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Chapter 15 Darwin's Theory of Evolution

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1 Chapter 15 Darwin's Theory of Evolution

2 15–1 The Puzzle of Life's Diversity
This variety of living things is called biological diversity. How did all these different organisms arise? How are they related? Evolution, or change over time, is the process by which modern organisms have descended from ancient organisms. A scientific theory is a well-supported testable explanation of phenomena that have occurred in the natural world.

3 Voyage of the Beagle Charles Darwin (born February 12, 1809 in England) 1831 – set sail on the H.M.S. Beagle

4 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. That hypothesis, now supported by a huge body of evidence, has become the theory of evolution.

5 On The Voyage Collected plants & animals on land
At sea – studied specimens, read, recorded observations Saw great diversity in the organisms – enormous numbers of species!

6 Patterns of Diversity Plants and animals seemed so well suited to their environments Impressed by the many ways organisms survive and reproduce Similar areas on different continents were inhabited by very different animals. Ex: why are there no rabbits on the Australian grasslands? No kangaroos in England?

7 Living Organisms and Fossils
Darwin also collected fossils Some fossils looked like organisms that were still alive Other fossils looked completely different! Darwin wondered: Why had so many of these species disappeared? How were they related to living species?

8 The Galápagos Islands 1000 km west of South America (Ecuador)
Islands are close together but very different climates Darwin was fascinated in particular by the land tortoises and marine iguanas

9 The shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited.

10 The Journey Home Darwin began to wonder if animals living on different islands had once been members of the same species. these separate species would have evolved from an original South American ancestor species after becoming isolated from one another

11 15-2 Ideas that shaped Darwin’s thinking
Geological Information Massive, rich fossil record – much older than the current age of the earth beliefs. James Hutton (1795) – old earth – great earth changes take time Charles Lyell (1831) – the processes shaping the Earth now are the same ones that shaped the earth in the past Could life change as earth has changed?

12 Jean Baptiste Lamarck 1809 “living things have changed over time”
Species descended from other species Lamarck’s theory of evolution: Tendency toward perfection Use and Disuse Inheritance of Acquired Traits Why was he wrong? Behavior doesn’t affect the DNA He was WRONG.

13 Thomas Malthus 1798 Population growth (if gone unchecked) would quickly over run the earth Why don’t maple trees cover the earth since they each release 1000s of seeds? Darwin’s questions: What causes the deaths of so many? What factors determine which survive and reproduce?

14 All species tend to produce more offspring than they can support
Turtle eggs Insect eggs Frog eggs

15 15-3 Darwin presents his case
Worked for years but scared to publish because of religious backlash 1858 – sent an essay by Alfred Russell Wallace summarizing Darwin’s theory of evolution 1859 – Darwin publishes “On the origin of species by means of natural selection”

16 What did Darwin say? Inherited Variation & Artificial Selection
Members of a species vary Artificial Selection = nature provides the variation and humans select the variations they find useful Examples: fat hog, fast horse, high milk producing cow Does something in nature select the same way?

17 Variation within a species

18 Artificial Selection

19 Evolution by Natural Selection
Compared nature to artificial selection

20 Struggle for Existence
Members of each species compete for food, space, mates, and other necessities of life Predators (that are better/faster) catch more prey Prey (faster, better camouflage) avoid being caught Examples: fast cheetah, small rabbit, stronger lion, more colorful butterfly

21 Producing more offspring than can possibly survive thus creating a struggle for existing resources
sunflower Preying Mantis

22 Survival of the Fittest
Fitness = being able to survive and reproduce in its specific environment Fitness results from adaptations Adaptations = inherited characteristics that improve an organisms chance of survival Successful adaptation  better suited to the environment  more fitness

23 Adaptations – Anatomical/structural (quills on a porcupine)
Physiological (photosynthesis) Behavioral (live/hunt in groups)

24 Low Fitness  organisms die off
High Fitness  survive + reproduce  Survival of the Fittest! Natural Selection of most fit organisms!

