Slide 1. Slide 2. Slide 3. Concepts of Evolution. Isn t Evolution Just A Theory? Evolution

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1 Slide 1 Concepts of Evolution Slide 2 Isn t Evolution Just A Theory? How does the scientific meaning of a term like theory differ from the way it is used in everyday life? Can the facts of science change over time? If so, how? Slide 3 Evolution Scientific theories Concepts based on the Reserved for a conceptual scheme supported by a large number of observations and not yet found lacking.

2 Slide 4 Cell Evolution All organisms are composed of cells. Biogenesis Gene Evolution Life comes only from life. Organisms contain coded information that dictates their form, function, and behavior. All living things have a common ancestor. Genetic changes in a population or species over generations have led to the diversity of life on Earth. Slide 5 How Do We Know Evolution Happens How do fossils give us a picture of change over time? What distinguishing feature of the fossil Pakicetus skull identified it as related to a whale? Why was this surprising? Why do scientists seek fossils that are intermediate in form and time between modern forms and their probable earliest ancestors? Slide 6 Fossil Called Missing Link from Sea to Land Animals What evidence from the fossil fish skeleton suggests it is an intermediate form between fish and land animals?

3 Slide 7 Slide 8 How Does Evolution Really Work? What are the 4 components of natural selection? What determines an individual hummingbird s beak length? What factors in the environment might select for beak length and shape within the hummingbird population? How can hummingbird DNA help Dr. Schindler determine the evolutionary history of hummingbirds? Slide 9 Natural Selection Natural selection The process by which The process that results in evolution.

4 Slide 10 Natural Selection Natural selection is based on variation: Individuals in a population differ from one another Many of these differences are genetic Genetic variation occurs because of Slide 11 Natural Selection Some variations may help individuals in a population to survive Increase the amount of offspring the individuals have These traits if inherited would be passed on to the offspring Over time, Slide 12 Natural Selection Examples: Peppered moths of England Snails in England Flat-tailed horned lizard Pesticide/antibiotic resistance Sickle cell disease Example of heterozygous advantage individuals who are heterozygous for sickle cell disease are resistant to malaria.

5 Slide 13 Natural Selection 2 key points about natural selection 1. Natural selection is more of an A pesticide does not create resistant individuals, but selects for resistant insects that were already present in the population Slide 14 Natural Selection 2. Natural selection depends on time and place It favors those characteristics in a varying population that fit the current, local environment. Environmental factors vary from place to place and time to time Slide 15 Microevolution Gene pool The total collection of genes in a population at any one time. Microevolution Occurs when the frequency of the alleles in a population change over a number of generations.

6 Slide 16 Microevolution Hardy-Weinberg Equilibrium States what conditions must exist in a population so that it doesn t change 1. The population must be very large 2. Individuals do not migrate into or out of the population. 3. Mutations do not alter the gene pool 4. Mating is random 5. Natural selection does not occur Slide 17 Microevolution One of the possible causes of microevolution is Genetic drift Bottleneck effect an event drastically reduces the number of individuals in the population. The surviving individuals do not have the same genetic makeup of the orginal population Slide 18 LE 13-9a Original population Bottlenecking event Surviving population

7 Slide 19 Founder Effect Microevolution Slide 20 LE Original population Evolved population Frequency of individuals Original population Phenotypes (fur color) Stabilizing selection Directional selection Disruptive selection Slide Natural selection can alter variation in a population in three ways Stabilizing selection: Directional selection: acts against individuals at one of the phenotypic extremes Disruptive selection: favors individuals at both extremes of the phenotypic range

8 Slide 22 Speciation Species A population or group of populations whose members can breed and produce fertile offspring. Speciation Slide 23 Speciation Causes of speciation include 1. Reproductive isolation Prezygotic barriers Postzygotic barriers prevent the development of offspring that can survive and reproduce Slide 24

9 Slide 25 Slide 26 Slide 27 Speciation 2. Geographical Isolation Allopatric speciation Gene flow is blocked. Physical separation mountain range, river.

10 Slide 28 LE 14-4 A. harrisi A. leucurus Slide 29 LE 14-5a Initial sample Starch medium of fruit flies Results of mating experiments Female Starch Maltose Male Maltose Starch Mating frequencies in experimental group Male Different Same Maltose medium Female Same Different population populations Mating frequencies in control group Slide 30 Speciation Speciation occurs when Example: White-tailed antelope squirrel and Harris s antelope squirrel separated by the Grand Canyon

11 Slide 31 LE 14-10b Time Slide 32 Speciation The fossil record shows how speciation has occurred over geological time. There are four eras (Precambrian, Paleozic, Mesozoic, and Cenozoic) in which mass extinctions were followed by rapid speciation. This evidence demonstrates punctuated equilibrium the concept that speciation occurs Slide 33 LE 14-10a Time

12 Slide 34 Speciation in the Fossil Record The gradualist model of species formation Populations evolve differences gradually as they become adapted to their local environments Speciation occurs by