evolution and natural selection

  • Created by: tia5sos
  • Created on: 22-11-20 18:55
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  • evolution and natural selection
    • natural selection increases advantageous phenotypes
      • 1. Populations of species usually show a lot of genetic variation - this means that there is a big mix of gene variants (alleles) present in the population.
      • 2. Variants arise when DNA randomly mutates.
      • 3. the resources living things need to survive are limited. Individuals must compete for these resources to survive - only some of the individuals will survive.
      • 4. some genetic variants give rise to characteristics that are better suited to a particular environment (e.g. being able to run away from predators faster). This means that these organisms have an advantageous phenotype. These individuals will have a better chance of survival and so have an increased chance of breeding and passing on their genes.
      • 5. This means that a greater proportion of individuals in the next generation will inherit the advantageous variants and so they'll have the phenotypes that help survival.
      • 6. Over many generations, the characteristic that increases survival becomes more common in the population. The 'best' characteristics are naturally selected and the species becomes more and more adapted to its environment.
    • evolution is a change in inherited characteristics
      • 1. natural selection leads to the evolution of species. Here's how evolution is defined:
        • Evolution is the change in inherited characteristics of a population over time, through the process of natural selection.
      • 2. The speed at which a species evolves depends partly on how quickly it reproduces - soem species reproduce very quickly (e.g. bacteria can be ready to start dividing in just 20 minutes), whereas others reproduce much more slowly (e.g. usually humans only start reproducing after around 20-30 years).
      • 3. Being quick to reproduce means that inherited characteristics are passed on to future generations much more quickly, so the time taken for the population to adapt to its environment is reduced.
      • 4. Evolution can mean that a species' phenotype changes so much that a completely new species is formed (i.e. the old and new version of the species wouldn't be able to breed together to produce fertile offspring, e.g. ligers).
      • 5. This can happen when a physical barrier separates two populations of a species - conditions on each side of the barrier will be slightly different so the phenotypes that are beneficial will be different for each population.
        • Natural selection acts on each population to increase the proportion of the advantageous phenotype in that population, until they are so different that they can no longer breed together.


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