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Chapter 22
Descent with Modification: A Darwinian View of Life
29
Biology
Undergraduate 2
09/09/2008

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Term
The Origin of Species
Definition
1. Many species of organisms presently inhabiting Earth are descendants of ancestral species that were different from the modern species.

2. Natural Selection was the mechanism for this evolutionary process.
Term
Natural Selection
Definition
A population can change over generations if individuals that possess certain heritable traits leave more offspring than other individuals.
Term
Evolutionary Adaptation
Definition
An accumulation of inherited characteristics that enhance organisms' ability to survive and reproduce in specific environments.
Term
Evolution
Definition
A change over time in the genetic composition of a population

- descent with modification
Term
Aristotle
Definition
(384-322 B.C.)

Species were fixed and unchanging through time.

Observed that life-forms existed on a scale of increasing complexity ("scala natura")
Term
Linnaeus
Definition
(1707-1778)

- Founder of taxonomy.

-no evolution

- Adopted nested classification system (grouped similar species into increasingly general categories)

- Interpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose.
Term
Taxonomy
Definition
the branch of biology concerned with naming and classifying organisms.

founded by Linnaeus
Term
Cuvier
Definition
(1769-1832)

• Paleontologist
• Found different fossils in different strata and inferred extinction
• Believed boundaries between strata due to catastrophes
• Ironically, staunch opponent of evolution.
- Believed strata differences due to migration after catastrophe
Term
Catastrophism
Definition
- each boundary between strata (the layers in rock) represents a catastrophe (flood or drought) that destroyed many of the species living at that time

- periodic catastrophes were usually confined to local geographic regions, which were repopulated by species immigrating from other areas
Term
Gradualism
Definition
idea that profound change can take place through the cumulative effect of slow but continuous processes
Term
Hutton
Definition
(1726-1797)

Purposed that Earth's geologic features could be explained by graudal mechanisms currently operating in the world

- gradualism
Term
Lyell
Definition
(1797-1875)

- incorporated hutton's thinking into a more comprehensive theory

- the same geologic processes are operating today as in the past, and at the same rate

-gradualism
Term
Lamarck's Theory of Evolution
Definition
"Use and Disuse": parts of the body that are used extensively become larger and stronger, while those that are not used deteriorate (ex: Giraffe's neck)

"Inheritance of Acquired Characteristics": an organism could pass these "acquired characteristics" off to their offspring

Transformism!

-recognized that evolutionary change explains the fossil record and organisms adapt to their environments

-failed to figure out why these changes occurred (improper change mechanisms)
Term
Descent with Modification
Definition
-summarized Darwin's take on life

-all organisms were related through descent from an ancestor that lived in the remote past

- as descendants o that ancestral organism spilled into various habitats over millions of years, they accumulated diverse modifications (adaptations) that fit them into specific ways of life
Term
3 Inferences of Natural Selection
Definition
1. Production of more individuals than the environment can support leads to a struggle for existence among individuals of a population, with only a fraction of their offspring surviving each generation

2. Survival depends in part on inherited traits. Individuals whose inherited traits give them a high probability of surviving and reproducing in a given environment have higher fitness and are likely to leave more offspring that less fit individuals

3. The unequal ability of individuals to survive and reproduce will lead to a gradual change in a population, with favorable characteristics accumulating over generations
Term
Examples of Natural Selection in Action
Definition
1. Differential Predation and Guppy Populations
2. The evolution of drug-resistant HIV
3. the decrease in effectiveness of penicillin
Term
Homology
Definition
similar characteristics among related species descendent from common ancestors even though they may serve very different functions
Term
Homologous Structures
Definition
Lecture: Similar anatomy of structures, regardless of function

Book: Variations on a structural theme that was present among a common ancestor

ex: arms, forelegs, flippers, and wings of different mammals
Term
Molecular Homology
Definition
- DNA, RNA are conserved across all living organisms
• Same genes guide development in plants and animals
• The genetic code is universal
Term
Vestigial Organs
Definition
- Structures of marginal importance to the organism
- remnants of structures that served important functions in the organism's ancestors
- homologous structures!

ex: snakes have vestiges of the pelvis and leg bones of walking ancestors
Term
Developmental Homology
Definition
- Structures that appear early in development are similar
- Embryo exhibits characteristics of the embryos of its
ancestors.
- many embryos possess gill slits and later exhibit a
tail (in human coccyx/tail bone).
Term
Biogeography
Definition
definition: the geographic distribution of species

- was a key part in Darwin's theory of evolution because closely related species tend to be found in the same geographic region

- evidence of evolution
Term
AR Wallace
Definition
- independently developed a theory of evolution almost identical to Darwin's
Term
Darwin's Five Observations
Definition
1. populations of all species would increase exponentially if all individuals that are born reproduced successfully

2. Populations tend to remain stable in size, except for seasonal fluctuations (despite #1)

3. Resources are limited

4. Members of a population vary extensively in their characteristics; no two individuals are exactly alike

5. Much of this variation is heritable
Term
Artificial Selection
Definition
- the process initiated by humans that modifies other species over many generations by selecting and breeding individuals that possess desired traits

example: pets that do not resemble their wild ancestors
Term
Malthus
Definition
- Economist

- resources will outstrip populations

?
Term
Analogous Structures
Definition
- similarity by a shared way of life

- arise because of functional constraints

- NO common ancestry

example: hydrodynamic shape, flying wings
Term
5 Pieces of Evidence for Evolution

(lecture)
Definition
1. Biogeography
2. The fossil record
3. comparative anatomy
4. Development (embryology)
5. The Molecular Record (biochemistry and molecular biology)
Term
Embryology
Definition
- Embryos exhibit characteristics of the embryos of its ancestors

- structures that appear early in development are similar

example: many embryos possess gill slits like a fish and later exhibit a tail
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