1. Introduction to Evolution

2. Review of Meiosis Humans have 23 pairs of chromosomes.
When you form sex cells, only one chromosome from each pair gets passed along.
The chromosome that gets passed along is random for each pair of chromosome.

4. Do the math!
If there are 23 pairs of chromosomes and they all separate randomly then there is a possible
223 (~ 8 Million) different types of sex cells one person can make.
Don’t forget that 2 sex cells are needed to make every person.

5. Egg and Sperm Needed for Fertilization

6. More math! Sperm = 223 possibilities Egg= 223 possibilities
Egg x Sperm=
223 x 223 =6.4 x 1013
There are a lot of different combinations just two people can make!!

7. The process of meiosis allows for genetic diversity in a population!

8. Mutations Also Increase Diversity
Mutations are changes in a DNA sequence.
Some mutations may cause a new trait.
New traits increase the diversity of a population.

9. Scientists believe that millions of years ago all humans had brown eyes.
Then a random mutation in one person’s DNA created blue eyes.
That trait was then passed down by meiosis!

10. Meiosis and Mutations cause diversity in all areas of nature.

11. Charles Darwin
In the 1830’s Darwin sailed aboard the HMS Beagle and landed on the Galapagos Islands.
He observed different animals and plant species and drew them in his notebook.
He took a particular interest in Finches.

12. Finches
Darwin observed that there were several different types of finches that occupied different parts of the islands.
What they looked like depended on where they lived on the island.

13. Observations
Darwin observed that the different finches had special traits that helped them survive in their environment.
For example, birds who at tiny insects had long, thin beaks and birds that ate large seeds had big, strong beaks.

14. Natural Selection
The finches that had traits that made them better adapted to their environment had a better chance to survive.
The birds that didn’t get the traits needed to survive in their environment died.
Darwin called this concept ‘Survival of The Fittest’ which today we refer to as NATURAL SELECTION.

15. Fitness
Since not all finches have the same traits, some finches will be better adapted to their environment than others.
Darwin said that finches that were better adapted to their environment had better ‘fitness’ because they can out-compete the other finches.
Fitness= The ability of an organism to survive and reproduce in it’s environment.

16. Which Giraffe is more fit?
The giraffes that are more ‘fit’ will survive and pass on their traits to their offspring.
The giraffes that are not ‘fit’ will most likely die and won’t pass on their traits.

17. Evolution
Eventually natural selection will cause the traits of an organism to change over time.
Change over time = Evolution

18. Evidence of Change Over Time
If you look at the fossil record, you can see that species have changed over time.
Example, the fossil record shows that the anatomy and bone structure of the horse had changed over time.