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Evolution
Evolution: A summary
• Evolution - The process of change
– Evolution applies to the universe also. Matter and the nature of
matter has changed over time
– Evolution applies to life, implies that life is not static, but
responds to the environment.
• Previous western thought held the universe, earth
animals, and man were created by a greater being/entity.
– Held the earth and life were created in the thousands of years in
the past..
– Life and the earth were thought to be static and unchanging.
• Modern evolution holds that the universe is billions of
years old (between 9-12b years)
• Earth was created approx 4.5b years ago.
• Human existence is only a small fraction of time since
the beginnings of the universe.
The Cosmic Calendar
• If the 12 billion year history of the universe
was fit into a calendar year, it would look
like this…..
Cosmic Calendar (From The Dragons of Eden - Carl Sagan)
Pre-December Dates
Big Bang
January 1
Origin of Milky Way Galaxy
May 1
Origin of the solar system
September 9
Formation of the Earth
September 14
Origin of life on Earth
~ September 25
Formation of the oldest rocks known on Earth
October 2
Date of oldest fossils (bacteria and blue-green algae)
October 9
Invention of sex (by microorganisms)
~ November 1
Oldest fossil photosynthetic plants
November 12
Eukaryotes (first cells with nuclei) flourish
November 15
DECEMBER
Monday
Sunday
Tuesday
Wednesday
Thursday
Friday
Saturday
1
Significant
oxygen
atmosphere
begins to develop
on Earth.
2
3
4
5
Extensive
vulcanism and
channel formation
on Mars.
6
7
8
9
10
11
12
13
14
15
16
First Worms.
17
Precambrian
ends. Paleozoic
Era and Cambrian
Period begin.
Invertebrates
flourish.
18
First oceanic
plankton.
Trilobites
flourish.
19
Ordovician Period.
First fish, first
vertebrates.
20
Silurian Period.
First vascular
plants. Plants
begin colonization
of land.
21
Devonian Period
begins. First
insects. Animals
begin
colonization of
land.
22
First amphibians.
First winged
insects.
23
Carboniferous
Period. First
trees. First
reptiles.
24
Permian Period
begins. First
dinosaurs.
25
Paleozoic Era
ends. Mesozoic
Era Begins.
26
Triassic Period.
First mammals.
27
Jurassic Period.
First birds.
28
Cretaceous
Period. First
flowers.
Dinosaurs
become extinct.
29
Mesozoic Era
ends. Cenozoic
Era and Tertiary
Period begin.
First cetaceans.
First primates.
30
First evolution
of frontal lobes
in the brains of
primates. First
hominids. Giant
mammals
flourish.
31
End of Pliocene
Period.
Quaternary
(Pleistocene and
Holocene) Period.
First humans.
December 31
Origin of Proconsul and Ramapithecus, probable ancestors of apes and men
~ 1:30 p.m.
First hominids A. afarensis
~ 10:30 p.m.
Widespread use of stone tools by Homo habilis
11:00 p.m.
Domestication of fire by Homo erectus
11:46 p.m.
Beginning of most recent glacial period. Homo Neanderthalis & Homo sapiens evolve
11:56 p.m.
Seafarers settle Australia
11:58 p.m.
Extensive cave painting in Europe
11:59 p.m.
Invention of agriculture
11:59:20 p.m.
Neolithic civilization; first cities. Colonization of North and South America across Bering straits
11:59:35 p.m.
First dynasties in Sumer, Ebla and Egypt; development of astronomy
11:59:50 p.m.
Invention of the alphabet; Akkadian Empire
11:59:51 p.m.
Hammurabic legal codes in Babylon; Middle Kingdom in Egypt
11:59:52 p.m.
Bronze metallurgy; Mycenaean culture; Trojan War; Olmec culture; invention of the compass
11:59:53 p.m.
Iron metallurgy; First Assyrian Empire; Kingdom of Israel; founding of Carthage by Phoenicia
11:59:54 p.m.
Asokan India; Ch'in Dynasty China; Periclean Athens; birth of Buddha
11:59:55 p.m.
Euclidean geometry; Archimedean physics; Ptolemaic astronomy; Roman Empire; birth of Christ
11:59:56 p.m.
Zero and decimals invented in Indian arithmetic; Rome falls; Moslem conquests
11:59:57 p.m.
Mayan civilization; Sung Dynasty China; Byzantine empire; Mongol invasion; Crusades
11:59:58 p.m.
Renaissance in Europe; voyages of discovery from Europe and from Ming Dynasty China; emergence of the
experimental method in science
11:59:59 p.m.
Widespread development of science and technology; emergence of global culture; acquisition of the means of
self-destruction of the human species; first steps in spacecraft planetary exploration and the search of
extraterrestrial intelligence
Now: The
first second
of New
Year's Day
Darwin & Natural Selection
•Modern evolutionary thought arose through the
inquiries of Charles Darwin.
•Darwin was a Naturalist aboard an exploration
ship called the HMS Beagle.
•Collected and catalogued biological specimens
for return to England.
The Voyage of the Beagle
The Galapagos Finches
Was fascinated by the species of
Finches he observed in the Galopagos
Islands.
Found that these birds were quite
similar to a species found on mainland
South America. However they differed
significantly in the shapes of their
beaks.
Darwin reasoned that these species of
finches arose from a common ancestor,
and gradually changed over to
accommodate their particular diets.
