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Evolution

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Evolution
“Of course, long before you mature,
most of you will be eaten.”
“The picture’s
pretty bleak,
gentlemen. The
earth’s climate is
changing, the
mammals are
taking over, and we
all have brains the
size of a walnut.”
“Now this
end is called
the
thagomizer,
after the late
Thag
Simmons.”
“Evolution’s been good to you, Sid.”
Top Ten Myths About
Evolution
1. Humans Evolved From
Monkeys
• Humans and great apes had a common
ancestor about 5 million years ago
• Humans and monkeys had a common
ancestor about 50 million years ago
2. It’s Only A Theory
“Theory” does not mean “hypothesis” or
“guess”
• Music Theory
• Stress Theory
• Quantum Theory
• Number Theory
“Theory” means an organized set of related
ideas.
3. If Nobody Saw It, We Can’t Be
Sure It Happened
• If you find your room trashed and your TV
and stereo missing, will you hesitate to call
the police because nobody saw it happen?
4. Science Can’t Say Anything
About Origins
• Maybe not. But once the origin happens,
everything after that is history. And
historical evidence is preserved in the
physical record.
5. Obsolete Concepts
“Survival of the Fittest”
• “The winner of the Super Bowl is the team
with the most points.”
• What does “fittest” mean?
6.
There Are No
Intermediate
Fossil Forms
7. Evolution Is Not Testable
• Darwin suggested birds had evolved from
reptiles in 1859; Archaeopteryx was
discovered in 1862.
• Piltdown Man
– Famous Early Fossil Man Hoax
– Controversial from the start because it
didn’t match evolutionary expectations.
8. Evolution Means Humans are
Just Animals
• Are you a vegetable or mineral?
• Humans have hair and nurse young just like all
other mammals
• Traits like nurturing, cooperation and
monogamy are often favored by evolution
because they enhance survival of species
9. Evolution is Just Random
• Is the following number sequence random:
592653589793238462643383279?
• It not only looks random: it is random.
• But lacking in meaning? No. These are the
digits of pi beginning with the fourth
decimal place.
• Random does not mean “meaningless”
The Scientific Meaning of Random
• Something cannot be predicted with better
accuracy than that predicted by statistics.
• The phenomenon is its own simplest
description
Randomness and Evolution
• Biological systems are far too complex to
describe or predict mathematically
• We have incomplete information
• Significant events like climate change or
asteroid impact are unpredictable.
10. Complexity Cannot Arise
Naturally
The Second Law of Thermodynamics is often
paraphrased as:
• ”Things always go from bad to worse”
• ”Disorder in the Universe is always increasing"
The Second Law of Thermodynamics
• The Second Law is about entropy
• Entropy = (Heat Absorbed)/Temperature
• Entropy can decrease locally if it increases
elsewhere
• Intuitive notions of “disorder” are of no
relevance whatsoever
Chemical Reactions are not Random
Na Cl Na Cl Na Cl Na Cl Na Cl Na
Cl Na Cl Na Cl Na Cl Na Cl Na Cl
Na Cl Na Cl Na Cl Na Cl Na Cl Na
Cl Na Cl Na Cl Na Cl Na Cl Na Cl
Na Cl Na Cl Na Cl Na Cl Na Cl Na
Cl Na Cl Na Cl Na Cl Na Cl Na Cl
Na Cl Na Cl Na Cl Na Cl Na Cl Na
Cl Na Cl Na Cl Na Cl Na Cl Na Cl
Channeled Scablands, Washington
Scabland Terrain, Oregon
The Geologic Record
• Physical evidence records mostly smallscale, gradual processes
• Fossils show a gradual increase in
complexity with time
• Fossil forms intermediate between major
groups are well documented
• Over most of its history, life on Earth was
simple
Were the Dinosaurs Failures?
• Human History = 5000 years
• Dinosaurs = 150,000,000 years
• Dinosaurs had:
– 30,000 years for every year of human history
– 80 years for every day
– 8 hours for every second
Prebiotic Evolution
• The basic molecules of organic chemistry are
easily made
• The first self-replicating molecule was almost
certainly not DNA
• DNA assembles from simpler materials all the
time
DNA
• Deoxyribonucleic acid
• Total length of human DNA in a single cell is
about a meter
• A human body contains about 20 trillion
cells
• The total length of DNA in a human body is
thus 20 trillion meters, or twenty billion
kilometers, the circumference of the orbit
of Pluto.
Plants and Animals
• CO2 + H2O + Energy = Sugars, Starches, etc.
