Descent with Modification: Darwinism
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Transcript Descent with Modification: Darwinism
DESCENT WITH MODIFICATION
Chapter 22
PRE-DARWINIAN THOUGHT
Earth only about 6000 years old
Each species is specially created
Adaptation to environment is the work of a
creator
Variations = imperfection
ARISTOTLE
Species were fixed
Perfect & permanent
Scala naturae or
Ladder of Life
Rank for everything
CAROLUS LINNAEUS
Binomial naming
system
Nesting fashion
Related Group &
specific name
Similar organisms
into general
categories
Creation pattern not
resemblance of
species
GEORGES
CUVIER
Father of Paleontology
Studied strata and fossil record
Catastrophism
Sudden events different than current mechanisms
Creator’s role in re-creation
THE CHANGING EARTH
James Hutton
Gradualism
Charles Lyell
Change from slow,
continuous processes
Valleys from river
flow
Uniformitarianism
Change constant over
time
What’s been has
always been
JEAN-BAPTISTE DE LAMARK
Proposed 1st mechanism for
evolution
Organisms innately driven to
complexity
Remembered for being wrong
Match to environment
Principles
Use and disuse
Inheritance of acquired
characteristics
Phenotypes don’t affect genotype ≠
inherited
INHERITANCE OF ACQUIRED TRAITS
CHARLES DARWIN
Father of evolution
Descent with modification
Organisms change to better fit
habitats
Decades of backlash and denial
Distorted to justify societal causes
(Nazi ideologies)
Cartoon of Darwin as half ape, half
human
200 years old this year
150 years since theory
DARWINIAN INFLUENCE TIMELINE
DARWIN’S RESEARCH
Observed adaptations
Realized adaptations
centered on natural
selection
Similarities stronger
between regions than
climates
Individuals with certain
inherited traits left more
offspring
Charles Lyell and
Thomas Malthus
influence
THEORIST OF EVOLUTION
Darwin reluctant to publish his ideas
Lyell didn’t unconvinced, but pushed publishing
Alfred Russel Wallace developed a similar
hypothesis
Important before someone else did
Published 1st
Wallace’s work with excerpts from Darwin
Wallace conceded because Darwin’s better supported
ON THE ORIGIN OF SPECIES BY MEANS OF
NATURAL SELECTION
Main ideas
Descent with modification
Natural selection
Avoided reference to
humans
Evolution not mentioned,
descent with modification
History of life like a
branched tree
Match organisms to
environment
Exclusions
Life’s unity & diversity
Matched with Linnaeus
Relied on familiar
examples
ARTIFICIAL SELECTION
All species Canis
familiaris, but different
breeds
Bred from artificial
selection
Common vegetables
from wild mustard
NATURAL SELECTION
Observations
Diversity in populations
Traits from parents to offspring
Over production of offspring common
Many offspring don’t survive
Inferences
Certain traits enhance probability of survival
Favorable traits will accumulate in populations
SUMMARIZING NATURAL SELECTION
Individuals with heritable characteristics survive
and reproduce at a higher rate
Over time, it can increase the match between
organisms and their environment
If an environment changes or individuals move,
adaptations to these can give rise to new species
KEY POINTS OF NATURAL SELECTION
Individuals do not evolve
Only heritable traits are diminished or amplified
Change between generations
Not encoded by genes = acquired characteristics can’t
be passed to offspring
Not goal directed
Is not a perfect process
Often trade-off of needs
Editing, not a creative, mechanism
EVOLUTIONARY EVIDENCE
FOSSILS
Record is relatively incomplete
Soft tissues are rarely preserved
Movement of the Earth’s crust
covered or destroyed many fossils
Fossils only formed in certain
environments and habitats
All the fossils haven’t been
discovered yet
Show differences in past and
present organisms
Document evolutionary changes
Can test evolutionary hypotheses
Radioactive dating
HOMOLOGOUS STRUCTURES
Similarity in structure due to common descent, but
different functions
Mammalian forelimbs = variations on a common theme
ANALOGOUS STRUCTURES
Similarity in structure based on adaptation for same
function, but not common descent
Convergent evolution, independent evolution of similar
features
VESTIGIAL STRUCTURES
Remnants of features that were important in an
organism’s ancestors
EVOLUTIONARY TREE
Reflects evolutionary
relationships among
groups of organisms
Homologous structure
pattern
All tetrapods have 4
limbs, but ancestors
don’t
Branch points
represent common
ancestors that
descended from it
BIOGEOGRAPHY
Geographic
distribution of species
Organisms evolved in
one location and then
spread
Many species are
endemic
Oldest fossils at origin
Galapagos finches
Influenced by
continental drift
Pangea & today’s
continents
CONTINENTAL DRIFT & PLATE TECTONICS
BIOCHEMICAL
Protein comparison
DNA comparison
Universality of the
genetic code