Evolution Theory Essentials

Introduction to Microevolution and Speciation

Overview

• Objective:
  • What processes underlie the formation of new species?
  • How does microevolution support these processes?
  • Connect these concepts to the Theory of Evolution.

Definitions

• Microevolution: Small-scale evolutionary changes within a species.

  • Key Aspect: Changes in allele frequencies.
  • Example: Different dog breeds demonstrate variations in allele frequency.

• Speciation: Process by which a species splits into new, distinct species.

  infoNote

  Examples of speciation include domestic animals adapting to various environments.

Significance

• Genetic Variation & Allele Frequencies:

  • Essential for linking microevolution to speciation.

• Genetic Diversity:

  chatImportant

  Crucial for adaptation and long-term survival, illustrated in evolutionary success stories.

Mechanisms of Microevolution

Mutations

• Mutations: Changes in DNA sequences that significantly contribute to genetic variation.
  • Point Mutations: Single nucleotide alterations.
    • Example: Sickle cell anaemia results from a point mutation in the haemoglobin gene.
  • Chromosomal Rearrangements: Structural changes such as inversions and translocations.
    • Example: Inversions reverse segments of chromosomes; translocations move segments to different locations.
• Sources:
  • Spontaneous: Naturally occurring, for example, during DNA replication.
  • Induced: Caused by external factors like radiation and chemicals.
• Conclusion: Mutations augment genetic diversity, enhancing adaptability and survival in dynamic environments.

Gene Flow

• Gene Flow: The transfer of alleles between populations, enhancing genetic diversity.
  • Mechanism:
    • Migration: Immigration and emigration facilitate gene flow, introducing new alleles.
  • Real-world Example: Historical human migrations.
• Importance: Gene flow is vital for maintaining genetic diversity within populations.

Genetic Drift

• Genetic Drift: Random fluctuations in allele frequencies, predominantly affecting smaller populations.
  • Key Events:
    • Bottleneck Effect: Dramatic population reductions causing significant genetic drift.
    • Founder Effect: Occurs when a small group establishes a new population.
  • Comparison with Natural Selection:
    • Genetic Drift: Random, independent of allele advantages.
    • Natural Selection: Alleles selected based on advantageous traits.
• Conclusion: Genetic drift can alter genetic diversity without advantage consideration, significantly affecting isolated populations.

Interaction Between Mechanisms

• Summary:
  • Mutations introduce new variants essential for genetic diversity.
  • Gene Flow distributes these genetic changes across populations.
  • Genetic Drift impacts allele frequencies, especially in smaller and isolated populations.

Introduction to Natural Selection in Microevolution

• Natural selection is fundamental to evolution, promoting traits that enhance survival and affecting the prevalence of traits in populations.
• Microevolution involves small-scale changes, such as shifts in allele frequency, driven by natural selection favouring advantageous traits.

Principles of Natural Selection

Variation

• Trait variation within a population provides crucial genetic diversity.
• Galapagos finches exemplify this with varied beak sizes adapting to particular food sources.

Inheritance

• Traits must be heritable for natural selection to occur.

Differential Survival

• Certain traits provide survival advantages, increasing survival likelihood.

Reproduction

• Organisms with beneficial traits have greater reproductive success.

Case Study: Peppered Moths

• Historical Impact: Industrialisation highlighted predation's influence on peppered moths, where darker moths thrived post-industrialisation.

Case Study: Galapagos Finches

• Beak size variation corresponds to different food sources, demonstrating adaptation to environmental pressures.

Introduction to Speciation

Speciation: The process by which new species evolve from existing ones through population division.

Allopatric Speciation

Definition & Process

• Allopatric Speciation: New species form due to geographic isolation.
  • Key Idea: Geographic barriers like mountains or rivers separate populations.
  • Process Steps:
    • Geographic isolation occurs.
    • Genetic divergence follows due to mutation and natural selection.
    • Reproductive isolation solidifies species divergence.

Examples:

• Darwin's Finches:
  • Location: Galápagos Islands.
  • Adaptations: Beak differences enable survival in varied ecological niches.
• Grand Canyon Squirrels:
  • Evolved into distinct species due to the Grand Canyon's physical barrier.

Sympatric Speciation

Definition & Mechanisms

• Sympatric Speciation: Species evolve without geographic separation.
  • Mechanisms:
    • Polyploidy: Rapid genetic changes commonly seen in plants.
    • Behavioural Shifts: Changes in mating patterns.

