Variation and Selection

16.1 What is Variation?

• Definition: Differences between individuals in a population.
• Types:
  1. Genetic Variation: Differences in genes or alleles.
  2. Environmental Variation: Differences due to environmental factors.

16.2 Genetic Variation

• Causes:
  1. Mutations: Changes in DNA sequence.
  2. Sexual Reproduction: Genetic mixing during fertilization.
  3. Crossing Over: Exchange of genetic material during meiosis.

16.3 Natural Selection

• Definition: Survival of organisms with advantageous traits.
• Steps:
  1. Variation exists.
  2. Advantageous traits increase survival.
  3. More offspring inherit these traits.

16.4 Adaptation

• Structural: Physical features that help organisms survive (e.g., camouflaged fur).
• Behavioral: Actions that help survival (e.g., migration).
• Physiological: Internal processes that help survival (e.g., water conservation in desert plants).

16.5 Artificial Selection

• Definition: Human-driven breeding for specific traits.
• Examples: Dog breeding, crop improvement.

16.6 Speciation

• Definition: Formation of new species due to genetic divergence.
• Process: Isolation → Genetic divergence → Reproductive isolation.

16.7 Evidence for Evolution

• Fossils, Comparative Anatomy, Embryology, and Molecular Evidence support evolution.