Transcript Evolution - fog.ccsf.edu

1. Define species.
• Explain this picture.
Figure 13.00a
Figure 13.00b
Figure 13.00c
Figure 13.00d
Evolution
Evolution means change over
time
The Earth today is not what it once
was
• The earth is thought
to be 4.5 billion years
old
• Life is thought to have
appeared ~3.8 billion
years ago
• The early atmosphere
had methane, carbon
monoxide, and
• Essentially no oxygen
Species that exist today did not
exist in ages past
• Species of the past
are radically different
from what exists on
earth today
• Converse is truethings that exist today
are not seen in the
past
Yet there are connections between
species of past and present
• Species of today have
physical similarities
• This archaeopteryx
fossil shows feathers
People did not know the earth was
ancient
• Anglican archbishop
James Ussher
• October 23, 4004BC:
Earth was created
Aquatic forms were found far from
land
Charles Lyell proposed that the
earth was much, much older
• Posited the idea that
continents have
moved over time
• Continents move very
slowly
• So earth must be very
old
Continents can collide to form
mountains
• This raises aquatic
sediments from ocean
bottoms
Charles Darwin became curious
about how species came about
• Flunked out of med
school
• Didn’t much like
Divinity school, either
• Became a naturalist
aboard the HMS
Beagle
The Voyage of the Beagle
Darwin’s critical observations were
comparisons between island
species and mainland species
Marine Iguana and South American
Iguana
Flightless cormorants live only on
the Galapagos
A Variety of Finches are found in
the Galapagos
Finches each
have
adaptations for
different small
island
environments
Darwin’s inference: The finches have a
common ancestor
Likewise, the marine iguanas must
have come from the mainland
Evidence for evolution
•
•
•
•
•
Fossil evidence
Biogeography
Comparative anatomy
Comparative embryology
Molecular biology
Layers of sediment are heaped
upon layers over time
Looking down layers is looking
back in time
• The principle of
superposition
• The layers of the
grand canyon go back
over 600 million years
Vestigial Structures suggest
terrestrial ancestry in whales
Fossil Evidence shows variant
species in different layers
Biogeography
• Marsupials are not
better adapted to
Australia
• Invasive placental
mammals are driving
many marsupials to
extinction
Comparative anatomy
• Similar structures
exist in dissimilar
animals, serving
dissimilar functions
• Homologous
structures suggest a
common ancestry
Comparative embryology
Figure 13.12a
Figure 13.12b
Evidence from Molecular Biology
• Similar animals have
similar DNA
sequences
• Less similarity of
species= less
similarity of DNA
But what was the mechanism?
• How did a species
change over time?
• Lamarch proposed a
mechanism:
-By repeated strain, a
giraffe acquires a long
neck
-The long neck is
inherited by the
offspring
Darwin’s Mechanism: Natural
selection
• Those best suited for
their environment are
selected for survival
• Genes are inherited by
the next generation
• Better-adapted species
pass on genes suited for
the environment
• Next generation is better
suited for environment
than previous generation
The parts of Darwin’s theory
• 1. Overproduction
• 2. Variation of individuals
• 3. Differential reproductive success
1. Overproduction
• Living things tend to
produce more
offspring than are
able to survive
2. Individual Variation
• Individuals in a
species are different
from each other
• Some are better
adapted to their
environment than
others
3. Differential Reproductive
Success
• Those that are better
adapted to their
environment are more
likely to survive
• Those that survive will
pass their genes to their
offspring
• Those that don’t, won’t
• Do horns on lizards
influence their survival?
Figure 13.17a
Figure 13.17b
Figure 13.17c
• Define evolution.
• Define natural selection.
• Do individuals evolve? Why or why not?
Many people didn’t like Darwin’s
theory
• One consequence of
the theory is that all
living things have a
common ancestor
• Humans are closely
linked with other
primates
• Darwin is disliked
today also
Consequences of Natural Selection
• Some insects can
tolerate pesticide
• Survivors pass
resistance genes to
the next generation
• Do these genes exist
before the crops are
sprayed?
• What other examples
are there of this?
What can be said about these
insects?
Figure 13.2a
Figure 13.2b
Figure 13.2c
A Population: All individuals of a
species in a given area
Individuals in a population have
different genes
Hardy-Weinberg Equilibrium
• Some genes are more common than
others
• Gene frequencies will result in populations
with known genotype frequencies
according to algebra’s quadratic equation:
• p2 +2pq + q2 = 1
• Equilibria can be plugged into a Punnett
square
Figure 13.20
Genetic Drift
• Natural selection is not the only
mechanism by which things evolve
• When populations are finite, gene
frequencies can fluctuate by chance
• Small populations flucuate dramatically,
large populations less so
Figure 13.22
Consequences of Genetic Drift
• What is gene extinction?
• How can genetic drift
remove diversity from a
population?
• How can diversity be
introduced into a
population?
• Do genes drift more in
small populations or large
ones?
Figure 13.23
Consequences of a bottleneck
• How can a bottleneck
reduce diversity in a
population?
The Founder EffectGenetic drift in a new
population
Cheetahs have high genetic
similarity between individuals
Figure 13.25
Figure 13.26
Figure 13.27
Kinds of natural selection
• Directional selection
• Disruptive selection
• Stabilizing selection
• Consequences:
• Speciation
• Change in gene frequency
Figure 13.28_1
Figure 13.28_2
Figure 13.28_3
Sources of natural selection
• Predation
• Disease
Unnumbered Figure 13_UN267a
Unnumbered Figure 13_UN267b
How old are these fossils?
Radiocarbon (carbon-14) dating
can tell the age of fossils
Carbon-14 has a half-life of 5600
years
• Plants take carbon-14
from CO2
• Animals eat plants
• When animals die,
the intake of C-14
stops
• Half of C-14 is gone
in 5600 years
• The older a sample,
the less C-14 it has
How long is C-14 dating useful?
Plate tectonics
• In the bay area, we
know that the earth
does not sit still
• Sudden, violent
movement of geologic
plates causes
earthquakes
• Meeting of two plates
is a fault line
Extra Photo 14.18x
Consequences of plate tectonics
• Environment in
various places has
changed dramatically
• Antarctica features
fossils of tropical
creatures
• Continents move
slowly, but a billion
years is a long time
The Ring of Fire
Mass Extinctions
• Dinosaurs disappeared
suddenly 65 million
years ago
• Evidence of a large
meteor hitting the earth
~65 million years ago
on the Yucatan
peninsula in Mexico
• Many other extinctions
Permian extinction, 250 mya
•
•
•
•
The “Great dying”
Cause unknown
Very large meteor?
96% of marine
species extinct
• 70% of terrestrial
species extinct