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Chapter 15 Evolution.

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Presentation on theme: "Chapter 15 Evolution."— Presentation transcript:

1 Chapter 15 Evolution

2 Think About It? What is evolution? Why does it happen?
How does it happen?

3 What is evolution? Change in a population over time  at genetic level
 mutations

4 Mutations Change in DNA code  can affect phenotype

5 REVIEW: From Gene to Protein

6 The Darwin Dude 5 year voyage on Beagle (1831-36)
Naturalist: surveyed coast of S.A. Wrote “Origin of Species”

7 The Darwin Dude Collected: Rocks Fossils Plants Animals
Charles Lyell’s Principles of Geology proposed Earth was millions of years old!

8 Lyell: Explained marine life at high elevation in the Andes
Giant fossil versions of smaller living mammals Earthquakes could lift rocks great distances very quickly.

9 Galapagos Island Facts
Part of Ecuador 13 main volcanic islands Formed between MYA

10 Darwin & Galapagos Organisms adapted to their environment
“Darwin’s Finches” Gould (ornithologist) finches were separate species not found any where else. Mechanism for evolution = Natural Selection

11 Artificial Selection:
Darwin believed new species appear gradually through small changes in ancestral species. Breeders – can promote specific traits by selecting and breeding organisms that have the most exaggerated expressions of those traits. Known as Artificial Selection!

12 Inference: If humans could change species by artificial selection, the same process could work in nature! Given enough time this process could produce new species!

13 Artificial Selection:

14 Noteworthy Species

15 Darwin’s Finches Adaptive Morphology

16 Why do species change? Variations & adaptations help organisms survive


18 Camouflage

19 Camouflage

20 Thomas Malthus: Human population, if unchecked, would eventually outgrow its food supply, leading to a competitive struggle for existence. Darwin believed Malthus’s ideas could be applied to the natural world. Some competitors are better equipped for survival than others!

21 Natural Selection Organisms with favorable traits survive & reproduce
Variation is key

22 Natural Selection (cont.)
Struggle for existence Species become better fit for their environment If not they could DIE!

23 Natural Selection (cont.)
4 Main Principles (pg 421): Variation Heritability Overproduction Reproductive Advantage

24 1. Variation: Individuals in a population differ from one another.

25 2. Heritability: Variations are inherited from parents. Example: X

26 3. Overproduction: Populations produce more offspring than can survive. Example: 48 white tiger litters produces 148 cubs 105 of them died without reproducing 71%

27 4. Reproductive Advantage:
Some variations allow the organism that possesses them to have more offspring than the organism that does not possess them. Example: White tigers have powerful jaws & teeth, very strong sense of smell, sharp eyesight, and excellent swimmers!


29 Types of Natural Selection
1. Stabilizing Selection: Average phenotype favored Ex. Human baby weight

30 Stabilizing Selection

31 Types of Natural Selection
2. Directional Selection: increases “extreme” versions of traits Ex. Peppered Moth, Darwin’s finches

32 Peppered Moth: Natural Selection

33 Directional Selection

34 Types of Natural Selection
3. Disruptive Selection: splits populations into 2 groups Both extremes favored Ex. Marine & Land Iguanas

35 Disruptive Selection

36               V = Variation: All life forms vary genetically within a population. It is this genetic variation upon which selection works. I = Inheritance: Genetic traits are inherited from parents and are passed on to offspring. S = Selection: Organisms with traits that are favorable to their survival get to live and pass on their genes to the next generation. T = Time: Evolution takes time. Evolution can happen in a few generations, but major change, such as speciation, often takes long periods of time.

37 Evidence of Evolution Fossil Record Fossils: preserved evidence
Found in Sedimentary rock

38 Evidence of Evolution Provides record of species that lived long ago.
Some similar to current ones! Some species unchanged!

39 Similar fossil forms: Glyptodon & Armadillos

40 Species unchanged: Horseshoe Crab!

41 “Soft parts” don’t fossilize
Fossil Record (cont) “Soft parts” don’t fossilize Specific conditions are needed to form fossils Hundreds of transitional fossils found


43 Classes of Traits: Two major classes of traits while studying transitional fossils: Derived traits: newly evolved features Ancestral traits: more primitive features that appear in ancestor forms.

44 Evidence of Evolution 2. Homologous Structures:
Anatomically similar structures Evidence of common evolutionary origin

45 Homologous Structures




49 Analogous Structures:
Can be used for same purpose and can be superficially similar in construction but are not inherited from a common ancestor.

50 Analogous Structures:

51 Evidence of Evolution 3.Embryology: similarities in embryos

52 Embryology: Embryo – early, pre-birth stage of an organism’s development. Vertebrate embryos exhibit homologous structures during certain phases of development.


54 Evidence of Evolution 4.Compararative Biochemistry: Organisms have similar DNA, genes and enzymes


56 Comparative Biochemistry:
The more closely related the species are, the greater number of amino acid sequences they will share. Ex. Chimpanzees and Humans share 96% similar sequences!

57 Humans & Chimpanzees: Human genome is 96% similar to great ape species. Pan troglodytes (species of chimp) used in study The number of genetic differences between humans and chimps is ten times smaller than that between mice and rats.

58 Pan troglodytes (common Chimp)

59 Evidence of Evolution 5. Vestigial Structures:
reduced in size, no longer have function Kiwi wings: too small to be any use in


61 What is Speciation? Formation of new species
Become genetically different

62 What are Species? Group of organisms that can interbreed & produce fertile offspring

63 Infertile Species Horse + Donkey = Mule 64 ch ch. = sterile

64 Liger
In addition to accidental Ligers there have been accidental Ti-Ligers (Female ligers who have bred with male tigers) and Li-Ligers (Female ligers who have bred with male lions). This has happened on several occasions due to wide spread myth. It was believed that the offspring of a Lion and a Tigress was infertile, therefore these beasts were often housed with other large cats. However, female ligers are not infertile and can (and will) produce offspring. These creatures resemble their fathers more than their mothers, this is believed to be due to the fact that they are then 75% of that type of cat, whether he be a lion or a tiger

65 Species Loop Hole Not a perfect definition Used for classification
Some different species can produce fertile offspring

66 Grizzly Bear & Polar Bear
“Pizzly” or “Grolar”

67 Rate of Speciation Gradualism: Evolution occurring at slow rate
Punctuated Equilibrium: Evolution occurring at irregular rates


69 Cause of Speciation Geographic Barriers Environment Changes
Mountains, Rivers, etc. Environment Changes

70 Cause of Speciation 3. Reproductive Isolation Examples:
mating at different times birds mating with others who sing a particular song.

71 Patterns of Evolution:
Adaptive radiation (divergent evolution) Coevolution Convergent evolution

72 1. Adaptive Radiation: Relatively short period of time
1 species gives rise to many Usually occurs after mass extinctions

73 2. Coevolution: Evolution of 1 species affects the evolution of another species.

74 3. Convergent Evolution:
Unrelated species evolve similar traits Under same environmental pressures Mara and Rabbits: Maras have stocky bodies, three sharp-clawed digits on the hind feet, and four digits of the forefeet. Maras have been described as resembling long-legged rabbits. Patagonian maras can run at speeds up to 29 km (18 mi) per hour. Maras can weigh over 11 kg (24 lb) in adulthood. Most maras have a brown head and body, a dark almost black rump with a white fringe around the base, and a white belly. Maras may amble, hop in a rabbit-like fashion, gallop, or bounce on all fours. They have been known to leap up to 6 ft (1.8 m).

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