Download BIOE 103

BIOE 103
Common ancestry of life
Great moments in evolution
Unusual tooth, found in forest by a
British doctor, Gideon Mantell (1822).
Leading biologists could not identify it
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The tooth looked liken an iguana’s
But was 20x larger!
Illustration by Mantell
Teeth from a green iguana
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Additional bones found in quarry in 1834.
Mantell reconstructed animal.
Named species “iguanodon” or “iguana tooth”
Estimated it was 40’ long.
(Keep in mind that no one had seen bones like this before)
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Iguanodon
In 1878, bones from
Belgium quarry
reconstructed.
And it became obvious
this was an extinct
species.
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By then, Mantell had died
His medical practice had
collapsed as he spent more time
digging for fossils.
His wife left him.
He died of opium overdose in
1852.
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Discovery of dinosaur skeletons in the 19th
century shocked scientists and public
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Mammoth skeletons also shocked everyone
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Scientists wondered whether dinosaurs & mammoths
were living creatures… or had gone extinct
“Such is the economy of nature, that in no instance can be produced her
having permitted any race of her animals to become extinct.”
– Thomas Jefferson
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Almost half of Americans believe humans and
dinosaurs lived together
This idea is common in popular culture, and is advocated
by biblical literalists.
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How could scientists test the hypothesis
that humans lived at the same time as
dinosaurs or mammoths?
Propose a way to answer this question using methods you could actually do.
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IF
Humans and dinosaurs lived at the same time
AND
We note which rock layers contain signs of humans and
dinosaurs
THEN
We should find human and dinosaur tracks, fossils, or
remains in the same rock layers.
Observation
Human bones, fossils, tools,
or footprints have never
been found in the same rock
layers as dinosaurs.
Footprints of human ancestors
3.5 million years old
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Distribution of fossils of humans and
dinosaurs in actual rock layers
Human fossils (young rocks)
Dinosaur fossils
in old rocks
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Conclusion:
Humans and dinosaurs do
not appear to have lived
together
Dinosaurs appear to have
lived a long time a before
humans.
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In contrast, archeologists have found numerous
mammoth remains with spear points
See “Naco kill site” & “Lehner Mammoth-Kill Site”
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Eight spear
tips found
in
mammoth
skeleton in
Arizona
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2. Faunal succession
In the early 19th century British constructed an
extensive canal system
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In 1816, canal surveyor William
Smith noticed…
Craig stratum
…each layer of rock
has distinctive
fossils…
Lower chalk stratum
Upper Oolite stratum
…and that rock layers
could be identified
by their fossils.
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Smith made charts showing
sequence of fossils.
Principle of faunal succession
The types of rocks varied,
but sequence of fossils did
not.
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Smith called this: “faunal succession”
Different rock layers
contain different fossils
Sequence of fossils is
predictable & consistent.
E.g. Human fossils are not found in
rock layers with (or below)
dinosaur fossils.
See “faunal succession”
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This was an example of faunal succession
Human fossils in young rocks
Dinosaur fossils
in old rocks
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Grand Canyon shows faunal succession
Different rock layers have different fossils
Trilobites, sponges +
Fish, amphibians, reptiles
Trilobites, sponges
No fish, amphibians, reptiles
No fossils except algae
or bacterial mats
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Grand Canyon Region shows faunal succession
Bryce Canyon:
Zion Canyon:
Grand Canyon
Bryce Zion
Mammals
Dinosaurs
Invertebrates, fish, reptiles
Grand Canyon
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Geologists spent middle of 19th century identifying
which fossils were present in which rocks
And they identified a
basic sequence that is
present everywhere in
the world
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Geologists divided earth’s history into different time
periods based on fossils
This diagram shows the “geologic time scale”.
It depicts divisions of the earth history inferred
from fossils in rock layers.
No single place on earth has rock layers from all
of these periods.
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Four major divisions in the Earth’s history
Cenozoic “New Life”
Dominated by modern mammals
Massive extinction
Mesozoic “Middle Life”
Dominated by dinosaurs
Massive extinction
Paleozoic “Old Life”
Trilobites, fish, amphibians
Precambrian
Very primitive organisms (e.g. sponges)
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Example of faunal succession: dinosaurs
Dinosaurs: 230 MYA – 65 MYA
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Example of faunal succession: trilobites
17,000 species
of trilobites in
these rock
layers
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Fossil record showed several major
extinction events
Dinosaur extinction
End Triassic extinction
End Permian extinction
End Devonian extinction
Ordovician extinction
And many less severe ones.
99.9% species extinct
Most species live for 10 MY
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There is also a trend towards
increasingly complexity
Birds
Modern
mammals
Dinosaurs
Reptiles
Amphibians
Fish
Unicelluar organisms
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Cenozoic “New Life”
Dominated by modern mammals
Massive extinction
Mesozoic “Middle Life”
Dominated by dinosaurs
Massive extinction
Paleozoic “Old Life”
Trilobites, fish, amphibians
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3. How to explain all this?
These patterns could not be
explained by a biblical creation 6000
years ago followed by a flood.
French paleontologist Alcide
d'Orbigny proposed in 1842 there
had been 27 creations and floods.
Alcide d'Orbigny
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Darwin argued:
**All living organisms are descended from a common
ancestor
**Different rock layers had different fossils because
species evolved over time
These diagrams show ancestry of living species.
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Watch history of life video
(available at: http://www.youtube.com/watch?v=5Q55z6EsL8M)
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Evolution
Definition. #1
The theory that all species are descended
with modification from a common ancestor.
