1. Phylogeny

2. A Shared History We’ve talked a lot about common ancestors
We’ve seen evidence that species are related to each other
Today we’ll examine how to demonstrate evolutionary relationships

4. Phylogeny
Phylogeny: the evolutionary relationships of different groups of species or organisms
Evidence for relationships is based on fossils, morphology, and genetic evidence

5. Phylogeny
This is an entire field of evolutionary biology where evolutionary relationships are demonstrated graphically

6. Phylogeny For example, birds and reptiles are closely related
Phylogeny attempts to map out their evolutionary history
If we have a common ancestry with this lamprey, phylogeny will illustrate it

7. Cladistics
Cladistics: a method of showing evolutionary relationships based on the presence of recently evolved (or derived) traits
Synapomorphy: A derived trait shared by two or more species or groups
Indicate a closer evolutionary relationship than to organisms that do not share this trait

8. Synapomorphy Basically a homologous structure
Feathers are an example of synapomorphy:
All birds have feathers, but reptiles do not therefore birds are more closely related to each other than to reptiles

9. Synapomorphy Cladistics makes inferences based on synapomorphies
This can be a challenge: sometimes suspected synapomorphies turn out to be false
Birds and humans both walk on two legs, but this trait arose independently (analogous feature)

10. A Visual Demonstration
Cladograms: are used to show the evolutionary relationships between groups of organisms

11. Cladograms Each branch represents a different group or species
Branching points represent the most recent common ancestor of groups
A dramatic demonstration of how species are related, and how far back

12. Cladograms

13. Cladograms

14. Cladograms

15. Cladograms

16. Cladograms

17. Cladograms

18. Cladograms

19. Beauty in Cladograms

20. Beauty in Cladograms

21. The Pace of Evolution How long does it take for a new species evolve?
How quickly does a species adapt to changes in its environment?
Single species can mutate fairly quickly, at the level of single genetic mutations
On the other hand, the giraffe neck took millions of years to evolve

22. The Theory of Gradualism
The Theory of Gradualism: as new species evolve, they appear very similar to the original species and only gradually become more distinctive
Small changes accumulate gradually over millions of years

23. Theory of Gradualism Is there support for this theory?
The fossil evidence for both horses and whales illustrates this pattern

24. The Theory of Punctuated Equilibrium
The fossil record does not always indicate many intermediate steps
In some cases the fossil record shows a fairly sudden appearance of new species

25. The Theory of Punctuated Equilibrium
The Theory of Punctuated Equilibrium: suggests that most evolutionary changes occur in relatively rapid spurts, followed by long periods of little or no change

26. The Theory of Punctuated Equilibrium
Three main assertions:
1) New species evolve rapidly
2) Speciation usually occurs in small isolated populations and leaves few transitional fossils
3) After the initial burst of evolution, additional changes are slow

27. Comparing Theories The differences lay partly in time:
Gradualism: small, progressive changes over a long period of time
Punctuated Equilibrium: abrupt changes occur, followed by long periods of little change

28. Comparing Theories
It is accepted that both theories play a role in evolution
In cases where there is little environmental change, evolutionary change can happen slowly
When an environment changes drastically, we can expect rapid evolution

29. Gaps in the Record
A major source of evidence for evolution is the fossil record
But we know that fossils form very rarely, and only in certain conditions
Species with delicate features are less likely to fossilize
As a result there are significant gaps in the fossil record

30. Gaps in the Record
Transitional Form: A fossil or species intermediate between two other species in a direct line of descent
In Darwin’s day, the fossil record was very limited, and few transitional forms were known

31. Missing Links
These gaps in the fossil record are called “Missing Links”
At one time, there was no fossil evidence of early birds, representing the earliest days of feathered flight
Until 1861, when the first fossil was found

32. Missing Links
Archaeopteryx

34. Missing Links One of the greatest mysteries of evolution:
How did we evolve from fish to land animals??

35. Missing Links
Throughout the years, paleontologists have searched for the transitional fossil between fish and land animals
The “Holy Grail” of fossils
This fossil would have to be able to live on land AND in water
For many years they could only find animals that lived only in water or only on land

36. Missing Links
In 2004, a team of researchers digging in Nunavut, Canada found an extremely interesting fossil
It had traits of both fish and tetrapods (4 legged land animals)

37. Fish-Like Traits
“Fishapod” Traits
Tetrapod Traits
Gills
Limb bones and joints
Rib bones
Scales
Wrist joint with radiating fin-toes
Mobile neck
Fins
Ear was half fish/half tetrapod
Lungs

38. Tiktaalik

39. Tiktaalik

40. The Importance of Evidence
Remember: a lack of evidence does not mean evidence against a theory
An understanding of evolution still allows evolutionary biologists to predict transitional forms

41. Filling in the Gaps Today we have a much larger fossil record
Many of these missing links have been found
Each new fossil provides new clues about evolution
And often raises more questions

42. Homework Questions
Page 355 in text # 4, 7, 8bcdef Page , build the cladogram