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Download Review Slides - Evolution
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THEORIES OF EVOLUTION Driving Question: How and why do species change over time? How they Agreed Life has changed gradually over time and was still changing Living things change to be better suited and adapted to their environments All organisms are related Life evolved from fewer, simpler organisms to many, more complex organisms. Jean-Baptiste Lamarck’s Theory of Evolution French scientist – published theory 1809 Main features of his theory: • the law of use and disuse • the law of inheritance of acquired characteristics Organisms could acquire or lose traits during their lifetime based on if they used them or not. Acquired traits would be passed to offspring. Charles Darwin’s Theory of Evolution English naturalist – published theory 1859 in book called On the Origin of Species Main features in his theory: • individuals compete for limited resources • individuals in a population show natural variation • individuals with characteristics best suited to their environment are more likely to survive to reproduce • 'successful' characteristics are inherited Which theory is right? Darwin’s theory has been supported by evidence including genetics Lamarck’s theory has been disproven Changes that occur during an animal’s life are not passed on to the animal’s offspring Only way traits are passed on is through genes What about Wallace? Alfred Wallace independently came up with a theory of evolution through natural selection 1858 his theory appears in a paper published along with Darwin’s paper 1859 Darwin publishes his book, gets all the credit James Hutton & Charles Lyell Earth is millions of years old Processes that changed Earth in the past are the same processes that operate today What this meant for Darwin If the Earth can change over time, why can’t life? Earth is old enough for evolution to have occurred. EVIDENCE FOR EVOLUTION Driving Question: How and why do species change over time? DNA The more similar the DNA coding of two organisms, the more closely related they are. Doesn’t mean they evolved from each other, but that they are more likely to share a common ancestor. Whale DNA is more similar to Artiodactyls DNA Mammals with even number of toes Pigs, deer, cows, goats, hippos, giraffes What? What is biogeography? The study of the geographic distribution of organisms. What is fauna? Animal life What is a faunal assemblage? A group of living or fossil animals found in a particular geographic area. Biogeography is the study of the geographic distribution of organisms Populations of the same species in different places adapt to different local environments. Similar but unrelated species - species living in similar environments have similar structures and behaviors. Influenced by geological processes (plate tectonics, sea level changes, etc) Fossils Record of life changing over time. Fossils in the bottom layers are very different from the organisms alive today. As you look at younger rock layers the fossils found there are more similar to organisms found today. Find intermediate species that show change over time. Embryology and Development Embryos of many different kinds of animals look very similar and it is often difficult to tell them apart. Many traits of one type of animal appear in the embryo of another type of animal. Human embryos have gill slits and tail Since animals develop similarly, it implies that they are related, have common ancestors, and they started the same and developed different traits through evolution. Comparative Anatomy Similarities in the anatomy of different organisms helps us understand how they are related. Homologous structures: Structures that are shared by related species. They are inherited from a common ancestor. Structures are similar but become modified through evolution. Many mammals have similar limb structures. Comparative Anatomy Homologous structures: Similar structure, not necessarily similar function. Comparative Anatomy Vestigial structures: structure in an organism that has lost all or most of its original function in the course of evolution Humans – appendix, tail bone, wisdom teeth, plica semilunaris Whale – pelvic bone Wings in flightless bird Comparative Anatomy Analogous structures: Body parts that have the same function, but different structure. These structures are not inherited from a common ancestor. Darwin’s Explanation of How Evolution Occurs Variations – differences between individuals of one species Variation is the rule, not the exception! Follows the normal distribution or bell curve: DARWIN’S THEORY OF EVOLUTION Driving Question: How and why do species change over time? Darwin’s Explanation of How Evolution Occurs There is a struggle to survive. Limited resources in the environment. Limited amount of food, water, space, etc. Organisms compete for these limited resources Darwin’s Explanation: 1. More individuals are born