04/13/2010 05:12 am ET Updated Nov 17, 2011

Five Reasons Why Evolution Is Important

Today is the 201st birthday of Charles Darwin. It is worth celebrating this anniversary not only because of Darwin's great contributions to science, but also because of the practical ways his theory of evolution improves our lives today.

Here are five reasons--drawn from medicine--why evolution is important:

1. H1N1 & Emerging Diseases

The outbreak of the H1N1 "swine flu" in 2009 reminds us of our vulnerability to emerging diseases. Like SARS in 2002, H1N1's abrupt appearance emphasizes the fact that viruses evolve, producing new and potentially pandemic-causing contagions. In our highly mobile world, new viruses can jump continents in mere hours via planes. Rapid evolution combined with rapid travel mean that emerging diseases threaten human health as never before--and therefore, understanding how these diseases evolve is vital as never before.

2. HIV
One reason no vaccine against HIV has yet been found is that HIV is one of the fastest evolving entities known to science. HIV's rapid, "Borg"-like adaptability means that the key to defeating this scourge may lie in better understanding of how viruses evolve.

Evolution helps us understand HIV's origins. Because we know that HIV and SIV (simian immunodeficiency virus) share a common viral ancestor, this opens other avenues of research into ultimately defeating HIV.

The technique of applying drug cocktails to HIV-infected patients has proven remarkably successful. The evolutionary idea with drug cocktails is that because HIV evolves so quickly, one single drug will usually leave some surviving viruses; a multi-drug approach has better success. Moreover, periodically switching the cocktail's components helps eliminate viruses which have evolved resistance. All of these techniques rest upon a scientific understanding of evolution.

3. Vaccines
With the exception of clean drinking water, few technologies have improved human health more than vaccines. While misinformed celebrities may peddle long-discredited superstitions about links between childhood vaccines and autism, the truth is that untold millions of adults are alive and healthy today because as children they received vaccines. Vaccines work so well, in fact, that today the horrors of smallpox and polio epidemics are fading memories.

Vaccines exploit the efficiency of our own immune system to recognize and eliminate microbial threats that have been previously introduced into our bodies. Because these threats evolve, vaccines must change too. The flu shot you received this year will not protect you against next year's bug because flu viruses evolve quickly. Evolution makes sense of the need for a new vaccine every year, and point the way toward developing it.

4. Antibiotic Resistance

Penicillin was once a "miracle" drug, but today medical professionals find a host of diseases--from staph infections to tuberculosis--evolving resistance to antibiotics.

The origin of antibiotic-resistant organisms is a textbook example of natural selection. Patients infected with a diverse population of bacteria are given an antibiotic that wipes out almost all the bacteria. If they start to feel better and do not finish the full course of antibiotics, what is left behind are those bacteria most resistant to the drug. Those survivors then become the nucleus of a new, resistant population. Understanding this evolutionary process is an important part of modern public health.

5. Drug Development
New drugs must be tested for a variety of safety factors, yet we cannot simply give unknown drugs to human test subjects and hope for the best. Because we know from evolution that we share a common ancestor with animals such as mice, dogs, and macaques, we can test drugs on these animals without endangering humans. The billions of dollars spent by pharmaceutical companies on animals testing depend on a practical application of evolution.

Evolution has also helped scientists identify sources of lifesaving drugs. The Pacific Yew tree, for example, was once the only source of Taxol, a remarkable drug used to fight ovarian, lung, and breast cancer. This endangered tree grows very slowly, however, and 4-6 trees would be destroyed to produce just one dose of Taxol.

Evolution came to rescue. Scientists used the evolutionary history of the Pacific Yew to trace back other trees in its family line, discovering Taxol-like compounds in more common trees. Evolution guided scientists in finding a replacement to the Pacific Yew, thus dramatically increasing the supply of Taxol available to cancer patients. Evolution saves lives.

These are only a handful of the reasons why evolution is important to medicine (and more information can be found here and here). There are a host of other applications of evolution--agriculture, forensics, bioengineering. But the importance of evolution extends beyond its practical side; evolution explains the diversity of life on this planet, shows us our connection to other living things, and reveals profound insights into the processes of nature.

Today, on Darwin's 201st birthday, take a moment to reflect on the importance of evolution.