Turned up to eleven: Fair and Balanced

Friday, August 01, 2003

An Evolution Argument

Back to the science type content, at least temporarily. I have repeatedly outlined arguments for Evolution v. Creationism here, but there is one strong argument that I have overlooked, or rather, not espoused. It is not an argument against Creationism per se, but it is a core argument of microbiology, and also of ecology, that is best explained by the Theory of Natural Selection. Of course, a Creationist "just so" story would also suffice, but would run afoul of Ockham's Razor, as usual. Nevertheless, here it is (note: this post is inspired in part by my current reading, The Future of Life, by eminent naturalist and entomologist E.O. Wilson);
It is a truism in microbiology that bacteria will live in the presence of carbon, phosphorus, nitrogen, sulfur and energy (which might come from light or from chemical sources, including organic and inorganic chemicals). It used to be thought that the Sun was the source of all biospheric energy, but the discovery of autolithotrophic bacteria (literally, bacteria that eat rock) put the lie to that. The truism goes even deeper than what is noted above, however; There is no sterile environment on Earth. Now of course, you can take a place, say the inside of an autoclave, and make it sterile, but there is simply no place on Earth that is naturally free of microbial life. To put it bluntly, microbes are the world's experts at extracting life from inorganic matter.
So why is this an argument for Evolution? Well, from my viewpoint, there are two possibilities-one is a Creationist "just so" story. God, in his or her wisdom, created that Universe, and filled it with life, squeezing a bacterium into absolutely every single conceivable niche. Alternatively, 4 billion years ago, the Earth coalesced from the swirl of hot gas and dust that was the Solar System, and a geologic blink later, microbes began to form to utilize the energies of the world around them. As they multiplied, they filled the abiotic world and started using the resources, along the way creating new environments and niches. At this point, I am telling an Evolutionary "just so" story (if we ignore the fossil record and molecular phylogeny data). However, a theory of Natural Selection suggests that living organisms will fill every available niche, i.e. will compete and adapt to utilize resources maximally. So Evolution makes a prediction-for every potential energy and nutrient source you will find an organism that uses it. This prediction can (and has) been tested. It has held up so well, that microbiologists don't even consider it a question anymore. It is so routine that a course can be (and often is) built with the following structure; 1)find a chemical, either naturally occuring or synthetic and 2) take a soil or water sample and add that chemical to it, 3) incubate for a couple of weeks at 30 or 37 deg. C, wait for bacteria that can use the chemical to grow. This virtually always works. Essentially, what you are doing is adding an energetic or chemical input to a very competitive system that is in equilibrium. When you add the new input, whatever organism can use it best will grow, until a new equilibrium is reached. As my recent boss wrote (to paraphrase) "With bacteria, you get what you ask for".
Unfortunately, I don't think that this argument works well for people who are not well versed in biology or microbiology. But it is a hugely useful thing to remember when thinking about life and ecosystems-nothing is wasted.