1. Natural Selection in Action
Holt - Chapter 7, Section 3

2. Foldable Format: Natural Selection in Action Changes in Populations
Forming a New Species

3. Changes in Populations:
Changes in populations are sometimes observed when a new force affects the survival of individuals.
1. Adaptation to Hunting
Ex: Elephant hunting in Uganda
1930’s – 1% of male elephants did not have tusks
Now – 15% do not

4. Changes in Populations: 1. Adaptation to Hunting
Why?
People hunt elephants for their tusks.
Fewer survive to reproduce, so more tuskless elephants are born.
They pass this tuskless trait on to their offspring.

5. Changes in Populations: 2. Resistance to Chemicals

6. Reading for Meaning Complete the “Before Reading” column.
Read the article, “Evolution of Antibiotic Resistance.”
Find evidence for or against each of the statements as you read.
Discuss your answers with a partner.
Discuss your answers with the class.

7. Antibiotic Resistance in Bacteria
Just as insects develop resistance to pesticides, bacteria develop resistance to antibiotics.
Bill Nye – Antibiotics (video clip)
PBS - Antibiotic Resistance

8. Changes in Populations: 3. Competition for Mates
Competition for mates can select for adaptations.
Ex:
In many bird species, females prefer to mate with colorful males.
Colorful males pass on their genes for color to the next generation, so the proportion of colorful males is likely to increase.

9. Forming a New Species
Species – a group of organisms that can mate with each other to produce fertile offspring.
A new species may form after a group becomes separated from the original population.
Over time, the new population adapts to its new environment.
Eventually, the two populations differ so much that they can no longer mate successfully.
Speciation – the formation of a new species as a result of evolution.

10. Forming a New Species

11. 3 Steps in Forming a New Species
Separation
Population becomes separated from the rest
Ex: physical barriers such as canyons, mountains, or lakes
Adaptation
Populations constantly undergo natural selection
Adaptations in the separated populations differ
Division
The separated groups evolve and become different from each other
No longer able to interbreed – two different species now

12. Summary
In Australia, many animals look like mammals from other parts of the world. But most of the mammals in Australia are marsupials (mammals that carry their young in a pouch after birth). Few kinds of marsupials are found anywhere else in the world.
What is a possible explanation for the presence of so many of these unique mammals in Australia?