06.10.2015

Evolution: Right in the Gut

People who downplay or deny evolution often forget that evolutionary processes have major, dynamic impacts on the quality and future of their lives. Case in point: microorganisms.

I was thinking about evolution and microbes after listening to a recent Science Friday podcast . There was a report about the microbiomes of people living in a remote region of the Venezuelan Amazon previously uncontacted by modern civilization. Imagine—you’ve never seen Westernized people before, and the first thing they do when you meet them is ask for samples of your poop. A peculiar beginning.

Both the podcast and the paper on which the report was based mention something really interesting. These remote, uncontacted tribespeople’s microbiomes contained genes for antibiotic resistance. How would those genes get in there? These people had never taken modern antibiotics.

That question is hard to answer unless you think about microbiology and evolution. We have some very clear, very recent, and very serious evidence for evolution when we observe present-day antibiotic resistance.

Americans use antibiotics all the time—via medicines, food, and contact with everyday objects. For example, the average American is given a prescription for antibiotics almost every year. Modern meat production relies heavily on massive doses of antibiotics to keep animals alive and gaining weight. We put antibiotics in our cutting boards and in our soap and in our children’s toys. Unfortunately for us, antibiotics aren’t working so well anymore—at least in part because of this near constant exposure we have to them. Drug resistant microorganisms are increasingly prevalent. At least 23,000 Americans die every year from antibiotic-resistant infections. Almost every family has had someone who needed multiple rounds of multiple drugs to kill some “stubborn bug.” Antibiotics are part of our daily lives, but we forget that antibiotics have only been available since the 1940s. Many of those early drugs are now almost completely ineffective. Resistance continues to develop. Common but serious diseases, like tuberculosis, are once again becoming untreatable.

How did we get here? Thank evolution. Over the last seventy years, antibiotics have killed bacteria that lack resistance while bacteria with resistance have survived to reproduce, passing on their genes to their clones. Crucially, bacteria don’t keep their genes to themselves the way we mammals tend do. Once a species of bacteria acquires antibiotic resistance, they can not only pass on the resistance by cell division, but they can also share their genes with all their friends. Bacteria can even exchange DNA between species, allowing beneficial mutations to spread through whole microbiomes. Environmental bacteria pick up the genes and share them as well, allowing microbial genetic traits to spread across great distances. Perhaps even into the depths of the Amazon; into the skin and the guts of human beings who have never taken an antibiotic.

Bacterial antibiotic resistance is a clear tie between evolution and human health. It's a really strong way to engage people in conversations about evolution. This recent news about microbial resistance in even the most isolated of human populations should make one thing clear: Antibiotic resistance is a problem that affects everybody. Our modern lifestyle relies on antibiotics in a lot of ways. And if we want to understand and successfully combat antibiotic resistance, we need to understand evolution.

Deny evolution and it's difficult to understand how drug-resistant genes could find their way into the microbiomes of distant people. Accepting evolution means accepting and understanding change over time; that we live as part of a dynamic living system on a dynamic planet. We are connected to other living things through profound selective pressures, and we exert profound selective pressures on other living things. Accepting evolution doesn’t just mean accepting theories about our origins. It means accepting our power as living things now and in the future, as well as our vulnerability.

Points worth talking about, the next time you have a conversation about evolution. Human selective pressure on microorganisms through the use of antibiotics has changed microbial populations worldwide. How else are human actions exerting selective pressure on other living things?