Darwin and Evolution

Before Darwin

• Earth was believed to be a few thousand years old
• Species remained the same since creation
• George Cuvier believed that fossils were the remains of individual species that went extinct and similar but new ones popped up

Natural selection and adaptation

• Mechanism for evolution
• Natural selection requires:   * Large population of species to pass on the traits   * Individuals with favourable traits pass them on and that they survive   * Heritable variation
• Ongoing process
• Only veriations of the genetic kind

Darwin vs Lamark

Darwin

• Giraffe neck length varied   * Shorter necks struggled to survive, longer necks had more offspring     * Most giraffes now have long necks

Lamark

• Giraffes had short necks   * Giraffes stretched their necks in order to reach the higher-up food     * Continued stretching caused longer necks

Convergent evolution

• When species occupy similar ecological niches and adapt in similar ways as a response to the pressures

Vestigial structures

• Anotomical structures taht are fully developed in one group of organisms but reduced and nonfunctional in other similar groups
• Eg   * Birds have well developed wings but not ostriches   * Humans have tailbone   * Whales and snakes hip bone and leg remnants
• Explained by connon desendant hypothesis

Homologous structures

• Anotomically similar structures explainable by inheritance from a common ancestor
• All vertebrate forelimbs contain the same set of bones organised in similar ways despite dissimilar functions

Analogous structures

• Structures that serve the same function but are not constructed similarly
• Eg   * Birds vs insect wings

Natural vs artificial selection

Natural

• Natural selection occurs as a result of an organism adapting ot its surroundings
• Eg   * Giraffe neck length

Artificial

• Selective breeding imposed by an external entity
• Eg   * Corn to enhance the size of the seeds/sex characteristicts

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