1. Evolution
Diversity of life

2. Definition
Evolution is the process by which modern organisms have descended from ancient organisms.
(Change over time)

3. Evolution
“Nothing in biology makes sense EXCEPT in the light of evolution.” Theodosius Dobzhansky
Charles Darwin in later years

4. Evolutionary timeline

5. The puzzle of life’s diversity

6. Charles Darwin the Naturalist

7. The person who contributed the
most to our understanding of
evolution was Charles Darwin.
In 1831, at age 22, he joined
the crew of the H.M.S Beagle
as a naturalist for
a 5 year voyage
around the world.

8. Darwin’s voyage of discovery
A reconstruction of the HMS Beagle sailing off Patagonia.

9. Darwin returned 5 years later in 1836
Darwin left England in 1831
Darwin returned 5 years later in 1836

10. Voyage of the Beagle
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.

11. Darwin’s observations

12. Patterns of diversity
Organisms were well adapted to whatever environment they inhabited.
Puzzled as to why similar habitats were inhabited by different animals.
Species were not evenly distributed
Australia had kangaroos, but no rabbits. But had the perfect habitat for rabbits.

13. Living organisms and fossils
Darwin collected both living organisms & fossils.
Some fossils resembled organisms that were still alive.
Some of them were unrecognizable creatures.
What happened to them? How are they related to todays species?

14. The Galapagos Islands
A small group of volcanic islands 1000 km west of South America
Very different climates on each island
Animals on the islands were unique
Tortoises
Iguanas
Finches

15. The Galapagos Islands Each island had long or short neck tortoises.
Island species varied from mainland species and from island-to-island species
Each island had long or short neck tortoises.

17. The Galapagos Islands
Finches unknown to him at the time were thought to be wrens, warblers and black birds.
But he noted that they had different types of beaks.

19. Darwin’s thoughts on his journey home.
Birds from the different islands looked different.
Tortoises also differed from island to island.
Darwin observed that the characteristics of many organisms varied noticeably among different islands of the Galapagos.
Had they once been the same species?
Did they come from a South American ancestor?

20. Ideas that shaped Darwin's thinking
Hutton and geological change
Lyell’s Principles of Geology
Lamarck’s evolution hypothesis
Population growth by Thomas Malthus

21. In Darwin’s days…
Most people believed that the earth and all life forms were only a few thousand years old and since then neither the planet nor any species had changed.
The fossil record altered this point of view to include many periods of creation.
But when Darwin’s observations did not fit these ideas his thinking changed dramatically.

22. Hutton’s theory of geological change
James Hutton, 1795, Scottish geologist
Described the geological forces and natural forces that have shaped the Earth over millions of years.
Proposed that the Earth was more than a few thousand years old.

23. Charles Lyell Principles of Geology
Published by Lyell just before the Beagle set sail and read by Darwin
Explained how awesome geological features could be built up or torn down over long periods of time.
Helped Darwin understand sea shells in the Andes mountains at 12,000+ feet
Expanded earth’s age

24. Geological influence
Darwin was influenced in 2 ways with his new understanding of geology.
1. If the Earth could change over time might life also change over time?
2. It would take an extremely long time for life to change in the way he thought. If so, it would only be possible if the Earth was really old.

25. Lamarck’s theory of evolution
An idea called law of use and disuse
If a body part was used, it got stronger
If body part was NOT used, it deteriorated.

26. Lamarck’s theory of evolution
Use and disuse - organisms could change the size or shape of organs by using them or not using them.
Blacksmiths & their sons (muscular arms)
Giraffe’s (necks longer from stretching)

28. Lamarck’s theory of evolution
Inheritance of acquired characteristics
Proposed that by selective use or disuse of organs, organisms acquired or lost certain traits or characteristics during their lifetime.
These traits could then be passed on to their offspring.
Over time this led to new species.

29. Lamarck’s theory of evolution
Inheritance of acquired characteristics
Traits acquired during ones lifetime would be passed to offspring
Clipped ears of dogs could be passed to offspring!

30. Lamarck’s theory of evolution
Tendency toward perfection
Organisms are continually changing and acquiring features that help them live more successfully in their environment.
Example: bird ancestors desired to fly so they tried until wings developed.

31. Lamarck’s mistakes
Lamarck did NOT know how traits were inherited (traits are passed through genes)
Genes are NOT changed by activities in life.
Change through mutation occurs before an organism is born.

32. Lamarck’s mistakes
Even though Lamarck was wrong he was one of the first to realize that organisms are adapted to their environments and come up with a hypothesis of evolution.
This paved the way for later biologists like Darwin.

33. Population growth Thomas Malthus, 1798 Economist
Observed babies being born faster than people were dying.
Population size limited by resources such as the food supply

34. Population growth
Malthus reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone.
Death rate will increase to balance population size and food supply.

35. Malthus’ influence
Darwin realized that this applied to plants and animals more so than humans.
Plants and animals produce more offspring
Why hasn’t the earth been over run?
The majority of the offspring die and only a few reproduce.
What factor or factors determine which organisms die and which ones live?

36. Darwin presents his case

37. Publication of “On the Origin of Species”
Upon his return to England, Darwin developed his observations into the theory of evolution
But he did not publish for 25 years
Why?

38. Publication of “On the Origin of Species”
Darwin knew that his theory would be extremely controversial and would be attacked.
His theory challenged established religious and scientific beliefs, particularly about the creation of man.

