Concepts of Evolution 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? Evolution Scientific theories Concepts based on the Reserved for a conceptual scheme supported by a large number of observations and not yet found lacking. Cell Biogenesis Gene Evolution Evolution All organisms are composed of cells. 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.
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? 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? 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?
Natural selection The process by which The process that results in evolution. 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 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, 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. 2 key points about natural selection 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 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 Microevolution Gene pool The total collection of genes in a population at any one time. Occurs when the frequency of the alleles in a population change over a number of generations. Hardy-Weinberg Equilibrium States what conditions must exist in a population so that it doesn t change The population must be very large Individuals do not migrate into or out of the population. Mutations do not alter the gene pool Mating is random Natural selection does not occur 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 Figure 13.23
Founder Effect Figure 13.28 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 Speciation Species A population or group of populations whose members can breed and produce fertile offspring. Speciation Causes of speciation include Reproductive isolation Prezygotic barriers Postzygotic barriers prevent the development of offspring that can survive and reproduce Geographical Isolation Allopatric speciation Gene flow is blocked. Physical separation mountain range, river. Figure 14.8
Speciation occurs when Example: White-tailed antelope squirrel and Harris s antelope squirrel separated by the Grand Canyon 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 Figure 14.12a The gradualist model of species formation Populations evolve differences gradually as they become adapted to their local environments Speciation occurs by Figure 14.12b