Macro-evolution observed in the laboratory

Evolution can easily be observed in the laboratory and in the world around us.  We can see moths evolve their coloring to match the color of soot that covers their habitat, watch bacteria evolve antibiotic resistance in hospitals, and my favorite variety of grapefruit (that’s Rio Star) was made by scientists who exposed seeds to radiation to increase the mutation rate. In the face of such overwhelming evidence  including knowing the exact DNA changes effecting such change  it is impossible for the creationists to deny evolution with a straight face.

To get around the problem, creationists often try to separate evolution into two types, micro-evolution and macro-evolution. They argue that micro-evolution can make minor changes, but can¹t build new structures or make other major changes to organisms. Although “the attempt to differentiate between micro-evolution and macro-evolution is considered to have no scientific basis by any mainstream scientific organization” (according to Wikipedia), creationists often claim that a chain of small micro-evolutionary steps can¹t add up to a macro-evolutionary step.

Indeed, it’s hard to simulate our planet’s biodiversity in a laboratory, because all laboratories are much smaller than the planet and have been operating for a far shorter period of time.  Nevertheless, we can now say that macro-evolution has been observed in the laboratory under carefully controlled conditions, and that the results can be replicated.  The results are described in a paper published in the Proceedings of the National Academy of the Sciences titledHistorical contingency and the evolution of a key innovation in an experimental population of Escherichia coli.

In 1988, scientists at Michigan State University created twelve population lines of E. coli so that they could watch them evolve.  Since then, the bacteria have been growing under carefully controlled conditions in a culture containing low concentrations of glucose and high concentrations of citrate.  Under oxic conditions (that is, when oxygen is present), E. coli cannot grow on citrate and “that inability has long been viewed as a defining characteristic of this important, diverse, and widespread species.”  Many traits were observed changing over time. Creationists dismissed these changes as micro-evolution.  For over 30,000 generations, the E. coli in the experiment did not evolve the ability to grow on citrate. Finally, one of the populations evolved, and gained this ability.

Each population experienced billions of mutations in the first 30,000 generations. Since every possible point mutation was tried many times, scientists were either looking at a rare mutation (such as a large piece of DNA inverting) or a mutation made possible by the cumulative mutation history of prior generations.  If this was just a rare mutation, then a sample of bacteria taken just before the trait first appeared would be no more likely to evolve the trait again than a sample taken from the other populations at the same point in time.  However, if the ability to use citrate was from an accumulation of “micro-evolutionary” changes, then a sample from earlier generations of the E. coli would be able to evolve the ability to use citrate again.

Fortunately, the scientists had frozen samples of each population every 500 generations.  Sure enough, when they revived earlier samples, they watched the citrate-growing ability evolve in the “micro-evolutionary” line, but not from samples taken from other lines.

We know that in one population, a series of changes that happened between the 15,000th and 20,000th generations laid the groundwork for a major evolutionary advance. Here we have a clear example of macro-evolution under carefully controlled laboratory conditions.

David Annis

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