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Macroevolution

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Concerned with major events in the history of life as found in the fossil record ... feather-bearing creatures, and feather-like structures preceded flight and hence ... – PowerPoint PPT presentation

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Title: Macroevolution


1
Macroevolution
2
Macroevolution
  • The origin of taxonomic groups higher than the
    species level
  • Concerned with major events in the history of
    life as found in the fossil record
  • Includes the origin of new design features such
    as feathers and wings in birds, upright posture
    of humans
  • Examines large scale evolutionary changes

3
Macroevolutionmajor questions of macroevolution
  • How do major novel features arise?
  • What accounts for apparently progressive trends
    found in the fossil record?
  • How has macroevolution been affected by global
    geological changes?
  • What explains the major fluctuations in
    biological diversity seen in the fossil record?

4
Macroevolution movie
5
Fossil of a fish perch
6
Fossils
  • Sedimentary rocks are the richest source
  • Formed from deposits of sand (compressed into
    sandstone) or silt (compressed into shale)
  • Usually form from mineral rich hard parts of
    organisms
  • Petrification minerals dissolved in the
    groundwater seep into the tissues of the dead
    organism and replace organic matter
  • Occasionally fossils retain organic matter (DNA)

7
Fossils come in variety of forms
8
Dinosaur National Monument dinosaur bone in
sandstone
9
Skulls of Australopithecus and Homo erectus
10
Petrified trees
11
Leaf impression
12
Dinosaur tracks (trace fossils)
13
Scorpion in amber
14
Mammoth tusks 23,000 years old (Siberia 1999)
15
(No Transcript)
16
Barosaurus
17
Limitations of the Fossil Record
  • A fossil represents a sequence of improbable
    events
  • A large fraction of species that have lived
    probably left no fossils
  • Most fossils that were formed have probably been
    destroyed
  • Only a fraction of the existing fossils have been
    discovered
  • So the fossil record is comprised primarily of
    species that lived a long time, were abundant and
    widespread, and had shells or hard skeletons

18
Early Earth Video
  • Early Earth Video

19
The Geologic Time Scale
20
Geological time scale movie
25T-01-GeologicTimeScale.mov
21
Dating
  • Relative Dating
  • Absolute Dating
  • Radiometric dating (error of less than 10)

Half-life Number of years it takes for 50 of
the original sample to decay Carbon-14
(half-life 5600 years) Best for dating material
less than 50,000 yrs old Uranium-238 (half-life
4.5 billion years)
22
Evolutionary novelties (1) how do new designs
evolve?
  • Higher taxonomic groups such as families and
    classes are defined by evolutionary novelties
    (such as wings in birds)
  • Mechanism is a gradual refinement of existing
    structures for new functions
  • Structures may have an evolutionary plasticity
    that makes alternative functions possible

23
Evolutionary novelties (2) how do new designs
evolve?
  • Preadaptation
  • When a structure evolved in one context and
    becomes co-opted for another function
  • Natural selection can not anticipate the future,
    but can improve on an existing structure
  • Example feathers in birds

24
Evolutionary novelties (3) how do new designs
evolve?
  • Genes that control development play a major role
  • A slight alteration in development becomes
    compounded in its effect on the adult
  • Allometric growth
  • Differences in relative rates of growth of
    various body parts. A slight change in these
    realtive growth rates may yield a substantial
    change in the adult

25
Allometric growth
26
Genes controlling development
  • Regulatory genes can effect hundreds of
    structural genes, so changes here have a great
    impact
  • Paedomorphosis Retention of features in the
    adult that were juvenile in ancestral species.

27
Paedomorphosis movie
24-21-PaedomorphosisAnim.mov
28
Paedomorphosis in axolotl (a salamander which
retains some larval (tadpole) characteristics)
29
Genes controlling development
  • Heterochrony evolutionary changes in the timing
    or rate of development.

30
Heterochrony and the evolution of salamander feet
among closely related species
Feet are shorter with more webbing, better for
climbing up a vertical surface. Possible
influence of an evolutionary change in a
regulatory gene which switches off foot growth
earlier in tree-dwelling species
31
Genes controlling development
  • Homeosis alteration in the placement of
    different body parts

32
Evolutionary trends (1)
  • At times it appears that there are trends in the
    fossil record (toward greater size, more
    feathers, etc.)
  • A trend does not mean macroevolution is
    goal-oriented
  • No intrinsic drive toward a preordained state of
    being is indicated by the presence of an
    evolutionary trend

33
Evolutionary trends (2)
  • Species Selection
  • Species that exist the longest and generate the
    greatest number of new species determine the
    direction of major evolutionary trends
  • Differential speciation may play a role in
    macroevolution similar to the role of
    differential reproduction (natural selection) in
    microevolution

34
Evolutionary trends (3)
  • A trend may cease or reverse itself under
    changing environmental conditions.
  • Conditions in the Mesozoic era favored giant
    reptiles, but by the end of that era the smaller
    species prevailed

