Microevolution

Microevolution is the occurrence of small-scale changes in allele frequencies in a population, over a few generations, also known as change at or below the species level.

These changes may be due to several processes: mutation, natural selection, gene flow, genetic drift and nonrandom mating.

Population genetics is the branch of biology that provides the mathematical structure for the study of the process of microevolution. Ecological genetics concerns itself with observing microevolution in the wild. Typically, observable instances of evolution are examples of microevolution; for example, bacterial strains that have antibiotic resistance.

Microevolution can be contrasted with macroevolution; which is the occurrence of large-scale changes in gene frequencies, in a population, over a geological time period (i.e. consisting of extended microevolution). The difference is largely one of approach. Microevolution is reductionist, but macroevolution is holistic. Each approach offers different insights into the evolution process.

Origin of the Term
Russian Entomologist Iuri'i Filipchenko (or Philipchenko, depending on the transliteration) first coined the terms "macroevolution" and "microevolution" in 1927 in his German language work, "Variabilität und Variation".

Since the inception of the two two terms, their meanings have been revised several times and even fallen into difavour amongst scientists who prefer to speak of biological evolution as one process. The term was returned, somewhat, to prominence in the last thirty years due to breakthroughs in evolutionary theory that seem to indicate that there are different processes involved in speciation than simple modification.