Introduction to Evolution

Evolution is the gradual change in the characteristics of organisms over successive generations, leading to the formation of new species. It explains the origin of biodiversity on Earth and the adaptation of organisms to their environment. For NEET aspirants, evolution is a highly conceptual chapter that connects genetics, ecology, and molecular biology.

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Origin of Life

The origin of life is explained by the theory of chemical evolution, proposed by Oparin and Haldane. According to this theory, life originated from non-living organic molecules present in the primitive Earth atmosphere.

The Miller-Urey experiment provided experimental evidence for chemical evolution by synthesizing amino acids under simulated early Earth conditions. This experiment is a frequently asked NEET topic.

Evidences of Evolution

Evolution is supported by several evidences:

1. Morphological and Anatomical Evidences:
Homologous organs indicate common ancestry, while analogous organs show convergent evolution.

2. Embryological Evidence:
Early embryos of vertebrates show similarities, suggesting a common origin.

3. Paleontological Evidence:
Fossils provide direct evidence of evolution and show transitional forms.

4. Molecular Evidence:
Similarity in DNA, RNA, and protein sequences indicates evolutionary relationships.

Theories of Evolution

1. Lamarckism:
Proposed by Jean Baptiste Lamarck, this theory suggested that characters acquired during an organism’s lifetime are inherited by offspring. Though largely discredited, it introduced the idea of evolution.

2. Darwinism (Theory of Natural Selection):
Proposed by Charles Darwin, this theory states that organisms with favorable variations survive and reproduce more successfully.

Key points of Darwinism include:

• Overproduction

• Struggle for existence

• Survival of the fittest

• Natural selection

Modern Synthetic Theory of Evolution

The modern theory of evolution integrates Darwinism with genetics and is also known as Neo-Darwinism. It explains evolution as a result of genetic variations caused by:

• Mutations

• Genetic recombination

• Gene flow

• Genetic drift

• Natural selection

This theory provides a comprehensive explanation of evolutionary mechanisms.

Hardy-Weinberg Principle

The Hardy-Weinberg principle states that allele frequencies in a population remain constant from generation to generation in the absence of evolutionary forces.

The equation:
p² + 2pq + q² = 1

Factors affecting Hardy-Weinberg equilibrium include:

• Mutation

• Migration

• Genetic drift

• Natural selection

• Recombination

This principle is extremely important for NEET numerical questions.

Adaptive Radiation

Adaptive radiation refers to the evolution of different species from a common ancestor to occupy various ecological niches.

A classic example is Darwin’s finches, where different species evolved different beak shapes according to food habits.

Speciation

Speciation is the process by which new species are formed.

Types of speciation include:

• Allopatric speciation

• Sympatric speciation

• Parapatric speciation

Geographical isolation plays a major role in speciation.

Human Evolution

Human evolution explains the origin and evolution of humans from ape-like ancestors.

Major stages include:

• Dryopithecus

• Ramapithecus

• Australopithecus

• Homo habilis

• Homo erectus

• Homo sapiens

Human evolution is supported by fossil records and molecular studies.

Evolutionary Significance of Natural Selection

Natural selection ensures the survival of organisms best adapted to their environment. It leads to:

• Adaptation

• Speciation

• Evolution of new traits

Examples include antibiotic resistance in bacteria and industrial melanism in moths.

Importance of Evolution for NEET

Evolution is a scoring chapter in NEET because:

• Many direct NCERT-based questions are asked

• Conceptual clarity ensures easy marks

• Numerical questions from Hardy-Weinberg principle are common

Quick Summary Table

Conclusion

Evolution explains the origin of life, diversity of organisms, and their adaptation to the environment. A thorough understanding of evolutionary principles is essential for NEET aspirants. With well-structured notes and conceptual clarity, students can score high in this chapter. StudentBro.in offers concise, NEET-focused Biology notes to support effective preparation.