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Descent With Modification
Chapter 22
Historical Context
• Darwin 1st to propose idea of
natural selection.
• Wrote The Origin of Species.
• After natural theology
(Creationism), creation of taxonomy
(system of naming organisms)
http://images-eu.amazon.com/images/P/0517123207.01.LZZZZZZZ.gif
• Darwin’s views influenced by fossils,
impressions of organisms from past
and other researchers.
• Strata (layers) of rock held fossils
dated from youngest (towards top
layer) to oldest.
• Study of fossils (paleontology)
supported idea that change had
happened.
• Cuvier – catastrophism - large
floods occurred between layers of
rock - new species repopulate
devastated area.
http://www.grisda.org/origins/images/05n1-cvr.jpg
• Lyell – uniformitarianism -geological
processes not changed throughout
history.
• 1809 - Lamarck - theory of
evolution based on observations of
fossil invertebrates.
• Use and disuse of parts and
inheritance of acquired
characteristics important in theory.
• No evidence that acquired
characteristics inherited.
http://www.africanfauna.com/images/giraffe.jpg
Darwinian Revolution
• Darwin set sail on The Beagle discover coastlines of South
America and to chart out South
American coastlines.
• Collected specimens - noticed they
differed between various parts of
the world.
• Origin of new species and
adaptation of species to
environment closely related
processes.
• Finches on Galapagos Islands
differed in beak sizes according to
what they ate.
• Darwin wrote The Origin of
Species.
• Outlined ideas on evolution and
natural selection (Darwinism)
• 1st major point of ideas - descent
with modification - all creatures
share common ancestor.
http://www.blackwellpublishing.com/ridley/images/evolution.jpg
• Organisms developed
characteristics to adapt to
surroundings.
• Closer related species are, more
recent their common ancestor.
• This evolutionary tree of the elephant family is
based on evidence from fossils.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 22.7
• Developed theory of natural
selection.
• Observations based on ideas:
• 1All organisms have potential to
have many offspring; something
must limit number.
http://www.mms.mcn.org/~sneri/computer/baby_animals15.jpg
• 2Populations of organisms tend to
remain steady in size over time.
• 3Environmental resources limited.
• Inference #1 - too many offspring
produced - struggle to survive
occurs - certain number of
offspring will survive.
http://savinganimals.smugmug.com/keyword/dogs#36007645
• 4No 2 individuals in population alike.
• 5Differences are inherited.
• Inference #2 – Survival depends on
heritable differences.
• Inference #3 – Favorable
characteristics – survive - more
offspring with favorable
characteristics.
http://evolution.berkeley.edu/evosite/evo101/images/vert_tree.gif
• Main points:
• 1Natural selection - unequal ability
of species to survive and reproduce.
• 2Based on ability to interact, adapt
to environment.
• 3Based on ability for
characteristics to be passed.
• For example, these related species of insects called
mantids have diverse shapes and colors that evolved
in different environments.
Fig. 22.10
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Thomas Malthus noticed humans
produce quicker than resources.
• Certain inherited characteristics
allow certain members of population
to survive such conditions.
• Differential reproduction - passing
on of favorable traits to offspring.
• Traits become more dominant in
population over time - evolution.
http://static.howstuffworks.com/gif/evolution-skull.jpg
• Artificial selection - organisms with
favorable traits selected to mate
with others like them - increases
frequency of traits in population
(breeding).
http://www.bbc.co.uk/schools/gcsebitesize/img/bidogtree.gif
• Darwinian view on life:
• 1Diversity comes from descent with
modification from ancestral
species.
• 2Modification - result of natural
selection over long period of time.
http://www.emc.maricopa.edu/faculty/farabee/biobk/jawevol_3.gif
• Population, not individual, evolves.
• Natural selection involves changes
between individual and environment
- ultimately population that evolves.
http://evolution.berkeley.edu/evosite/misconceps/images/misconceptions_beavers.gif
• Population - group of interbreeding
individuals of single species that
share common geographic area.
• Evolution measures change in
relative proportions of heritable
variation in population over
succession of generations.
http://islandfox.org/uploaded_images/babyKrisWillis-730268.jpg
• Evolution increase or decrease
inherited traits, not individual
traits that person may have
acquired over lifetime.
• Natural selection situational.
• Some traits are helpful in one
environment; not helpful in other.
http://www.biologyreference.com/images/biol_01_img0111.jpg
Examples of natural selection
• Insects - resistant to insecticides.
• Those survived insecticide survived
to pass gene on.
• Result - immunity to certain
pesticides.
Fig. 22.12
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Natural selection favors
characteristics in variable
population that fit current, local
environment.
• Drug resistance - evolution has
occurred.
• Drug-resistant strains evolve
rapidly in HIV population, making
drug treatment difficult.
Other evidence
• Evidence of gradual change
throughout fossil history.
• New species evolve by
modifications as populations adapt
to new environments.
• Similarity in characteristics
resulting from common ancestry homology.
http://www.plyojump.com/courses/biology/images/homologous.jpg
• Anatomical similarities among
species - wing of bird, arm of
human - different functions, similar
anatomy.
• Forelimbs of human, cats, whales,
bats share same skeletal elements homologous structures.
• Study of comparing similar
structures - comparative anatomy.
• Vestigial organs do not have any
importance to current organism,
had important functions in
ancestors.
• Some snakes - have pelvic, leg
bones.
http://www.answersingenesis.org/home/area/magazines/tj/images/v14n2_vestigial_structures.gif
• Darwin studied biogeography - led
to evolution.
• Species that lived close tended to
be more similar than species that
lived further away.
• Sugar glider, flying squirrel
adapted to same mode of life - not
closely related.
Like a marsupial
mammal
Like a placental mammal
• Islands show strong evidence for
evolution - many species of plants
and animals that are endemic
(found nowhere else in world)
Why is it a theory?
• Those who dismiss Darwin’s theory
unable to separate main parts of
theory.
• Natural selection well accepted can be tested and proved.