Evolution and Natural Selection (copy)

Charles Darwin and Evolution

• Sections 16.1 and 16.2 focused on Charles Darwin.

• The aim was to provide a historical context and the evidence he collected to support the existence of evolution.

• By section 16.3, Darwin felt confident enough to present his theory of evolution.

Evolution vs. Natural Selection

• Evolution: Change over a long period.

• Natural Selection: The process by which evolution occurs.

• Section 16.3 will focus on natural selection and its components.

Three Conditions for Natural Selection

Struggle for Existence

• Darwin was influenced by Malthus, who suggested humans multiplied faster than they died, leading to a struggle for survival.

• Malthus believed disease, famine, and war kept the population in check.

• Darwin applied this to nature: more individuals are produced than can survive.

• Offspring compete for resources like food, living space, and reproductive capabilities.

• Competition is essential for natural selection to occur.

Variation and Adaptation

• Variation is necessary for a struggle to occur.

• Individuals better suited to their environment are more likely to survive.

• Heritable characteristic: A trait that can be passed to offspring.

• Adaptation: Any heritable characteristic that increases an organism's ability to survive.

• Adaptations can be structural or behavioral.

• Example: Owls

  • Adaptations such as larger eyes for better night vision.

  • Sensitive ears for hunting rodents.

  • Talons for grabbing prey.

Survival of the Fittest

• Fitness: How well an organism can survive and reproduce in its environment.

• High fitness: Organisms likely to survive and reproduce.

• Low fitness: Organisms not well-suited to their environment, likely to die without reproducing.

• Survival of the fittest relies on struggle, variation, and the goal of survival.

Natural Selection Explained

• Natural selection: Organisms with variations best suited to their environment survive and produce more offspring.

• Occurs under three conditions:

  • More individuals are born than can survive (struggle).

  • Natural heritable variation within the population.

  • High fitness leads to survival.

• Examples:

  • Katydid: Camouflage adaptation for survival.

  • Moth: Eye-like patterns on wings to deter predators.

Evolution and Common Descent

• Natural selection is the process of evolution.

• Darwin proposed adaptations lead to new species over generations when changes prevent reproduction between original and new populations.

• Living species descended with modification from a common ancestor.

• Tree of life: Illustrates Darwin's idea of a common ancestor at the base, branching into diverse species.

• Common descent: All species (living and extinct) are descended from ancient common ancestors.

  • Examples: Dragonflies, trees, crayfish, and dinosaurs are all related through common descent.

Artificial Selection

• Focus on the word "artificial."

• Breeders know organisms vary, and these variations are inheritable.

• Artificial selection: Nature provides the variation, and humans select desired traits for breeding.

• Goal: To produce offspring that are most useful to humans.

• Examples:

  • Dogs: Selective breeding for specific traits (e.g., size in Chihuahuas).

  • Pigeons: Darwin bred pigeons, selecting for desired characteristics.

• Darwin believed variation in nature provides the raw material for evolution, but without human selection.