Evolution
The Unifying Principle of Biology
• http://www.pbs.org/wgbh/evolution/educato
rs/teachstuds/svideos.html
Background
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Each branch of physical science has at its core one or more unifying principles. These principles provide
predictions that can be (and have been extensively) tested and verified experimentally.
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Those that study these sciences do not blindly assume that these are true – every experiment, every piece of data, provides a
new test for the principle.
Remember that hypotheses are grouped together into theories. “A theory” is a laundry list of hypotheses under a single
umbrella.
Successful theories make predictions that are experimentally verified through many lines of independent work. Data that
refutes theories results in revisions of the theory.
Through many revisions, a theory eventually becomes solid enough that additional experimention continually validates the
underlying hypotheses again and again.
Over the course of time, theories mature into principles, or laws.
Physics
General Relativity, Quantum Mechanics
Chemistry
Atomic Theory, Thermodynamics
Geology
Plate Tectonics
Biology
Cell Theory, Gene Theory, Evolution Theory
Common misconceptions
• Evolution Theory does not describe how life
began.
• Evolution theory says nothing about the
origins of the universe, the big bang, or the
laws of thermodynamics.
• The only concept that evolution addresses is
the diversity of life on earth. Not its origins,
not its future. It simply explains why the
family tree of life is so branched.
Part I
Historic Perspective
Popular Beliefs up through the 1800s
Commonly held beliefs were not based on looking at the world, or
examining nature.
They were based on stories handed down from generation to generation,
in both oral and written forms. The Bible and Catholic dogma was the
most influential force on thought.
Therefore, when the world and nature was examined, anything that was
observed was interpreted according to what was already believed.
Beliefs based on these forces:
The earth was young.
Species were made and did not change.
When observations were made that did not fit what was already believed,
new theories were contrived to fit the data into the context of what was
already believed.
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Fixity of Species
Lamark: The first cohesive theory
Darwin: Natural Selection
Mendel: factors of inheritance
Modern Synthesis: Connected Darwin and
Mendel
Jean-Baptiste Lamarck (1744-1829)
A major contributor to Cell Theory
One of the first to use “biology” in its modern sense
Started out as an “essentialist” who believed species
did not change. But his own work on mollusks
convinced him that change had to have occurred.
Was the first to propose a cohesive theory of evolution
(inheritance of acquired characteristics)
George Cuvier (1769-1832):
paleontologist, father of
comparative anatomy
He worked with fossils (he found and named pterodactyl in
Bavaria).
He thought Lamark’s ideas were ridiculous, and firmly
believed in the fixity of a species.
He came up with the principle of “correlation of parts” – The
notion that comparative anatomy was so accurate that after
inspecting a single bone, the class and sometimes genus of
an animal could be inferred.
This is because the number, direction, and shape of the
bones composing each part of a body are always in a
necessary relation to all parts such that a great deal can be
inferred with only a few bones.
That was in 1798.
Modern Synthesis
• The modern synthesis solved difficulties and
confusions caused by the specialisation and poor
communication between biologists in the early years of
the twentieth century. Discoveries of early geneticists
were difficult to reconcile with gradual evolution and
the mechanism of natural selection. The synthesis
reconciled the two schools of thought, while providing
evidence that studies of populations in the field were
crucial to evolutionary theory. It drew together ideas
from several branches of biology that had become
separated, particularly genetics, cytology, systematics,
botany, morphology, ecology and paleontology.
Part II
Natural Selection
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1. heritable variation
functional, phsical, behavioral variations. IT IS COMPLETELY RANDOM
2. more offspring are produced than the environment can support.
Organisms struggle to exist. The work of Malthus: humans reproduction is held in check by death and famine
due to the fact that populations tend to increase faster than their food supply does. Darwin applied this concept
to ALL of life.
reproductive potential of elephants: assuming 100 year lifespan with breeding of 30-90 years, a single female
would bear ~6 young. If all of these survive and reproduce at the same rate, after only 750 years, a single pair of
elephants would produce 19 million.
3. some individuals survive better than others as a result of their variations
the most fit capture a disproportionate amount of resources. This is converted to a disproportionately larger
number of offspring that also survive. What determines fitness differs for different populations (it depends on the
environment)
Humans carry out artificial selection (breeding)
THERE ARE OTHER MECHANISMS BESIDES NATURAL SELECTIION: gene flow, nonrandom mating, genetic drift
ONLY natural selection leads to adaptation to the environment. the others drive diversity.
Part III
Sources of Genetic Variation
Part IV
Lines of Evidence
http://en.wikipedia.org/wiki/Evidenc
e_of_common_descent
Part V
Controversies
Controversies
Short answer: there aren’t any.
Scientists argue about the mechanism, not
underlying idea.
Of all Western Countries, Americans believe in
evolution the least. The next country is
Turkey.
Why?
It’s not just religion
Politicizing Evolution
In America, those who say they are pro-life, pro
death penalty, and anti- gay marriage also do not
believe in evolution.
In Europe, there is no correlation between these
and evolution belief.
• Christian fundamentalists have made evolution a
political issue. Less people in America believe in
evolution today than they did a few years ago.
The Exception of Evolution
Why is evolution so contested even today, when the last
century of work has done nothing but deepen our
confirmations of the underlying principles?
It is the one theory that directly impacts our personal
identity. The very thing that makes us human causes
strife.
Evolution leads many to ponder the core questions of our
very existence – where did we come from, where are
we going, why are we here – what is our purpose?
However, evolution theory does not address these
questions, contrary to what popular belief states.
Controversies
• “Young Earth” Creationists
• “Expelled” the movie
– http://www.discovery.org/expelled/
– http://www.rottentomatoes.com/m/expelled_no_inte
lligence_allowed/
• The Creationist MUSEUM
– http://www.creationmuseum.org/
– http://www.discovery.org/
– http://friendlyatheist.com/2007/09/18/video-of-mycreation-museum-speech/