Tara has been given the task of pointing out some of the flaws in Chapter 7 of Jonathan Wells’s The Politically Incorrect Guide to Darwinism and Intelligent Design. From what I can gather, this is the chapter in which Wells claims that biology does not need evolution because evolution has no applications in medicine or agriculture. In doing so, Wells reveals he does not understand the difference between natural and artificial selection:
The clinical use of antibiotics creates a highly artificial situation. Antibiotic-producing microbes must be isolated from their natural surroundings and grown in pure culture with special nutrients. Then the antibiotic has to be purified and concentrated to a degree never seen in nature. When the antibiotic is finally administered to a patient, there is nothing “natural” about what follows. The greenhouses and livestock pens of domestic breeders are more natural than a hospital room or a doctor’s office.
In the introductory biology course at my university, the students perform an experiment in which they study the evolution of antibiotic resistance in a population of bacteria. We expect the students to understand the difference between artificial and natural selection. The distinguishing factor is not human involvement, but human intent.
Artificial selection includes things like domesticating livestock, selecting crops for larger fruits, and breeding dogs and pigeons (Darwin’s example). During artificial selection, humans directly determine which individuals breed, thereby changing allele frequencies in the population. Natural selection occurs when there are heritable differences in reproductive success based on the organisms’ interactions with their environment. The evolution of antibiotic resistance in bacteria has been the result of natural selection, NOT artificial selection.
Regardless of whether natural or artificial selection is responsible for changes in allele frequencies, they are united in that both work via differential reproduction due to heritable variation. In fact, artificial selection is an excellent example of how natural selection works. Charles Darwin knew this, and he used the breeding of pigeons (artificial selection) to make his points about natural selection clear.
Tara also points out that Wells doesn’t quite understand how antibiotic resistance spreads through a population:
Wells actually gets about a paragraph or so mostly right on pages 77-78, describing factors which contribute to the emergence of antibiotic resistance. However, he blows it again by the middle of page 78, writing that antibiotic resistance “…spreads from microbe to microbe–mechanisms involving gene transfer among organisms rather than Darwinian descent with modification.” Yes, that is the sound of jaws dropping everywhere–isn’t the acquisition of genes and the passing of them on to progeny “descent with modification?” Additionally, while this horizontal gene transfer is one mechanism for the development of antibiotic resistance, it’s certainly not the only way bacteria become resistant.
This is something else we expect our introductory biology students to understand. We make it quite clear that genes for antibiotic resistance can be transferred from bacterium to bacterium via horizontal transfer. But they can also increase in frequency because resistant individuals reproduce (by binary fission) leaving two bacteria carrying the resistance gene. In the presence of an antibiotic, the antibiotic sensitive bacteria won’t be able to reproduce, giving the resistant individuals a selective advantage. The resistance allele increases in frequency because only resistant individuals are able to reproduce. This is natural selection in its purest form.
If Jonathan Wells were in the introductory biology course at my university, he would struggle. The previous two examples are core concepts that a student must understand for one of the more important laboratory exercises. Students who fail to grasp these two points (there are very few of them) won’t be able to clearly summarize their findings in their required lab report. The intelligent design movement is being led by people who don’t understand freshman level biology.