1. A mechanism that is easily observable in nature and experiments
Natural Selection
A mechanism that is easily observable in nature and experiments

2. Environment presents challenges for individuals to overcome
Certain individuals are better suited to overcome challenges
They are said to “fit” the environment
These individuals live longer, reproduce often, and pass their traits on
Successful traits become more common
Environmental
Challenges
Favorable
Traits
Survival
of the
“fittest”
Apparent
“adaptation”

3. Factors for Natural Selection
VARIATION
There are five basic steps for natural selection to take place
They are all observable in nature and experiments
OVERPRODUCTION
(CONSTANT STRUGGLE)
ENVIRONMENT “SELECTS”
CHANGE IN ALLELE FREQUENCY
POPULATION APPEARS TO ADAPT

4. 1. Genetic Variation is raw material
There must be differences (variation) among individuals that affect their survival
These physical differences are due to genetic differences

5. 1. Cont. Sources of Genetic Variation in Species
Mutations
Random changes in DNA can lead to changes in the physical organism
Meoisis
When sex cells divide, chromosomes sort themselves randomly, leading to new combinations of genes
Sexual Reproduction
Combines genes from two individuals, leading to new genetic combinations

6. 2. There is a constant struggle for survival
Organisms produce more offspring than can survive
The environment poses challenges to stay alive and/or find food

7. 3. Environment “selects” individuals
Organisms that have traits best suited to the environment survive
These are deemed “fittest” individuals
Only the survivors are able to reproduce

8. 4. Natural selection leads to genetic change in the species
The “fit” organisms possess certain genes
Offspring that are produced have “fit” genes
Frequencies of successful genes increases

9. 5. Population appears to adapt to the environment
Over time, it looks as if the species changed itself to adapt
Why is it wrong to say that organisms adapt themselves to their environment?