in a species than the environment can support. There is a struggle to survive. Organisms compete for limited resources. Darwin’s Explanation of How Evolution Occurs Variations – differences between individuals of one species Variation is the rule, not the exception! Gene Pool – combined genetic information of all the members of a population. Genetic variation – variation in alleles of genes in a gene pool Darwin’s Explanation of How Evolution Occurs Darwin’s Explanation: 2. Within every species there is naturally variation. Sources of Genetic Variation: Mutations - changes in the DNA. Gene flow - any movement of genes from one population to another. Sexual Reproduction - genetic shuffling can introduce new gene combinations into a population. Lateral Gene Transfer – pass genes from one individual to another, common in bacteria – important process in the evolution of antibiotic resistance Darwin’s Explanation of How Evolution Occurs Advantageous traits are adaptations. Adaptation: an inherited characteristic that increases an organism’s chance of survival. Adaptations increase fitness. Fitness: ability of an individual to survive and reproduce in its specific environment. Darwin’s Explanation of How Evolution Occurs Natural Selection – selection pressures in each environment causes changes in the inherited characteristics of a population. It directs these changes in ways that increase a species’ fitness in its environment. Darwin’s Explanation of How Evolution Occurs Survival of the Fittest – Individuals better suited to their environment – high fitness – survive and reproduce more successfully. Not the biggest, strongest, fastest Darwin’s Explanation of How Evolution Occurs Descent with Modification – over time, natural selection produces organisms with different traits. Organisms descend, with changes, from their ancestors. Darwin’s Explanation of How Evolution Occurs Darwin’s Explanation: 3. Some variations give organisms an advantage over others in the struggle to survive. Quick reaction time, can get away faster Evolution in Action – Do you know why deer have eyes on the side of their head and we have eyes on the front of our head? Wider eye distance, better peripheral vision. Closer eye distance, better depth perception. Prey vs. Predator. Darwin’s Explanation of How Evolution Occurs Darwin’s Explanation: 4. More of these individuals will survive and reproduce than will those with less favorable traits. Natural Selection – Types of Selection Directional, Stabilizing, Disruptive Stabilizing Selection: When individuals near the center of the curve have higher fitness than individuals at either end. Directional Selection: When individuals at one end of the curve have higher fitness than individuals in the middle or at the other end. Evolution causes an increase in the number of individuals with the trait at one end of the curve. Disruptive Selection: When individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle. Creates two distinct phenotypes. Artificial Selection Artificial Selection: Humans breed animals or plants for particular traits. They select the variations they want. Humans can cause species to evolve. Natural Selection Change in the gene pool is not by chance. Due to selection pressures Survival of the fittest = Reproduction of the fittest Sexual selection Genetic Drift Activity Genetic Drift – in a small population, an allele can become more or less common by CHANCE. By chance some individuals have more offspring, so over time, their alleles can become more frequent in the population. Genetic Drift Bottleneck effect – a change in allele frequency following a dramatic reduction in the size of a population. Can reduce the gene pool (genetic diversity). Usually caused by a disaster like a disease Founder effect – allele frequencies change as a result of the migration of a small subgroup of a population For example, several members of a fruit fly population ended up in Hawaii. The fruit flies evolved in several hundred species. Darwin’s Explanation of How Evolution Occurs Darwin’s Explanation: 5. Many traits are passed from parents to offspring. 6. More individuals with favorable traits reproduce, so the # of individuals with favorable traits increases in each generation. The # with less favorable traits decreases. Darwin’s Explanation of How Evolution Occurs Darwin’s Explanation: 7. Eventually the favorable trait becomes the most common form and over many generations (and usually millions of years) such differences accumulate until a new species results. Speciation Isolating Mechanisms Adaptive Radiation Genetic Equilibrium What does equilibrium mean? A population that is not evolving, allele frequencies in the gene pool do not change Hardy-Weinberg Principle Allele frequencies in a population should remain constant unless one or more factors cause the frequencies to change. Five conditions that can disrupt genetic equilibirum and cause evolution to occur: 1. 2. 3. 4. 5. Nonrandom mating (sexual selection) