Download 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

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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