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Transcript
The Theory of Evolution In science, theories are statements or models that have been tested and confirmed many times. Theories have some important properties: •They explain a wide variety of data and observations •They can be used to make predictions •They are not absolute •They serve as a model of understanding the world and can be changed as the world view changes The Theory of Evolution is considered a Unifying Theory of Biology, because it answers many of these questions and offers an explanation for the data. How does evolution explain the origin and development of species? The Beginning of the Story Evolution begins with variation. NO VARIATION = NO EVOLUTION What causes variation? What causes variation? 1. List 5 types of variation. 2. List 3 things that can cause variation in an organism? 3. Write them on your clear board. 4. Transfer them into your notes. In the real world, how do mutations come about? 1. Internal 1. Replication errors 2. High energy molecules generated within the organism – free radicals. 2. External 1. Chemicals, i.e. mutagens 2. Radiation, e.g. UV, cosmic rays See video. Mutations may: A. B. C. D. Have positive effects Have negative effects Have no effect All of the above All of the following can be causes of mutation except: A. B. C. D. Mutagenic chemicals An organism’s need to be successful Radiation from the sun Free radicals Whether a mutation is positive or negative depends the location of the mutation in the genome: True False Whether a mutation is positive or negative depends on the environment of the organism. True False Which of the following statements is false: A. Mutations occur all the time. B. Everyone has mutations. C. Mutations always lead to a decrease in success of the organism. D. Mutations can be caused by a variety of factors. Tracking Mutations • Mutations occurring in the genes of the gametes are inherited by offspring. • These mutations may show up through thousands of generations as the same chromosome is transmitted from parent to child. • Understanding these mutations can tell us a lot about the ancestry of organisms including humans. What specific name do we have for inherited mutations? A. B. C. D. Chromosomes Markers Genes Gametes What genetic material does a man always inherit? A) B) C) D) His mother’s paternal chromosomes His father’s paternal chromosomes His father’s Y chromosome All of his fathers chromosomes What is the name of the people the scientist is investigating? A. B. C. D. Koi San Africans Kenyans Aborigines Why is Dr. Wells so interested in these bushmen? A. He thinks they may have some special genes that can be used in medicine. B. He thinks they may be the group most closely related to our ancestors who left Africa. C. He thinks they may have invented the bow and arrow. D. He thinks they may have invented spoken language. Meiosis and fertilization allow for great diversity in sexual species compared to asexual species. In evolutionary terms, sex is more important than life itself. Sex fuels evolutionary change by adding variation to the gene pool. The powerful urge to pass our genes on to the next generation has likely changed the face of human culture in ways we're only beginning to understand. Why Sex? Traits can be positive, negative or neutral in a given environment. The alleles coding for negative traits are likely to be reduced in the presence of alleles for more favorable ones. Team Question The types of variation we have been discussing can have an impact on the success of an organism. Biologically speaking, what is “success?” Essential requirements for Evolution Variation: All life forms vary genetically within a population. It is this genetic variation upon which selection works. Inheritance: Genetic traits are inherited from parents and are passed on to offspring. Selection: Organisms with traits that are favorable to their survival get to live and pass on their genes to the next generation. Time: Evolution takes time. Evolution can happen in a few generations, but major change, such as speciation, often takes long periods of time. CHARLES DARWIN – 1809-1882 • English • Traveled around the world on the Beagle – famous in the Galapagos islands • Observed many species and fossils • Why did some species survive while others became extinct? • Natural selection Voyage of the HMS Beagle Stopped in Galapagos Islands 500 miles off coast of Ecuador I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection. —Charles Darwin from "The Origin of Species" NATURAL SELECTION Organisms with traits well suited to an environment are more likely to survive and produce more offspring than organisms without these favorable traits Types of selection There are three types of selection: disruptive, stabilizing and directional. Selection causes some traits to survive and spread, while others are lost. A selection pressure determines which traits are successful. Starting population has a normal distribution of traits. number of individuals Selection can be represented using graphs showing the distribution of individuals with a particular trait. mode trait Types of selection Selection can cause the mode and/or distribution to change. mode number of individuals mode number of individuals number of individuals mode trait disruptive Selection pressure toward the extremes creates two modal values. trait stabilizing Selection pressure toward the center increases the number of individuals at the modal value. trait directional Selection pressure toward one extreme moves the mode in this direction. LaMarck Earlier ideas on Evolution – evolution by acquired traits • creatures developed traits during their lifetime • give those traits to their offspring – example • in reaching higher leaves giraffes stretch their necks & give the acquired longer neck to offspring – not accepted as valid Darwin’s view of Evolution – giraffes that already have long necks survive better – leave more offspring who inherit their long necks • variation • selection & survival • reproduction & inheritance of more fit traits Could Darwin explain everything? Darwin made extensive use of specimens and fossil evidence to explain his theory of evolution, but because DNA and genes had not yet been discovered, he was unable to explain why traits varied within individuals or how they were inherited. Victorian scientists found it difficult to test Darwin’s theory. For his theory to work, the Earth needed to be millions of years old, but its age was not known at that time. In addition, little was known about the process of fossilization or how to explain gaps in the fossil record. Natural Selection 1. 2. 3. 4. Overproduction Competition Variations Survival of the fit 1. Overproduction Organisms produce more offspring than the environment can support. There is not enough food or living space for all the offspring. 2. Competition Overproduction leads to a struggle. All the organisms compete for food, water, and the other necessities of life. Only those organisms that are well suited to their surroundings survive and reproduce. The rest die. 3. Variations Organisms of the same species are very similar. But they do have individual differences among traits, or variations. These differences are important in the ”struggle for survival.” For example, extra speed can mean the difference between life and death. A fast wildebeest may escape an attacking lion. A slower neighbor may become the lion’s next meal. 4. Survival Of The Fit Organisms with traits that make them well adapted, or suited to the environment, survive and reproduce. Darwin used the term natural selection to describe the survival of organisms with favorable traits. They, in turn, pass their favorable traits to their offspring. The offspring are then more likely to survive. As the process of natural selection goes on over many generations, species change. Galápagos finches In the Galápagos, Darwin noticed that different islands had different types of finches, with different types of beak. Some finches had strong and claw-like beaks, suitable for crushing seeds. Other finches had thin and delicate beaks, suitable for picking insects from holes in the ground. Darwin thought all the finches could have evolved from one type of finch that came from the mainland. Natural variation meant that some finches had slightly different beaks. These finches would have been able to eat different types of food and avoid competition. They would therefore have survived and passed on their genes. Darwin’s finches Darwin’s conclusions – variations in beaks • differences in beaks in the original flock • adaptations to foods available on islands – natural selection for most fit • over many generations, the finches were selected for specific beaks & behaviors – offspring inherit successful traits • accumulation of winning traits: both beaks & behaviors – separate into different species Peppered moths Peppered moths rest on tree trunks during the day. Some are light colored and others are dark. When cities were very polluted in the 19th century the number of previously rare dark colored moths increased, as they were better camouflaged against predators on soot-stained trees. Cities are cleaner now. What difference has this made? The number of light colored moths is increasing. These changes can result in the appearance of a new species. Evolution by natural selection occurs.