Darwin Theory of Natural Selection: An Overview and Example

Who Was Charles Darwin?

Charles Darwin was an English naturalist who revolutionized the view of the world in the natural sphere. His greatest contribution, the theory of evolution by natural selection as epitomised in his seminal work entitled "On the Origin of Species" in 1859. He had made very extensive observations and a lot of collecting while travelling in the HMS Beagle, which he used as the basis for his reasoning regarding the evolution of species over time.

Darwin's theory of natural selection has become one of the most important concepts of modern biology. It is a scientific explanation for life's diversity and for how organisms adjust to the environment. He suggested that species change and evolve slowly over time, with survival qualities particular to an environment becoming dominant within a population. He founded a challenge to the prevailing thought of fixed and immutable species. His work has affected scientific understandings in all fields from genetics and ecology to medicine and conservation.

Biological Evolution

Biological evolution is the process by which changes in the characteristics of organisms are exhibited over generations through genetic variation, mutation, and recombination. Evolution helps in the diversity of life on Earth, the adaptation of living organisms to their environment, and the common ancestry followed by the diversification of all species.

Darwin's theory of evolution placed a very strong emphasis on this step-by-step process of such changes. He proposed that small differences passed from generation to generation and are inherited in an organism. It makes the organism survive and reproduce in its environment. This ultimately results in the formation of new species and the amazing diversity of life forms we observe today.

The theory of evolution is supported by evidence of evolution such as fossil record, comparative anatomy, molecular biology, and biogeography. Fossils document the history of extinct organisms, comparative anatomy detects homologous structures, suggesting common ancestry. Molecular biology compares inter-species DNA sequences that exhibit similarities, or differences, in genes between two species. Biogeography studies the impact of the evolutionary process in influencing their dispersal and diversification.

Natural Selection And Genetic Drift

The two principal mechanisms that underlie evolutionary change are natural selection and genetic drift. The process of selection is deterministic, and that of genetic drift is stochastic; the effects of genetic drift differ between populations.

Natural Selection

Natural selection is a process by which certain heritable traits become more common in a population because they provide advantage in survival and reproductive health. The characteristics an organism has affect on its survival and reproduction, and so, organisms with adaptive traits are more likely to survive, reproduce, and hence successfully pass on these to their offspring. This leads to adaptation through time in populations to their environments. The process of natural selection could be directed, stabilizing, or disruptive according to the pressures in the environment at the time and the variation available in a population.

Genetic Drift

Genetic drift is defined as the natural variation of allele frequencies in a population, mostly taking place in small groups. It could be because of random fluctuations, like a natural disaster causing the random death of some portion of the population, or a founder effect in which a small number of individuals establish a new population. Unlike genetic drift, natural selection favours advantageous traits but can lead to a loss of genetic diversity.

Natural selection and genetic drift lead to the evolution of species and their genetic makeup as they adapt to various changes in the environment.

Mechanisms Of Natural Selection

Natural selection works through mechanisms that define what in the population characterizes its favoured traits, which include mechanisms such as survival of the fittest and types of natural selection.

Survival Of The Fittest

Survival of the fittest simply means that those individuals possessing the character that fit with their environment are more likely to survive, therefore reaping fitness in terms of reproduction, and not physical fitness and strength. This principle could explain the reason why beneficial traits are spread throughout the population over time.

Types Of Natural Selection

Natural selection can occur in different patterns depending on how environmental pressures act on a population. These patterns influence which traits become more common or rare over time. Studying the types of natural selection helps us understand how species adapt to changing conditions. It also explains variations within a population and contributes to the process of evolution. Natural selection falls into these classes of categories:

Directional Selection

• One of the extreme phenotypes is favoured while others are selected against.

• Moves the average phenotype in the entire population in one direction.

• Example: The increase in bacterial resistance to antibiotics.

Stabilising Selection

• Intermediate phenotypes are selected for but extremes are selected against.

• Reduces variation, it maintains the status quo of the population.

• Example: Birth weights of humans, such that with a very high or meagre birth weight, the survival rate is lowered.

Disruptive Selection

• The intermediate phenotypes are discarded while two of the extreme phenotypes are selected in an environment.

