Natural selection is a fundamental biological process explaining how populations of living organisms change and adapt over time. It represents a cornerstone of evolutionary theory, providing a mechanism for the diversity of life observed on Earth. This process describes how certain traits become more common within a population across generations.
Variation
Individuals within any population of organisms display a range of observable differences. For instance, within a group of birds, some might be larger, others smaller; some may have brighter plumage, while others are duller. These variations can also include differences in speed, disease resistance, or metabolic efficiency. Such variations arise randomly, often from genetic mutations or from the shuffling of genetic material during sexual reproduction.
Inheritance
Some of the variations present in a population are heritable, meaning they can be passed from parents to their offspring. This transmission occurs primarily through genetic material, such as DNA. For example, a tall parent tends to have tall children, indicating that height often has a heritable component. In contrast, traits acquired during an organism’s lifetime, like a scar from an injury or a learned skill, are generally not passed down to the next generation. Only heritable traits are relevant to the process of natural selection.
Overproduction
Most organisms produce more offspring than the environment can possibly support. Individuals must compete for limited resources, including food, water, shelter, and potential mates. This intense competition ensures that not all offspring will survive to maturity and reproduce themselves.
Differential Survival and Reproduction
Survival and Reproduction
Due to the overproduction of offspring and the resulting competition for resources, individuals with heritable traits that are better suited to their specific environment are more likely to survive. These individuals also have a greater chance of successfully reproducing and passing their advantageous traits to offspring. For example, a bird with slightly better camouflage might evade predators more effectively, increasing its chances of living long enough to reproduce. Conversely, individuals with less advantageous traits are less likely to survive or reproduce successfully.
Long-Term Adaptation
The concept of “survival of the fittest” in natural selection refers to those individuals whose inherited traits provide the best match for their current environmental conditions. This process, repeated over many generations, leads to a gradual increase in the frequency of beneficial traits within a population. Over time, this leads to the adaptation of the population to its environment, as the proportion of individuals with advantageous characteristics grows, ultimately driving evolutionary change.