JAMB Biology Note- Evolution: Theories of Evolution

Table of Contents

• 1. Lamarck’s Theory of Evolution
• 2. Darwin’s Theory of Evolution
• 3. Organic Theory of Evolution
• Objectives
• Summary:

1. Lamarck’s Theory of Evolution

Overview: Lamarck’s theory, known as the “Theory of Inheritance of Acquired Characteristics,” proposed that organisms evolve due to the influence of their environment. He suggested that:

• Use and disuse: Traits or organs used more frequently would become more developed, while those used less would diminish over generations.
• Inheritance of acquired characteristics: Traits that were acquired by an organism during its lifetime (such as stronger muscles from regular use) could be passed on to the offspring.

Example:

• Lamarck suggested that giraffes originally had short necks, but over time, they had to stretch their necks to reach higher leaves. The longer necks, according to Lamarck, were then passed on to offspring, leading to the modern giraffe with long necks.

Criticisms:

• Lamarck’s theory was criticized because the inheritance of acquired traits is not supported by modern genetics. Traits acquired during an organism’s life (e.g., muscle development) do not alter the genetic code passed on to the offspring.

2. Darwin’s Theory of Evolution

Overview: Charles Darwin’s theory of evolution is often referred to as natural selection. According to Darwin:

• Variation: Within any population, individuals vary in traits, and some variations are more favorable than others.
• Survival of the fittest: Those individuals with favorable traits are more likely to survive and reproduce. Over generations, these beneficial traits become more common in the population.
• Descent with modification: All organisms share a common ancestor and evolve over time, with small changes accumulating across generations.

Key Concepts in Darwin’s Theory:

• Adaptation: Organisms develop traits that increase their chances of survival and reproduction in their environment.
• Natural Selection: The environment “selects” for individuals with advantageous traits, which are passed down to the next generation.
• Speciation: Over time, the accumulation of differences in isolated populations can lead to the formation of new species.

Evidence for Darwin’s Theory:

• Fossil Record: Fossils show a gradual change in species over time.
• Comparative Anatomy: Similarities in the structure of different species (homologous structures) suggest a common ancestry.
• Embryology: Similarities in the early development of different species indicate common origins.
• Biogeography: The distribution of species around the world supports the idea of adaptation to different environments.

3. Organic Theory of Evolution

Overview: The organic theory of evolution explains that evolution is the result of adaptive changes in organisms over long periods of time, leading to the diversity of life forms we see today. It emphasizes the gradual accumulation of small changes in organisms over generations.

Key Concepts:

• Adaptive Changes: Organisms evolve in response to environmental pressures, leading to the development of new forms, structures, and functions that increase their chances of survival.
• Diversity: Over time, these adaptive changes result in a wide variety of species with different characteristics and abilities.
• Common Ancestor: All living organisms are thought to have originated from a common ancestor, and through the process of evolution, they have diversified into the variety of species observed today.

Examples:

• The development of antibiotic resistance in bacteria is a modern example of organic evolution.
• The evolution of the peppered moths in England, where moths changed color due to industrial pollution, is a classic example of natural selection.

Objectives

By the end of this lesson, students should be able to:

1. Relate organic evolution: Organic evolution is the total sum of adaptive changes that have occurred over time, leading to the diversity of forms, structures, and functions among organisms.
2. Examine contributions of Lamarck and Darwin:
   • Lamarck: Contributed the idea of acquired characteristics and the influence of the environment on evolution.
   • Darwin: Introduced the concept of natural selection and descent with modification, which is foundational to modern evolutionary biology.
3. Know evidences in support of organic evolution:
   • Fossils show the gradual transition between species.
   • Comparative anatomy reveals similarities and differences between species.
   • Embryology demonstrates common developmental pathways.
   • Biogeography provides evidence of adaptation to diverse environments.
   • Genetic evidence supports the idea of common ancestry and variation within species.

Summary:

• Lamarck and Darwin both contributed to our understanding of evolution, but Darwin’s theory of natural selection is more widely accepted today due to the advent of genetic and molecular evidence.
• Organic evolution explains the long-term process of change in organisms, resulting in the diversity of life forms observed today.
• Evidence supporting organic evolution comes from various scientific fields, including fossils, anatomy, embryology, and biogeography.