• Can lead to two opposing phenotypes, and sometimes, to speciation.

• Illustrative example: beaks of finches in an area where many of the seeds are large while others are extremely minute, but there are not a lot of medium.

Conclusion

Darwin's theory of natural selection changed forever our perception of life's history and biodiversity and of processes that govern evolutionary change. His observations and insights established the basis of modern evolutionary biology and resolved the scientific paradigm explaining how and why species adapt and evolve.

The evolution of biology as a field continues with ever-enhancing research. Continuing with recent research in mechanisms of evolution, the genetics of adaptation, and the interaction of ecological complexity continues to enlighten more. Understanding these processes is also very critical for the other fields that depend on biology; an essential technique in medicine, agriculture, and conservation of biodiversity.

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MCQs on Darwin Theory of Natural Selection

Q1. Identify the true statement about the Origin of Species

1. Two species may originate from a single ancestor

2. It is similar to the original population

3. Species cannot be adapted to the environment

4. Species do not possess variation

Correct answer: 1) Two species may originate from a single ancestor.

Explanation:

In Origin of Species, new species are developed from a single ancestor. It is different from the original population. The species become abundant when they adapt to the environment. Species possess variation which is beneficial to them in another environment.

Hence, the correct answer is option 1) Two species may originate from a single ancestor.

Q2. Which one of the following describes features of Darwin's theory of natural selection?

1. Natural selection is a random process that leads to the evolution of new species.

2. Natural selection is a process by which organisms intentionally modify themselves to better adapt to their environment.

3. Natural selection operates through the interaction between variation, heredity, and differential reproductive success.

4. Natural selection occurs only in species with large populations and is not relevant in smaller populations.

Correct answer: 3) Natural selection operates through the interaction between variation, heredity, and differential reproductive success

Explanation:

Option 3 accurately describes one of the salient features of Darwin's theory of natural selection. The theory states that natural selection operates through the interaction between variation, heredity, and differential reproductive success. This means that individuals within a population have variations in their traits, some of which are heritable. If some of these variations give individuals an advantage in surviving and reproducing in their environment, those traits are more likely to be passed on to future generations. Over time, this process can lead to the evolution of new species.

Option 1 is incorrect because natural selection is not a random process but rather a non-random mechanism for evolution.

Option 2 is incorrect because organisms cannot intentionally modify themselves through natural selection.

Option 4 is incorrect because natural selection can occur in populations of any size Over time, this process can lead to the evolution of new species.

Hence, the correct answer is option 3) Natural selection operates through the interaction between variation, heredity, and differential reproductive success.

Q3. Which of the following options perfectly describes the concept of adaptation in Darwin's theory of natural selection?

1. Adaptation deals with the idea that organisms develop certain traits based on their needs and desires in a given environment

2. Adaptation deals with the idea that organisms change their behaviour and habits to better suit their environment over time.

3. Adaptation refers to the process by which organisms inherit traits that allow them to better survive and reproduce in a given environment, ultimately leading to the evolution of species.

4. Adaptation refers to the idea that organisms can choose to modify their genetic makeup to better suit their environment over time.

Correct answer: 3) Adaptation refers to the process by which organisms inherit traits that allow them to better survive and reproduce in a given environment, ultimately leading to the evolution of species.

Explanation: Adaptation refers to the process by which organisms inherit traits that allow them to better survive and reproduce in a given environment, ultimately leading to the evolution of species.

Incorrect Option 1: Adaptation is not driven by an organism's needs and desires, but rather by natural selection acting on genetic variation.

Incorrect Option 2: While organisms may change their behaviour and habits in response to their environment, adaptation in Darwin's theory refers specifically to genetic changes that occur over many generations.

Incorrect Option 4: Organisms cannot choose to modify their genetic makeup. Adaptation occurs through the process of natural selection acting on genetic variation, with advantageous traits becoming more common in a population over time.

Hence, the correct answer is option 3) Adaptation refers to the process by which organisms inherit traits that allow them to better survive and reproduce in a given environment, ultimately leading to the evolution of species.

Also Read:

• MCQs on Darwin Theory of Natural Selection

• Mutation Theory

• Molecular Basis of Inheritance