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 Yuri Filipchenko (or Philipchenko, depending on the transliteration) first coined the terms "macroevolution" and "microevolution" in 1927 in his German language work, "Variabilität und Variation". The term was brought into English-speaking by Theodosius Dobzhansky in his book Genetics and the Origin of Species (1937).

Since the inception of the two terms, their meanings have been revised several times and even fallen into disfavor amongst scientists who prefer to speak of biological evolution as one process.