Examples:

• Cichlid Fish:
  • Location: African Lakes.

Reproductive Isolation Mechanisms

Isolation Types:

• Prezygotic:
  • Temporal Isolation: Mating occurs at different times.
  • Habitat Isolation: Different living spaces prevent mating.
  • Behavioural Isolation: Unique courtship behaviours.
• Postzygotic:
  • Viability Issues: Affect hybrid survival.
  • Hybrid Sterility: Hybrids like ligers or zonkeys.

Overview and Importance of Genetic Variation

• Genetic Variation : Differences in genetic makeup within a species, vital for evolution.
• Essential For: Generates the raw material for evolutionary processes.

Mechanisms Contributing to Genetic Variation

• Mutations:

  • Spontaneous changes in DNA.

• Recombination:

  • Occurs during meiosis.

• Gene Flow:

  • Exchange of genetic material through population migration.
  • Key Role: Facilitates genetic diversity across populations.

Impact on Microevolution

• Genetic variation underpins processes like natural selection, genetic drift, and gene flow.
• Facilitates adaptation to changing environments.
  • Example: Development of antibiotic resistance in bacteria.

Visual Aids and Diagrams

• Diagram:
  • 

Introduction

• Environmental Factors: Essential drivers of evolutionary processes, altering allele frequencies: Relative frequency of an allele in a gene pool, and selection pressures: Environmental forces favouring certain traits.
  • Example: The peppered moth illustrates how pollution-driven changes favoured darker moths.

Habitat Changes and Their Impact

• Defined Impacts: Habitat destruction, fragmentation, and alteration as primary factors.
• Habitat Fragmentation:
  • Definition: The separation of ecosystems into smaller, isolated areas.
  • Consequences: Increases isolation, potentially leading to speciation.
  infoNote

  Habitat Fragmentation: A breakdown in habitat continuity.

• Urbanisation: Leads to new ecological niches.

Competition as a Factor

• Niche Partitioning:
  • Definition: Division of resources and distinct environmental roles.

Climate Change

• Physiological and Behavioural Changes:
  • Example: Polar bears adjusting hunting methods and fasting periods.

Case Studies on Environmental Change

• Industrial Melanism in Moths:
  • Narrative: Pollution during the industrial revolution.

Convergent and Divergent Evolution

• Convergent Evolution:
  • Example: Sharks and dolphins developing fin-like structures.
• Divergent Evolution:
  • Example: Darwin's finches.

Rapid Evolutionary Changes

• Stages of Evolutionary Change:
  infoNote

  Example: Antibiotic resistance in bacteria highlights rapid evolutionary change phases.

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Historical Overview of Evolutionary Theory

Origins

• Charles Darwin: Known for promoting the theory of natural selection. He observed Galápagos finches with various beak shapes adapted to local food sources.

• Alfred Russel Wallace: Similar findings were made by Wallace during his explorations in the Malay Archipelago.

• Modern Synthesis: Integration of genetics with evolutionary concepts, providing a cohesive framework for understanding.

  • Key Figure: Theodosius Dobzhansky's works cemented genetic diversity's role in evolution.

Key Mechanisms of Evolution

• Natural Selection: Variation, advantageous traits, and reproductive success.

• Genetic Drift: Critical in small populations where random events significantly influence genetic make-up.

Advancements in Genetic Understanding

• DNA and Genetics: DNA serves as an instruction guide for organism development.

• Epigenetics: Describes how chemical "tags" affect gene activity.

Visual Summary and Practical Applications

Practice Questions with Solutions

1. What is microevolution?

   • Solution: Microevolution refers to small-scale evolutionary changes within a species, specifically changes in allele frequencies in a population over relatively short periods of time.

2. Which of the following illustrates sympatric speciation?

   • Solution: Sympatric speciation occurs when new species evolve from a single ancestral species while inhabiting the same geographic region. An example would be cichlid fish in crater lakes that have evolved into different species despite living in the same lake, due to adaptations to different ecological niches.

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Understanding Key Concepts

• Genetic Drift: Genetic drift causes random changes in allele frequencies, particularly in small populations.

• Natural Selection: Natural selection involves adaptation, where organisms better suited to their environment tend to survive and reproduce more.

Analysing Questions

• Read each question carefully.