Evolution and Natural Selection

Objectives

  • Describe adaptations of organisms on the Galapagos Islands.

  • Explain the mechanisms of evolution.

Overview of Evolution

  • Evolution: Process where modern organisms descend from ancient organisms; involves inherited change over time.

  • A scientific theory is well-supported and tested, not merely a belief.

Key Historical Figures and Concepts

  • Jean-Baptiste Lamarck (1809): Proposed the idea of inheritance of acquired characteristics; stated organisms strive for complexity, and modified traits can be passed on.

  • Charles Darwin (1831): Notable for his observations on the Galapagos Islands, where he noted variations among tortoises and finches.

  • Charles Lyell: Influenced Darwin with the idea of uniformitarianism from his work "Principles of Geology".

  • James Hutton: Suggested geological processes occur gradually over millions of years, proposing an ancient Earth.

Darwin's Theory of Evolution

  • Introduced in "On the Origin of Species" (1859), proposing natural selection as a mechanism for evolution.

  • Descent with Modification: Suggests all species share a common ancestor but diverge over time due to adaptations.

Natural Selection Process

  1. Overproduction: More offspring are produced than the environment can support.

  2. Variation: Individuals in a population exhibit differences; some variations are advantageous.

  3. Struggle for Survival: Competition for resources leads to a struggle for existence.

  4. Survival of the Fittest: Those with advantageous traits reproduce more successfully.

Evidence Supporting Evolution

  1. Fossil Record: Comparison of fossils shows changes in organisms over time.

  2. Geographical Distribution: Similar species in different areas suggest common ancestry.

  3. Homologous Structures: Similar structures in different species with different functions.

  4. Vestigial Organs: Nonfunctional remnants from ancestors, such as the human appendix.

  5. Molecular Biology: Similar DNA across species indicates common genetic heritage.

Genetic Variation and Mechanisms of Evolution

  • Gene Pool: Total genetic information available in a population.

  • Sources of Variation: Mutations and gene shuffling (meiosis).

  • Genetic Drift: Random changes in allele frequencies affecting small populations (Founder Effect and Bottleneck Effect).

Hardy-Weinberg Equilibrium

Conditions for stability include:

  • Random mating, large population size, no migration, no mutations, no natural selection.

Types of Selection

  1. Directional Selection: Favors one extreme phenotype.

  2. Stabilizing Selection: Favors the average phenotype.

  3. Disruptive Selection: Favors extreme phenotypes, leading to two distinct groups.

Reproductive Isolation and Speciation

  • Geographic Isolation: Populations separated by physical barriers.

  • Behavioral Isolation: Different mating rituals prevent interbreeding.

  • Temporal Isolation: Different mating seasons or times.

Mechanisms of Evolution Beyond Natural Selection

  • Divergent Evolution: Isolated populations evolving differently.

  • Convergent Evolution: Different species adapting similarly to environmental challenges.

  • Coevolution: Species evolving in response to interactions with others.

  • Adaptive Radiation: Rapid evolution of diverse species from a common ancestor.

  • Punctuated Equilibrium: Evolution occurs in rapid bursts followed by long periods of stability.