1. Topic 8 – Natural Selection
Day 1

2. Natural Selection: A Mechanism of Change
Theory of Evolution
Natural Selection: A Mechanism of Change

3. What are we learning today?
Benchmarks
SC.912.L – Describe the conditions required for natural selection, including: overproduction of offspring, inherited variation, and the struggle to survive, which result in differential reproductive success.
Learning Objectives
I will analyze the reasoning in Darwin’s theory of evolution by natural selection.
I will relate the concepts of adaptation and differential reproductive success to the theory of natural selection.

4. What is the essential Question?
“It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is most adaptable to change.”
Charles Darwin
After reading the quote above and learning about Darwin’s theory of natural selection, what do you think he meant by it?

5. Who is Charles Darwin?
Greatest contributor to our understanding of evolution.
Evolution is:
the change of allele frequencies in a population over time.
process by which modern organisms have descended from ancient organisms.
Darwin was born in England on February 12, Why might the date sound familiar?
Son of a wealthy doctor
As a medical student in Edinburgh, he was horrified by operations, which were performed without anesthetics.
Dropped out of medical school against his family’s wishes
Went on to Cambridge University to become a minister

6. Darwin’s travels to the Galapagos islands
1831: voyage on the HMS Beagle
5 year voyage around the world to Australia, S. America, Galapagos Islands, and Africa
Made several observations on the different species he found
He noticed 3 patterns of biodiversity
Species vary Globally
Species vary locally
Species Vary over time

7. Other scientists thinking about evolution
Jean-Baptiste Lamarck
Suggested organisms change during their lifetime
Suggested individuals pass on acquired traits to offspring
Recognized a link to an organism’s environment and its body structures
Where did Lamarck go wrong in is theory?
We now know individuals do not evolve in their own life time
We also know that acquired traits cannot be passed on to offspring.

8. Acquired trait vs. inherited trait
Inherited Traits
Are passed on from the genes of parents to offspring
Will affect the traits of future generations of offspring
Acquired traits
are obtained by the individual in their life time
If you were to get a tattoo, that would be an acquired trait

9. Other scientists thinking about evolution
James Hutton and Charles Lyell
Concluded that earth was extremely old
Processes that changed earth in the past are the same ones changing the earth now
Principles of Geology
Thomas Malthus
English Economist
Reasoned that is populations grew unchecked, there would not be enough space, food, resources for everyone

10. What is an Adaptation?
Eyes with light reflective retina to see in the dark
Stripes to help them hide
An adaptation is any inherited characteristic that increases an organism’s chance of survival.
Loose abdomen skin to reduce injury when kicked
First notes.
*Write down adaptation.
-Anything that increases an organism’s ability to survive.
Long, sturdy tail to help with balance
Razor sharp teeth with muscular jaws to kill prey
Long, retractable claws to grab prey

11. What Adaptations improve this organism’s ability to survive?
Have S relay question back to you.
What adaptions do these animals exhibit?
How does the adaptation help them survive and reproduce?

12. Darwin’s 4 tenets of natural selection
Natural Selection: process by which organisms with variations most suited to their environments survive and leave more offspring
Natural selection is the driving force, the mechanism, of evolution
Darwin proposed that in order for evolution to occur by natural selection, 4 conditions must be met (4 tenets)
Overproduction of Offspring
Inherited variation within the population
Struggle for existence
Differential reproduction

13. What is overproduction of offspring?
What is taking place in this picture?
Grasshoppers can lay over 200 eggs at a time.
Only a small fraction of these offspring survive to reproduce.
Organisms produce more offspring than can survive.

14. What is inherited Variation?
What are some of the differences you see in the population of grasshoppers?
What do you think causes these variations?
Inherited variations are the heritable differences that exists in every population.
Mutations
Recombination
Inheritable variation is the basis for Charles Darwin's theory that natural selection is the mechanism for evolutionary change. Natural selection:
· Increases the frequency of inheritable variations that favor the reproductive success of some individuals over others.
· Results in adaptation, the accumulation of inheritable variations that are favored by the environment.
· In the face of environmental change, genetic variation increases the likelihood that some individuals in a population will have inheritable variations that help them cope with the new conditions.
There are two sources of genetic variation:
1. Sexual reproduction: independent assortment in meiosis I, crossing over in prophase of meiosis I, and random fusion of gametes during fertilization.
2. Mutation, which is rare structural change in a gene.
Inherited variation is the genetic variation of obtaining the different genes from both parents and genetic variation refers to diversity in gene frequencies. Inherited variation comes about through mutation, random assortment of chromosomes through meiosis of genes.
Where this variation comes from

15. What is The struggle to survive?
How would you describe the environment in which the grasshopper lives?
Which grasshopper is better adapted to survive in this environment?
What would happen to this population if a drought caused the grass to turn brown?

16. What is The struggle to survive?
Certain heritable variations, called adaptations, increase an individual’s chance of surviving and reproducing.
Heritable variation includes brown and green body color.
Green coloration is an adaptation that allows grasshoppers to blend into their environment to be less visible to their predators.
Adult - Fully grown grasshoppers range in length from 19 to 38 mm. Coloration varies with species. Redlegged grasshoppers are reddish brown with a yellow underside. The differential grasshopper is basically brownish yellow or olive green with contrasting black markings on the hindlegs which distinctively resemble chevrons. Greenish yellow in color, the twostriped grasshopper has two pale stripes running down its back from the head to the wing tips.

17. What is Differential Reproductive Success?
What do you think it means that “green grasshoppers have a greater differential reproductive success than brown grasshoppers?”
Green grasshoppers survive and reproduce more often than do brown grasshoppers in this environment.

18. Differential Reproductive success
Organisms whose traits are best suited to the environment experience better reproductive success and become more common
more grasshoppers are born than can survive,
individuals vary in color, a heritable trait, and
green individuals have a higher differential reproductive success in the current environment
Some organisms may have an advantage (e.g., height) and will have more offspring. When lower and middle vegetation are removed for some reason, taller organisms would be able to reach the higher vegetation, giving a definite benefit over shorter organisms. The shorter organisms may not be able to find enough food and would subsequently not produce as many offspring as their taller cohorts. The condition creates what is referred to as differential reproductive success, due to the fact that the benefit of being tall will be passed on to the next generation. The shorter organisms would not be as successful in producing offspring, because they may be occupied finding food and gaining nourishment; thus the differential of "differential reproductive success."

19. Summary of Darwin’s theory (natural selection)
Individuals organisms within a species are different.
Some of these differences are passed down from parent to offspring, or heritable.
Individuals produce more offspring that can survive due to limited resources creating a struggle for existence.
Individuals best suited, or adapted, to their environment survive to experience higher differential reproductive success.
Individuals within a population vary in their traits. Some of these variable traits are heritable, passed on to offspring. More offspring are produced than can survive because of limited resources, such as food and nesting sites. Individuals with advantageous traits will survive and reproduce.