(a brief overview)
ORGANIC EVOLUTION VIA NATURAL SELECTION
THE UNDERLYING ARGUMENT:
HOW SELECTION OPERATES & HOW SELECTION GIVES RISE TO
PUBLISHED IN 1859: "ON THE ORIGIN OF SPECIES"
THE UNDERLYING ARGUMENT
1. Most species have great reproductive potential.
Populations would increase exponentially if all young survived to reproduce.
2. Most natural populations are stable over the long term.
3. Most young produced do not survive to reproduce.
Resources needed for survival & reproduction are limited.
4. Individual members of a species display variation in all possible characters.
5. These variations are heritable.
6. Because of differences in key characters, some individuals are more likely to survive & reproduce more successfully than others, i.e., are better adapted to current conditions.
7. Because of the differential survival & reproduction of individuals, the "average" state of a character within a population changes through time.
Favorable forms of characters are preserved & increase in frequency.
Unfavorable forms of characters decrease in frequency & may eventually be eliminated.
8. Natural selection can give rise to new species as changes in characters accumulate through LONG periods of time. = GRADUALISM.
Selection acts at the level of the (whole) individual.
Evolution occurs at the level of the population.
Artificial Selection mimics Natural Selection.
Microevolution leads to Macroevolution.
ORIGINS OF GENETIC VARIABILITY
1. MUTATION = NEW GENES
2. SEXUAL RECOMBINATION OF EXISTING GENES
GENETIC VARIATION IS THERANDOM COMPONENT
NATURAL SELECTION IS THE DETERMINISTIC COMPONENT
SELECTION CAN NOT ACT ON ACQUIRED CHARACTERISTICS