UNIT 1 – LESSON 2 NOTES
Natural Selection and Evidence for Evolution:
The mechanism for evolution is called Natural Selection to distinguish it from Artificial Selection.
Evolution occurs at the population level because genetics don’t change. The frequencies of different genetic types (genotypes) within a population do change over time & can create new species.
There is genetic variation in all populations; some individuals are successful at surviving and finding resources & produce offspring sharing the same genotype as the parent.
Enough mutations are selected within the population to create new species.
Conditions needed for evolution to occur:
Variation Within Population; differences in size, shape, physiology and reproductive abilities. Evolution requires variation within the population. o
Struggle for Existence (survival of the fittest); Darwin was influenced by Thomas Malthus—High birth rates and shortage of basic needs (food/shelter) forces organisms to compete for survival. The ability to survive in an environment is called fitness. o
Descent with Modification (ability of survivors to pass on their traits to the next generation); fitness traits must be heritable, species descended with changes from other species over time, appearing different from ancestors.
Natural selection occurs without human intervention, bringing changes in the inherited traits of the population, leading to create new species.
Pesticides don’t kill all insects; a few individuals have mutations that give them some resistance to it. When they reproduce they pass on this trait to their offspring. Since all non-resistant insects are killed, this allows the few resistant insects to take over the population---over time all insects in the area become pesticide resistant.
Six Evidences of Evolution;
1. Fossils; (H.M.S. Beagle Voyage) & layers of sediment and volcanic ashes show how species changed over time. o
2. Geographic Distribution of Living Species; organisms face environment selection pressures & develop similar features (not necessarily related). o
3. Comparative Anatomy; anatomical structures reveal evolution in 3 ways; homologous, analogous, & vestigial structures.
Homologous; Structures have similar anatomy, but differ in function. Shares a common ancestor, & provides evidence of descent with modification. Example; fingers used for grasping.
Analogous; Structures with similar functions and appearance, but different anatomy. Not a common ancestor. Example; wings made using different materials and bones (bats vs. birds).
Vestigial; Structures with no current functions, but are homologous to functional structures in related organisms. o
4. Comparative Embryology; all vertebrate embryos inherit the same basic genetic plan for development from their shared ancestors. o
5. Comparative Biochemistry & Genetic Evidence; ability to measure genetic and biochemical similarities; similarities in chromosome structure, sequence of amino acids in proteins & similarity in DNA composition—these all provide evidence of evolution. o
6. Artificial Selection; selective breeding (interference of humans). Natural and human activities can change environment causing evolution; black coloration (melanism) of peppered moths caused by industrial pollutants--Pollutants would discolor bark on trees darker moths increased as lighter moths were preyed on.
The theory of evolution by natural selection selects organisms best adapted to its environment & better able to survive under those conditions.
Darwin used fossils, geographic distribution of living species, artificial selection, comparative anatomy, & comparative embryology to support his theory of evolution. Mostly collected during the H.M.S. Beagle voyage.
Wild turkeys can fly. Domesticated turkeys can’t fly—if a population of domesticated turkeys escaped into a new environment where flying isn’t important for survival, they would survive in bushy lowlands/grasslands...
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