1. NOTES 30 – Evidence of Evolution

2. How is the theory of evolution supported?
The theory of evolution is supported by two types of evidence:
Evidence that shows species have changed over time
Proves that species have not always existed in their current forms
Evidence that shows different species come from common ancestors
Proves that one species can split into two different species over time

3. Fossils

4. Dimetrodon

5. What types of evidence show that species have changed over time?
Fossils – fossils are the remains of ancient organisms (bones, etc.)
Fossils have been found that are not like any species alive today
Fossils have been found that are similar to species alive today
Fossils show that other kinds of life have existed and that species have changed over time

6. Fossils & Ancient Life
Water carries small rock particles to lakes and seas
Dead organisms are buried by layers of sediment which eventually forms new layers of rock
The preserved remains may later be discovered and studied

7. Fossils & Ancient Life
From fossils, scientists can infer what past life forms were like: their structure, what they ate, what ate them, & the environment where they lived
They group similar organisms together & arrange them in the order that they lived, from oldest to most recent
Together, all this information about past life is called the fossil record

8. Fossils & Ancient Life
Relative dating - determining the age of a fossil by comparing its placement with that of fossils in other layers

9. Horse Fossil Record

10. Horse Fossil Record

11. Fossils & Ancient Life
The fossil record shows that more than 99% of all species that have ever lived on Earth have become extinct
The dodo has been extinct since the mid-to-late 17th century. It is commonly used as the archetype of an extinct species because its extinction occurred during recorded human history, and was directly attributable to human activity.

12. What types of evidence show that species have changed over time?
Vestigial Organs – body parts found in species that have little or no use
These organs are parts that had uses in the ancestors of the species but as new species evolved they were no longer necessary for survival
EX. the human appendix is a small tube on the end of the large intestine that has no modern function but was necessary to digest rough plant matter which was a large part of the diet of our non-human ancestors
Vestigial organs show that species have changed over time

14. Vestigial Organs
Some snakes and whales show the remains of pelvis and leg bones from walking ancestors
Non-functioning eyes on blind cave fish
Human tail bone

15. Why would whales have pelvis and leg bones if they were always sea creatures?

19. Homologous Structures

20. What types of evidence show that species come from common ancestors?
Homologous Structures – body parts in different species that are built in a similar way even though they may have different functions
EX. the bones in the arm of a human are similar to the bones in the front leg of a cat and in the front fin of a whale
Homologous structures are similar because the two species shared a common ancestor with a similar body part that evolved as the species changed over time

21. Homologous structures
Forelimbs of human, cats, whales, & bats share same skeletal structures
similar structure
similar embryological development
different functions
evidence of common ancestor (branched off from common 4-limbed ancestor)

22. Homologous Structures

23. Comparative Anatomy Looking at structures in different organisms in order to determine relationships between them, how they are alike, and how they are different

24. Comparative Anatomy Looking at structures in different organisms in order to determine relationships between them, how they are alike, and how they are different

25. Embryology

26. What types of evidence show that species come from common ancestors?
Embryology – the study of animal embryos (the early stages of development before birth)
Different species go through similar stages in early development
Closely related species have very similar embryos (EX. human and pig)
If species are not closely related, the embryos begin to look different earlier (EX. human and fish)

27. Comparing Embryos

28. What types of evidence show that species come from common ancestors?
Molecular Biology – studying the molecules that make up living things
Closely related organisms have common DNA
All living things have DNA which is built of the same ingredients
All living things have some DNA in common
The closely related 2 different species are, the more DNA they have in common (EX. humans and chimps share about 99% of their DNA)
Closely related organisms have common proteins

29. What does all the evidence mean?
Species alive today are NOT the same species that have always been on the Earth
Species have changed over time
Many species that have existed in the past are now extinct
It appears that different species share common ancestors and that all life can be traced back to the appearance of the first living things – this explains why different species alive today share so many characteristics (cells, DNA, etc.)

30. Evolution explains both the unity and diversity of life