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Transcript
Chapter 7
Evolution and the Fossil Record
1
Chapter 7 - Guiding Questions
• What lines of evidence convinced Charles Darwin that organic
evolution produced the species of the modern world?
• What are the components of natural selection?
• What is the source of the variability that is the basis of natural
selection?
• What role does geography play in speciation?
• What factors lead to evolutionary radiation?
• Why is convergence one of the most convincing kinds of evidence that
evolutionary changes are adaptive?
• Why do species become extinct?
• What is mass extinction?
• In what ways can evolutionary trends develop?
2
Evolution
Evolution
– changes in populations,
which consist of groups
of individuals that live
together and belong to the
same species
– a change in gene
frequencies
– populations evolve, not
individuals
• YOU can’t evolve!
Extinct ground sloth (20 ft long)
3
Evolution
Adaptations
– specialized features of
animals and plants (or any
other organism) which
perform one or more useful
functions
– allow that organism to excel
in its environment
– YOU can only modify
characteristics over which
your genes have control; e.g.,
tanning
Cat skull
Horse skull
Venus Flytrap
4
Inefficient Evolution
• can only operate by changing what is
already present;
• it’s the business of remodeling rather than
new construction from scratch
• e.g., to make a new structure, natural
selection starts by modifying an already
existing one
– e.g., how could ‘night vision’ evolve?
5
Charles Darwin
• 1831
– set sail on the Beagle
– schooled in
uniformitarianism
• Lyell’s Principles of
Geology
– a keen observer of
natural phenomena
• 1859-On the Origin of
Species by Natural
Selection
6
Some of Darwin’s Observations
• Rhea
– large flightless birds
– found only in South
America
– also found extinct,
fossil forms
• Some similarities but also
obvious differences from
ostrich (Africa) and emu
(Australia)
7
More of Darwin’s Observations
• sloths and extinct
armadillos
– unique to the Americas
8
More of Darwin’s Observations
• Oceanic islands
– many barren; Hawaii
has no native snakes,
frogs, FW fish, etc.
– species must have
originated elsewhere
• Galápagos Islands
– tortoises with shells
unique on each island
– shared a common
ancestry
– followed later by
differentiation
9
Galapagos Islands
Range from 3 to 5 my old
10
Galapagos Tortoises
• 14 subspecies, 11 extant, several with very
small populations
– e.g., Lonesome George
11
Lonesome George
Isla Pinta
12
Darwin’s Famous Finches
• Finches of the Galápagos
– different beak types
• slender-insectivorous
• sturdy-seed crushing
• woodpecker-like-tool user
– differentiation based on lifestyle
– curiously resemble a South American
mainland finch
13
Adaptive Radiation of Darwin’s Finches
14
Feeding Adaptations of Ground Finches
15
Charles Darwin
• Additional observations
– Anatomical relationships
• embryos of many vertebrates are quite similar, even
superficially indistinguishable
16
17
Charles Darwin
• Additional observations
– Anatomical relationships
• embryos of many vertebrates quite similar
• homology
– presence in two different groups of animals or plants of
organs that have the same ancestral origin but serve
different functions
18
19
Charles Darwin
• Additional observations
– Anatomical relationships
• embryos of many vertebrates quite similar
• homology
– presence in two different groups of animals or plants of
organs that have the same ancestral origin but serve
different functions
• vestigial organs
– organs that serve no apparent purpose but resemble organs
that perform functions in other creatures
20
Pelvic structures in whales and snakes
21
Vestigial Structures
22
Theory of Evolution
• Natural Selection- ‘survival of the fittest’
– the process that operates in nature but parallels
the artificial selection by which breeders
develop new varieties of plants and animals
• success of an individual determined by advantages it
has over others
– survives to bear offspring with same trait
23
24
25
Antibiotic Resistant Bacteria
26
The Basis for Natural Selection
• There is much variation between members
of a species.
27
28
The Basis for Natural Selection
1. There is much variation between members
of a species
2. Reproduction is way in excess of the
number that the habitat can survive
e.g., Robins
29
E.g., Robins
30
The Basis for Natural Selection
1. There is much variation between members
of a species
2. Reproduction is way in excess of the
number that the habitat can survive
e.g., Robins
3. Differential reproductive success-those
best adapted survive to reproduce the most
31
Will the all survive?
