Transcript Descent with Modification: A Darwinian View of Life Chapter 22

Descent with Modification: A
Darwinian View of Life
Chapter 22
Pre-Darwin: Scale of Nature and Natural Theology
• Greek philosophers who influenced Western culture.
• Plato believed in 2 worlds: real and illusory
• Aristotle believed all living forms could be arranged on a scale
or ladder of increasing complexity (scale of nature); species
are perfect and never evolve.
• Natural theology- philosophy dedicated to discovering the
Creator’s plan by studying nature
• Linnaeus: taxonomy- branch of biology concerned with
naming and classifying diverse forms of life; developed 2 part
binomial system: according to GENUS and SPECIES. This
grouped similar species before Darwin.
Cuvier, Fossils, and Catastrophism
• Fossils- relics or impressions of organisms from the past,
mineralized in rock. Most fossils found in sedimentary rockssand and mud settle at bottoms of seas, lakes, and marshes.
• Paleontology- study of fossils
• Cuvier: noted each stratum in sedimentary rock have unique
group of fossil species. Catastrophism-each boundary b/w
strata corresponded in time with a catastrophe like a flood or
drought, and destroyed species in that time.
Gradualism
• Hutton: proposed it is possible to explain various land forms by looking at
mechanisms currently operating the world. Hutton explains Earth’s
geological features by gradualism- change is a constant, consistent, slow
process.
• Lyell: incorporated gradualism with Uniformitarianism:-Lyell’s idea that
geological processes have not changed throughout Earth’s history.
Darwin influenced by Hutton and Lyell observations:
1. If geological change is slow and continuous, then Earth is much older than
6000 years according to biblical refence.
2. Slow and subtle processes persiting over a long period of time can cause
substantial change.
Lamarck
• Aristotle saw one ladder of life, while Lamarck saw many. He thought
species could move up ladders and reach greater complexity. Species at
bottom of ladder are simple, microscopic organisms made from nonliving
material, while species at top are complex. Species try to move up ladder
and be more complex, attain perfection, and be better adapted to
environments. Thus, evolution responds to organism’s “felt needs”.
• Lamarck proposed 2 ideas of how species evolve to specific adaptations:
• 1. Use and disuse: parts of body to cope with environment get bigger and
better, and parts not used deteriorate.
• 2. Inheritance of acquired characteristics: modifications organism acquires
during its lifetime is passed on to offspring.
• Lamarck’s theories not accepted because evolution was not yet accepted,
and they also thought that certain characteristics cannot simply be passed
on.
Darwin
• Collected 13 similar but different species of finches: certain
came from certain individual islands, or neighboring islands.
• It occurred to him that a new species could arise from an
ancestor by gradual accumulation of adaptations to a
different environment.
• If geographical barrier isolates two populations of a single
species, the populations would change in appearance to
adapt to local environment.
• Hypothesis: over many generations, 2 population can be
dissimilar enough to be considered a separate species.
• Wallace published almost identical theory of natural selection
before Darwin, but Darwin’s evidence proved it to be more
convincible evolution accepted within a decade
Origin of Species
• Descent with Modification- Darwin perceived a unity of life,
where all organisms related descent from unknown prototype
that lived in the past. As the descendents moved into
different habitats over millions of years, they underwent
adaptations.
• Linnaeus connected Darwin with idea of “groups subordinate
to groups”; major taxonomic categories: KINGDOM, PHYLUM,
CLASS, ORDER, FAMILY, GENUS, SPECIES
Ernst Mayr: Inferences and Observations
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Ernst Mayr dissected Darwin’s theory:
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Observation #1: All species have great chance of fertility that the population would
greatly increase if all individuals reproduced successfully. TREMENDOUS
FECUNDITY
Observation #2: Populations tend to remain stable in size; except for seasonal
fluctuations. STABLE POPULATIONS
Observation #3: Environmental resources limited. LIMITED ENVIRON. RESOURCES
Inference #1: Production of individuals cause struggle in population.
Observation #4: No two individuals are exactly alike. VARIATION AMONG
INDIVIDUALS
Observation #5: Variation is heritable. HERITABILITY
Inference #2: Those with best fitting traits likely to have more offspring.
Inference #3: Unequal ability of individuals to survive gradual change in
population w/ favorable characteristics accumulating over generations
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Summarizing Darwin’s Main Ideas
• 1. Natural selection is differential success in
reproduction
• 2. Natural Selection occurs by interaction b/w
environment and individuals in population ability to
inherit variables.
• 3. Product of N.S. is adaptation of populations of
organisms in their environments.
Malthus
• Human suffering (disease, famine,
homelessness, and war) is the inescapable
consequence of potential for human brings to
increase faster than supplies and resources;
the capacity to overproduce
• Artificial selection: breeding of plants and animals;
can cause substantial change in pop.
• Two Main features of Darwinian view of life:
• 1. Diverse forms of life have risen by descent with
modification from ancestral species
• 2. Mechanism of modification is natural selection
working over long periods of time
Subtleties of Natural Selection
• Population- group of interbreeding individuals belonging to particular
species and sharing common geographic area; smallest unit that can
evolve.
• Individuals to not evolve, POPULATIONS EVOLVE OVER TIME.
• Evolution can be measured only as changes in relative proportions of
variations in a population over many generations.
• There is no evidence that characteristics acquired during a lifetime can be
inherited.
• * Read exmaple of natural selection in action on pg. 422.
Evidence of Evolution
• Biogeography- geographical distribution of species: Islands have
indigenous species (native, found nowhere else), closely related to species
of nearest mainland or neighboring islands.
• Fossil record- In the fossil record, prokaryotes are the ancestors of life and
predicts bacteria should precede all eukaryotic life; fossils help link older
fossils to modern species. EX: fossilized leg bone of whale
• Homology- similarity in characteristics resulting from common ancestry.
• Homologous structures- anatomical signs of evolution.
• EX: forelimbs of humans, cats, whales, and bats have similar structures but
different functions. So they had a common ancestor, which modified
characteristics to take on new functions over time.
• Vestigial organs- parts left in body no longer necessary, but functioned in
ancestors . EX: human appendix/ pelvis and leg bones on whales. Vestigial
organs represent changes in an organisms’ embryonic development
wrought by natural selection.
• Comparative embryology: Closely related organisms go
through similar stages in embryonic development (EX: fish
and humans develop gill pouches, and fish develop further
into gills, humans further develop Eustachian tubes
connecting ear to throat).
• Ontogeny (development of individual organism) is a replay of
phylogeny (evolutionary history of the species).
• Molecular biology supports Darwin’s speculation that ALL
forms of life are related to some extent through branching
descent from the earlier organisms, common ancestry
connected by comparisons of amino acids.