Genetic Drift vs. Natural Selection: What's the Difference?

Natural selection is a directed evolutionary process that shapes species over time.Initially, a population of moths might have different colorations. Here, we have mostly light-colored moths, with a few darker variants.As the Industrial Revolution progresses, pollution darkens the tree bark where these moths rest.Birds can more easily spot and prey upon the light-colored moths against the darker background.This selective pressure reduces the light moth population, while dark moths survive better.The surviving moths reproduce, passing their coloration to their offspring. Dark moths have more offspring due to their higher survival rate.Over generations, this process leads to a population with more dark-colored moths, better adapted to their environment.This example demonstrates how natural selection works: variation in traits exists, environmental pressures favor certain traits, and these beneficial traits are passed to future generations.Genetic drift occurs when random events change the frequency of genes in a population.In this small population of birds, we have an equal number of blue and brown feathered individuals.Unlike natural selection, genetic drift is purely random. The color of the feathers doesn't affect survival chances.Let's say a storm hits this population. Some birds survive while others don't, purely by chance.When these surviving birds reproduce, their offspring inherit their colors. Now there are more blue birds in the population, even though blue feathers didn't provide any survival advantage.Over generations, these random changes can dramatically shift the genetic makeup of small populations.This increase in blue feathers happened entirely by chance. In a larger population, such random events would have less impact on the overall genetic makeup.Now let's examine the key differences between natural selection and genetic drift.Natural selection is directed by environmental pressures, leading to predictable, adaptive changes.In contrast, genetic drift causes random changes that may or may not benefit the organism.Population size plays a crucial role in these evolutionary processes. Let's look at a large population of one hundred individuals.Compare this to a small population of just ten individuals, where random events can have a much bigger impact.In large populations, natural selection typically has a stronger effect than genetic drift.However, in small populations, genetic drift can actually overpower the effects of natural selection.Let's review the key points about these evolutionary processes.Natural selection is directed while genetic drift is random. Population size affects both processes, but small populations are especially vulnerable to drift. Together, these processes shape the evolution of species.Thank you for learning about evolutionary processes with Spark.E!