Natural Selection and Darwin


  • The concept of natural selection is at the core of Charles Darwin's theory of evolution. It's a fundamental process by which species change over time and adapt to their environments. Here, we'll explore the essence of Darwinian Theory, the genetic basis of selection, key concepts, how it contrasts with Lamarckism, and provide an example of natural selection.

 Example of Natural Selection: Moth Industrial Melanism

  • Industrial melanism is a phenomenon that refers to the adaptation of moth populations in response to environmental changes, particularly in industrialized regions. It is a classic example of natural selection and evolution in action.
  • Before the Industrial Revolution, many regions were covered in light-colored lichen and tree bark. Moths in these areas typically had light-colored wings, providing them with effective camouflage against tree trunks. The most well-known moth species demonstrating this trait was the peppered moth (Biston betularia).
  • The rise of industrialization brought about significant changes to the environment. Factories released pollutants, primarily sulfur dioxide, which led to the darkening of trees and surfaces due to soot and other industrial residues. As a result, the once-light-colored trees became darkened and less reflective.
  • In this altered environment, light-colored moths became more conspicuous to predators, while dark-colored moths gained an advantage. Birds and other predators could more easily spot and capture light-colored moths against the darkened background, leading to a decrease in their population.
  • Conversely, dark-colored moths had a higher chance of survival because they blended into the now darkened environment. Over time, the population of dark-colored moths increased, demonstrating the process of natural selection.
  • One of the most notable studies on moth industrial melanism was conducted by Bernard Kettlewell in the mid-20th century. He used the peppered moth to investigate the phenomenon, confirming that the color change in moth populations was a result of adaptation to the polluted environment.
  • In more recent years, efforts to reduce industrial pollution have led to a partial reversal of industrial melanism. As environmental conditions improved and tree trunks became lighter again, light-colored moths regained their advantage, and their population began to recover.

Essence of Darwinian Theory:

  • Darwinian evolution is fundamentally about natural selection. The rate at which new forms appear is linked to the life cycle or life span of organisms.
  • Microbes, with their rapid division, can give rise to new forms within hours. For instance, a colony of bacteria with inherent variations in metabolic capabilities can lead to new species when exposed to a change in the environment.
  • The fitness of these new variants is determined by their ability to adapt and survive in the new conditions.

 Genetic Basis of Selection:

  • Natural selection is based on characteristics that are inherited. Hence, there must be a genetic basis for getting selected and evolving.
  • Adaptive ability, which is inherited, plays a critical role in determining an organism's fitness in its environment.

 Key Concepts of Darwinian Theory:

1. Branching Descent: The idea that species descend from common ancestors, forming a branching tree of life.

2. Natural Selection: The process by which organisms better adapted to their environment have a higher chance of surviving, reproducing, and passing on their advantageous traits.

 Evolution as a Process or Result:

  • The concept of evolution can be seen as both a process and a result. When describing the story of the world, we depict evolution as a process.
  • When considering the story of life on Earth, it is often viewed as a consequence of natural selection.
  • There is ongoing debate about whether to regard evolution and natural selection as processes or end results of unknown processes.

 Influence of Malthus and Observations:

  • Thomas Malthus's work on population growth likely influenced Darwin.
  • Natural selection is grounded in factual observations, including the limited availability of resources, stable population sizes with variations, and the heritability of traits.
  • Darwin's insight was in recognizing that heritable variations leading to better resource utilization would result in the survival and reproduction of those individuals, ultimately leading to a change in the population's characteristics and the emergence of new forms.