Speciation (AQA GCSE Biology): Revision Notes
Speciation
What is speciation?
Speciation means the formation of new species. This happens when one species splits into two or more different species over time.
The key to understanding speciation is recognising that it's a gradual process that occurs over many generations. Species don't suddenly appear - they develop slowly through the accumulation of genetic differences between populations.
How do new species form?
The process of forming new species follows these key steps:
Step 1: Populations become separated
Groups of the same species get separated from each other. This is called geographical isolation.
Examples of geographical isolation include:
- Moving to different islands
- New rivers forming between groups
- Volcanic eruptions splitting populations
- Mountain-building processes creating barriers
Step 2: Different environments create different pressures
Each separated group now lives in a different environment. Natural selection favours different characteristics in each location.
Environmental pressures can include differences in climate, food sources, predators, and available shelter. These factors determine which traits will be advantageous for survival and reproduction in each location.
Step 3: Populations gradually change
Over many generations, natural selection causes gradual changes in each population. Different traits become common in each group.
Step 4: New species are formed
The characteristics of each population become so different that they are now separate species. Individuals from the two groups can no longer breed together to produce fertile offspring.
The inability to produce fertile offspring is the key test for whether two populations have become separate species. This is called the biological species concept.
Alfred Wallace (1823-1913)
Alfred Wallace was a key scientist who helped develop the theory of evolution by natural selection.
What Wallace did:
- Worked worldwide to gather evidence for evolution
- Developed his theory independently from Darwin
- Published work with Darwin in 1858
- His work encouraged Darwin to publish "On the Origin of Species" one year later
Wallace's other important work:
- Studied warning colours in animals like caterpillars that are toxic to predators
- Developed the theory of speciation
- Proposed that hybrids (offspring from two different species) would be less well adapted than their parents
- Called this idea the "Wallace effect" - it helps drive speciation
Wallace's independent development of natural selection theory shows how scientific ideas can emerge when the evidence and timing are right. His collaboration with Darwin demonstrates the importance of scientific cooperation.
Examples of speciation
Real-World Example: Anole Lizards in the Caribbean
- Each island has its own anole species
- Islands further from others have more unique species
- DNA evidence shows all species are closely related
- Different environments on each island led to different characteristics
This example perfectly demonstrates how geographical isolation leads to adaptive radiation - one original species evolving into multiple species adapted to different environments.
Real-World Example: Flightless Birds in New Zealand
- Many flightless bird species live on New Zealand islands
- All related to species that could fly in nearby Australia
- New Zealand has no natural predators
- Without predators, birds didn't need to fly, so they evolved to be flightless
This shows how environmental pressures (or lack of them) can lead to the loss of traits that are no longer necessary for survival.
Key Points to Remember:
- Speciation is the formation of new species from existing ones
- Geographical isolation separates populations and starts the process
- Natural selection acts differently in different environments
- Alfred Wallace helped develop the theory of evolution and speciation
- New species cannot breed together to produce fertile offspring