1. Evolution

2. Darwin’s Theory of Natural Selection
MAIN IDEA: Charles Darwin developed a theory of evolution based on natural selection.

3. Why was Darwin’s work controversial?

4. Evolution vs. Creationism
Creationism – belief that God created all living things to be unique
Evolution – theory that organisms have changed over time.

5. Until the 1800s
People thought the same types of organisms on earth were always in existence
This changed when scientists found fossils of organisms no longer on earth

6. What made Darwin question previous assumptions on how different organisms came to be?

7. Scientists observed… Fossil evidence Many different species
Variations (differences) within species

8. Change in Thought
Scientists began to wonder how and why these changes took place
2 biologists believed organisms changed in response to their environments:
French Jean Baptiste Lamarck
British Charles Darwin

9. Lamarck’s Theory 1809 – Lamarck proposed his theory of evolution
Theory based on 2 hypotheses:
Organisms develop traits by the use and disuse of body parts
Acquired characteristics – passed from parents to offspring

10. According to Lamarck, why do giraffes have long necks?

11. Lamarck’s giraffe example(Don’t Copy)
Lamarck assumed giraffes had short necks originally and ate grass
Grass died due to climate change
Giraffes ate leaves off trees
As giraffes stretched necks, necks grew
Giraffe’s acquired long necks – passed to future generations
Scientists questioned this theory…

12. Charles Darwin
Born in 1809
Age 22, went on voyage on HMS Beagle (British ship) as a naturalist
Mapping expedition of S. America and S. Pacific

13. Darwin’s Thoughts (Don’t Copy)
Charles Lyell’s book influenced Darwin -Lyell said Earth was millions of years old
Observed fossils of marine animals on mountains, etc
Observed changing earth: earthquakes, volcanoes, etc; saw change in the land
Thought organisms would have to adapt to these changes

14. Darwin’s Studies Observed thousands of different species
Took careful notes
Collected specimens
Studies fossils

15. Galapagos Islands (Don’t Copy)
Off coast of Ecuador
Observed MANY different species
Many similar to those on coast of S. America
Observed tortoises, iguanas, finches, etc with slight differences on different islands
Ex: different beaks of finches

16. Help from Gould (Don’t Copy)
John Gould, another British naturalist
Concluded finches were different species, and were not on mainland of S. America
Darwin though species changed after reaching islands

17. DO NOW
What is the difference between natural selection and artificial selection?
What is the difference between natural selection and evolution?

18. Artificial vs. Natural Selection
Artificial - breeding for desired traits
Natural – naturally “desired” traits are bred more often – causes gradual change in species over time (evolution)

19. Darwin’s Theory
Published book: On the Origin of Species by Means of Natural Selection with help from another scientist, Alfred Russel Wallace
Theory based on 4 main ideas:
Variations
Inheritance of traits
Overproduction
Survival of the fittest

20. Variations
Variations (differences) occur among members of the same species
Ex: different breeds of dogs, horses, cats, etc.
Inheritance of Variations
Traits are inherited

21. Overproduction
Organisms produce more organisms than can survive and reproduce
This ensures that some offspring will survive to reproduce
Ex: fish, insects, frogs, etc.

22. Survival of the Fittest
Organisms with traits that are better for adapting survive to reproduce
Pass on these useful traits
Natural selection – environment determines which variations will be selected

23. Peppered Moth Example (DON’T COPY)
Early 1800s, England
Peppered moths were mostly light gray; few were white, few were black (variations)
Gray blended with tree trunks – birds didn’t see or eat them, so they survived, but black ones were eaten

24. Peppered Moth Cont’d (DON’T COPY)
Industrial Revolution – many factories built
Black soot on trees
Which moths were NOW more likely to survive?

25. Do Now
Once, many years ago, horses were the size of cats. Now, they are obviously much bigger. How would Lamarck explain this change? How would Darwin explain it?

26. Evidence of Evolution
Fossils
Anatomy
Embryos
Molecules
Biogeography

27. Fossil Evidence Show extinct species
Show relationships between current and ancient organisms
Show intermediate species – those in between ancient and modern species
Difference in traits – derived vs. ancestral

28. Anatomical Evidence
Similar structures found in closely related species; have common ancestor
Diverse vertebrates have similar limb structures, but may not have same function –homologous
Vestigial structures – structures not currently used by organism; evidence of an organism’s evolutionary past Ex: hind limbs of dolphins/whales

29. Homologous Structures

30. Homologous vs. Analogous
Remember, homologous – similar STRUCTURE
Analogous – structures with similar FUNCTIONS, but different structures/origins
Ex: bat’s wing and bird’s wing - analogous

32. Evidence in Embryos Vertebrates have a common ancestor
Pattern of meiosis (gametes)  fertilization  mitosis (adults)
All vertebrate embryos have homologous structures that may not be in adults:
Tails (most adults keep their tails!)
Limb buds – become limbs
Vertebrates have a common ancestor

34. Molecular Evidence DNA: Basic genetic code for each species
Ex: humans all have same basic genetic code
Species that are similar have many similarities in their DNA
Species with a more distant ancestor have more differences in DNA

35. Molecular Evidence Proteins:
Because of similar DNA, organisms of the same species have the same basic proteins
Similar species – similar amino acid sequences in their proteins

36. Biogeography Study of distribution of organisms on earth
Similar environments lead to similar adaptations in organisms, even if far apart

37. Adaptations Traits that allow for survival
Fitness – way to measure how effective traits are
Examples of adaptations:
Camouflage
Mimicry

38. Remember that… Not all traits evolve slowly; Ex: bacteria
Not all traits increase fitness
Mutations can be a source of new traits

39. Evolution and Genetics

40. Population Members of same species living in same area
All genes in a population = gene pool

41. Population Genetics
Allele frequency – percent of certain alleles (gene types) in a population’s gene pool
Ex: all homozygous red flowers have a 100% frequency for red alleles
Usually remains stable in a population

42. Changes in the Gene Pool
Changes can occur in the gene pool, which could cause evolution
Kinds or percentages of genes can change
4 things cause these changes
Natural selection
Mutation
Migration
isolation

43. 4 Factors Change the Gene Pool
1. Natural selection
Well-adapted organisms survive to reproduce
Pass on genes to next generation, increasing the gene frequency

44. 4 Factors Change the Gene Pool
2. Mutation
Adds a new gene to the gene pool
Can cause small, immediate change, or go undetected for generations
Can be helpful, harmful, or neutral

45. 4 Factors Change the Gene Pool
3. Migration
Movement of organisms into or out of a population
Causes gene flow – movement of genes in or out of populations

46. 4 Factors Change the Gene Pool
4. Isolation
Organisms become separate from other organisms (geographic isolation)
Caused by physical barriers, natural disasters, etc
Causes speciation
Causes reproductive isolation between the now separate species

47. Create
With your group, pick any species, and create a scenario as to how it may evolve based on your assigned factor. Base your predictions on facts about the species. Describe and/or draw your predictions, and then present to the class!

48. The Rate of Evolution

49. Gradualism Evolution through slow change
Believed to be true by Darwin and many other scientists
Fossil evidence supports this

50. Punctuated Equilibrium
Species remain unchanged for thousands of years, then suddenly undergo rapid changes
Fossil evidence of trilobites – unchanged for millions of years, then suddenly died off