Evolution

Evolution:  change over time; the process by which modern organisms have descended from ancient organisms

Scientific Theory:  a well supported testable explanation of phenomena that have occurred in the natural world

Charles Darwin:  born in England 1809, on the same day as Abraham Lincoln  traveled around the world on H.M.S. Beagle

Charles Darwin:  Made numerous observations and collected evidence that led him to propose a hypothesis about the way life changes over time, the theory of evolution

Darwin’s Observations:  Patterns of diversity: he observed such a large variation of species in similar environments  EX: He saw rabbits in England but not in Australia even though the environment was similar

Living Organisms and Fossils:  He observed that fossils of ancient organisms resembled organisms that were still alive.  Others looked unlike anything he had ever seen

Galapagos islands:  many islands close together with very different climates.  Darwin observed that the characteristics of many animals and plants varied noticeably among the different islands

Ex: Tortoises  The differences = to the environments in which the respective tortoises live, and the types of food they eat.  domed tortoises tend to live in the moist high-lands and take their food from grasses and low-lying shrubs.  saddle-backed tortoises live in arid regions and feed on plants that are mostly above their head. The arched shell permits them to stretch their heads high, giving them a longer vertical reach.

On the Origin of Species:  Darwin’s book published in 1859 that summarized all his findings from his trip around the world.

Artificial Selection:  nature provides the variation and humans select those variations that they find useful.  ** Used to improve crops and livestock  Selective breeding transformed teosinte's few fruitcases (left) into modern corn's rows of exposed kernels (right).

Natural Selection:  Over time, results in changes in the inherited characteristics of a population and increase fitness (ability of an individual to survive and reproduce in its specific environment) of a species.

Darwin's illustrations of beak variation in the finches of the Galápagos Islands,  which hold 13 closely related species that differ most markedly in the shape of their beaks.  The beak of each species is suited to its preferred food, suggesting that beak shapes evolved by natural selection.

Adaptation:  an inherited characteristic that increases an organism’s chance of survival.

Struggle for Existence:  members of each species compete regularly to obtain food, living space and other necessities of life.  In general, organisms produce more offspring than limited resources can support, and organisms therefore compete for survival.

Descent with modification:  natural selection produces organisms that have different structures,  establish different niches  or occupy different habitats.  This causes today’s species to look different from their ancestors.

Common Descent: all living organisms are related to one another

Evidence of Evolution: Fossil record

Evidence of Evolution:  Homologous Body Structures:  structures that have different mature forms but develop from same embryonic tissues  (Wings and legs all descended from the fish fin)

Evidence of Evolution: Vestigial Organs: remnants of organs that have no function now

Evidence of Evolution:  Similarities in Embryology

Evolution of Populations:  A population is a group of individuals of the same species that interbreed and share a common group of genes

Gene pool-  all the genes, including all the different alleles, that are present in a population

Relative frequency of an allele-  the number of times that the allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur. Expressed as a percentage

Evolution-  any change in the relative frequency of alleles in a population

Single-gene traits – any traits controlled by one gene. (EX: widow’s peak in humans) natural selection on single-gene traits can lead to changes in allele frequencies and thus to evolution

Polygenic Traits- aany traits controlled by 2 or more genes ((EX: eye color and skin color)

Natural selection  can affect the distributions of phenotypes in any of three ways: directional selection, stabilizing selection or disruptive selection.

Directional selection:  when individuals at one end of the curve have higher fitness than individuals in the middle or at the other end. (EX: seed size and bird beak size)

Stabilizing selection:  when individuals near the center of the curve have higher fitness than individuals at either end of the curve. (EX: weight of human infants at birth)

Disruptive selection:  when individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle (EX: seed size and bird beak size)

Genetic Drift:  in a small population, individuals that carry a particular allele may leave more descendents than other individuals, just by chance.  Over time, a series of chance occurrences of this type can cause an allele to become common in a population

Name 3 chance events that could cause genetic drift to occur?

Founder effect:  genetic drift due to the migration of a small subgroup of a population.  (EX: Fruit Flies migrating from mainland to different Hawaiian Islands)

Hardy-Weinberg Equilibrium:  allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change.  Also called genetic equilibrium  Five conditions are required to maintain genetic equilibrium from generation to generation  Random mating  Large population  No movement into or out of the population  No mutation  No natural selection

Speciation: formation of new species  Reproductive isolation: when the members of 2 population cannot interbreed and produce fertile offspring

Behavioral isolation:  when two populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior.

Geographic isolation:  when 2 populations are separated by geographic barriers such as rivers, mountains, or bodies of water.

Temporal isolation-  when 2 or more species reproduce at different times