1. Evolution
&
Natural Selection

2. Vocab
Evolution - change in a kind of organism over time; process by which modern organisms have descended from ancient organisms
Theory - well-tested explanation that unifies a broad range of observations

3. Voyage of the Beagle (1839 - 1844)
Darwin’s Voyage - During his travels, Darwin made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time. What was it?

4. Galapagos Islands
During his travels, Darwin was amazed how different organisms were so well adapted to many different environments. (“Perfect fit”)
He saw patterns of diversity
Not just in living organisms, but also in fossil records.
The Galapagos Islands were a microcosm of Evolution

5. Darwin’s Finches

6. Development of Evolutionary Theory
What could cause such great diversity?
Why have so many species died out?
Why have some species not changed at all?
Charles Darwin offered an
explanation based on careful
observations.

7. Idea’s that shaped Darwin’s Thinking
James Hutton and Charles Lyell helped scientists recognize that Earth is many millions of years old, and the processes that changed Earth in the past are the same processes that operate in the present.
Thomas Malthus (English Economist) - reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone.
Jean-Baptiste Lamarck proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. These traits could then be passed on to their offspring. Over time, this process led to change in a species

8. Lamarck (His theory is wrong)
Tendency Toward Perfection
Innate tendency toward complexity and perfection
Birds acquired the urge to fly
Kept trying to fly
Use and Disuse
Using a trait (wings) causes them to become stronger and larger
Disuse causes it to disappear
Inheritance of Acquired Traits
Passing acquired traits from one generation to the next

9. Lamarck

10. “The Survival of the Fittest”
Evolution
Development of Evolutionary Theory
“The Survival of the Fittest”
But …
What determines Fitness???

11. Development of Evolutionary Theory
Darwin Concluded:
Physical traits and behaviors enable organisms to survive and reproduce (Fitness)
Fitness results from adaptations
Darwin reasoned that adaptations result from natural selection and result in evolution
Evolution is the process by which living things change and diversify over time

12. Natural Selection

13. Premises of Natural Selection
Evolution Through Natural Selection
Premises of Natural Selection
Populations overproduce.
Resources are limited, so competition ensues.
Genetic variations directly impact the ability of organisms to survive.
Organisms with beneficial differences will have a better chance of survival.
Surviving individuals pass their traits onto future generations.
This results in a slow change in populations over time.

14. Evolution Through Natural Selection
These end results can be attributed to 3 distinct selection type models. All of which are as a result of environmental pressures.
Directional Selection
Stabilizing Selection
Disruptive Selection

15. Directional Selection
Evolution Through Natural Selection
Directional Selection
form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve

16. Directional Selection
Evolution Through Natural Selection
Directional Selection

17. Directional Selection – e.g.
Evolution Through Natural Selection
Directional Selection – e.g.

18. Stabilizing Selection
Evolution Through Natural Selection
Stabilizing Selection
form of natural selection by which the center of the curve remains in its current position; occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end

19. Stabilizing Selection
Evolution Through Natural Selection
Stabilizing Selection

20. Stabilizing Selection – e.g.
Evolution Through Natural Selection
Stabilizing Selection – e.g.

21. Evolution Through Natural Selection
Disruptive Selection
form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle

22. Evolution Through Natural Selection
Disruptive Selection

23. Disruptive Selection e.g.
Evolution Through Natural Selection
Disruptive Selection e.g.
What will disruptive selection eventually result in?

24. WHY? Are we as Human Beings exempt from Natural Selection?
QUESTION???????
Are we as Human Beings exempt from
Natural Selection?
WHY?

25. QUESTION???????
Biologists believe that Achaebacteria living today are similar to ancient achaebacteria. Many of these are found in extreme locations. Some scientists believe that this provides a good example of the origins of life.
Why do you think that these organisms have not changed over the years?
Why would understanding the origins of life on earth help with discovering life on other planets?

27. Genetic Drift
Genetic Drift - random change in allele frequencies that occurs in small populations
In small populations, individuals that carry a particular allele may leave more descendants than other individuals do, just by chance. Over time, a series of chance occurrences of this type can cause an allele to become common in a population.
founder effect - change in allele frequencies as a result of the migration of a small subgroup of a population

28. Genetic Drift and Founder Effect

29. Does Evolution occur all of the time?

30. Hardy-Weinberg principle
The principle that allele frequencies in a population will remain constant unless one or more factors cause the frequencies to change
If there are no factors causing allele frequencies to change then the population is in……..
genetic equilibrium - situation in which allele frequencies remain constant

31. Genetic Equilibrium
Five conditions are required to maintain genetic equilibrium from generation to generation:
random mating
the population must be very large
there can be no movement into or out of the population
no mutations (that filter into the gene pool)
no natural selection

32. Do Now…..
Describe how natural selection can affect traits controlled by single genes.
Describe three patterns of natural selection on polygenic traits. Which one leads to two distinct phenotypes?
How does genetic drift lead to a change in a population’s gene pool?
What is the Hardy-Weinberg principle?

33. When evolution DOES OCCUR
The process of SPECIATION - formation of new species
Speciation has occurred when – population have become reproductively isolated from one another
reproductive isolation - separation of species or populations so that they cannot interbreed and produce fertile offspring
Reproductive isolation can develop in a variety of ways, including behavioral isolation, geographic isolation, and temporal isolation.

34. Behavioral Isolation Examples
form of reproductive isolation in which two populations have differences in courtship rituals or other types of behavior that prevent them from interbreeding
Examples
Mating calls
Mating dances

35. Geographic Isolation
form of reproductive isolation in which two populations are separated physically by geographic barriers such as rivers, mountains, or stretches of water

36. Temporal Isolation
form of reproductive isolation in which two populations reproduce at different times

37. Speciation of Darwin’s Finches
Speciation in the Galápagos finches occurred by the:
founding of a new population
geographic isolation
changes in the new population’s gene pool
reproductive isolation
ecological competition