Evolution

Notes

Introduction

Evolution is the gradual change in living organisms over millions of years, resulting in the formation of new species.

Definition

Evolution is the process by which organisms change genetically over generations due to variations and natural selection.

Origin of Life

Theory of Special Creation

Life was created by God.

Based on religious beliefs.

Not accepted scientifically.

Theory of Spontaneous Generation

Life originated from non-living matter.

Proposed by Aristotle.

Disproved by Louis Pasteur.

Theory of Biogenesis

Life arises only from pre-existing life.

Supported by Pasteur's Swan-neck Flask Experiment.

Chemical Evolution Theory (Most Accepted)

Proposed by:

A.I. Oparin

J.B.S. Haldane

Main Points:

Primitive Earth had a reducing atmosphere.

Simple inorganic molecules combined to form organic molecules.

Organic molecules formed complex compounds leading to the first living cells.

Miller-Urey Experiment (1953)

Scientists:

Stanley Miller

Harold Urey

Experiment:

Simulated primitive Earth's atmosphere.

Passed electric sparks through methane (CH₄), ammonia (NH₃), hydrogen (H₂), and water vapor (H₂O).

Observation:

Amino acids were formed.

Conclusion:

Organic molecules can be synthesized under primitive Earth conditions.

Evolution of Life Forms

Timeline:

Earth formed: 4.5 billion years ago

First life: 3.5 billion years ago

First eukaryotes: 2 billion years ago

Multicellular organisms: 1 billion years ago

Humans: ~2 lakh (200,000) years ago

Evidences for Evolution

1. Morphological Evidence

Similarity in external structures.

Example:

Wings of birds and bats.

2. Anatomical Evidence

Similarity in internal structure.

Homologous Organs

Same origin

Different functions

Examples:

Human hand

Whale flipper

Bat wing

Horse forelimb

Significance: Indicates divergent evolution.

Analogous Organs

Different origin

Same function

Examples:

Wings of butterfly and bird.

Significance: Indicates convergent evolution.

3. Vestigial Organs

Structures with little or no function.

Examples:

Vermiform appendix

Wisdom teeth

Coccyx

Ear muscles

4. Embryological Evidence

Proposed by:

Ernst Haeckel

Embryos of vertebrates show similarities in early stages.

5. Palaeontological Evidence

Study of fossils.

Father of Paleontology:

Georges Cuvier

Importance:

Provides direct evidence of evolution.

Helps determine evolutionary history.

Fossils

Definition:

Preserved remains or…