Download Evolution: Evidence of Change

Evolution
Evidence of Change
What is Evolution?
The change in gene frequencies in a
population over time
Evolution and Life’s Diversity
• The idea that life has and is changing over
time is not new.
• Evolution is the process by which modern
organisms have descended from ancient
organisms
Charles Darwin
(1809-1882)
• Born in England
• Attended medical school,
HATED IT, and dropped out to
become a priest
• Liked to stuff birds instead of
dissect humans
• Didn’t like grave robbing for
bodies
• Boarded the H.M.S. Beagle for
a 5 year UNPAID journey as a
naturalist
Charles Darwin
• “Descent with
modification” from an
ancestral species
• November 24th 1859
The Origin of Species
Occurrence of Evolution
Descent with Modification
all organisms related through descent from some unknown
ancestral population
diverse modifications (adaptations) accumulated over time
Mechanism of Evolution
Natural Selection and Adaptation
natural selection is the differential success in
reproduction
natural selection occurs from the interaction between the
environment and the inherit variability in a population
variations in a population arise by chance
Can selection actually cause substantial change in a
population?
Journey of the H.M.S. Beagle
Darwin’s Field Research
• South American flora/fauna distinct from European flora/fauna
•S. American temperate species were more closely related to S. American
tropical species than European temperate species
•S. American fossils were distinctly S. American
Tropical Rainforest of South America
Alfred Russel Wallace
(1823-1913)
Presented a paper with
identical ideas as Darwin on
July 1, 1858 at the Linnaean
Society meeting
Was a botanist who came up
with virtually the same
concept of natural selection
more or less independently
through his studies on the
Malay archipelago. Darwin
panicked because he was not
ready with his book yet!
Diversity of Life
• Organisms come in a very wide variety of
size, shape, and habit
• In one day, Darwin collected 68 kinds of
beetles
• Estimates are about 10 million species
exist today
• Estimates are that 99.9% of all species
that have ever lived on earth are extinct!
Diversity of Life
• 2 questions:
• if the estimates are correct,
– Where did they all come from?
– Why did so many disappear?
Fitness
• Darwin noticed most animals and plants seemed
very well suited to do the things they do.
• The combination of physical traits and behaviors
that helps an organism survive and reproduce
Darwin called “Fitness”.
• How did the organisms develop structures that
give them their fitness?
• Why are there such a variety of techniques for
survival?
Evolution
• Evolution is a long, slow process of change in a
species over time.
• Common Descent – species that have
descended from common ancestors
• Adaptation – a process that causes fitness
(better able to survive and reproduce)
• Long legs and neck of giraffe are adaptations
• Long legs and neck allow giraffes to eat leaves
too high for most grazing animals
Age of Earth
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Age of the Earth
Evidence suggests
earth is over 4 billion years old
life has changed dramatically over time
common descent
History of Earth in 1 Calendar Year
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EventAge (approx)
(Million years) Calendar date
Earth formed
4,550 Jan. 1
Oldest rocks (sedimentary)
3,800 Mar. 1
1st life forms (stromatolites)
3,500 Mar. 25
Oxygen in atmosphere (banded iron fm)
2,000 Jul. 24
1st organized cells (eukaryotes)
1,000 Oct. 12
1st multi-celled animals
680 Nov. 7
1st fossils (hard skeletons)
570 Nov. 16
1st vertibrate animals
450 Nov. 25
1st land plants
430 Nov. 27
1st fish
400 Nov. 29
History of Earth in 1 Calendar Year
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1st primates
Extinction of the dinosaurs
Collision of India with Asia
Antarctica splits from Australia
1st horses
1st apes
Neanderthal man
Historical record (Sumeria)
Establishment of U.S.
Life of a student (20 years)
80
65
65
53
26
25
0.042
0.005
0.00022
0.00002
Dec. 25
Dec. 26 9:00 pm
Dec. 26 9:00 pm
Dec. 27
Dec. 29 10:00 pm
Dec. 29 midnight
Dec. 31 11:55:16 pm
Dec. 31 11:59:25
Dec. 31 11:59:58.47
Dec. 31 11:59:59.86
History of Earth in 1 Calendar Year
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1st amphibians
1st insects
1st reptiles
1st conifer trees
Extinction of trilobites
1st mammals
1st dinosaurs
Opening of the Proto-atlantic
1st birds
Breakup of Gondwanaland
Opening of N. Atlantic
Opening of S. Atlantic
365
350
320
300
285
200
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200
160
150
120
92
Dec. 2
Dec. 3
Dec. 6
Dec. 7
Dec. 9
Dec. 15
Dec. 15
Dec. 15
Dec. 19 5:00 am
Dec. 19 11:00 pm
Dec. 22
Dec. 24
Evidence in Stone
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In the past, people believed
earth was only a few thousand years old
earth remained unchanged
humans rarely, if ever, witnessed the earth
changing
• Scientists in the 18th and 19th Century
examined the earth and suggested the earth
• is very old
• changed slowly by forces such as weather
Evidence in Stone
• James Hutton (1788) proposed that rocks, mountains
and valleys had been changed by rain, heat, cold, and
activity of volcanoes
• 1830 (right before Darwin sailed) – Charles Lyell argued
that scientists must always explain past events in terms
of their observations
• While examining the earth and rocks, geologists began
to discover fossils
• Fossils are the preserved remains of ancient organisms
• Some resembled organisms still alive, some did not.
