5.3.7 evolution summarised

• The theory of evolution explains how living things have changed over time.
• Charles Darwin proposed the theory of evolution of natural selection. This theory proposes that all species evolved from simple life forms that first appeared on Earth more than three billion years ago.
• What theory explains how living things have changed over time?

  Theory of Evolution
• In a population (group of individuals) or species, different individuals have different combinations of genes. This is called genetic variation.
• Who proposed the theory of evolution by natural selection?

  Charles Darwin
• Individuals best adapted to their environment are more likely to survive. This is survival of the fittest.
• What is the name given to the different combinations of genes in a population or species?

  Genetic variation
• Individuals that survive are more likely to breed successfully and have lots of offspring.

  This means that the characteristics that helped the individual survive are more likely to be passed on to the next generation.
• Lots of people didn't agree with Darwin's theory of evolution by natural selection.

  People said he didn't have enough evidence and that his ideas went against religious beliefs that God created the world. Genes had not been discovered yet, so Darwin couldn't suggest a method of how characteristics were passed between parents and offspring.
• Speciation is the formation of a new species. Individuals are members of the same species if they can breed together to produce fertile offspring.
• Individuals that are better adapted to their environment are more likely to survive. Individuals that survive are more likely to breed successfully and have lots of offspring
• Speciation can happen when two populations of the same species become geographically separated.

  The two populations show genetic variation, and the environments which they are in are different, so natural selection acts differently on the two populations.
• What defines a species?

  Individuals that breed together to produce fertile offspring
• Eventually the two populations become so different that they cannot breed successfully together anymore. They are now two different species.
• What are the key features for speciation to happen?

  Two populations become geographically separated

  Natural selection acts differently on the two populations
• The main evidence for the theory of evolution is fossils, antibiotic resistant bacteria and genes. Fossils show gradual changes in organisms over really long periods of time.
• Bacteria have developed resistance to antibiotics through the process of natural selection. Bacteria with mutations that make them resistant survive and reproduce, passing on this mutation to the next generation.
• What are the main sources of evidence for the theory of evolution?

  Fossils

  Genes

  Antibiotic-resistant bacteria