1. Darwin and Natural Selection

2. Species
A group of organisms with similar characteristics that can reproduce fertile offspring
Evolution – change in a species over time
Modern species evolved from earlier species and share a common ancestor
Species evolve, individual organisms DO NOT evolve

3. Speciation Production of a new species
Members of a species are separated from the rest - geographic isolation, reproductive isolation
Different mutations occur in the two groups
Eventually they cannot mate

4. Charles Darwin – Evolution by Natural Selection
Mutations occur in sex cells & are passed on
There is PREEXISTING genetic variation in a species
A change in the environment occurs (temp. changes, droughts, new organisms, etc.)

5. Some members of the species have variations that cause them to be better suited to the changed environment (adaptations)
Competition for resources occurs – those better suited will win the competition

6. Individuals with the beneficial adaptation will survive and pass their traits on to their offspring
Members without the adaptations will die and NOT spread their traits
Over time, the species will evolve (change)

7. If they do not evolve, the species will become extinct
Natural selection = organisms with traits best suited to their environment are more likely to survive, reproduce and pass on their traits
Survival of the fittest…
It isn’t about being stronger, it is about having the needed mutation

8. Example Elephants have a variety of trunk sizes (long, medium, short)
A drought occurs = less food and water
Longer trunks are better suited to the new environment, they have a beneficial adaptation

9. Short trunked elephants die
Long trunked elephants survive = offspring have long trunks
Eventually, all elephants have long trunks
The species has evolved because their preexisting variation allowed some of them to be better suited to their environment