Led him to develop his theory of
evolution through Natural Selection
Darwin & Evolution
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The notion of evolution was dominated by 2 theories.
Lamarckian Theory of Inheretance of acquired characteristics
– Held that traits acquired throughout life of an organism would be passed on to
offspring.
– "Use it, or lose it principle"
– Eg. If you lifted weights during your life, your children would be stronger or, if you
did'nt exercise your children would be weaker
– Theory has been replaced by Darwin's theory of natural selection.
•
Natural selection:
– Based on following premises:
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There are not enough resources for all organisms to survive.
Some organisms are more "fit" to survive.
Fitness refers to:
The ability of an organism to survive in its environment.
The ability of an organism to survive long enough to reproduce.
Natural pressures "weed-out" those individuals "less fit" to survive. Thus changing a
species over time.
– New genes/traits arise from random mutations.
– Most are either Neutral (no effect), or disadvantageous (decrease an organism's
chance for survival).
Natural Selection : The Peppered Moth:
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The peppered moth is a species of
moth which uses camouflage against
tree bark to avoid being eaten by
birds. It is normally a light grey color.
During England's industrial revolution,
pollution caused a darkening of the
bark of the trees.
There was a natural variation in moth
coloration with some being darker than
others.
Those moths of a lighter color, were
easier to spot and eat by birds. And
were eaten at a faster rate.
The survivors tended to be darker, and
when they mated, their offspring
tended thus to be darker also.
Over time, this resulted in the species
becoming darker in color.
Lamarck vs. Darwin
Effects of Natural Selection
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Natural selection can have many
different effects on species phenotypes.
These types of natural selection have
been named as:
1. Directional selection
2. Stabilizing selection
3. Disruptive selection
Directional Selection:
• Eliminates one extreme variation from an array of
possible phenotypes. Results in a shift towards
the other extreme.
Stabilizing Selection:
• Selection acts to eliminate both extremes of an
array of phenotypes. Results in an increase in
individuals exhibiting an intermediate phenotype.
Disruptive Selection
• Selection acts to remove the intermediate
phenotypes favoring the extreme phenotypes:
Convergence
•
Convergence occurs when
species evolve into a common
phentoypic form due to a
common need. For example the
diagram below portrays a shark,
ichthyosaurus, a penguin and a
dolphin. These are fish, reptile.
bird and mammal respectively
(very different families of
animals). Yet they all have a
torpedo body shape, pectoral,
caudal and dorsal fins. This is
based on their common need to
swim rapidly in an aquatic
environment.
Divergence / Adaptive Radiation
•Divergence occurs
when species evolve
in several directions
away from a
common ancestor.
This happens
usually to fill a
vacant ecological
niche. Also known as
adaptive radiation.
Convergence and Divergence Together
By contrasting North American
placental mammals with
Australian marsupials. One can
see how convergence and
divergence works together.
•In each case an ancestor
mammal evolved into several
ecological niches.
•Since each niche required a
specific phenotype, what results
are 2 groups of mammals which
have NEVER made contact,
evolving into similar shapes.
Rates of Speciation:
Two models exist to describe the rates of
speciation.
• Gradualism:
– Refers to the model which holds that evolutionary
change occurs in a gradual linear fashion. A species
will change its morphology over time.
• Punctuated equilibrium
– Describes the process in which a species remains
relatively unchanged for relatively long periods of
time. Following which, a period of stress causes
rapid change, followed by another period of relative
stability.
Rates of Speciation:
Evidences of Evolution
Fossils:
•Formed when animal remains are trapped
in sedimentary layers.
•Organic material replaced by minerals
over millions of years.
•Result is a "mineral cast" of the dead
organism.
•Where a fossil is located in the
sedimentary strata can indicate it's age.
•Successive changes in fossil forms of an
organism can help in developing a fossil
record of an organism's evolution.
•Some rare fossils can show "soft tissues"
which give invaluable information on an
organism's physiology
•Example: paleontologists recently
discovered a dinosaur with a fossilized
heart. This indicates that this species
was most likely warm blooded.
Fossilized Trilobite
Fossilized Dinosaur Heart
Radiometric Dating:
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Based on the fact that radioactive materials decay at a fixed rate.
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Rate is known as a half-life: The amount of time in which only 1/2 of a radioactive sample remains
By measuring the amount of radioactive material in a fossil, one can determine how old it is.
Example is 14C dating.
14C is an isotope of 12C which radioactively decays to 14N.
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It occurs naturally in the environment, and is ingested by organisms while alive.
Once an organism dies, 14C intake stops, and the 14C begins to decay
One can then measure the amount of 14C remaining in a sample, and determine its age.
Similarities in Embryological Development
• In early embryological
development, it appears
that embryos "play out"
their evolutionary history.
• Known as Ontonogy
recapitulating
Phylogeny.
• Implies that genetically,
we have not "forgotten"
our evolutionary history,
only built upon it.
Homologous Structures
• Refers to the fact that
organisms' structures are
formed from similar
anatomy.
• Example the wing of a
bird, arm of a man, wing
of a bat, and flipper of a
whale, all appear to be
formed from a common
set of bones.
• Implies that these
organisms evolved from
some common ancestor.
Vestigal Structures:
• Refers to the fact that
organisms have
structures which are
disused
• These structures,
however, a remnants of
structures the
organisms used earlier
in their evolutionary
history.
• Examples:
• Hip bones in whales
• Tail in humans
• Appendix in humans
• Legs/hips in snakes