Unit 3: Product of Evolution

1. Micro-evolution and Macro-evolution

Evolution occurs at different scales, ranging from small-scale changes in allele frequencies to the large-scale patterns of life's history.

Micro-evolution

Micro-evolution refers to small-scale changes in allele frequencies within a single population over a few generations. It is driven by mutation, natural selection, gene flow, and genetic drift (e.g., development of antibiotic resistance in bacteria).

Macro-evolution

Macro-evolution refers to large-scale evolutionary changes that take place over long periods of geological time, resulting in the formation of new species and higher taxonomic groups (genera, families, etc.). It deals with the origin of new designs and broad trends in evolution.

2. Speciation: Concept and Types

Speciation is the evolutionary process by which populations evolve to become distinct species.

Biological Species Concept

"Species are groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups." — Ernst Mayr.

Types of Speciation

• Allopatric Speciation: Occurs when a population is divided by a geographic barrier (mountains, rivers, etc.). The isolated populations evolve independently until they can no longer interbreed.
• Sympatric Speciation: Occurs without geographic isolation. It happens within the same territory due to genetic (polyploidy), behavioral, or ecological differences.
• Parapatric Speciation: Occurs when populations are in a continuous area but mate non-randomly; individuals are more likely to mate with their geographic neighbors.

3. Isolating Mechanisms

Reproductive isolation is essential for speciation. These mechanisms prevent different species from producing viable, fertile offspring.

Pre-zygotic Barriers (Prevent fertilization)

• Habitat Isolation: Different environments.
• Temporal Isolation: Mating at different times/seasons.
• Behavioral Isolation: Different courtship rituals.
• Mechanical Isolation: Structural differences in genitalia.

Post-zygotic Barriers (After fertilization)

• Hybrid Inviability: Hybrid zygotes fail to develop.
• Hybrid Sterility: Hybrids are healthy but cannot reproduce (e.g., Mules).
• Hybrid Breakdown: First-generation hybrids are fertile, but their offspring are feeble or sterile.

4. Adaptive Radiation and Adaptation

Adaptive Radiation

The process in which a single ancestral species evolves into a variety of forms adapted to different environments or niches. A classic example is Darwin’s Finches on the Galápagos Islands.

Adaptation

Adaptation is any heritable trait that increases an organism's ability to survive and reproduce in its environment. Adaptations can be:

• Morphological: Physical traits (e.g., camouflage, webbed feet).
• Physiological: Internal processes (e.g., concentrated urine in desert animals).
• Behavioral: Actions (e.g., bird migration).

5. Exam Focus Enhancements