+ O2 (toxic waste). O2 is actually toxic
(even to us!)
• 6CO2 + 6H2O пѓ C6H12O6 +(glucose) + 6O2
• Idea: Take the sugars and starches (from
somebody else) combine it with the waste
O2, and get energy
Amazing Events in Life History
•
•
•
•
“Invention of Sex” - Who Needs It?
We are a team - Mitochondria
The Great Freeze 900-600 m.y. ago
Mass Extinctions
– Dinosaurs = 4th worst
– Permian extinction (220 m.y. ago) took out 90% of
all species
Selection
• Deliberate selection for desirable traits by
humans (only since ca. 1700)
• Unsystematic selection for desirable traits
by humans (domesticated animals and
plants)
• Unconscious and unintentional selection by
humans (self-domestication of animals)
• Natural selection with no human
intervention at all
Lessons from Selection
• Artificial selection has produced organisms
radically different from their natural state
• Natural selection has resulted in dramatic
changes in natural populations with and
without human intervention
• Microorganisms and viruses change with
dazzling speed (mutation of flu viruses,
resistance to antibiotics, move to new
hosts)
This Descended from Wolves?
Evolution By Natural Selection
• Charles Darwin and Alfred Russell Wallace,
1859
• Organisms are adapted to their
environments
• Individuals vary
• More organisms are born than can possibly
survive
• Variations best suited to the environment
tend to survive and be passed on.
Mutations
•
•
•
•
•
•
•
Change in DNA code
“If you fix it often enough, you’ll break it”
Most organisms already adapted
Chance of random beneficial change small
Many mutations are neutral
Radical changes usually harmful
Mutations may be useful if the rules change
Radiation
• If no competitors or predators, otherwise
harmful variations may flourish
– Example: loss of flight or sight
• After mass extinctions
• Spread into unoccupied habitats
• Rapid proliferation of variations
Convergent Evolution
• Unrelated organisms may develop similar
features
• Often dictated by physical constraints
• Shark, tuna, dolphin, seal, squid, penguin,
ichthyosaur
• Deer, pronghorn, impala
• Albatross, pterosaur
Exaptation
• Modification of existing structure to serve new
function
• Fin – paw – wing – hand
• Scale – feather
• There are no half-formed organisms
What Good is Half an Eye?
What Does a Bug See?
What Does a Bug See?
What Good Is Half An Eye?
• A “partially-developed” eye can be very useful
• Selection will favor:
– More Receptors (Sharper Image)
– Wider Angular Spread (Better direction
discrimination)
– Better Image Processing
What Good is Half a Wing?
Powered Flight
• Insects
• Birds
• Bats
• Pterosaurs?
Gliders
• Squirrels
• Lemurs
• Marsupials
• Fish
• Frogs
• Snakes
• Lizards
Physics of Gliding
• Terminal Velocity
• Air Resistance = Gravitational Acceleration
– 200 km/hr for a human
– 20 km/hr for a mouse
• Gliders are All Small
• Can Survive Fall
• Selection favors duration and control
Two Bumblebee Myths
Theoretically, bumblebees should not be able
to fly.
• Bumblebees can’t glide well. Neither can
many aircraft
A bumblebee can carry more than its own
weight, something no airplane can do.
• C-5A empty 238,000 lb., maximum takeoff
weight 840,000 lb.
Classification of Dogs and Humans
•
•
•
•
•
•
•
Kingdom
Animalia
Phylum
Chordata
Class
Mammalia
Order Carnivora (Dogs) Primates (Humans)
Family Canidae
Hominidae
Genus Canis
Homo
Species familiaris
sapiens
“Actually, I considered
this an extreme honor.
Besides, I knew no one
was going to write and
ask to name a new
species of swan after
me. You have to grab
these opportunities
when they come along.”
Strigiphilus
garylarsoni
Below Species
• Ideally, species is a genetic group
capable of breeding
• Subspecies
• Race
– As used for humans, has little scientific
meaning
• Population
The Five Kingdom System
•
•
•
•
•
•
Animals
Plants
Protista (one-celled organisms)
Fungi
Bacteria*
Ediacaran Fossils? (ca. 700 m.y. ago)
What’s Bigger Than a Kingdom?
• Bacteria differ from all other kingdoms in
lacking a cell nucleus
• We need a bigger box
• Superkingdoms or Domains
– Monera (Bacteria)
– Archaea
– Eukarya (have cell nucleus)
• Need electron microscopes and molecular
biology to see differences
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