Download The Evidence for Evolution

The Evidence
for Evolution
Chapter 21
1
Evidence of Natural Selection
Darwin collected a closely related group of 14
finch species in the Galápagos Islands
– All similar except for beak characteristics
– Darwin hypothesized that different beak
shapes were related to food gathering
– Darwin wrote “…one might really fancy
that…one species has been taken and
modified for different ends.”
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Evidence of Natural Selection
Darwin’s finches
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Evidence of Natural Selection
• Modern research verified Darwin’s selection
hypothesis
• 3 conditions of natural selection
– Variation must exist in population
– Variation must lead to differences among
individuals in reproductive success
– Variation among individuals must be
genetically transmitted to the next generation
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Evidence of Natural Selection
• Peter & Rosemary Grant studied medium ground finch
• beak depth variation among members of population
• Average beak depth changed from year to the next in
a predictable fashion
- Droughts: birds with deeper, more powerful beaks
survived better
- Normal rains: average beak depth decreased to its
original size
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Evidence of Natural Selection
Evidence that natural selection alters beak shape
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Evidence of Natural Selection
• When environment changes, natural
selection often favors different traits in a
species
• Biston betularia: peppered moth
– Light gray with black specks to jet
black coloration
– Black individuals have dominant allele
– Dominant allele rare in population
until 1850s
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Evidence of Natural Selection
• J.W. Tutt hypothesized that light-colored
moths declined because of predation
• Light moths were easily seen by birds
on darkened (sooty) trees
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Evidence of Natural Selection
• Bernard Kettlewell tested hypothesis
– Dark tree trunks = more dark-colored
moths survived
– Light tree trunks = more light-colored
moths survived
• When environmental conditions reverse,
so does selection pressure
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Evidence of Natural Selection
• Industrial melanism: phenomenon in
which darker individuals come to
predominate over lighter ones
• Pollution control resulted in lichen
growing on trees and bark color being
lighter again
• Light-colored peppered moths now are
dominant in population
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Evidence of Natural Selection
• Agent of selection may be difficult to pin down
• Could poisoning by pollution be agent of natural
selection?
Selection against melanism
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Artificial Selection
Laboratory Experiments
• Drosophila melanogaster (fruit fly)
– Selected fruit flies with many bristles on abdomen
– Chose only those with most bristles to reproduce
– 86 generations later: average # of bristles à 4X
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Artificial Selection
Artificial selection in the laboratory
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Artificial Selection
Agriculture
Corn looks very different from its ancestor
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Artificial Selection
Domestication of silver foxes result of artificial selection
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Artificial Selection
Can
selection
produce
major
evolutionary
changes?
Breeds of dogs: Differences among dog
breeds are greater than differences
displayed among wild species of canids.
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Fossil Evidence of Evolution
• Fossils: preserved remains of once-living
organisms
• Rock fossils: created when three events occur
– organism buried in sediment
– Ca++ in bone/hard tissue mineralizes
– surrounding sediment hardens to form rock
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Fossil Evidence of Evolution
• Absolute dating: age of fossils estimated by
rates of radioactive decay
• Relative dating: fossil’s position in sediment
• Isotopes, like U238, transform at precisely
known rates into nonradioactive forms
• Rate of decay à isotope’s half-life
C14 half-life: 5,280 yrs
K40 half-life: 1.28 million yrs
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Fossil Evidence of Evolution
Radioactive Decay
5 Major Extinctions
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Hypotheses for Cambrian Explosion
• Filling in ecological barrel:
many habitats/niches to exploit
• Unrestricted genetic design:
freedom to try new/different morphological forms;
some successful/others do not workà extinct
• Stealth predator: Anomalocaris canadensis
natural selection for 20 million yrs pressuring prey
to adapt/evolve new structures to escape predator
Cambrian Explosion
Anomalocaris canadensis
Burgess Shale
Environmental Changes
Geological Studies
I. Continental Drift
II. Plate Tectonics- 6 Major Plates
