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 Many biologist hypothesize that major environmental changes have had tremendous impact on the formation of new species. These scientist believe that evolution occurs in spurts.

NATURAL SELECTION All species have genetic variation. The environment presents many challenges Organisms tend to produce more offspring than the environment can support - competition ( struggle for survival) Some individuals are better suited to cope with the challenges ( survival of fittest) Characteristics best suited to environment tend to increase in a population over time

peppered moth 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