Genetic Mutations and the Speed of Evolution

A single genetic mutation is the first step on the evolutionary path; a subtle change in the genotype that may affect phenotype. The cell replication process is fraught with errors, and mutations are an inevitable by-product of cell division (when the genetic material is duplicated).

Most of the time these mutations are harmless; they do not have a deleterious effect on the organism. Sometimes the mutations go the wrong way; they are bad for the organism and can prove to be fatal.

Occasionally a mutation may confer a benefit, an advantage that permits an organism to adapt to a change in its environment. For example, a genetic mutation that prevents an animal from succumbing to a particular disease - i.e. resistance to a viral pathogen. The advantageous mutation is then "selected for" and passed down to subsequent generations.

When these genetic changes generate differences within the organisms of a population, but do not bring about a new species, it's known as microevolution. It accounts for some of the variations seen in some species. And it happens faster for animals in warmer climates.

Examples of microevolution are;

House sparrows - house sparrows in the north of America have larger bodies than those in the south.

Pathogens - microevolution by bacteria and viruses that confers resistance to therapeutics.

Temperature affects the rate of molecular evolution with the changes occurring faster in organisms in warmer climates than those in cooler ones. It has been an often commented phenomenon of ectotherms, organisms that have their body temperatures controlled by the environment. It's been witnessed in plant species and in some marine animals. It is believed that temperature increases the rate at which germ cells divide and so there are more opportunities for advantageous mutations to appear. But it also appears that climate may affect the speed of molecular evolution in endotherms; animals that regulate their own body temperature.

Scientists from the Auckland University of Technology compared the DNA of 130 pairs of mammals living in different environments. They found that the rate of DNA change was much faster in those creatures living in warmer habitats. This is the first time that microevolution has been reported in mammals, and the findings were published in the Proceedings of the Royal Society B.

Each of the pair lived at a different latitude or elevation, and mutations were studied in the gene that codes for a protein known as cytochrome b. This same gene was also compare with a 'reference' gene in a common ancestor.

The researchers were looking for small changes in the DNA, where one letter of the genetic code is substituted for another. It turns out that the rate of this microevolution was about 1.5 times faster in animals from warmer climates.

The Discovery of the Link Between Radiation Exposure and Genetic Mutation

Len N. Gillman, D. Jeanette Keeling, Howard A. Ross, and Shane D. Wright

Latitude, elevation and the tempo of molecular evolution in mammalsProc. R. Soc. B published online before print June 25, 2009, doi:10.1098/rspb.2009.0674