Presentation on theme: "Evidence of Evolution Fossil record Homologous structures Comparative Geological Distribution of organisms Homologous structures Comparative embryology."— Presentation transcript:
5Natural selectionNatural selection can affect the distributions of phenotypes in any of three waysDirectional selectionStabilizing selectionDisruptive selection
6Directional selection When individuals at one end of the curve have higher fitness than individuals in the middle or at the other end, directional selection takes place.The range of phenotypes shifts as some individuals fail to survive and reproduce while others succeed.
10Disruptive selectionWhen individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle, disruptive selection takes place.In such situations, selection acts most strongly against individuals of an intermediate type.
11Disruptive selection Disruptive Selection Key Largest and smallest seeds become more common.KeyLow mortality, high fitnessPopulation splits into two subgroups specializing in different seeds.Number of Birds in PopulationNumber of Birds in PopulationHigh mortality, low fitnessBeak SizeBeak Size
12Stabilizing selection When individuals near the center of the curve have higher fitness than individuals at either end of the curve, stabilizing selection takes place.This situation keeps the center of the curve at its current position, but it narrows the overall graph This situation keeps the center of the curve at its current position, but it narrows the overall graph
14Founder effectA situation in which allele frequencies change as a result of the migration of a small subgroup of a population is known as the founder effect.This can lead to new species!
15Founder effect Sample of Original Population Descendants Founding Population AFounding Population B
16Homologous body structures Further evidence of evolution can be found in living animals. By Darwin’s time, researchers had noticed striking anatomical similarities among the body parts of animals with backbones.
21Comparative embryology The early stages, or embryos, of many animals with backbones are very similar.It is clear that the same groups of embryonic cells develop in the same order and in similar patterns to produce the tissues and organs of all vertebrates.
23The Process of Speciation As new species evolve, populations become reproductively isolated from each other.Behavioral isolationDifferent courtship ritualsGeographic isolationRivers, mountains, body of waterTemporal isolationDifferent time of reproduction
25Reproductive Isolation results fromIsolating mechanismswhich includeBehavioral isolationTemporal isolationGeographic isolationproduced byproduced byproduced byBehavioral differencesDifferent mating timesPhysical separationwhich result inIndependently evolving populationswhich result inFormation of new species
26coevolutionSometimes organisms that are closely connected to one another by ecological interactions evolve together.Flowers and their pollinatorsAnemones and anemonefish (clown fish)Ants and treesMantids and plants or flowersMitochondria/humans & chloroplast/plants?