Theories of Origin of Life | Zoology Optional Notes for UPSC PDF Download

Introduction

The origin of life involves the emergence of heritable and evolvable self-reproduction. It's a complex and often controversial subject, with two opposing scientific theories—intelligent design and creationism. The big bang theory of the Universe has influenced ideas about biological evolution, suggesting that complex life forms, including humans, developed over time from simple bacterial-like cells through self-organization akin to the evolution of the Universe.

Theories on the Origin of Life

Special Creation

• Life formation on Earth attributed to supernatural or divine forces.
• Hindu Concept: Lord Brahma created the entire world, including plants, oceans, rivers, humans, and animals.
• Christian & Islam Concept: God created the universe, plants, oceans, rivers, and all living organisms in six days.

Extraterrestrial Origin (Panspermia)

• Proposed by Richer in 1865, this theory suggests that life's "seeds" exist throughout the Universe and may have originated elsewhere.
• Variations: Litho panspermia, Ballistic panspermia, Directed Panspermia.
• Panspermia doesn't explain evolution or pinpoint life's origin in the Universe.

Spontaneous Origin

• Life evolving from non-living matter under primitive Earth conditions.
• Francesco Redi and Louis Pasteur's experiments disprove spontaneous generation.
• Spontaneous generation is the incorrect hypothesis that nonliving things can produce life.

Theory of Biochemical Evolution

• Presented by A. I. Oparin and J. B. S. Haldane in the 1920s.
• Life's origin through organic chemical reactions leading to complex biochemical structures.

Chemical Evolution

• Formation of simple inorganic compounds in the primitive Earth's atmosphere.
• Formation of simple organic molecules through interactions and solar radiation.
• Polymerization in oceanic water leading to complex organic molecules.

Biological Evolution

• Initiation from the ocean containing organic compounds.
• Formation of coacervates, primary living organisms, and autotrophs.
• Cognogeny: Adaptation to aerobic respiration, evolution of various organisms.

Simple Beginnings

• Proposes life began with small, simple molecules interacting in cycles of reactions.

RNA World

• RNA's self-replicating properties and its role in the origin of life.
• RNA World theory suggests life began with a simple, self-replicating RNA molecule.

Chilly Start

• Ice-covered oceans 3 billion years ago protected organic compounds from UV light and cosmic impacts.
• Cold temperatures facilitated the survival and interaction of early organic molecules.

Deep-Sea Vents

• Life's possible origin within hydrothermal vents in the deep ocean.
• Concentration of molecules and mineral catalysts within vents may have facilitated life's emergence.

Community Clay

• Hydrocarbons meeting on clay surfaces, concentrating organic compounds.
• Clay minerals organizing organic molecules into patterns, playing a key role in chemical evolution.

Electric Spark

• Lightning as a potential catalyst for the beginning of life.
• Electric sparks generating amino acids and sugars from atmospheric elements.
• Miller Urey experiment supports the idea that lightning contributed to life's building blocks.

In conclusion, the origin of life is a multifaceted topic with various theories providing different perspectives on how life began on Earth.