Descent with Modification: A Darwinian View of Life

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Descent with Modification A Darwinian View of
Life

• Chapter 22

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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 Creators 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.

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Cuvier, Fossils, and Catastrophism

• Fossils- relics or impressions of organisms from
  the past, mineralized in rock. Most fossils found
  in sedimentary rocks-sand 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.

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Gradualism

• Hutton proposed it is possible to explain
  various land forms by looking at mechanisms
  currently operating the world. Hutton explains
  Earths geological features by gradualism- change
  is a constant, consistent, slow process.
• Lyell incorporated gradualism with
  Uniformitarianism-Lyells idea that geological
  processes have not changed throughout Earths
  history.
• Darwin influenced by Hutton and Lyell
  observations
• If geological change is slow and continuous, then
  Earth is much older than 6000 years according to
  biblical refence.
• Slow and subtle processes persiting over a long
  period of time can cause substantial change.

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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 organisms 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.
• Lamarcks theories not accepted because evolution
  was not yet accepted, and they also thought that
  certain characteristics cannot simply be passed
  on.

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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 Darwins
  evidence proved it to be more convincible?
  evolution accepted within a decade

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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

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Ernst Mayr Inferences and Observations

• Ernst Mayr dissected Darwins theory
• 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 Darwins 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.

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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

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• 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

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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.

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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.

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• 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 Darwins 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.