Which of the following is NOT considered a main force of evolution?

The concept of evolution is underpinned by several main forces that contribute to the genetic variation and adaptation of populations over time. Gene flow, natural selection, and mutation are all critical mechanisms that drive evolutionary change.

Gene flow refers to the transfer of genetic material between populations, which can increase genetic diversity and introduce new alleles into a population. Natural selection is the process by which advantageous traits become more common in a population because they enhance survival and reproductive success. Mutation introduces new genetic variations by altering the DNA sequence, providing raw material for evolution to act upon.

In contrast, the term "radiation" in this context does not align with the accepted main forces of evolution. While the concept of adaptive radiation can refer to the diversification of species from a common ancestor into various forms that adapt to different environments, it is not a mechanism that directly causes evolutionary change like the other forces mentioned. Instead, adaptive radiation is an outcome of the processes of evolution influenced by the other forces.

Therefore, radiation is not considered a main evolutionary force but rather a phenomenon that occurs as a result of evolution driving diversification in the presence of various selective pressures.