Issue Date: March 11, 2013
Misnomer? What Misnomer?
Edward A. Boudreaux’s letter about directed evolution defines evolution as “a natural process whereby a product of change has attained some degree of complexity relative to its initial state” (C&EN, Jan. 7, page 5). He further states that no evolution has occurred when genes are modified in a microorganism by directed evolution since it is the same organism with different acquired traits.
Boudreaux’s description does not agree with the definition of evolution on the National Academies’ website, which does not mention complexity (http://bit.ly/ZIYZth). Here evolution is defined as “changes in the heritable traits of a population of organisms as successive generations replace one another.”
Long-term evolution occurring over geologic time can result in the formation of new species and broader taxonomic groups. A good example is the formation of 14 different species of Darwin’s finches from a common ancestor over the past 2 million or 3 million years (http://bit.ly/Q4z0an). Evolution can also result in changes of a group of organisms within a species that do not result in a new species. An example is the formation of antibiotic-resistant bacteria that use various methods to deal with the antibiotic (http://bit.ly/zGvq0I). This change can occur over a very short period of time.
In humans, an Icelandic study found that every newborn baby has 36 spontaneous mutations, which are the raw material for all human evolution (Science, DOI: 10.1126/science.338.6104.189). Note that most mutations are deleterious and human evolution is very slow.
Evolution thus may or may not result in a more complex organism. In general, when an organism evolves by natural or sexual selection, it has a better chance of surviving in its environment. In the three examples above, the complexity of the finches, bacteria, and humans has probably not increased, but finches, bacteria, and humans have evolved because their heritable traits (genes) have changed. So the term directed evolution is not a misnomer.
Harvey F. Carroll
Lake Forest Park, Wash.
It’s hard to tell what point Boudreaux is trying to make in his letter objecting to C&EN’s use of the term directed evolution. Boudreaux’s eccentric definition of evolution as “a natural process whereby a product of change has attained some degree of complexity relative to its initial state” is one that no biologist would use.
Directed evolution is the accepted term of art for studies in which selection pressures imposed by experimenters are used to guide the changes in a biological system—usually, changes in the sequence of a gene and its protein product. “Directed evolution” appears in the title of hundreds of scientific publications in top journals, and C&EN should not be averse to using it.
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