6. Evolution of Species

• A mutation is the random change in an organisms genetic information.
• Mutations are spontaneous and are the only source of new alleles.
• There are various environmental factors that can increase mutation rates:

  • Chemical - Mustard gas, cigarette smoke
  • Radiation - UV rays, X rays
• Some mutations give organisms an advantage over other individuals. These mutations increase the ability of the organism to survive and reproduce and are called advantageous.
• Some mutations are neither beneficial or detrimental to the ability of the organism to reproduce or survive.

  These forms of mutations are called neutral.
• Some forms of mutations are disadvantageous. This is where they disadvantage the survival of the organism.
• Natural selection is known as the survival of the fittest.
• Individuals that are better suited to their environments are more likely to survive.
• Species grow and produce more offspring than the environment can sustain.
• Individuals in a species show genetic variation. Variation results from mutation.
• The environment imposes abiotic and biotic factors which act as selection pressures. This leads to natural selection taking place.
• Individuals in a population that are not well adapted will die.
• The best adapted individuals will survive to reproduce and pass on favourable alleles to their offspring that gave them a selective advantage. This is known as survival of the fittest.
• Alleles with the selective advantage will increase the frequency within the population.
• Natural selection is the survival of organisms best suited to their environment. This is the process which drives evolution.
• Speciation is the form of new species.
• Speciation usually involves many new species being produced from a few original species.
• The first stage of speciation involves a population being split by a barrier. These can be:

  • Geographical barrier
  • Ecological barrier
  • Reproductive barrier
• Once the barrier has split the two species up, the original population now turns into a sub-population.
• Over the time different mutations take place in each of the sub-populations.
• Natural selection selects for different selection pressures in the new sub-population. The individuals who are best suited to their environment survive and reproduce.
• Each sub-population evolves until they become so genetically different that they are two different species.
• Even if the barrier is removed, the two sub-populations cannot interbreed as they are now two different species.
• Species produce more offspring than the environment can sustain. Natural selection or survival of the fittest occurs when there are selection pressures. The best adapted individuals in a population survive to reproduce, passing on favourable alleles that confer the selective advantage. These alleles increase in frequency within the population.
• Speciation occurs after a part of population becomes isolated by a isolation barrier, which can be geographical, ecological or behavioural. Different mutations occur in each sub-population. Natural selection selects for different mutations in each group, due to different selection pressures. Each sub-population evolves until they become so genetically different that they are now two different species.