Natural Selection: Darwin’s Theory and Predominance of the Traits

Introduction:

Evolution refers to the continuous and gradual process of change that occurs over a period of time. During evolution, characteristics of living organisms undergo changes and lead to the formation of new species. Scientists have predicted that the Earth is around 4.6 billion years old. Around 3 billion years ago, the first life on Earth appeared. It was a tiny unicellular prokaryote. Around 2 billion years ago, these tiny prokaryotic cells evolved into larger cells that contain a nucleus. Later on, smaller prokaryotic cells resided in larger cells and got transformed into organelles over the course of evolution (Example: Mitochondria). Around one billion years ago, multicellular organisms evolved. It is also anticipated that various animals and plants have been evolving for the past 500 million years.

History of Evolutionary Thoughts:

It is anticipated that the emergence of thoughts about the process of evolution of species began during the fourth century BC. Several theories of evolution have been proposed by various scientists. Most importantly, Greek philosophers Plato and Aristotle provided their views on the evolution of species on Earth. They believed that each organism on Earth had been created in its present form and remained unchanged. Various evolutionary theories have been proposed by different scientists at different time periods. French biologist, Jean Baptiste Lamarck (1744-1829), has proposed that living things could transfer the acquired traits to their offspring. Later on, this idea was opposed by biologists.

Darwin’s Theory of Evolution by Natural Selection:

Darwinism is the most widely accepted theory of biological evolution. It was proposed by Charles Darwin (1809 – 1882), the British naturalist. He coined the phrase “descent with modification.” Darwinism states that every species has descended from pre-existing species by reproduction. It also states that species undergo change over time.

Process of Natural Selection

Natural selection refers to the process that causes populations to change over time. Darwin explained the mechanism of evolution through natural selection. According to Darwin, the evolution of living organisms takes place in such a way that over a period of time, populations adapt themselves to their living environment. He also states that natural selection is totally dependent on a specific environment.

Concepts of Darwinism:

The following are the important concepts of Darwinism.

1. Overproduction
2. Struggle for survival
3. Variations
4. Natural selection
5. Speciation

Over Production:

Living organisms produce more offspring. This leads to overcrowding.

Example: An oyster has the capability to produce 60 – 80 million eggs per year

The Struggle for Survival:

When more individuals are reproduced by living organisms, there is an increase in the need for food, space, and other resources required for the survival of these organisms. Therefore, these organisms compete with each other for food and other resources for their survival. This is known as the struggle for survival. This competition could occur between members of the same species (intraspecific struggle) or different species (interspecific struggle).

Variations:

Differences in characteristics between individuals of a population are referred to as variations. These variations may occur due to genetic or chromosomal changes. These variations may produce useful, neutral, or harmful effects. During evolution, small continuous variations may be transferred to the next generation, which in turn could lead to the formation of new species.

Natural Selection:

Living organisms with variations that are favorable for their survival in a particular environment continue to live. Whereas other organisms which do not have variations do not survive. This phenomenon of nature is referred to as “survival of the fittest”. Nature decides the fitness/unfitness of an organism. This process of selecting living organisms with favorable variations is known as natural selection.

Speciation:

Through the process of natural selection, only those organisms with favorable variations continue to live in a particular environment. These favorable variations are transferred from one generation to the next generation. This procedure leads to the formation of new species.

The predominance of Traits:

Trait refers to the specific characteristics of an individual. Environmental and genetic factors play an important role in determining the trait.

Example: Skin color, eye color, height, etc.

According to Darwin, the genetic traits of a species undergo changes over a period of time. Some traits get inherited from parents to their offspring. Environmental factors play an important role in determining the trait of an organism. Living organisms with variations that are favorable for their survival in a particular environment continue to live. Whereas other organisms which do not have variations do not survive. These favorable variations are transferred from one generation to the next generation. This method leads to the formation of new species. Therefore, certain traits are predominant in a living environment.

Examples of Predominant Traits:

The following are some of the examples of traits that have evolved to be dominant in a living environment.

Peppered Moth and Industrial Melanism:

The phenomenon of industrial melanism was studied by Henry Bernard Davis Kettlewell (1907 – 1979), a British scientist. Biologists consider industrial melanism as an example of natural selection. Industrial pollutants, such as sulfur dioxide gas and dark soot deposits in the environment, result in an evolutionary change in several animal species. It has been observed that moths that live in these industrial areas have developed melanin pigments. These pigments help them to match their body to surroundings that are soot-covered. Therefore, these moths blend with their environment and hide from predators.

Other examples:

• DDT–resistant mosquitoes
• Antibiotic-resistant bacterial species
• Humans with sickle cell anemia are resistant to malaria