39. Publication of “On the Origin of Species”
He refused to publish until he received an essay from Alfred Wallace
Fellow naturalist
Independently developed the same theory
After 25 years, someone else had come to the same conclusions from their observations of nature.

40. Wallace’s contribution
Alfred Russel Wallace independently came to same conclusion as Darwin that species changed over time because of their struggle for existence.
When Darwin read Wallace’s essay, he knew he had to publish his findings.

41. Publication of “On the Origin of Species”
Darwin presented Wallace’s essay and some of his work at a scientific conference of the Linnaean society in July of 1858.
Then he started on his book “Origin of Species”
It took Darwin 18 months to complete the book.
But what did he say?

42. Natural variation and artificial selection
He abandoned the idea that species were perfect and unchanging.
He observed significant variation in all species
He observed that farmers use variation to improve crops and livestock
This was called selective breeding or artificial selection.

43. Natural variation and artificial selection
In artificial selection, nature provided the variation among different organisms, and humans selected those variations that they found useful.

45. Evolution by natural selection concepts
The struggle for existence (compete for food, mates, space, water, etc.)
Survival of the fittest (strongest able to survive and reproduce)
Descent with modification (new species arise from common ancestor replacing less fit species)

46. The struggle for existence
Left unchecked, the number of organisms of each species will increase exponentially, generation to generation
In nature, populations tend to remain stable in size
Environmental resources are limited.

47. The struggle for existence
Production of more individuals than can be supported by the environment leads to a struggle for existence among individuals.
Only a fraction of offspring survive each generation
Survival of the fittest

48. Survival of the fittest
Fitness
Ability of an individual to survive and reproduce in its environment.
Adaptation
Inherited characteristic that increases an organisms chance for survival.

49. Survival of the fittest
Adaptations can be:
Physical
Speed, camouflage, claws, quills, etc.
Physiological processes
Photosynthesis by plants
Behavioral
Solitary, herds, packs, activity, etc.

50. Survival of the fittest
Fitness is central to the process of evolution
Individuals of a population vary extensively in their characteristics with no two individuals being exactly alike.
Much of this variation between individuals is inheritable.

51. It’s the Survival of the fittest
Individuals with low fitness are likely to die or produce few offspring
It’s the Survival of the fittest
Individuals who inherit characteristics most fit (high fitness) for their environment are likely to leave more offspring
AKA Natural selection
Nature is selecting for the best.

52. Natural Selection
Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species fitness in its environment.
With favorable characteristics accumulating over generations a new species could evolve.

53. Natural Selection

54. Descent with modification
Takes place over long periods of time
Natural selection can be observed as changes in
Body structures
Ecological niches
Habitats

55. Descent with modification
Species today look different from their ancestors
Each living species has descended, with changes from other species, over time.
Evolution of a new species from an ancestor.

56. Descent with modification
Common descent
All species, living and extinct, were derived from common ancestors.
Implies that all living organisms are related
Single tree of life

57. Major problem in Darwin’s theory
No mechanism to explain natural selection
How could favorable variations be transmitted to later generations?
With the rediscovery of Mendel’s work in the first half of the 20th century, the missing link in evolutionary theory was found. .

58. Opposition to evolution
The upheaval surrounding evolution began with Darwin’s publication of on the origin of species by means of natural selection
The debate continues nearly 150 years later

59. Theory of evolution today
Supporting evidence
copyright cmassengale

60. Evidence of evolution
Darwin argued that living things have been evolving on earth for millions of years. Evidence for this process could be found in:
The fossil record
The geographical distribution of living species
Homologous structures of living organisms
Similarities in embryology (early development)

61. Fossil record Earth is billions of years old
Fossils in different layers of rock (sedimentary rock strata) showed evidence of gradual change over time.

62. Geographic distribution of living species
Different animals with similar anatomies and behaviors on different continents.
Different animals on different continents have similar adaptations due to similar environments.

63. Homologous Structures

64. Homologous body structures
Scientists noticed animals with backbones (vertebrates) had similar bone structure
May differ in form or function.
Limb bones develop in similar patterns
Arms, wings, legs, flippers

65. Homologous body structures
Structures that have different mature forms but develop from the same embryonic tissues
Strong evidence that all four-limbed animals with backbones descended, with modification, from a common ancestor
Help scientist group animals (Taxonomy)

66. Homologous body structures
Not all serve important functions
Vestigial organs (traces)
Appendix in man
Legs on skinks

67. Similarities In Embryonic Development
Evidence for Evolution - Comparative Embryology
Similarities In Embryonic Development

68. Similarities in early development
Embryonic structures of different species show significant similarities
Embryo – early stages of vertebrate development
copyright cmassengale

69. Human fetus – 5 weeks

70. Chicken
Turtle
Rat

71. Summary

72. Darwin's theory
Individual organisms in nature differ from one another. Some of this variation is heritable.
Organisms in nature produce more offspring than can survive, and many that do survive, do not reproduce.

73. Darwin's theory
Because more organisms are produced than can survive, members of each species must compete for limited resources.
Because each organism is unique, each has different advantages and disadvantages in the struggle for existence.
Individuals best suited to their environment survive and reproduce successfully – passing their traits to their offspring. This process of natural selection causes species to change over time.

74. Darwin's theory
Species alive today have descended with modifications from species that lived in the past.
All organisms on Earth are united into a single tree of life by common descent.