ADAPTATIONS AND EVOLLUTION OF SPECIES
What is evolution? •The change in the genetic make-up of a species over time
How does evolution occur?
• GRADUALISM
– gradual process that goes on all the time
• PUNCTUATED EQUILIBRIUM
– periods of rapid change are separated by periods of little or no change
NATURAL SELECTION
1 All species have genetic variation. 2 The environment presents many challenges 3 Organisms tend to produce more offspring than the environment can support competition ( struggle for survival) 4 Some individuals are better suited to cope with the challenges ( survival of fittest) 5 Characteristics best suited to environment tend to increase in a population over time
INDUSTRIAL MELANISM
* The darkening of an organism over time due industrial pollution * peppered moth
BALANCING SELECTION
• Selection that acts in opposite directions
Example: Malaria The allele for sickle cell anemia affects the population in opposing ways: (1) tends to eliminate the allele in homozygous individuals because sickle cell anemia is lethal for these individuals (2) tends to preserve the allele because the heterozygote is resistant to malaria
DIRECTIONAL SELECTION
• The frequency of one allele tends to move in one direction
Example: 1. Birth weight in offspring 2. Seed size
SPECIES FORMATION
• Begins with divergence
• Results in reproductive isoloation
• Speciation occurs
MECHANISM FOR REPODUCTIVE ISOLATION
• • • • • Geographical isolation Ecological isolation Temporal isolation Mechanical isolation Reproductive failure
MICROEVOLTION LEADS TO MACROEVOLUTION