1. Evolution Guided Reading

3. Charles Darwin
Charles Darwin was a naturalist who traveled on the British ship HMS Beagle on a five year trip around the world
Darwin observed plants and animals he had never seen before and wondered why they were so different from those in England.
These observations led him to develop the theory of evolution by natural selection

4. Darwin’s Observations
Included:
The diversity of living things
The remains of ancient organisms
Characteristics of organisms on the Galapagos Islands

5. Diversity Darwin was amazed by the diversity
Insects that looked like flowers
Ants that marched like armies
Sloths that moved very slowly and hung from trees
Today scientists have identified more than 1.7 million species of organisms on Earth
What is a species?

6. Species
A group of similar organisms that can mate with each other and produce fertile offspring
Fertile: can have their own babies

7. Fossils
Fossil: a preserved remains or traces of an organism that lived in the past
The fossils were similar to animals he saw, but he wondered why they had differences.
What had happened to the creatures from the past?

8. Galapagos Organisms
The Galapagos Islands are a chain of islands off the coast of South America
Here, Darwin observed that there were many similarities and differences between the organisms on the islands and those in South America

9. Important Differences of the Galapagos Organisms
Iguanas had large claws that allowed them to grip slippery rocks where they fed on seaweed
Iguanas on the mainland had smaller claws to climb trees and eat leaves

10. Darwin hypothesized that a small number of different plant and animal species had come to the islands from the mainland
What is this process called?

11. Dispersal The movement of organisms from one location to another
Some might have blown out to sea during a storm
Some may have set adrift on a fallen log
Once the plants and animals reached the islands, they reproduced.
Eventually their offspring became different from the mainland species

12. Comparisons Among the Islands
Darwin noticed many differences among organisms from one island to the next
Tortoises on one island had dome-shaped shells
On another island they had saddle-shaped shells

14. Adaptations
Like the tortoises, Finches on the Galapagos were noticeably different from one island to the next
The most obvious differences were in the sizes and shapes of the beaks.
Why did birds on different islands have different shaped beaks?

15. Adaptations
They had adapted to the different food sources on their specific island
adaptation: a trait that helps an organism survive and reproduce
Finches with narrow, needle-like beaks ate insects
Finches with strong, wide beaks ate seeds

17. Adaptations What are some other adaptations we have talked about?
Adaptations can be for
getting food: speed, sharp teeth
avoiding being eaten: poison, bad taste
aid in reproduction: bright colors of a flower attract insects

18. Evolution
Darwin reasoned that plants or animals that arrived on the Galapagos Islands faced conditions that were different from those on the mainland.
He hypothesized that the species gradually changed over many generations and became better adapted to the new conditions.
The gradual change in a species over time is called evolution.

19. Scientific Theory
Darwin’s ideas are referred to as the theory of evolution
A scientific theory is a well-tested concept that explains a wide range of observations
After his many observations, Darwin concluded that the organisms had changed over time, but he did not know how the changes happened.

20. Selective Breeding
Darwin studied other examples of changes in living things to help him understand evolution
He studied animals produced by selective breeding such as horses

21. Natural Selection
Darwin published the book The Origin of Species in which he proposed that evolution occurs by means of natural selection
Natural Selection: the process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species

22. Factors that affect natural selection
Overproduction
Species produce more offspring than can possibly survive
Variations
Members of a species differ from one another in many of their traits, this is called variation
Competition
Food and other resources are limited

23. Selection
Some variations made individuals better adapted to their environment
These individuals are more likely to survive and reproduce
The offspring will inherit these helpful characteristics and will be more likely to survive and reproduce
Over time helpful variations may gradually accumulate while unfavorable ones may disappear

24. Genes and Natural Selection
Darwin could not explain what caused variations or how they were passed on
Today we know that they can result from mutation and the shuffling of alleles during meiosis
Genes are passed from parent to offspring on chromosomes, because of this, only traits that are controlled by genes can be acted upon by natural selection

25. Environmental change
Change in environment can lead to natural selection
Peppered moths of Manchester England
Moths had been adapted to living on the lichen covered trees
Industrial revolution put soot into the air which turned the trees darker and killed the lichen
Now the darker moths which once stood out and were eaten first, were able to blend in to the newly darkened trees

26. Before After

27. Evidence of Evolution Fossils Similarities in Early development
Similar body structures
Similar body structures that related species have inherited from a common ancestor are called homologous structures