25 Nature (the environment) will determine which organism is the fittest to Survive

26 Natural Selection Results from NO human intervention, control, or direction Results in changes in the inherited characteristics of a population Increases a species’ fitness in the environment (over time!)

27 Descent with Modification
Over large amounts of time… natural selection produces organisms: with different structures establishes different niches occupies different habitats organisms look different than their ancestors Descent with modification = each living thing has descended with changes, from other species over time.

28 Common Ancestors Implies that organisms are all related to one another. Tiger, panther, cheetah – related Horses, dogs, cats – related farther back Mammals, birds, reptiles, fish – related even farther back All living things – related! Single Tree of Life!


30 Evidence of Evolution

31 Living things have been evolving on Earth for millions of years…
Evidence.. Fossil Record Geographic distribution of living species Homologous body structures body part with the same basic structure and embryonic origin as that of another organism, though not necessarily sharing the same function Similarities in early development (embryology)

32 The Fossil Record Fossils = remains of ancient life
Different layers of rock were formed at different times during Earth’s history. Darwin proposed that organisms had coming into being, lived, and vanished. Life had changed over time!

33 Fossil Cephalopods  

34 Fossil record of the modern horse

35 Fossil record of the camel

36 Since Darwin… The number of known fossils has gone up dramatically!
Researchers have discovered many hundreds of transitional fossils that document various intermediate stages in the evolution of modern species from organisms that are now extinct. Gaps remain in the fossil records These gaps do not indicate weakness in the theory of evolution itself. Rather, they point out uncertainties in our understanding of exactly how some species evolved.

37 Geographic Distribution of Living Species
Darwin wondered about the finches he found in the Galapagos Islands. Where were they similar but still different? Also.. Slightly different from S. American mainland species Could the birds have changed as they adapted to local environments? => descended with modification from a common mainland ancestor

38 Convergent Evolution Darwin found entirely different species of animals on the continents of South America and Australia. Similar environments on those continents  he sometimes saw different animals that had similar anatomies and behaviors. The existence of similar but unrelated species was a puzzle to Darwin.

39 Similar Species in Similar Environments

40 Convergent Evolution The adaptive evolution of superficially similar structures, such as the wings of birds and insects, in unrelated species subjected to similar environments.

41 Unrelated organisms come to resemble one another

42 Analogous Structures Structures that serve the same function in different species but they evolved independently same function, different structure Ex: bat wing, butterfly wing

43 Divergent Evolution two or more related species becoming more and more dissimilar

44 Homologous Body Structures
striking anatomical similarities among the body parts of animals with backbones of reptiles, birds, and mammals—arms, wings, legs, and flippers—vary greatly in form and function. all constructed from the same basic bones limbs has adapted in ways that enable organisms to survive in different environments

45 Homologous Body Structures
structures that have different mature forms in different organisms but develop from the same embryonic tissues

46 Vestigial Organs organ that serves no useful function in an organism
Why would an organism possess organs with little or no function? One possibility = presence of a vestigial organ may not affect an organism's ability to survive and reproduce  natural selection would not cause the elimination of that organ.


48 The human appendix has no function in humans but is very important in cows and other animals

49 Human tailbone is a vestigial vertebrate tail
consists of fused vertebrae that no longer function as a tail

50 Similarities in Embryology
embryos of many animals with backbones are very similar many embryos look especially similar during early stages of development

51 chickens, turtles, and rats
Pharyngeal slits Dolphin

52 Summary of Darwin's Theory
Individual organisms differ, and some of this variation is heritable. Organisms produce more offspring than can survive, and many that do survive do not reproduce. Because more organisms are produced than can survive, they compete for limited resources.

53 Each unique organism has different advantages and disadvantages in the struggle for existence. Individuals best suited to their environment survive and reproduce most successfully. These organisms pass their heritable traits to their offspring. Other individuals die or leave fewer offspring. This process of natural selection causes species to change over time. Species alive today are descended with modification from ancestral species that lived in the distant past. This process, by which diverse species evolved from common ancestors, unites all organisms on Earth into a single tree of life.

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