extinction rates. Furthermore, projections estimate that over one third of species will be eradicated by 2050 due to the changing climate rendering habitats inhospitable .
“The issue is that our well-being depends upon an abundance of nature, and right now we’re not talking about selective loss of species, we’re talking about wholesale loss,” Dr. Bernstein added. “I don’t think we’ve been able to take the full measure of what this loss puts at stake for ourselves.”
The more tangible and immediate reasons to protect ecosystems and genetic diversity become clear when one examines the direct implications for human health. “If you consider what keeps a human healthy, every determinant is underpinned by nature: for food, for water, for medicines, for understanding what is going on in human health and disease. So really what’s at stake with the loss of biodiversity is our own health,” Dr. Bernstein said.
Biomedical Implications: Medicine, Disease, and Research
Modern medicine depends on a wealth of diverse natural sources. Compounds derived from nature have historically served as therapeutic agents as long ago as 2600 BCE, when the Mesopotamians were recorded using the opium poppy as an analgesic . Even today, natural products have served as the conceptual starting points for nearly half of the new drugs developed between 1981 and 2006 .
One of the best-known examples of a mainstream pharmaceutical developed from a natural product is quinine. Native populations of South America used the bark of the Chinchona tree to prevent fevers, and in 1820 scientists isolated quinine from the tree for treatment of malaria, a disease caused by the parasite Plasmodium falciparum that affects around 250 million people per year. Although more effective anti-malarial drugs have since been developed, some of them also derived from plants, quinine derivatives are still commonly used due to their cost-effectiveness.
Natural products do not come solely from plants. Compounds currently under research have also been derived from mammals. Bears hibernate throughout the winter but nevertheless manage to maintain their bone density. This is in stark contrast to bedridden or paralyzed patients, who frequently suffer from a thinning of the bones caused by long periods of forced inactivity. The bears’ blood appears to contain a compound that induces the formation of bone and inhibits its degradation in experimental systems, and may provide insight into a new direction of treatment for osteoporosis .
The benefits for human of a diverse range of natural products are not limited to medical advances. While these natural products may benefit the individual as therapies, they may benefit whole communities as a valuable commodity as well. Madagascar has recognized the potential for developing natural products as a new segment of their economy, and restricts export of microorganisms believed to produce pharmacologically active natural products in order to better preserve their value . Although this may hinder research, it may also provide valuable income for developing countries as well as incentives for curating nature’s library of compounds . There are clearly new and exciting biomedical gains to be made by protecting and investigating the natural world, and even, perhaps, economic gains as well.
Human nutrition also depends on biodiversity. This concept may seem counterintuitive; after all, the food we eat today has been inbred for centuries — even millennia — specifically for traits that make it consistently palatable. Although we may depend on a few limited species of plants for food, they depend, in turn, on other species for nutrition, protection, and propagation.
An example of this interdependence can been seen in the pollination of crops, which depends heavily on pollinators such as the honeybee. A 2006 study reviewed in Scientific American has found that, as the diversity of pollinator populations declines, plant diversity declines as well — whether this is a cause-and-effect relationship or just a correlation remains unknown . Regardless, in face of the massive die-off of honeybees in recent years, the concern for our crops was so great that military scientists and academic researchers teamed up to discover that a lethal combination of virus and fungus was responsible for the widespread colony collapse .
Furthermore, our dependence on only a handful of species of crops such as rice, wheat, corn, and potatoes as major global food sources may decrease our food security . Although growing the same varieties of wheat across the world may ensure predictability of taste and texture, the effect of a virus or fungus that could effectively infect crops of one strain or species would be devastating. Preserving genetic diversity within our cultivated crops, and the diversity of “underutilized crops” that have high nutritional and economic values , is essential to ensure that agriculture will be able to adapt to the emergence of new plant pathogens and to changing climate.
As individuals, it’s easy to feel impotent in the face of global developments that require policy changes for any meaningful improvement. Dr. Bernstein argues that individuals can reduce their carbon footprint though, and in that way reduce the stress that climate change is putting on ecosystems.
“The single greatest use of home energy is heat, and most of our homes are incredibly heat inefficient,” Dr. Bernstein said, “We are being flooded with marketing that says buy our product because it’s green, but too few of us have been given an adequate education.”  He argues that by insulating our homes and improving the efficiency of our furnaces, a small investment can pay back in reduced energy expenditures and our carbon footprints, therefore helping to stem the decline of biodiversity that will otherwise limit our medicines, our research, and our food sources.
Rachel Becker is a PhD student in the Immunology program at Harvard Medical School.
 Barnosky AD, Matzke N, Tomiya S, Wogan GO, Swartz B, Quental TB, et al. Has the Earth’s sixth mass extinction already arrived? Nature. 2011 Mar 3;471(7336):51-7.
 Personal Interview, Aaron Bernstein. Nov. 17, 2011.
 Thomas CD, Cameron A, Green RE, Bakkenes M, Beaumont LJ, Collingham YC, et al. Extinction risk from climate change. Nature. 2004 Jan 8;427(6970):145-8.
 Chivian, Eric (Ed.).“Biodiversity: Its Importance to Human Health”, Interim Executive Summary of Harvard University’s Center for Health and the Global Environment (2003, 2nd edition). http://chge.med.harvard.edu/programs/bio/documents/Biodiversity_v2_screen.pdf
 Kingston DG. Modern natural products drug discovery and its relevance to biodiversity tconservation. J Nat Prod. 2011 Mar 25;74(3):496-511.
 Stolton, Sue and Nigel Dudley. “Vital Sites: The contribution of protected areas to human health”, Arguments for Protection, a research report by WWF and Equilibrium Research (2010). http://assets.panda.org/downloads/vital_sites.pdf
 Biello, David. “Bee and Flower Diversity Decline in Tandem”, Scientific American, July 21, 2006. http://www.scientificamerican.com/article.cfm?id=bee-and-flower-diversity
 Johnson, Kirk. “Scientists and Soldiers Solve a Bee Mystery”, New York Times (October 6, 2010).
 “Plant Genetic Resources, Use Them or Lose Them”, factsheet from Commission of Genetic Resources of the UN Food and Agriculture Organization http://www.fao.org/fileadmin/templates/nr/documents/CGRFA/factsheets_plant_en.pdf
 “Meeting the Millennium Development Goals with Agricultural Biodiversity”, report by International Plant Genetic Resources Institute. http://www.underutilized-species.org/documents/PUBLICATIONS/Meeting%20the%20MDGs.pdf