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Evolutionary Theory Holt Ch. 16 Glencoe Ch. 15.

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1 Evolutionary Theory Holt Ch. 16 Glencoe Ch. 15

2 Evolution: Process by which species change over time.
Descent with Modification

3 Charles Darwin 1809-1882 English Naturalist HMS Beagle 1831-1836
Sailed around world gathering specimens and fossils and observing geology

4 Route of HMS Beagle

5 Darwin collected fossils
Some fossils looked like modern animals.

6 Some fossils were different:
Giant Ground Sloth from Patagonia

7 Fossil Record = All fossils known to science
Younger fossils lie above older fossils in undisturbed rock layers Comparing fossils shows a gradual change from past to present life We keep finding new fossils, but the fossil record will still have gaps

8 Layers of rock include fossils
shows history of life over millions of years.

9 Fossils support Evolution
From looking at the fossil record, Darwin suggested that whales may have come from a 4-legged land mammal.

10 Evolution of horse hoof

11 Evidence of Geologic Change
Darwin found marine fossils high in the mountains How did they get there?

12 Convergent plate boundaries push up mountains


14 Galapagos Islands


16 Galapagos Islands = hot spot
Islands formed by hot magma reaching surface of crust Older islands (4 million years old) are eroded and lower. Newer islands (7000 years) are steeper

17 Darwin found unique animals
Marine iguana Many other species that live no other place on earth.

18 Galapagos Island Finches

19 Darwin’s Thinking… Perhaps a few finches from the S. Am. mainland migrated to the new islands.

20 Darwin noticed that the finches on different islands were slightly different:
Different beaks Different diets

21 Over time their descendents were “modified” as different groups specialized in eating different foods.

22 Each type of finch occupies a different niche (ecological role) so competition is reduced.

23 Adaptive radiation - one species diversifies into several species, each adapted to a different niche

24 Darwin didn’t invent evolution…

25 Jean Baptiste Lamarck (1744-1829)
Proposed a theory of evolution in which a trait could change due to use or disuse AND those changes would be passed to offspring = Acquired Characteristics

26 Lamarck’s Evolution

27 According to Lamarck, this body builder’s offspring would be born buff.

28 Galapagos Tortoises Darwin noticed that the giant tortoises on different islands had different characteristic. How would Lamarck explain these differences? Galapagos tortoise closeup!

29 Why are the animals different?
Each island has slightly different weather: lower islands are barren and dry, higher islands are wetter So, different islands have different vegetation, different habitat.

30 Tortoises with longer necks could reach the higher vegetation in drier areas, so they survived and reproduced, passing their long-necked genes to their offspring. Tortoises in wetter areas had plenty to eat and didn’t need long necks to survive and reproduce. Galapagos tortoise

31 Natural Selection: Individuals that have traits better suited to their environment are more likely to survive and reproduce. “survival of the fittest”

32 What are the 4 steps of natural selection?

33 Darwin’s steps of natural selection:
Variation –inherited variation in every population Overproduction – populations produce more offspring than can possibly survive (leads to competition for resources!) Selection – individuals with favorable traits leave more offspring Adaptation – over time, favorable traits become more common in a population

34 Darwin considered More Evidence:
Artificial Selection Population growth (Malthus) Age of the Earth (Lyell & Hutton)

35 Darwin’s Artificial Selection
When breeding livestock, humans choose the parents with traits they want in the offspring. Ex: dogs, cows, horses, pigeons

36 Population growth: Thomas Malthus pointed out that food supplies were limited and the human population could not keep increasing exponentially. Darwin applied this to all populations: organisms must COMPETE for limited resources!

37 Age of the Earth In Darwin’s time most Europeans believed in the biblical age of the Earth (a few thousand years). James Hutton and Charles Lyell were geologists who studied fossils and rock layers and suggested that the Earth was much older (millions of years)! …long enough for species to evolve gradually.

38 On the Origin of Species by Means of Natural Selection
Darwin hesitated to publish his ideas because they conflicted with popular religious beliefs about the origin of life. He waited until 1858 when Alfred Wallace convinced him to go public with his book, On the Origin of Species.

39 Evolution: A change in an inherited characteristic of a population over time. Individuals DO NOT evolve!

40 Adaptation: An Inherited trait present in a population because it helps individuals survive AND reproduce in a given environment. Individuals may have adaptations, but they DO NOT CREATE adaptations through use. (That’s Loser Lamarck!)

41 Now, work with the person sitting next to you to think of a particular organism’s adaptation. Be prepared to explain how that adaptation might have evolved.

42 Macroevolution (forming new species) is a slowww process
Macroevolution (forming new species) is a slowww process! It takes many generations to develop adaptations!!!

43 Microevolution is a change in the gene frequencies of a population.
Can happen quickly Ex: antibiotic resistant bacterial colonies

44 Speciation: New species evolve and no longer interbreed with the ancestor. What is a species? Morphological (what they look like) Biological (reproduction) Molecular (DNA)

45 Evolution is a unifying theory
Darwin brought together evidence from geology, biogeography, ecology, paleontology. Today Evolutionary Theory also includes evidence from developmental biology, genetics, and biochemistry.

46 What are homologous traits or homologies?

47 Anatomy gives clues to evolutionary relationships:
Homologous structures: traits that are similar in 2 or more species, inherited from a common ancestor.

48 Biogeography Study of the locations of organisms around the world.

49 Large, flightless birds are found in similar habitats, different locations.

50 Embryology - study of developing embryos
Compare the development of embryos of different species. All vertebrate embryos have a tail at some point in development.

51 Genetics: Compare DNA sequences to find hereditary relationships.
The more similar the genes, the more closely related the organisms.

52 Biochemistry: All life is built from the same 20 amino acids.
compare differences in amino acids of same protein.

53 Darwin’s Theory Weakness: 1. Darwin didn’t know about genes.
Strengths: 1. Organized notes, observations, evidence. 2. Showed the mechanism of change. 3. Showed that variation was starting point of evolution. Weakness: 1. Darwin didn’t know about genes.

54 Cladogram – a tree-like diagram that shows evolutionary relationships.

55 Evolutionary novelty: a characteristic shared by one branch of the cladogram

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