Natural selection in the evolution of populations

• Natural selection - The process by which organisms better adapted to their environment survive and reproduce and pass on their advantageous alleles to their offspring, while those less well adapted fail to do so
• In a population not all organisms will survive and be able to reproduce:

  Selection pressures - Some individuals will die or fail to reproduce due to predation, disease, or competition for resources (food, water, space, mates, light)
• Organisms with variations that make them more likely to reproduce are said to have a selective advantage

  • They are more likely to reproduce and pass on those alleles to the next generation, so these favourable alleles increase in frequency in the gene pool
• Evolution - The change in the frequency of a gene in the population
• How natural selection drives evolution:

  1. There is variation in a population
  2. Due to mutation, some individuals have favourable alleles which help them to survive and reproduce
  3. They pass on these favourable alleles to offspring, so the frequency of these alleles in the population increases
  4. If no interbreeding with other populations occurs, then new species can be formed (speciation)
• Natural selection in evolution of populations:

  1. Random mutation can result in new alleles of a gene
  2. Many mutations are harmful but, in certain environments, the new allele of a gene might benefit its possessor, leading to increased reproductive success
  3. The advantageous allele is inherited by members of the next generation
  4. As a result, over many generations, the new allele increases in frequency in the population
• Natural selection:

  Within any population of a species there will be a gene pool containing a wide variety of alleles

  • Random mutation of alleles within this gene pool may result in a new allele of a gene - (may give its possessor an advantage over other individuals in the population)
• Natural selection:

  • Individuals with new allele of a gene by mutation may give its possessor an advantage over others in population
  • More likely to obtain the available resources and so grow more rapidly and live longer
  • As a result, they will have a better chance of breeding successfully and producing more offspring - passing on favourable alleles to next generation
• If selection pressures are different for different populations (eg if they have been separated into different environments), then evolution can occur, and new species can emerge once the populations can no longer interbreed (as they have become geographically isolated from each other)