Claim CB101:
Most mutations are harmful, so the overall effect of mutations is harmful.
Source:
Morris, Henry M. 1985. Scientific Creationism. Green Forest, AR: Master Books, pp. 55-57.
Watchtower Bible and Tract Society. 1985. Life--How Did It Get Here? Brooklyn, NY, pg. 100.
Response:
Most mutations are neutral. Nachman and Crowell estimate around 3 deleterious mutations out of 175 per generation in humans (2000). Of those that have significant effect, most are harmful, but the fraction which are beneficial is higher than usually though. An experiment with E. coli found that about 1 in 150 newly arising mutations and 1 in 10 functional mutations are beneficial (Perfeito et al. 2007).
The harmful mutations do not survive long, and the beneficial mutations survive much longer, so when you consider only surviving mutations, most are beneficial.
Beneficial mutations are commonly observed. They are common enough to be problems in the cases of antibiotic resistance in disease-causing organisms and pesticide resistance in agricultural pests (e.g., Newcomb et al. 1997; these are not merely selection of pre-existing variation.) They can be repeatedly observed in laboratory populations (Wichman et al. 1999). Other examples include the following:
Mutations have given bacteria the ability to degrade nylon (Prijambada et al. 1995).
Plant breeders have used mutation breeding to induce mutations and select the beneficial ones (FAO/IAEA 1977).
Certain mutations in humans confer resistance to AIDS (Dean et al. 1996; Sullivan et al. 2001) or to heart disease (Long 1994; Weisgraber et al. 1983).
A mutation in humans makes bones strong (Boyden et al. 2002).
Transposons are common, especially in plants, and help to provide beneficial diversity (Moffat 2000).
In vitro mutation and selection can be used to evolve substantially improved function of RNA molecules, such as a ribozyme (Wright and Joyce 1997).
Whether a mutation is beneficial or not depends on environment. A mutation that helps the organism in one circumstance could harm it in another. When the environment changes, variations that once were counteradaptive suddenly become favored. Since environments are constantly changing, variation helps populations survive, even if some of those variations do not do as well as others. When beneficial mutations occur in a changed environment, they generally sweep through the population rapidly (Elena et al. 1996).
High mutation rates are advantageous in some environments. Hypermutable strains of Pseudomonas aeruginosa are found more commonly in the lungs of cystic fibrosis patients, where antibiotics and other stresses increase selection pressure and variability, than in patients without cystic fibrosis (Oliver et al. 2000).
Note that the existence of any beneficial mutations is a falsification of the young-earth creationism model (Morris 1985, 13).
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