Transcript Adaptation
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