B3 Revision Notes

Evolution

• There have been lots of species on Earth, but the majority have become extinct.
• The first life forms were very simple, but they evolved to become more complex and varied.
• There are two kinds of evidence for Evolution:
  • The Fossil Record shows species getting more and more complex as time goes on. The Fossil Record is quite empty for some species, but quite full for others, such as Horses.
  • DNA is also some evidence - all living things have similarities in their DNA - the more similar the DNA, the closer related the species are, and the more different the less related they are. Scientists can use DNA to show how life has evolved.
• Life on Earth started around 3,500 million years ago (three-thousand, five-hundred million).
• There are three main theories on how life started:
  • God created it.
  • It came from outer space.
  • It started when a chemical that could replicate its self (reproduce) formed.

Natural Selection

• There is variation between individuals in each species.
• Resources are limited.
• Some individuals with helpful characteristics have a better chance of winning those resources, surviving and reproducing.
• This means that more of the next generation will have these better genes.
• Over a large period of time, the entire species will be well adapted to its environment.
• This is natural selection AKA Survival of the Fittest.
• Artificial Selection AKA Selective Breeding is where humans choose what characteristics they want in the next generation, such as finer wool or produces more milk.

Mutations

• Mutations are when the chemicals in the DNA changes.
• Mutations are caused by various things, such as:
  • Radiation.
  • Chemicals.
  • Mistakes during cell division.
• Although…