What causes evolutionary (genetic) change?

1. What causes evolutionary (genetic) change? 

  • There are four forces of evolution: mutation, natural selection, genetic drift, and gene flow. These forces result in genetic change over time.
  • Mutations are DNA coding errors involving perma- nent changes in the structure or amount of genetic material in cells. They are the only source of new genetic material.
  • Only mutations in gametes can affect offspring, so they have greater importance for evolution than do mutations in somatic cells.
  • During natural selection, population members with advantageous characteristics survive and reproduce in greater numbers than do members lacking the same characteristics. Allele frequencies can increase, decrease, or remain the same owing to natural selection.
  • Advantageous characteristics can be visible physical attributes and/or invisible, biochemical attributes.
  • Genetic drift is change in gene frequency due to chance. It is likelier within smaller populations.
  • Gene flow is the transfer of genes across population boundaries.

2. How is evolutionary (genetic) change measured, and how is the cause determined? 

  • Deviation from the proportions of gene frequencies and genotype frequencies as defined by the Hardy– Weinberg law of equilibrium is used to measure evolu- tionary change.
  • There is no apparent evolution of a gene in a popula- tion if there is no change in frequency over time.
  • If gene frequency is changing, then evolution is likely occurring owing to one or more forces of evolution, but the Hardy–Weinberg law does not indicate which particular force (or forces) is the cause. The scientist examines the context for change, such as change in climate, migration of populations across territorial or geographic boundaries, introduction of new diseases, and change in diet.