Geologic Time Scale: A Clock in the Rocks
• Geologic Time Scale – a record in the rocks
• certain layers appeared in the same vertical
order wherever they were found
• Position of the layers relative to each other that
tells how old they are.
• Lower is older
• Relative Dating – technique to determine age of
fossils by comparing the layers they are found in
• Could not tell actual age (only relative)
Radioactive Dating
• Middle of this century, our understanding of radioactivity
gave scientists a tool to determine actual age of rocks
• Radioactive elements break down or decay into
nonradioactive elements at a constant rate
• Half life – length of time required for half of the element
to decay
• 1 half life - ½ radioactive element broken down
• 2 half lives – ¾ radioactive element broken down
• 3 half lives – 7/8 radioactive element broken down
Radioactive Dating
• Each element has a different half life
• Potassium – 40 has a half life of 1.3 billion
years
• In one half life of P-40, one half of the
atoms decay to argon –40.
• Uranium 238 has a half life of 4.5 billion
years – during that time, ½ of the atoms
become lead-206
• 13-8 – half lives of radioactive elements
Absolute Dating
• Using this information, scientists can date very
accurately. This is called absolute dating
• Using this, scientists have divided the earth’s
history into units called eras
• Eras are divided into periods
• Periods are divided into epochs
• Based on this information, scientists have
determined that the earth is 4.5 billion years old.
The Fossil Record
• Animals and plants that are preserved by
natural means
• Can be Trapped in tree sap - amber
• Trapped in sedimentary rock
• Minerals replace the organic components
(usually shell or bone)
The Fossil Record
• Most in sedimentary rock
• Sand and small rocks settle down and
compact making layer upon layer
• Older on bottom
• Like a jigsaw puzzle
• Not as complete as we would like
The Fossil Record
• For every organism that leaves a fossil, many do not
leave anything
• Also depends on where the organisms lived. If they lived
in the mountains, chances are smaller that they would
leave a fossil
• Finding fossils can be difficult, but nature sometimes
helps – weather or water may erode newer layers
exposing fossils
• Some fossils are not as well preserved as others.
• Some – we can see microscopic detail, others are not as
clear
Half Lives
Isotope Pair
Half-life (yrs)
Useful Range
(yrs)
Carbon-14 to
Nitrogen-14
5730
60,000
Uranium-235 to
Lead-207
700 million
Over 500 000
Potassium-40 to
Argon-40
1.25 billion
Over 500 000
Uranium-238 to
Lead-206
4.5 billion
Over 100 million
Half Lives
• Sometimes use different materials, half life of
Potassium-40 is too long to use for some living
things
Fossils
• Paleontologists – scientists who study
fossils
• Collect “fossil record” that represents
preserved collective history of Earth’s
organisms
• Horse evolution – page 281 13-15
Fossils
• Location of fossils shows major changes in
earth climate and geography
• Shark teeth found in Arizona – Must have
been covered with seas
• Giant fossil ferns in Canada – must have
been warmer, tropical climate
• Changes followed changes on earth
• Paleontology - Study of Fossils
Fossil - preserved evidence of past life
a. Relative dating
b. Radioactive dating
• HOMOLOGY is a characteristic shared by
two species (or other taxa) that is similar
because of common ancestry.
Types of homology
• morphological homology – species placed in the
same taxonomic category show anatomical
similarities.
• ontogenetic homology - species placed in the
same taxonomic category show developmental
(embryological) similarities.
• molecular homology - species placed in the
same taxonomic category show similarities in
DNA and RNA.
MORPHOLOGICAL
HOMOLOGY
• Structures derived from a common ancestral
structure are called:
HOMOLOGOUS STRUCTURES
Ontogenetic Homology
The human embryo has gills, a post-anal tail,
webbing between the toes & fingers, & spends
its entire time floating and developing in
amniotic fluid has similar salt concentration as
ocean water
Pharyngeal
pouches
Post-anal
tail
Chick embryo
Figure 22.15
Human embryo
MORPHOLOGICAL
HOMOLOGY
• A structure that serves the same
function in two taxa, but is NOT
derived from a common ancestral
structure is said to be an
ANALOGOUS STRUCTURE
•Some similar mammals that have adapted to
similar environments
–Have evolved independently from different ancestors
NORTH
AMERICA
Sugar
glider
AUSTRALIA
Flying
squirrel
Examples of Analogous
structures:
• wings of bat, bird, and butterfly
• walking limbs of insects and vertebrates
• cranium of vertebrates and exoskeleton head
of insects
• 4 chambered heart in birds & mammals
Molecular Homology
Vestigial Structures
• Have marginal, if any use to the organisms in
which they occur.
• EXAMPLES:
• femurs in pythonid snakes and pelvis in
cetaceans (whales)
• appendix in humans
• coccyx in great apes