Evolution by natural selection

• Evolution

  The change in the inherited characteristics of a population over time through a process of natural selection
• Natural selection

  1. Genetic variation within a population

  2. Individuals with beneficial traits more likely to survive and reproduce

  3. Beneficial traits passed on to offspring

  4. Traits become more common in population over generations
• The Earth is teeming with living organisms, including large animals, small animals, and plants
• There are nearly 9 million different species of animals and plants on Earth, not including microbes
• Only about 1% of the total species that have ever lived on Earth are still alive today, the rest are extinct
• Life first developed on Earth more than 3 billion years ago, starting with very simple single-celled organisms
• All species of living things have evolved from these simple life forms
• Genetic variation within a population

  • Individuals have slightly different combinations of alleles inherited from parents
  • Some alleles provide beneficial traits like thicker fur, better eyesight, or better hearing
• Environment changes (e.g. gets colder)

  Individuals with beneficial traits more likely to survive and reproduce
• New predator moves into area

  Individuals with beneficial traits like better eyesight or hearing more likely to survive and reproduce
• Speciation

  When two populations of the same species become so different that they can no longer interbreed to produce fertile offspring, they are considered separate species
• Speciation example

  • Normal-sized rabbits and pygmy rabbits