Evolution by Natural Selection

Introduction

Understanding microevolution is integral as it illustrates the process by which minor changes accumulate, leading to new species' formation through macroevolution. This understanding is essential in explaining how species evolve, forming the foundation of biodiversity.

Key Terms Definitions

Important Definitions

Historical Development of Evolutionary Theory

Contributions and Timeline

• Charles Darwin and Alfred Russel Wallace made significant contributions to the theory of natural selection.
  • Darwin's "On the Origin of Species," published in 1859, is foundational to our understanding.
• Key Milestones for the Theory:
  • 1831-1836: Darwin's expedition on the HMS Beagle.
  • 1858: Wallace reached similar conclusions independently, leading to a joint presentation.
• Modern Understanding:
  • Further developed through genetics and fossil research.

Core Principles of Natural Selection

• Variation: Genetic differences existing within a population.
• Inheritance: Traits passed from parents to offspring.
• High Population Growth Rate: Many offspring, but only a few survive.
• Differential Survival and Reproduction: Individuals with advantageous traits reproduce more effectively.

Mechanisms Facilitating Microevolution

Mutation and Gene Flow

• Mutation: Spontaneous alterations in DNA introducing new genetic material.
• Gene Flow: The movement and introduction of alleles via migration.
• These processes are fundamental in increasing genetic diversity, which is crucial for evolutionary adaptability.

Genetic Drift

• Definition: Random fluctuations in allele frequencies.
  • Significantly influence smaller populations through mechanisms like the Bottleneck and Founder effects.
• Examples:
  • Bottleneck: The reduced genetic diversity in Northern elephant seals.
  • Founder: Common traits in the Amish community.

Speciation as an Evolutionary Output

Overview

• Speciation is essential to biodiversity: The means by which evolutionary processes yield new species.

Mechanisms of Speciation

• Allopatric Speciation: Occurs due to geographic separation (e.g., Galápagos finches).
• Sympatric Speciation: Arises without geographic barriers through behavioural and temporal isolation or niche differentiation.

Reproductive Isolation

Prezygotic and Postzygotic Barriers

• Prezygotic: Prevents fertilisation through mechanisms like habitat isolation.
• Postzygotic: Affects hybrid survival and fertility.

Integration of Evolutionary Theories

Punctuated Equilibrium vs. Gradualism

• Punctuated Equilibrium: Stability interrupted by sudden changes:
  • Rapid shifts observed in marine invertebrates.
• Gradualism: Slow and continuous evolutionary change:
  • Fossil records, such as those of horse evolution, show gradual transformations.

Understanding Through Fossils

• Fossil records, including transitional fossils, provide connections between different evolutionary stages.
• Recognise significant events such as the Cambrian Explosion.

Biodiversity: An Evolutionary Result

Levels of Biodiversity

• Genetic Diversity: Variation in DNA within a species (e.g., varied traits in dog breeds).
• Species Diversity: Range of species, evident in ecosystems like the Amazon.
• Ecosystem Diversity: Variety of ecosystems within the biosphere, including forests, oceans, and deserts.

Key Highlights

• Visual aids such as diagrams of Darwin's finches assist in comprehending evolutionary processes.
• Evaluate how environmental shifts influence allele frequencies and drive microevolution.