28. Similarities in early development
A opossum, chicken, fish and salamander all have a tail and tiny slits along their throats during the early stages of development

30. Similarities in Body Structures
Fish, amphibians, reptiles, birds, and mammals are classified in one group because they have similar body structure
Scientists have recently discovered fossils of ancient whale-like creatures that have legs and walked on land

31. Inferring Species Relationships
Scientists have combined the evidence from DNA, protein structure, fossils, early development, and body structure to determine evolutionary relationships among species
The more closely related species are, the more similar their DNA sequences
Elephant shrew is more closely related to elephants than to rodents

33. Combining Evidence
Dogs are more similar to wolves than they are to coyotes
Giant pandas are more closely related to bears
Lesser pandas are more closely related to raccoons
Branching trees can be used to show how scientists think different groups of organisms are related

34. Branching Tree

35. Did birds evolve from Pterosaurs?
What is the common ancestor of Crocodilians and Modern Birds?
Are modern birds more closely related to Archaeopteryx or to the first reptiles?

36. How Do New Species Form
A new species can form when a group of individuals remains isolated from the rest of its species long enough to evolve different traits
Isolation can occur from a river, a volcano, or a mountain range

38. Populations of squirrel separated by Grand Canyon

39. Fossil Record Formation of fossils is rare
Most form when organisms that die become buried in sediments
Sediments are particles of soil and rock
Bone and shell easily become fossils
Petrified Fossils: remains of organisms that are actually changed into rock
Molds are a hollow space in sediment left after the hard parts of the organism has dissolved
Casts are a copy of the shape made from a mold

40. Determining a Fossil’s Age
Scientists can reconstruct the history of life on earth
Two methods
Relative dating
Radioactive dating

41. Relative Dating
In layers of sedimentary rock, the oldest layer is usually at the bottom. Each higher layer is younger than the layers below it
Think of a pile of clothes in the corner of your room; the oldest clothes are at the bottom of the pile, and the ones you wore yesterday are thrown on the top
This method can only help scientists determine whether one fossil is older than another

42. Radioactive Dating
Scientists use unstable elements that decay, called radioactive elements, to determine the actual age of a fossil
The half-life of a radioactive element is the time it takes for half of the atoms in a sample to decay
For example Potassium-40 breaks down into Argon-40 over time
Scientists compare the amount of a radioactive element in a sample to what it breaks down into to find the age.

44. What is the half-life of strontium-90? How do you know?
If you started with 8 grams of strontium-90, how long would it take until there was only one gram left?

45. Half life = 28 years 8/2 = 4 4/2 = 2 2/2 = 1
Every 28 years, half of what you have will break down
8/2 = 4
How long did this take?
28 years
4/2 = 2
This took another 28 years, so how many years total?
56 years
2/2 = 1
This took another 28 years in addition to the 56. How long did it take to get to 1 g?
84 years

46. What Do Fossils Reveal
The millions of fossils that scientists have collected are called the fossil record
There are gaps in the fossil record because not all organisms can be or have been fossilized.
Fossils provide a way for scientists to learn about extinct species

47. The Geologic Time Scale
A calendar of Earth’s history
Largest span of time is the Precambrian Time
Covers the first 4 billion years of Earth’s history
Scientists know very little of this time because there are few fossils
After Precambrian Time, the time scale is divided into three major blocks of time or Eras
Eras are divided into shorter periods
The T Rex lived in the Mesozoic Era during the Cretaceous period

48. Three Eras
Paleozoic
Mesozoic
Cenozoic

49. Unanswered Questions Causes of mass extinctions
When many types of organisms become extinct at the same time
Several have taken place
End of the Cretaceous Period about 65 million years ago
Rate at which evolution occurs
Two theories
Gradualism and Punctuated Equilibira

50. Gradualism Evolution occurs slowly but steadily
Tiny changes gradually add up to major changes over very long periods of time
Should have intermediate forms between fossil organism and its descendants
Often long periods of time in which fossils show little or no change then suddenly fossils appear that are distinctly different
Could be explained by gaps in the record

51. Punctuated Equilibria
This theory accounts for the gaps in the fossil record
Says species evolve quickly during relatively short periods
These periods are separated by long periods of little or no change
Today scientists believe evolution can occur gradually at some times and more rapidly at others