Antibiotic-resistant bacteria: evidence for evolution?

Antibiotic-resistant bacteria: evidence for evolution?

by Harlan Brown


The textbook Biology: The Dynamics of Life says on page 430, “Examples of bacterial resistance to antibiotics, such as penicillin, provide scientists with direct evidence for evolution in progress.” Is this true?


Microevolution vs. macroevolution

First, we must distinguish between microevolution and macroevolution:

microevolution  Variation, adaptation, and recombination of existing traits

macroevolution The appearance of new and different genes, body parts, and traits


Antibiotic resistance in bacteria is an example of microevolution. In “Do Bacteria Evolve Resistance to Antibiotics?” ( John D. Morris, Ph.D., describes it like this:

In a given population of bacteria, many genes are present which express themselves in a variety of ways. In a natural environment, the genes (and traits) are freely mixed. When exposed to an antibiotic, most of the microbes die. But some, through a fortuitous genetic recombination, possess a resistance to the antibiotic. They are the only ones to reproduce, and their descendants inherit the same genetic resistance. Over time, virtually all possess this resistance. Thus the population has lost the ability to produce individuals with a sensitivity to the antibiotic. No new genetic information was produced; indeed, genetic information was lost.


Superwimps and loss of information

Antibiotic resistance in bacteria typically involves a loss of genetic information, not the addition of new information. “Such mutations are often harmful in an ‘ordinary’ environment without antibiotics,” Dr. Jonathan writes in “Anthrax and antibiotics: Is evolution relevant?” ( “It is well documented that many ‘superbugs’ are really ‘superwimps’ for this reason.”


As described in “Superbugs not super after all” ( by Carl Wieland, when the antibiotic is removed, the antibiotic-resistant bacteria begin to die out. ‘Supergerms’ are actually not ‘super’ at all. They are generally less hardy, and less fit to survive in a normal environment.


No progress toward macroevolution

Thus antibiotic resistance in bacteria is not an example supporting the theory of evolution (macroevolution). It represents a trait that is deleterious in a natural environment but happens to have the side benefit of survival in an unnatural (antibiotic) environment.


Practical implications

Antibiotic resistance in bacteria has a number of practical implications.


When you receive an antibiotic

Suppose you receive an antibiotic and the doctor says to take it for seven days, and you feel better after five days. What happens if you stop after five days instead of seven? It is possible that after five days a small number of resistant bacteria survive that would die if given seven days of the antibiotic. So, instead of killing all of the bacteria, you have just created a population of antibiotic-resistant bacteria that can grow and reproduce.


Overuse of antibiotics

Although antibiotics have saved many lives, if they are overused, they can lead to more and more resistant bacteria. In fact, although antibiotic-resistant bacteria existed before the modern use of antibiotics in medicine, bacteria have become increasingly antibiotic-resistant since the use of antibiotics became widespread. Pharmaceutical researchers are continually developing more powerful antibiotics to cope with the increased resistance.


Antibacterial hand soap

Increased use of antibacterial hand soap may pose a similar danger. A study at Tufts University concluded that triclosan and other antimicrobials have valid uses in clinical areas, but cautioned against their indiscriminate use ( See also “Antibacterials? Here's the Rub” ( by Mindy Pennybacker and “The Truth About Antibacterial Soaps--And Why You Should Avoid Them” ( and “Antibacterial Soaps Popularity May be Spreading Resistant Bacteria” ( by Dr. Joseph Mercola.


Superbean or Frankenfood?

RoundUp glyphosate herbicide provides a convenient way to remove weeds from a driveway. It kills all the plants. Large acreages of soybeans and corn are now being sprayed with Round-Up, killing everything except genetically engineered varieties of the crops. Some people have the misconception that RoundUp Ready® plants are genetic advancements, improved varieties exemplifying the marvels of generic engineering. However, a particular metabolic pathway has been crippled, and the yield is slightly decreased. Some farmers tolerate this because weed control becomes so much easier.


In addition to the concern that environmentalists have about soil and water pollution, RoundUp Ready soybeans have 29% less choline and 27% more trypsin inhibitor. Choline is a nutrient, part of the Vitamin B complex. Trypsin inhibitor is an allergen that interferes with protein digestion. See “Buried Data in Monsanto's Study on Roundup Ready Soybeans” by Barbara Keeler (



In conclusion, antibiotic-resistant bacteria do not provide evidence for the theory of evolution, but understanding antibiotic resistance can help in practical ways.         2005/02/24

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