MEVE 017: Unit 12 - Theories of Evolution

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 UNIT 12: THEORIES OF EVOLUTION

12.0 Introduction

This unit explores the fascinating concept of evolution—how living organisms have changed over time. It helps us understand where different species come from, how they adapt, and how new species develop. It also explains the major scientific theories proposed by Charles Darwin, Jean-Baptiste Lamarck, and others to describe how evolution takes place.

12.1 Objectives

By the end of this unit, you will be able to:

  • Understand how species originated and evolved
  • Learn about Darwin’s Theory of Natural Selection
  • Understand Lamarck’s theory of acquired traits
  • Explore the idea of “Survival of the Fittest” and its meaning
  • Learn about modern research supporting evolutionary theories

12.2 The Origin of Species

12.2.1 The Concept of Species

A species is a group of similar organisms that can reproduce and produce fertile offspring. All human beings, for example, belong to the same species. Differences in species develop over time due to changes in their environment or behavior.

12.2.2 The Origin of Species

The idea of the origin of species was famously explained by Charles Darwin in his book “On the Origin of Species” (1859). He suggested that species evolve slowly over generations through natural processes rather than being created all at once.

12.3 The Concept of Darwin

12.3.1 Darwin and His Voyage of the Beagle

Charles Darwin traveled around the world on a ship called the HMS Beagle. During this journey, he observed different animals and plants, especially on the Galápagos Islands. These observations helped him develop his ideas about evolution.

12.3.2 Evolution by Natural Selection

Darwin’s main idea was that evolution happens through natural selection. This means that in nature, only the organisms best suited to their environment survive and pass on their traits to the next generation. Over time, this leads to changes in the species.

12.3.3 Darwin’s Inventiveness

Darwin used simple observations, scientific reasoning, and examples from nature to explain how species change. His theory was revolutionary because it challenged the older belief that all life was fixed and unchanging.

12.3.4 Evidence for the Theory of Evolution

Darwin’s theory is supported by many kinds of evidence:

  • Fossils showing how animals changed over time
  • Similar bone structures in different species (comparative anatomy)
  • Similar embryos of different animals during early development
  • DNA and genetic similarities

12.3.5 Examples of Natural Selection in Real Time

Even today, scientists see natural selection at work. For example, bacteria that become resistant to antibiotics or insects that become immune to pesticides are real-time examples of evolution.

12.3.6 Recent Research on Evolution and Natural Selection

Modern science, including genetics and molecular biology, continues to support Darwin’s ideas. New research shows how DNA mutations and genetic variation help in evolution.

12.4 Lamarckism

Jean-Baptiste Lamarck was another scientist who proposed a theory of evolution before Darwin.

12.4.1 Theory of Inheritance of Acquired Characters

Lamarck believed that organisms could pass on traits they developed during their lifetime to their offspring. For example, he said that giraffes got long necks because they stretched to reach tall trees, and this trait was passed on.

12.4.2 Evidences in Favour of Lamarckism

Some scientists found Lamarck’s theory useful in explaining certain adaptations. The idea that environment influences traits has some truth in it, though not in the exact way Lamarck imagined.

12.4.3 Criticism of Lamarckism

Lamarck’s theory is mostly rejected today because modern genetics shows that traits developed during life (like muscles from exercise) are not inherited. Evolution happens through genetic changes, not physical effort.

12.5 Relevance of Survival of the Fittest and the Struggle for Existence

The phrase “Survival of the Fittest” means that only those organisms that can adapt well to their environment survive. This leads to a struggle for existence, where living beings compete for food, shelter, and mates. This idea is still very relevant today in understanding how nature works.

12.6 Let Us Sum Up

Evolution is a natural process through which life has changed and developed over time. Darwin’s theory of natural selection is the most widely accepted explanation of evolution. Lamarck’s theory, though important historically, has limited scientific support today. The concepts of struggle for existence and survival of the fittest help explain how only the best-suited species thrive. New scientific research continues to prove that evolution is a real and ongoing process in nature.

 

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