Evolution -
1. Descent with modification.
2. Process in which closely related species resemble one another because of common inheritance and differ from one another because of hereditary differences accumulated since the separation of their ancestors.
3. Change in gene frequency over time.
Jean Baptiste de Lamarck - Inheritance of Acquired Characteristics
Charles Darwin
Beagle
Galapagos Islands
T. R. Malthus - Essays on the Principle of Population
Alfred Russel Wallace
1859 - Darwin published On the Origin of Species by Means of Natural Selection
Four Theories Of Evolution - Proposed by Darwin
1. Common Descent
Homology - evidence for common descent
similarity of structures because of descent from a common ancestor, without regard to function.
Ernst Haeckel - Biogenetic Law -Ontogeny (individual development) Recapitulates (repeats) Phylogeny (evolutionary descent)
Thought that evolutionary change occurred by adding stages onto the end of ancestral ontogeny.
Karl von Baer - early developmental features were simply more widely shared among different animal groups than later ones.
2. Multiplication of Species
How do ancestral species branch to form two or more descendant species???
A. Allopatric Speciation -
- vicariant event - fragmentation of a species' habitat.
10,000 years ago the Mojave Desert was not a desert.
- founder event - small number of individuals disperse to a distant place
The smaller the isolated group - the greater the difference in genetic structure.
B. Non-allopatric Speciation
Sympatric speciation
Hybridization
C. Adaptive Radiation - production of ecologically diverse species from a common ancestral stock.
3. Gradualism
small continuous changes in the phenotypes that are present in natural populations. These changes accumulate over 1000's of yrs producing major changes.
Eldredge and Gould - alternate theory to gradualism = Punctuated equilibrium - explains discontinuous evolutionary changes seen throughout geological record.
4. Natural Selection
Explanation for the origins of adaptation.