Defining Natural Selection
Natural selection is a fundamental process driving evolution, proposed by Charles Darwin. It describes how populations of living organisms adapt and change over time. It occurs when individuals within a population possess heritable traits that give them a survival and reproductive advantage over others in a specific environment. This differential success leads to certain traits becoming more common in subsequent generations.
Four Key Principles of Natural Selection
Natural selection operates based on four key principles: variation (individuals in a population differ in their traits), inheritance (these traits are passed from parents to offspring), overproduction (organisms produce more offspring than can survive), and differential survival and reproduction (individuals with advantageous traits are more likely to survive and reproduce, passing those traits on). These principles collectively lead to changes in allele frequencies within a population over generations, which is the definition of evolution.
Example: The Peppered Moth
A classic example is the peppered moth (Biston betularia) in England. Before the Industrial Revolution, light-colored moths were camouflaged against lichen-covered trees, making them less visible to predators. Darker moths were rare. As pollution darkened tree trunks, dark-colored moths became camouflaged, while light moths stood out. Consequently, dark moths survived and reproduced more effectively, leading to an increase in their population. When pollution decreased, light moths became prevalent again. This demonstrates how environmental changes drive natural selection.
Natural Selection's Role in Evolution and Adaptation
Natural selection is the primary mechanism by which populations become adapted to their environments, leading to the diversity of life on Earth. It explains phenomena from bacterial resistance to antibiotics to the complex ecosystems found globally. By consistently favoring individuals with advantageous traits, it sculpts species to be better suited to their ecological niches, causing evolutionary change over vast timescales. This process is continuous and ongoing, constantly shaping life.