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Many students wonder:
“Isn’t evolution just a
theory?”
“Don’t many scientists
doubt it?”
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4. Testing Evolutionary Theory
Characteristics of a good theory
• Simple
• Explains available observations
• Makes testable predictions
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Let’s see what this theory can EXPLAIN
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On odd observation: Animals with very
different lifestyles have similar sets of bones
Can evolution explain this?
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Can evolution explain?:
Why vertebrates have similar limbs?
These animals have very different bodies, but similar limb structure.
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Can evolution explain:
Why humans have “tail” bones?
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Darwin sailed around the world 1831-1836
Made observations that led to theory of evolution
His stop in the
Galapagos Islands
proved to be
particularly
influential.
See “Second voyage of HMS Beagle”
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Observations that intriguied Darwin
“The most striking and important fact for us in regard to the inhabitants of islands, is their
affinity to those of the nearest mainland, without being actually the same species. [In] the
Galapagos Archipelago... almost every product of the land and water bears the
unmistakeable stamp of the American continent. There are twenty-six land birds, and
twenty-five of these are… distinct species, supposed to have been created here; yet the
close affinity of most of these birds to American species in every character, in their habits,
gestures, and tones of voice, was manifest.... The naturalist, looking at the inhabitants of
these volcanic islands in the Pacific, distant several hundred miles from the continent, yet
feels that he is standing on American land. Why should this be so? why should the species
which are supposed to have been created in the Galapagos Archipelago, and nowhere else,
bear so plain a stamp of affinity to those created in America? There is nothing in the
conditions of life, in the geological nature of the islands, in their height or climate, or in the
proportions in which the several classes are associated together, which resembles closely
the conditions of the South American coast: in fact there is a considerable dissimilarity in all
these respects.”
- Charles Darwin, On the Origin of Species (1859)
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Can evolution explain?
Why Galapagos and Cape Verde Islands have
similar climate, soil, size, but different birds.
Galapagos Islands: birds similar
to S. America
Cape Verde Islands: birds
similar to Africa
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How could the common descent
hypothesis explain these
observations?
Galapagos Islands:
birds similar to S.
America
Cape Verde Islands:
birds similar to Africa
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Evolutionary explanations
Vertebrates have similar limbs
because all evolved from a
common ancestor.
Birds on islands similar to
mainland because mainland birds
colonized island and then evolved
Galapagos Islands:
birds similar to S.
America
Cape Verde Islands:
birds similar to
Africa
Humans have a tailbone
because human ancestor had a
tail, and it never evolved away
completely.
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Humans
apparently still
have genes for a
tail.
(although they are
usually not expressed)
For more information, see http://www.anatomyatlases.org/AnatomicVariants/SkeletalSystem/Images/19.shtml
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Humans have many “vestigial” genes
E.g. Humans have half a gene for
L-gulonolactone oxidase
(The enzyme that synthesizes vitamin C)
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Another vestigial trait:
Blind mole rats have small eyes covered with skin
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Another vestigial trait:
Leg bones in whales
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What does this theory PREDICT?
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One prediction of common
descent hypothesis
Fossil record
should show
transitional
species.
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Horse lineage shows many
transitional fossils
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Time
Transitional fossils: Archaeopteryx
A dinosaur-like skeleton with feathers
Archaeopteryx, discovered 1861
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Transitional fossils: Early amphibian
Tiktaalik
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Transitional fossils: early humans
Ardipithecus
ramidus “Ardi”
4.4 MYA
Brain: 325 cc
Transitional fossils: Early whales
“Evolution of cetaceans”
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5. Darwin developed theory of
evolution before DNA discovered
Evolutionary theory and genetics predicts that closely
related species will be genetically similar
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DNA sequences provided an
independent test of evolution theory
Human
Chimp
Mouse
Bird
Frog
Trout
Fly
Corn
CTACAACTCTTTCCGTTCTTCTAAAAATAATACTTCACAAGGGTCACGGTG
..................................................A
........T..................C..GT.......C...........
...T.......C...............C.GGT...T..............A
....................TC.G...C.GGT...T...............
...T...GA..C..T......CGT...C.GGT.......C.......A..A
...........C..T......G.C..GC.CGT.GCG..GC...........
T.GGGTTGACGA...C.......G..G.TC.GG.....GC.C.........
Humans are genetically similar to chimpanzees and other mammals
Less similar to fish, insects, and corn.
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6. Could the earth and organisms have
been created this way?
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Sure. E.g., Douglas Adams suggested that the entire earth was
made in a giant factory with all fossils built into place.
The Matrix suggested “reality” was a computer simulation.
Testing hypotheses like these is probably impossible
because they do not make any predictions. In other words,
they can not be refuted.
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But how do species change?
That is what we will discuss next lecture.
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Study guide
Read the section on evolution in the book (Ch. 5)
Be able to describe evidence for common ancestry of all living
organisms.
Be able to use evolutionary theory to explain seemingly odd
observations.
Be able to interpret an evolutionary “tree.”
Be able to explain the difference between evolution and natural
selection.
Be able to describe the requirements for natural selection and
describe how natural selection occurs in nature.
Be able to analyze a change in a population and determine whether
it is evolution.
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Sample exam questions
Describe some of the fossil evidence that species have evolved,
and explain how this evidence is interpreted.
Cheetahs (large African cats) are able to run faster than 60 miles
per hour when chasing prey. How would a biologist explain how
the ability to run fast evolved in cheetahs, assuming their
ancestors could run only 20 miles per hour?
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The end
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