By Aaron Bernstein, MD, MPH, physician in Medicine at Children’s and faculty, Center for Health and the Global Environment
One hundred and fifty years ago today, The Origin of Species was published. At more than 500 pages, Charles Darwin’s occasionally dry and stodgy tome is hardly the page-turning and catchphrase-coining stuff of today’s New York Times bestsellers list. Be not fooled. Even if the revolutionary sheen has faded from its imprint, the ideas Darwin wrote about in The Origin of Species remain as relevant as ever, particularly when it comes to our health. Here’s how.
Several children I recently cared for at Children’s Hospital Boston were diagnosed with H1N1 influenza. In most cases, we presume that children who develop flu-like symptoms have H1N1. However, when a child is admitted to the hospital we test for the virus using a technique known as the polymerase chain reaction or PCR. PCR employs a bacterial protein that can, from just a few pieces of DNA, manufacture millions of copies. For PCR to work, however, the normally paired strands of DNA must be separated and that takes heat, about 200 degrees Fahrenheit, a temperature that would cook our cells and the proteins they contain like an egg on a hot griddle.
Fortunately for us, some species like it hot. The bacterial protein that serves as an indefatigable xerox machine for us to detect H1N1, as well as many other infections, thrives at a temperature just below that required to separate DNA strands. The original and most widely used protein used in PCR (several newer models have been rolled out since) comes from Thermus aquaticus (pronounced THUR-mus a-KWAT-i-kus) a bacterium discovered in 1969 by Thomas Brock and Hudson Freeze in Yellowstone National Park’s Mushroom Spring. Mushroom Spring’s temperature remains more or less at a sultry 150 degrees Fahrenheit year round thanks to the Earth’s molten core serving as the spring’s inexhaustible furnace.
So what business do bacteria have living in near boiling water? (Note: T. aquaticus like most bacteria does not cause illness in humans.) That’s where Darwin comes in. That T. aquaticus thrives in a hot spring is a result of what is known as natural selection, the groundbreaking idea captured in The Origin of Species. Natural selection refers to the process by which certain heritable traits become more common in a population over successive generations as they confer a survival advantage to those individuals that possess them. In the context of T. aquaticus, you might imagine that the ability to copy DNA at high temperatures would have provided a survival advantage to some bacteria over others trying to live in a hot spring. This adaptation to life at high temperatures formed the basis of PCR, one of the most important discoveries in the history of medical research, and our ability to diagnose H1N1.
Adaptations have also enabled the development of new drugs. The children I cared for with H1N1 received oseltamivir or Tamiflu to treat their infection. Although the drug’s design was deduced in a lab, we would be unable to make it without help from the Chinese Star Anise Tree, which produces shikimic acid, a key building block in the synthesis of oseltamivir. Shikimic acid can be made in the lab but not nearly as cheaply nor as efficiently as the Chinese Star Anise Tree makes it in its seeds. What the shikimic acid does for the tree and why the Chinese Star Anise Tree makes more shikimic acid than its closest relatives, no one knows, but the utility of its adaptation to us, especially now as we try to stave off H1N1, is abundantly clear.
Another feature of Darwin’s theory of natural selection is that it implies that all species descend from common ancestors, and our common heritage with other animals has enabled research on human diseases by the study of other animals as they share with us many aspects of body design, organ function, and response to disease. In the case of H1N1, much of what we know about how the virus makes people sick, how it’s transmitted, and the effectiveness of vaccines has come from research on ferrets, small meat-eating mammals. Almost accidentally, ferrets were found to be susceptible to infection with human influenza virus more than 80 years ago. Today, they have become one of the most important animal models for studying H1N1.
So here are but a few examples, among countless others, that demonstrate that we owe much of our health to ideas Charles Darwin wrote about 150 years ago. Perhaps in this light, our eyes may see more glimmer and less gray in the imprint of this great book.
Also read the post I wrote about extremely deadly viruses found in other parts of the world.