Evidence for Biological Evolution

Evolution results from 4 factors:  Potential for a species to increase in number  Heritable genetic variation  Due to mutations and sexual reproduction  Competition for limited resources  Reproduction of organisms better able to survive in the environment

Inherited variation & Artificial selection  Individuals of each species vary.  Darwin argued that variation was important.  In artificial selection, humans select from the naturally occurring genetic variations in a species.  Example: Dogs: all descended from wolves  Selective breeding for color, hair, size, behavior  Interbreeding reduces genetic variation

Artificial Selection  Wheat, corn, for resistance to rust, fungi, etc.  USDA spends $ to breed new resistant varieties.  Unintentional artificial selection  Antibiotic resistance in bacteria  Penicillin, Streptomycin, Tetracycline, etc.  “Multidrug resistant” tuberculosis  Pesticide resistance in insect pests  DDT, Chlordane, etc.

Remember…  Adaptation = any inherited characteristic that increases an organism’s chance of survival  Anatomical, physiological, behavioral  Successful adaptations enable organisms to become better suited to their environment.  Fitness = the ability of an individual to survive and reproduce in its specific environment.  Result of adaptation.  Survival of the fittest = individuals with adaptations that make them better suited to their environment survive and reproduce.

Natural Selection  Natural selection = the traits being selected, and increasing over time, contribute to an organism’s fitness in its environment.  Results in changes in the inherited characteristics of a population, which increase a species’ fitness in its environment.

Evolution by Natural Selection  Darwin proposed that a type of artificial selection occurred in nature.  Members of each species compete regularly to obtain food, living space, and other resources.  Selection removes (some) individuals with unfavorable traits.  Selection preserves (some) individuals with favorable traits.  The struggle for existence was central to Darwin’s theory of evolution.

Common Ancestry  Homologous “same” structures, different fucntions  Comparing the anatomy of fossils and living organisms All tetrapods have similar limb bones

Common Ancestry examples:  All primates have 5 fingers  Apes and humans lack a tail

Common Ancestry  Embryological evidence suggests common ancestry  Homologous structures develop different functions

Common Ancestry  The early embryonic stages of a (a) lemur, (b) pig, and (c) human show strikingly similar anatomical features.

Common Ancestry: Fossil Record  The only record that species changed over time

Darwin’s Concept: Natural Selection  Genetic variation exists within a population due to mutations and sexual recombination  Competition for resources yields the survival of the fittest for a certain environmental condition  Adaptations are changes in genetic traits over time  Natural selection favors traits ( variations ) that make an organism more fit for its environment, leading to adaptations in a population over many generations.

Darwin’s Finches  Galapagos Islands: 14 species of finches with one common ancestor  Variety of beak adaptations due to isolation of populations on different islands  Ongoing competition for resources