Model Answer
0 min readIntroduction
The theory of natural selection, proposed independently by Charles Darwin and Alfred Russel Wallace in 1859, is a cornerstone of modern evolutionary biology. It explains how populations of living organisms adapt and change over time. At its core, natural selection posits that individuals within a population exhibit variations, and those with traits better suited to their environment are more likely to survive and reproduce, passing on these advantageous traits to their offspring. This leads to a gradual shift in the genetic makeup of the population over generations.
Core Principles of Natural Selection
Natural selection operates based on four key principles:
- Variation: Individuals within a population differ in their traits. For example, beak size in finches.
- Inheritance: Traits are passed from parents to offspring. This was less understood by Darwin, but is central to the modern synthesis.
- Selection: Environmental pressures (e.g., food availability, predators) favor certain traits. Finches with beaks suited to available food sources survive better.
- Time: These changes accumulate over many generations, leading to significant evolutionary adaptations.
Mechanism & Examples
The process isn't random; it's driven by environmental factors. Consider the peppered moth (Biston betularia) during the Industrial Revolution in England. Before industrialization, light-colored moths were camouflaged against lichen-covered trees. Pollution darkened the trees, giving dark-colored moths a survival advantage. This is an example of directional selection.
Types of Selection
| Type of Selection | Description | Example |
|---|---|---|
| Directional | Favors one extreme phenotype | Peppered Moth |
| Stabilizing | Favors intermediate phenotypes | Human birth weight |
| Disruptive | Favors both extreme phenotypes | African cichlid fish with large/small mouths |
The modern synthesis integrates Darwin’s observations with Mendelian genetics, explaining the source of variation (mutations and genetic recombination) and the mechanisms of inheritance.
Conclusion
In essence, natural selection is a powerful mechanism driving evolutionary change. It’s not about ‘survival of the fittest’ in terms of strength, but rather reproductive success – the ability to pass on genes to the next generation. Understanding natural selection is crucial for comprehending the diversity of life on Earth and addressing contemporary challenges like antibiotic resistance and conservation biology.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.