ZIMSEC O Level Combined Science Notes: Selection

  • Each time male and female individuals reproduce they create an offspring that is different from themselves
  • This changes accrue over time to bring about much change in the descendants as there is inter-breeding between many individuals in each generation
  • This changes might result in the offspring having certain advantageous characteristics that are not present in their contemporary offspring
  • This means the offspring with the advantageous is more likely to survive and thrive compared with the one that does not have that advantage
  • For example during a breeding cycle there are two calves born of different parents
  • One is born with genes that are resistant to diseases and the other is not
  • The one born resistant is more likely to survive and grow up
  • The environment decides or select which offspring will survive
  • This phenomenon is known as natural selection
  • Natural selection-is when the environment decides which offspring will survive usually the strongest members of the given species will survive to breed the next generation
  • Nature selects which offspring will survive to grow and produce the next generation
  • Because the species with the advantageous characteristics survives and breeds the next generation that trait/characteristic is passed on to the next generation
  • For example if there are many calves born and more of those which are resistant to diseases survive and breed the next generation
  • The result is that in each succeeding generation more and more calves are born with those genes
  • With time each generation will be different and should be better suited to the environment in which it lives
  • The weaker members who lack the advantage die off and less of them breed
  • Natural selection has been happening for millions of years
  • It is a slow process
  • Humans can influence the selection process to their advantage
  • For example farmers can choose and plant the breeds they want to produce based on their needs
  • Scientists breed crops that grow best in the local conditions for example drought resistant crops breeds and crop breeds that mature more quickly
  • This is known as artificial selection
  • Artificial selection-this is when humans influence the selection process to their advantage for example hybrid breeding of crops
  • Typically the male and female individuals are carefully selected and mated
  • Agriculture benefits greatly from artificial selection
  • Breeds of cattle, sheep and goats that are suited to local conditions are bred
  • Important features such as improved milk and meat yields, increased drought tolerance and increased resistance to diseases are fostered in the breeding process

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