32
Theory of Evolution
• Darwin didn’t have all the tools we have today to
explain his idea.
• Genetics was in its infancy—Mendel’s ideas, though
contemporary with Darin, weren’t appreciated for
decades.
• Genes-hereditary factors
• Particulate inheritance
– Gregor Mendel’s idea that organisms retain identities through
generations
– Peas
• No blending
• Colors could be masked for generations
33
34
Theory of Evolution
• Mutations
– alteration of genes
– provides for variability
– very few are helpful
• DNA
– Deoxyribonucleic Acid
– transmits chemically
coded information
– mostly found in
chromosomes
35
36
Theory of Evolution
• sexual recombination
– each parent contributes one half of its chromosomes to offspring
via a gamete
• special reproductive cell containing one of each type of chromosome
– female ovum/egg; male sperm
– yields new combinations-e.g., my kids aren’t exact copies of me;
genes of their mother and me are both present.
• mutations increase variability—and we all have them!
• gene pool
– sum total of genetic components of a population or group of
interbreeding individuals
– you have only a small subset of the human gene pool
• reproductive barriers limit the pool and keep species separate
• speciation
– origin of a new species from two or more individuals of a
preexisting species
37
Reproductive Isolation
Spring breeder
Fall breeder
38
Origination
• Evolutionary radiations
– pattern of expansion from some ancestral adaptive
condition represented by descendant taxa
• adaptive breakthrough
– appearance of key features that allow radiation to occur
• fossil record documents patterns
– E.g., Jurassic corals
39
Jurassic Corals
40
Origination
• Rates of speciation
– Galápagos Islands-formed millions of years ago
– Lake Victoria
• 13,000 years old
• 497 unique species of cichlid fish, many with specialized
adaptations
• Molecular clock
– assume average rate of mutation
– determine pace of change
– extrapolate timing of change
41
Convergence
• Evolution of similar
forms in two or more
different biological
groups
• Marsupials and
placental mammals
– similar form
– isolated, adaptive
convergent evolution
after initial divergence
42
• caused by extreme
impacts of limiting
factors
Extinction
– predation
– disease
– competition
• pseudoextinction
– species evolutionary
line of descent
continues but
members are given a
new name
• high rates of
extinction make
useful index fossil
– ammonoids
43
Extinction
• rates
– average rate has
declined through
time
• mass extinctions
– many extinctions
within a brief
interval of time
– largest events peak
at extinction of
>40% genera
– rapid increase
(radiation) follows
44
Modern Mass Extinctions
• fossil patterns
reflected in modern
– tropical species
– large animals
• loss of habitat
• direct exploitation
• likely replacement by
opportunistic species
45
Evolutionary Trends
• Cope’s rule
– body size increases
during evolution of a
group of animals
– structural limitations
on size
• specialized adaptations
limit evolution
– elephants
– manatees
46
Evolutionary Trends
Whales
• terrestrial origin
– 50 Ma
– small (2 m)
mammals with
feet
• marine adaptation
–
–
–
–
40 Ma
lost hind limbs
no pelvic bones
up to 20 m
47
Phylogeny
• Phylogeny
– complex, large-scale
trend within a
branching tree of life
– gradual large-scale
change from one
species to another is
rare
• e.g., Jurassic coiled
oysters
48
Phylogeny
• Axolotl
– example of rapid speciation
from parent species
• parent is amphibious
• offspring is aquatic
throughout life after one
simple genetic change
49
Phylogeny
• rates
• gradualistic model
– very slow rates
• punctuational model
– rapid evolution with
little change between
steps
– bowfin fish
• little change in 60 m.y.
50
Phylogeny
• Horses
– increase in body size
– evolved tall complex molars
and single-hoofed toe
– change driven by climate
• expansion of grasslands
• Dollo’s law
– evolutionary transition from
at least several genetic
changes is highly unlikely
to be reversed by
subsequent evolution
51
52
53