4.3.12 Adaptation

Adaptations from evolution by natural selection

• Environmental factors that affect the chance of survival of an organism are known as 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 and therefore better able to survive and reproduce. These features are known as adaptations
  • For example, a favourable allele in the lion population could result in a higher proportion of fast-twitch muscle fibres in their legs. This adaptation 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 its environment

Types of adaptations

• Adaptations enable organisms to survive in the conditions in which they normally live
• An adaptation can be anatomical, physiological or behavioural
• Anatomical adaptations
  • Structural or physical features
  • 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

Types of Adaptations Table

Convergent evolution

• 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

• In some cases, however, species that do not share a recent common ancestor and live in completely different parts of the world can show very high levels of similarity in terms of the adaptations they possess
• This occurs when the two habitats, in which the two species have evolved and to which they have become adapted, are very similar
• This process is known as convergent evolution
• For example, marsupial moles that live in the Australian desert (whose ancestors migrated to Australasia 50 million years ago) and the European mole (a placental mammal) have evolved separately and in isolation from each other but show convergent evolution - their adaptations have converged (become more and more similar)
• Both species burrow through soil and very rarely emerge in daylight. They are both adapted to their similar niches in the following ways:
  • Both have short and powerful limbs, with large, strong front claws for shovelling soil out of the way
  • Both have no external ears (these are not necessary underground) and have simple ear canal openings in their fur
  • Both have limited eyesight (again, this is not needed underground) - the loss of an unnecessary feature is still an adaptation!
  • Both have very similar, highly silky and fine fur that allows them to move efficiently underground

• You would have to travel back many millions of years to find the common ancestor of these species, which would have looked nothing like a mole and would not have possessed any of the adaptations described above
• Despite this, these two completely separate species are now incredibly similar in terms of the adaptations they possess