: Darwin & Wallace’s theory on the Origin of Species a] rejected the concept of a static world; 2] proposed that all life evolved from a common ancestor; 3] provided a mechanism (natural selection) to account for diversity
- Early ideas on biological "evolution" or change:
- Greek philosophers
- Middle Ages – animals could arise from organic matter
- Naturalists – observation that species change
- Lamarck (1809) – proposed a theory evolutionary change via inheritance of acquired characteristics
- Charles Darwin (1809-1882) and Alfred Russell Wallace (1813-1913)
- Passion for natural history; Darwin had experiences with artificial breeding of plants and animals
- Both traveled extensively and were systematic collectors & observers
- Age of earth though to be 1000s of years
- Both men began to search for mechanisms to explain the patterns of relationships they observed between organisms and their geographic distributions
- The Darwin-Wallace Theory had 2 components:
- They postulated that all life is descended from a common ancestor
(the Theory of Common Descent)
- They proposed a mechanism by which evolutionary change occurs
(the Theory of Natural Selection)
- Because of differential survival and reproduction due to inherited traits, some individuals leave more offspring than others (i.e. not due to chance, due to inherited characteristics)
- Darwin synthesized information from several unrelated fields
- Biology
- Economics – Malthus’ Essay on the Principles of Population
- Geology – Hutton & Lyell – age of earth much older than previously thought
- The concept of Natural Selection was founded on the following observations:
- Individuals differ in various characteristics
- Organisms reproduce at rates that exceed the ability of the environment to support them. Therefore, the vast majority of organisms die without ever reproducing.
- Natural agents of mortality regulate population growth
- "struggle for existence"
- only those individual organisms having the most favorable characteristics for survival in their particular environment survive and reproduce
- over long periods of time, continuous ‘minor’ selective changes or variations can lead to considerable changes, and ultimately to the formation of new species
_ Natural selection is the mechanism that produces change over time and descent with modification.
Very succinctly…
- individuals differ slightly in various characteristics
- survival and reproduction appear to depend on these characteristics
- some variants are more successful; their characteristics are passed on to the next generation = Natural Selection
• Natural Selection acts on the PHENOTYPE not the genotype.
→ Natural Selection does not necessarily increase a species’ perfection, complexity, efficiency, etc.; it is not an optimizing process; works with existing variation
ADAPTATION:
- a structure, physiological process, or behavior that makes an organism better able to survive or reproduce
- the evolutionary process that leads to the development or persistence of such a trait
FITNESS: the relative contribution an individual makes to the gene pool of the next generation; measured in terms of the number and quality of offspring (and relatives) that it successfully contributes to succeeding generations
EVOLUTION is:
1] Genetic change in a population of organisms over time. It is produced by the effects of natural selection on variation within the population. It produces a change in a population’s allele frequencies.
2] Evolution is a characteristic of populations, not individuals
Example: Galapagos finches