“Natural selection” and “evolution” are often used interchangeably, leading to widespread confusion about their distinct meanings. While deeply connected, they are not the same. Understanding their distinction is important for grasping how life on Earth has changed and diversified. This article clarifies what each term means and how they fit together.
Understanding Evolution
Evolution refers to the process of change in the heritable characteristics of biological populations over successive generations. It explains the diversity of life on Earth and how new forms arise from pre-existing ones through accumulated modifications.
A core idea within evolution is “descent with modification,” suggesting that all life shares a common ancestor. The vast array of species seen today have diversified from these ancestors through gradual changes. These changes are not about individual organisms changing during their lifetime, but shifts in the genetic makeup of populations across generations. For example, humans and oak trees share distant common ancestry, having diverged over millions of years.
Understanding Natural Selection
Natural selection is a specific mechanism explaining how evolution occurs. It is the differential survival and reproduction of individuals due to differences in their observable traits, also known as phenotypes. Charles Darwin, along with Alfred Russel Wallace, popularized this concept as a driver of change in species.
This process operates on three principles. First, variation must exist within a population. Second, these traits must be heritable. Third, individuals with certain traits are more likely to survive and reproduce successfully. This differential success makes advantageous traits more common over generations.
Natural Selection as a Driver of Evolution
Natural selection is a primary driver of evolution. It acts on existing variation within a population, favoring individuals whose traits enhance their survival and reproductive success in a given environment. This process is not random; it systematically increases the frequency of beneficial traits in a population over time.
Individuals with advantageous traits survive and reproduce more successfully, passing on their genetic information to offspring. Over generations, this increases the proportion of beneficial alleles. This change in allele frequencies within a population defines evolution at its most basic level. For instance, if a particular beak shape allows finches to access food more efficiently during a drought, those finches are more likely to survive and reproduce, leading to an increase in the frequency of genes for that beak shape in subsequent generations.
Other Mechanisms of Evolution
While natural selection is a powerful force, it is not the sole mechanism driving evolutionary change. Evolution can also occur through other processes that alter the genetic makeup of populations.
Genetic drift involves random changes in allele frequencies within a population, particularly impactful in smaller populations. Chance events, such as a natural disaster, can drastically reduce a population’s size, leading to the random loss or fixation of certain alleles, regardless of their adaptive value. Gene flow occurs when individuals migrate between populations, introducing new alleles or altering existing allele frequencies. This movement can make different populations more genetically similar over time. Mutation, a random change in the DNA sequence, serves as the ultimate source of new genetic variation. Although mutation rates are low, these random changes can introduce new alleles that, combined with other evolutionary forces, contribute to significant changes in a population’s genetic diversity.