4. Natural selection

• Randomly-occurring mutations sometimes result in new allele being formed. Can be harmful, which usually means that the mutated allele quickly dies out. However, some mutations can produce allele that are beneficial for organisms (e.g protein is produced that works better than original ) helping organism to survive in certain environments
• When allele codes for characteristic that increases chances of organisms surviving, its frequency within population can increase. Process is natural selection
• Natural selection:

  1. Not all individuals are as likely to reproduce as each other. In other words, there’s differential reproductive success in population - more likely to survive, reproduce and pass on their genes than individuals with less advantageous alleles
  2. Means that greater proportion of next generation inherits beneficial allele
  3. In turn, are more likely to survive, reproduce and pass on genes
  4. Frequency of beneficial allele in population increases from generation to generation
  5. Over generations this leads to evolution as advantageous alleles become more common in population
• Adaptations are features that help organisms to survive in their environment. They can be behavioural, psychological or anatomical
• Behavioural adaptations:

  These are ways an organism acts that increase its chance of survival. E.g. Possums sometimes ‘play dead’ - if they’re being threatened by a predator they play dead to escape attack. Increases their chance of survival.

  E.g Scorpions dance before mating - this makes sure they attract mate of same species, increasing likelihood of successful mating
• Physiological adaptations:

  Processes inside organism‘s body that increase its chance of survival.

  E.g. Brown bears hibernate - they lower their rate of metabolism ( all chemical energy taking place in their body) over winter. This conserves energy, so they’re don’t need to look for food for months when its scarce - increasing their chance of survival.

  E.g. Some bacteria produce antibiotics - these kill other species of bacteria in area. Means there’s less competition, so they’re more likely to survive
• Anatomical (structural adaptations:

  Structural features of an organism‘s body that increase its chance of survival. E.g. Otters have streamlined shape - making it easier to glide through water. Makes it easier for them to catch prey and escape predators, increasing their chance of survival

  E.g. Whales have thick layer of bladder (fat) - this helps to keep them warm in cold sea. Increases their chance of survival in places where their food is found