🦎 Evolution Explains Biodiversity
Big Idea: Biodiversity exists because species change over time. This long-term change is called evolution—like nature’s way of trying new things!
Evolution happens when some individuals have traits that help them survive and have more babies. Over time, these helpful traits become more common.
Natural Selection: How Evolution Works
Natural selection is like a filter—nature keeps what works best.
Nature doesn’t pick the strongest, just what works best for the environment.
Simple Example: Birds and Beaks
Imagine a group of birds that eat different foods.
- Small beaks are great for picking up tiny seeds
- Big beaks are better for cracking hard nuts
- Birds with the right beak for the food survive more easily
- Over time, the population changes to match the food available
Best fit for the environment = more babies!
The Four Steps of Natural Selection
- Genetic variation – no two are exactly alike (like different hair colors in people)
- Survival advantage – some traits help survival (e.g., faster, better camouflaged)
- Reproduction – survivors have more babies
- Inheritance – helpful traits get passed on
Exam tip: Always mention variation → survival → reproduction → inheritance.
Camouflage Example
If an insect blends in with tree bark, birds can’t see it as easily.
- Harder to spot = less likely to be eaten
- Lives longer
- Has more babies
- Camouflage trait becomes more common
Changing Environments
Environments don’t stay the same. When things change, species must adapt or they might disappear.
- Food sources can change (e.g., drought kills plants)
- Climate can shift (e.g., gets hotter or colder)
- Adapting takes time
- If change is too fast, some species can’t keep up and may go extinct
If the environment changes faster than species can adapt, they may die out.
Speciation: How New Species Form
Speciation happens when groups get separated and change in different ways.
- A group gets isolated (e.g., on an island)
- Different environments = different adaptations
- Genetic differences build up over time
- Eventually, they can’t breed with the original group
Island Example
If a few birds end up on a new island, they might evolve differently from the original group. Over time, they can become a new species.
Real example: The dodo (Mauritius): Ancestors of the dodo were flying pigeons that reached the island of Mauritius. Once isolated, there were no large predators and food was available on the ground. Over many generations, these birds became larger, lost the ability to fly, and evolved into a new species — the dodo.
Isolation + different conditions + time = new species
Why Evolution Matters for Biodiversity
- Evolution creates new species
- Natural selection helps species adapt
- Speciation increases biodiversity
- More biodiversity = stronger, more resilient ecosystems
For top marks: Link evolution → biodiversity → resilience.