What is the fundamental definition of extinction?

Extinction is the permanent disappearance of a species from Earth, occurring when the last surviving individual of that species dies. It signifies that the species can no longer reproduce and pass on its genes.

How does speciation differ from extinction?

Speciation is the evolutionary process where new, distinct species are formed, increasing biodiversity. Extinction is the opposite process where existing species are lost, decreasing biodiversity.

Why might a new competitor lead to the extinction of a native species?

A new competitor may be more efficient at gathering limited resources like food or water. If the native species cannot secure enough resources to survive and reproduce, its population will decline to zero.

What is the difference between a mass extinction and background extinction?

Background extinction is the slow, natural rate at which individual species disappear over time. Mass extinction is a rare, catastrophic event where a significant percentage of all species on Earth die out in a relatively short geological timeframe.

What is a common misconception about why species go extinct?

A common error is thinking species go extinct because they are 'weak.' In reality, they go extinct because they are poorly adapted to a *specific change* in their environment, even if they were highly successful previously.

How can a single catastrophic event cause global extinction?

Events like asteroid impacts can cause immediate physical destruction and long-term environmental shifts, such as blocking sunlight with dust. This disrupts the entire food chain by stopping photosynthesis, leading to the collapse of many species.

Why are island species often more vulnerable to extinction from new predators?

Island species often evolve in isolation without major predators, so they may lack defensive adaptations like flight or fear responses. When humans introduce new predators, these 'naive' species are easily hunted to extinction.

What role does genetic variation play in preventing extinction?

High genetic variation increases the likelihood that some individuals possess alleles that allow them to survive a new environmental pressure. Without this variation, the entire population may be equally susceptible to a change, leading to extinction.

How does rapid climate change lead to extinction compared to gradual change?

Gradual change allows time for species to migrate or for natural selection to produce adaptations over many generations. Rapid change happens faster than the species can evolve or move, leading to a population crash.

What is the 'Common Error' regarding the speed of extinction?

Students often assume extinction is always a slow process. While it can be gradual, catastrophic events or the introduction of a highly virulent disease can cause a species to go extinct in a very short period.

Extinction | AQA GCSE Biology

Inheritance, Variation & Evolution

Extinction

Summary

Extinction is the permanent loss of a biological species, occurring when the last individual of that species dies. It is a natural component of the evolutionary process, typically resulting from a species' inability to adapt to rapid environmental changes, new biological threats, or catastrophic events.

1. Definition & Core Concepts

Extinction is defined as the point at which there are no remaining individuals of a particular species alive anywhere on Earth. Once a species is extinct, its unique genetic information is lost forever and cannot be recovered through natural means.
The process is often the result of a failure in natural selection; if a population cannot evolve beneficial adaptations quickly enough to survive changing conditions, its birth rate will fall below its death rate until the population reaches zero.
While extinction is a natural part of Earth's history, the current rate of extinction is significantly higher than the 'background' rate due to various external pressures.

A graph showing population size declining over time following an environmental change, eventually reaching zero at the extinction point.

2. Abiotic Factors: Environmental & Geological Changes

Climate Change: Rapid shifts in global or local temperatures can destroy habitats. For example, if an organism is adapted to cold climates and the environment warms too quickly for the species to migrate or evolve, it may face extinction.
Geological Activity: Events such as massive volcanic eruptions or tectonic plate movements can alter landscapes, change sea levels, or release toxic gases into the atmosphere, making survival impossible for specialized species.
Catastrophic Events: Single, high-impact events like asteroid strikes can cause immediate and widespread extinction by blocking sunlight (halting photosynthesis) and causing extreme temperature fluctuations.

3. Biotic Factors: Biological Interactions

New Predators: If a new predator is introduced to an ecosystem, prey species that have not evolved defense mechanisms (like camouflage or speed) may be hunted to extinction before they can adapt.
New Diseases: A novel pathogen can spread rapidly through a population with no natural immunity. If the disease is highly lethal and spreads faster than the population can recover, the species may collapse.
Competition for Resources: When a new, more successful competitor enters an environment, it may outcompete native species for limited food, water, or nesting sites, leading to the decline of the less efficient species.

4. Human Impact on Extinction Rates

5. Key Distinctions

6. Exam Strategy & Tips