1) North American
2) South American
3) Eurasian
4) African
5) Antarctican
6) Pacific
A. Subduction Zones: plates collide
formation of islands, mountains, volcanoes
B. Transform Faults: plates slide past
earthquakes
C. Oceanic Ridges: plates pull apart
deep sea vents
Fossil Evidence of Evolution
Fossil
records
document
the course
of life
through
time
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Fossil Evidence of Evolution
Fossils document evolutionary transition
• Oldest known bird fossil: Archaeopteryx
found in 1859
intermediate between bird & dinosaur
possesses some ancestral traits &
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some traits of present day birds
Archaeopteryx
reptilian
bird
Fossil Evidence of Evolution
Recent discoveries
– Four-legged aquatic mammal
• Important link in evolution of whales &
dolphins from land-dwelling, hoofed
ancestors
– Fossil snake with legs
– Tiktaalik: a species that bridged gap
between fish & first amphibian
– Oysters: small curved shells to large flat
shells
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Tiktaalik
Fish
375 million yr old fossil
head of a crocodile & gills of a fish
Fossil Evidence of Evolution
Whale “missing links”
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Fossil Evidence of Evolution
Evolutionary change: horse body size & toe reduction
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Anatomical Evidence for Evolution
• Homologous structures: structures with
different appearances & functions that all
derived from same body part in a common
ancestor
• Bones in forelimb of mammals: homologous
structures
• Different functions, same ancestor structure
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Anatomical Evidence for Evolution
I. Anatomical Homology: mammalian forelimb bones
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Anatomical Evidence for Evolution
• Strongest anatomical evidence supporting
evolution comes from comparisons of how
organisms develop.
• Early vertebrate embryos possess pharyngeal
pouches that develop into:
– In humans: glands & ducts
– In fish: gill slits
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Anatomical Evidence for Evolution
II. Embryological homology: à descent from common ancestor
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Anatomical Evidence for Evolution
• Neck vertebrae
– Geese: 25
– Plesiosaurs: 76
– Mammals: 7
• Giraffe: 7 vertebrae, very large in size,
to make up for length of neck
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Anatomical Evidence for Evolution
• Eyes
– Molluscs:
photoreceptors face forward
focusing lens move forward-backward
– Vertebrate:
photoreceptors face backward
focusing—lens scrunched by muscles
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Anatomical Evidence for Evolution
Eyes of vertebrates
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Anatomical Evidence for Evolution
Eyes of Mollusks
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Anatomical Evidence for Evolution
• Vestigial structures: no apparent function but
resemble structures their ancestors possessed
Vestigial structures of a whale
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Anatomical Evidence for Evolution
• Humans
– Muscles for wiggling ears
• Boa constrictors
– Hip bones & rudimentary hind legs
• Manatees
– Fingernails on their fins
• Blind cave fish
– Nonfunctional eyes
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III. Biochemical Homology
bacteria/yeast to humans
same codons & amino acids
1953 Miller & Urey
Chemical Evolution
7 days
4 amino acids
urea
fatty acids
Convergent Evolution
• Biogeography: study of the geographic
distribution of species
– Some plants & animals have similar
appearance but are only distantly related
• Convergent evolution: independent
development of similar structures in organisms
that are not directly related
• Convergent evolution: usually seen in animals
& plants that live in similar environments
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Convergent Evolution
• Marsupials & placentals
– Marsupials: young born in an immature
condition & held in a pouch until they develop
– Placentals: young are not born until they can
safely survive in the external environment
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Convergent Evolution
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Convergent Evolution
Convergence among fast-swimming
predators
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Biogeographical Record
• Darwin noted on his voyage that
– Islands: often missing plants & animals
common on continents
– Species present on islands often diverged
from continental relatives
– Island species usually more closely related to
species on nearby continents
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Biogeographical Record
• Darwin concluded:
– Species arrive on islands by dispersing
across water
– Dispersal from nearby areas more likely than
distant sources
– Species that can fly, float or swim can inhabit
islands
– Colonizers often evolve into many species
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