1. ‘Living Fossils’ Morphological stasis in horseshoe crabs 200 mya 280
400
‘Living Fossils’

3. What about lungfish?

4. Punctuated equilibrium
Nobody changes
‘Living fossils’ are just the rare group that is not diverse
clams
The more the diversity the more possibility for change in the clade.
In some clades there is substantial change
e.g. horses

6. Balance between origination
and extinction

7. For change: Species Selection Variation among taxa Taxa don’t change
They produce (via speciation) other
similar taxa
Differences in speciation
or extinction rates
Species Selection

8. Increase versus decrease
in ‘body size’
Extinction
Origination

9. If this is the real pattern of the tree of life
It may not be possible to tell which is ancestral
and which is derived. With little change there
may be no way to resolve the split. With the
ancestor persisting there must be a polytomy
What will the reconstructed
phylogeny look like?

10. Many, unresolvable polytomies
may be the signature of
Punctuated Equilibrium

11. History/Origins of Mammals
Humans
The Cambrian Explosion
All Animal Phyla
Common threads?
Evolution and Complexity

13. Jaw architecture and muscle morphology
Tooth variety
Gait differences
Homeothermic and associated characters
Large brains
Distinctive reproduction ---> lactation

14. Triassic (up to 200)
Permian ( )
Pennsylvanian (310 my)

15. Large diversity
Major extinctions
Survival of few lineages

16. Human evolution
Who are our relatives?
What makes us unique?
What makes us human?

19. Evidence of a bushy hominid lineage
Times when multiple species
Numerous extinctions
Some survive
Contingency -- Future events are shaped by
small, chance events.
Replaying the tape

20. Cambrian Seas -- increase in atmospheric oxygen and primary
productivity (key to
multicellularity)
-- possible mass extinction
of Ediacaran fauna -->
ecological opportunity
Conway Morris 1998

21. The Cambrian Explosion What, if anything, exploded?
Precambrian 560 mya
Ediacaran fauna
first multicellular
Cambrian 543 mya
‘explosion’ of diversity
all body plans
~all phyla (some extinct)

22. Not even an explosion of morphologies--an explosion of fossils
Appearance of most phyla within few
million years--nearly instantaneous
Molecular clock evidence
Book tries to reconcile the two: Cambrian
Explosion is an explosion of animal
morphologies but not necessarily of lineages
Not even an explosion of morphologies--an explosion of fossils

23. The central role of development

24. Hox genes and phylogenies

25. Pushing back still further
--Key Innovations associated with the development of multicellularity
--cell adhesion molecules
--epithelial sheets of cells
--hierarchical gene action
--Key Innovations for Eukaryota
--organelles
--mitosis
--nucleus

26. Complex traits
evolution vs. intelligent design
complex eyes of vertebrates and squid; wings
-- incipient evolution of new features
-- evolution of highly complex adaptations

27. Hypotheses for the Incipient Evolution of Complex Adaptations
In its initial form, the feature is sufficiently well-developed
to provide an advantage (e.g., Mimicry genes)
The new feature is not initially adaptive, but is a
developmental by-product of other adaptive features
(e.g., Pierine wing color)

28. One ancestral function of a feature becomes accentuated
“With malleus the mammalian ear evolved from two
Aforethought bones from the lower jaw, the
Mammals articular and the quadrate
Got an earful
Of their ancestors’
Jaw”
--J.M.Burns
A change in the function of a feature alters the pattern of selection,
leading to its modification

29. 4. a change in the function of a feature alters the pattern of selection,
leading to its modification
penguin
extinct flightless auk
Great Auk
flying auk
gull

30. 1. photosensitive epithelium
2. simple eye cup
3. deeper cup; more
directional information
4. gradual evolution toward a
“pinhole” eye
5. refractive lens; from
increased protein concentration
6. Flat, pigmented iris surrounding
lens improves focusing
15 lineages have independently evolved
eyes with a distinct lens

31. Patella Pleurotomaria Haliotis
eye cup deeper eye cup pinhole eye
Turbo Murex Nucella
closed eye lens eye lens eye

32. Evolution of highly complex adaptations
-- intermediate stages in the evolution of complex
features are advantageous
-- key innovations - lift restrictions
allow entry into a different adaptive zone
Amniote eggs
tracheal respiration
ruminant digestion .

33. Evolution of highly complex adaptations, cont.
-- release of functional constraints
- functional divergence of redundant elements
diversification of serially repeated structures
trilobite legs: gills, feeding structures, locomotion
insects: separate appendages and/or structures
- decoupling of functions and structures
percoid fish: oral jaws collect and manipulate food
pharyngeal jaws transport food to esophagus
labroideid fish: pharangeal jaws manipulate food
oral jaws diversify in food collection
-- functional integration (“acquired dependence”)
advantageous ---> essential ---> evolution of other traits

34. Summary 1. Living fossils are survivors of sparse lineages
2. Species selection can proceed analogously to natural selection
3. Polytomies may be the real signature of puctuated equilibrium
4. Examples illustrate the bushiness of evolutionary trees
Contingency
5. The Camrian explosion may not have been that explosive
6. Developmental (cell biological) changes have shaped many major
evolutionary transitions
7. Complex traits may be advantageous in incipient stages or may change
function with modification. There are repeated motifs in the
evolution of complex adaptations.