• Environmental factors that affect the chance of survival of an organism are?selection pressures
  • For example, there could be high competition for food between lions if there is not plentiful prey available; this environmental factor ‘selects’ for faster, more powerful lions that are better hunters

   

• These selection pressures can have different effects on the?allele frequencies?of a population through?natural selection
• Certain alleles within a species population can produce features that make an organism better suited to its environment -?adaptations
• When new alleles of genes result from mutation there is the potential for relatively rapid change in a species if their?environment changes
• For example, a favourable allele in the lion population could result in a higher proportion of fast-twitch muscle fibres in their legs, which is advantageous for sprinting after prey
• Natural selection will?select for favourable alleles?that produce adaptations
  • The lions with the advantageous alleles are more likely to catch prey and survive
  • These lions will produce more offspring
  • The allele frequency will increase in the population
  • The resulting adaptation will become more common in the population
  • The species will be better suited to their environment

   

• Natural selection will?select against unfavourable alleles
  • The slower lions that have the unfavourable allele are less likely to catch prey and survive
  • These lions will produce less offspring
  • The allele frequency will decrease in the population
  • The species will be better suited to their environment

   

• This means that over time natural selection will cause favourable allele frequencies to increase and unfavourable allele frequencies to decrease, making the?species better adapted to their environment

Types of Adaptations

• Adaptations enable organisms to survive in the conditions in which they normally live
• An adaptation can be anatomical, physiological and behavioural
• Anatomical adaptations
  • Structural/physical feature
  • Example: The white fur of a polar bear provides camouflage in the snow so it has less chance of being detected by prey

   

• Physiological adaptations
  • Biological processes within the organism
  • Example: Mosquitos produce chemicals that stop the animal’s blood clotting when they bite, so that they can feed more easily

   

• Behavioural adaptations
  • The way an organism behaves
  • Example: Cold-blooded reptiles bask in the sun to absorb heat

   

• Adaptation and selection contribute to the large diversity of living organisms and are major factors in the process of?evolution
• Evolution is the?change in adaptive features of a population over time as a result of natural selection
• If an environment is static and does not change, then selection pressures will not change and evolution will not occur
• If the?environment changes?or a chance?mutation?produces a new allele, selection pressures may favour individuals with different characteristics or with the?new allele
• Natural selection results in a process of?adaptation, which means that, over generations, those features that are better adapted to the environment become more common
• This means whole populations of organisms become better suited to their environment
• If two populations of one species are?isolated?from each other and become so different in phenotype that they can?no longer interbreed?to produce fertile offspring, they have formed two new species
• The formation of new species (speciation) from pre-existing species over time, is a result of?accumulated genetic differences
• Evolution?drives speciation?and so is responsible for the large number of species that exist on earth