20.5 - Extinction

Extinction

• A species is extinct when no individuals of that species remain alive.
• The fossil record contains many species that no longer exist, showing extinction has happened throughout the history of life.

Causes of extinction

• Rapid environmental change - The environment changes too quickly for the species to keep up, e.g. its habitat is destroyed or conditions shift faster than the population can adapt.
  • Natural selection works gradually, over many generations, so when change is rapid there may not be time for better-adapted individuals to spread through the population, and the whole species can be lost.
• A new predator - Arrives and kills them all, e.g. where humans have hunted species to extinction.
• A new disease - Spreads through the population and kills them.
• A new competitor - Arrives and out-competes them for food or another resource the species depends on.
• Overharvesting - People take wild animals or plants faster than the population can breed and replace them.
• Pollution - Poisons the habitat the species depends on.
• A catastrophic event - More rarely, a single event wipes out the species all at once, such as a major volcanic eruption or an asteroid striking the Earth.