35
The branched evolution of horses
Hyracotherium to modern horses. Smooth
progressive trend toward increased size, less
toes and grazing teeth??? Not a straight line. It
is just that Equus is the only survivor of a much
more complicated evolutionary tree.
36
Biogeography and Continental Drift
37
Earths crustal plates and plate tectonics
(geologic processes resulting from plate
movements)
38
Crustal plate boundaries
39
San Andreas fault
40
History of continental drift
PANGEA Ghana and Brazil are separated by 3000 km
of ocean, but matching fossils in both areas show
the areas were once connected.
41
Mass Extinctions and Adaptive Radiations
  • Mass extinctions were followed by extensive
    diversification of some of the taxonomic groups
    that survived extinction.
  • Surviving species are able to undergo new
    adaptive radiations into the vacated habitats and
    produce new diversity

42
Adaptive radiations
  • Examples
  • Flying Insects
  • Mammals

43
Mass Extinctions
  • Why? Habitat destruction? Unfavorable
    environmental conditions?
  • Permian Extinctions
  • About 250 million years ago
  • 90 of species were eliminated
  • Cretaceous Extinctions
  • About 65 million years ago
  • Over 50 of species eliminated

44
Diversity of life and periods of mass extinction
45
Trauma for planet Earth and its Cretaceous
lifeThe Asteroid Impact Hypothesis
Immediate effect-Cloud of hot vapor and debris
that could have killed most plants and animals in
N. America in minutes?
46
Mass Extinction Video
Mass Extinction Video
47
The Sixth Extinction
The Earth may be on the brink of a sixth mass
extinction on a par with the five previous
episodes This time it appears that the cause is
the activities of a growing human
population. Rate of species extinction estimated
from the fossil record is about 10-100 per year.
In tropical habitats alone the current rate may
be 27,000 per year.
48
Systematics
  • Phylogeny the evolutionary history of a species
    or group
  • Systematics the study of biological diversity
    in an evolutionary context.
  • Taxonomy identification and classification of
    species

49
Hierarchical classification
50
Homology/Analogy
  • Homology
  • Likeness attributed to a shared ancestry
  • Forelimbs of mammals are homologous structures
  • Analogy
  • Similarities due to convergent evolution, not
    common ancestry
  • Insect wings and bird wings are analogous
    structures

51
Homologous structures anatomical signs of
descent with modification
52
Convergent evolution
  • Acquisition of similar characteristics in species
    from different evolutionary branches due to
    sharing similar ecological roles with natural
    selection shaping analogous structures.

53
Convergent evolution and analogous structures
Ocotillo of SW North America
Allauidia of Madagascar
54
Convergent evolution (bird beaks)
55
Systematics connects classification and phylogeny
56
Molecular Biology tools for systematics
  • Protein comparison
  • DNA sequence comparison
  • These can be used to access relationships even
    between species so distantly related that no
    morphological similarities exist.

57
Phylogenetic Tree
  • Cladogram
  • A dichotomous tree that branches repeatedly
  • Classifies organisms according to the order in
    time that branches arise.
  • Each branch point is defined by novel homologies
    unique to the various species on that branch

58
Cladograms
59
Constructing a cladogram
60
Cladistics and taxonomy
61
Molecular clocks
  • Based on the observation that some regions of
    genomes evolve at constant rates.
  • By comparing DNA sequences from these regions or
    the proteins that result, an estimate of the time
    since the groups diverged can be estimated.

62
Dating the origin of HIV-1 M with a molecular
clock
Using a molecular clock method, a date for the
origin of HIV infections in humans can be
inferred. HIV seems to have descended from
related viruses that infect chimpanzees and sooty
mangabeys. When did the virus make the jump to
the human species?? Projecting backward, the
1930s are the probable time of first human
invasion by HIV.
63
Modern systematics is shaking some phylogenetic
trees
Traditionally, lizards, snakes, and crocs are
classified together in the Class Reptilia with
birds in a separate class (Aves)
But crocodiles may actually be more closely
related to birds than to lizards and snakes
64
Evolution of birds
Archaeopteryx
65
  • Often you may hear critics of evolution theory
    claim that it is "just a theory," and that even
    scientists disagree about many of the details of
    the Earth's past and the origin of life. 
    However, even though scientists do have heated
    discussions on the details, they do not disagree
    about the general claim of natural selection.  As
    an example, currently there is a vigorous debate
    on exactly how and when birds evolved from
    dinosaurs.  Although there is not agreement on
    every detail -- science is an on-going critical
    activity -- the evidence is solid that birds are
    the living descendants of theropod dinosaurs,
    birds are not the sole feather-bearing creatures,
    and feather-like structures preceded flight and
    hence did not evolve in connection with it. 
    Darwin's theory predicts that a very important
    survival trait may initially evolve for a
    completely different reason than that for which
    it becomes a key survival trait.  Feathers may
    have evolved in some dinosaurs for the purpose of
    communicating with potential mates and enemies or
    for moderating body temperature. Excerpt from
    Natural History Magazine.

66
Evolution of birds
67
Evolution of birds
4-winged dinosaur
http//www.npr.org/templates/story/story.php?story
Id931047
Possible Feather evolution
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