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