Transcript ch18_lecture

The Macroevolutionary Puzzle
Chapter 18
Fossils and the Great Deluge
• Fossils of seashells have been found in
rock layers high in the mountains
• How did they get there?
• Initial explanation was that they had been
deposited during the biblical flood
Evidence of Past Life
• 1700s
• Excavations unearthed similar fossil
sequences in distant places
• Scholars began to view these findings as
evidence of the connection between Earth
history and the history of life
What Do Fossils Tell Us?
• As a result of mutations, natural
selection, and drift, each species is a
mosaic of ancestral and novel traits
• All species that ever evolved are related
to one another by way of descent
Macroevolution
The large-scale patterns, trends,
and rates of change among
families and other more inclusive
groups of species
Fossils
• Recognizable evidence of ancient life
– Fossilized hard parts (most common)
– Trace fossils (indirect evidence)
Fossilization
• Organism becomes buried in ash or
sediments
• Rapid burial and a lack of oxygen aid
in preservation
• The organic remains become infused
with metal and mineral ions
Stratification
• Fossils are found in sedimentary
rock
• This type of rock is formed in layers
• In general, layers closest to the top
were formed most recently
Radiometric Dating
parent isotope in
newly formed rock
after one half-lives
after two half-lives
Geologic Time Scale
• Boundaries based
on abrupt
transitions in fossil
record
• Correspond to
mass extinctions
• Archean eon
(oldest interval)
• Proterozoic eon
• Paleozoic era
• Mesozoic era
• Cenozoic era
(most recent)
Record Is Incomplete
• Fossils have been found for
about 250,000 species
• Most species weren’t
preserved
• Record is biased toward the
most accessible regions
Continental Drift
• Idea that the continents were once joined
and have since “drifted” apart
• Initially based on the shapes
• Wegener refined the hypothesis and
named the theoretical supercontinent
Pangea
Changing Land Masses
420 mya
260 mya
65 mya
10 mya
Evidence of Movement
• Wegener cited evidence from glacial
deposits and fossils
• Later was discovered that magnetic
orientations in ancient rocks do not align
with the magnetic poles
• Discovery of seafloor spreading provided
a possible mechanism
Plate Tectonics
• Earth’s crust is fractured into plates
• Movement of plates is driven by
upwelling of molten rock at mid-oceanic
ridges
• As seafloor spreads, older rock is forced
down into trenches
Forces of Change
crustal margin of one
plate being thrust under
margin of another plate
mid-oceanic
range
plumes of
molten material
Comparative Morphology
• Comparing body forms and structures of
major lineages
• Guiding principle:
– When it comes to introducing change in
morphology, evolution tends to follow the
path of least resistance
Morphological Divergence
• Change from the body
form of a common
ancestor
• Produces homologous
structures that may serve
different functions
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1
3
Morphological
Divergence
PTEROSAUR
4
1
2
CHICKEN
3
STEM
REPTILE
2
2
PENGUIN
3
1
3
4
1
5
2
3
4
5
PORPOISE
1
2
BAT
3
1
2
3
4
5
4
5
HUMAN
Morphological Convergence
• Individuals of different
lineages evolve in similar
ways under similar
environmental pressures
• Produces analogous
structures that serve similar
functions
Comparative Development
• Each animal or plant proceeds through a
series of changes in form
• Similarities in these stages may be clues
to evolutionary relationships
• Mutations that disrupt a key stage of
development are selected against
Altering Developmental
Programs
• Some mutations shift a step in a
way that natural selection favors
• Small changes at key steps may
bring about major differences
• Insertion of transposons or gene
mutations
Development of Larkspurs
• Two closely related
species have
different petal
morphology
• They attract
different pollinators
side view
front view
D. decorum flower
side view
front view
D. nudicaule flower
Development of Larkspurs
Petal length (millimeters)
• Petal difference arises from a change in
the rate of petal development
6
D. decorum
4
2
D. nudicaule
0
0
10
20
40
Days (after onset of meiosis)
Similar Vertebrate Embryos
• Alterations that disrupted early development
have been selected against
FISH
REPTILE
BIRD
MAMMAL
Similar Vertebrate Embryos
Adult
shark
Aortic arches
Two-chambered
heart
Certain veins
Early
human
embryo
Developmental Changes
• Changes in the onset, rate, or time of
completion of development steps can
cause allometric changes
• Adult forms that retain juvenile
features
Proportional Changes in Skull
Chimpanzee
Human
Comparative Biochemistry
• Kinds and numbers of biochemical
traits that species share is a clue to
how closely they are related
• Can compare DNA, RNA, or
proteins
• More similarity means species are
more closely related
Comparing Proteins
• Compare amino acid sequence of proteins
produced by the same gene
• Human cytochrome c (a protein)
– Identical amino acids in chimpanzee protein
– Chicken protein differs by 18 amino acids
– Yeast protein differs by 56
Sequence Conservation
• Cytochrome c functions in electron
transport
• Deficits in this vital protein would be
lethal
• Long sequences are identical in wheat,
yeast, and a primate
Sequence Conservation
Yeast
Wheat
Primate
Nucleic Acid Comparison
• Use single-stranded DNA or RNA
• Hybrid molecules are created, then
heated
• The more heat required to break hybrid,
the more closely related the species
Molecular Clock
• Assumption : “Ticks”
(neutral mutations) occur
at a constant rate
• Count the number of
differences to estimate
time of divergence
Taxonomy
• Field of biology concerned with
identifying, naming, and classifying
species
• Somewhat subjective
• Information about species can be
interpreted differently
Binomial System
• Devised by Carl von Linne
• Each species has a two-part
Latin name
• First part is generic
• Second part is specific name
Higher Taxa
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Kingdom
Phylum
Class
Order
Family
• Inclusive groupings
meant to reflect
relationships among
species
Phylogeny
• The scientific study of evolutionary
relationships among species
• Practical applications
– Allows predictions about the needs or
weaknesses of one species on the basis of
its known relationship to another
A Cladogram
shark
mammal
crocodile
fur
lungs
heart
bird
feathers
Five-Kingdom Scheme
• Proposed in
1969 by Robert
Whittaker
Monera
Protista
Fungi
Plantae
Animalia
Three-Domain Classification
• Favored by microbiologists
EUBACTERIA
ARCHAEBACTERIA
EUKARYOTES
Six-Kingdom Scheme
EUBACTERIA
ARCHAEBACTERIA
PROTISTA
FUNGI
PLANTAE
ANIMALIA
Transitional Forms
Dromaeosaurus
Archaeopteryx