natural selection

• Genetic mutations and recombination contribute to the genetic variation within a population, which provides the raw material for natural selection to act upon.
• • Evolution - process by which populations of organisms change over time through changes in the genome (gene pool); can lead to formation of new species
• • Population - group of individuals of the same species
• • Gene pool - the set of all genes in any population; a larger gene pool means more genetic variation
• Evolution is not

  • Not an individual changing from one species to another! 
  • Not random! Traits are “selected” or more fit than others (these traits benefit the POPULATION not the organism) 
  • Does not suggest the beginning of life! Only how life forms have changed over time!   
• Common ancestry- concept in evolutionary biology that suggests one species is the ancestor of two or more species
• Fossils - remnants of ancient organisms; lower layers are more primitive than upper layers
• • Punctuated Equilibrium - changes that occur quickly (usually from a disaster) with long periods of little change within a species; can demonstrate speciation 
• • biogeography - the study of the geographical distribution of organisms (or fossils); provides information about how and when species may have evolved
• Homologous structures- structures similar in appearance but different in function; may have been shared with common ancestor 
• Vestigial structures- structures that have no current function; appear to have been used by ancestors
• Analogous structures-  structures of different species that are similar in function but not in structure and DO NOT derive from common ancestry 
• Embryo-  initial stage of development of a multicellular organism; some homologous structures can be seen between species only during embryo development
• DNA-  two closely related organisms will have similar DNA sequences/ amino acid sequences 
• • Cladogram - classifies organisms according to the order they MAY have evolved from a common ancestor; based on DERIVED characteristics (traits)
• Artificial Selection is the process by which humans select traits through breeding.
• “Struggle for Existence”: Resources are finite and cannot be quickly replaced; this leads to competition and for those better adapted to survive
• Heritability is the ability of a trait to be passed down.
• • Natural Selection - evolutionary mechanism by which individuals that have inherited beneficial adaptations survive and reproduce more offspring; “survival of the fittest” 
• Fitness is a measure of the ability to survive and produce more offspring
• Natural Selection Lies:

  • An individual organism can evolve new characteristics in response to environmental change
  • An individual organism can acquire a characteristic or trait as needed
  • Organisms are evolving or progressing toward “perfection”
• Natural Selection has four principles:

  1. Variation
  2. Adaptation
  3. Overproduction
  4. Descent with Modification
• 1. Variation is the difference in DNA sequences between individuals; must be inherited
• Adaptation is a feature of an organism that allows them to be better suited to their environment
• Overproduction is having more offspring than can survive; leads to competition
• Descent with Modification individuals with beneficial traits will be more likely to survive and pass these traits on to their offspring; changes allele frequency within the population gene pool over time
• Natural Selcetion - mechanism of evolution that works on ADAPTATIONS; organisms fit for an environment SURVIVE and REPRODUCE; decreases genetic variation
• Gene Flow - mechanism of evolution that works when individuals move into new populations and reproduce; also known as MIGRATION; increases genetic variation
• Mutations - mechanism of evolution that works when there is a change in DNA; increases genetic variation
• Recombination - mechanism of evolution that works when new combinations of alleles form during meiosis (crossing over) and sexual reproduction; increases genetic variation
• Genetic Drift - mechanism of evolution when there is a RANDOM change in allele frequencies due to chance; decreases genetic variation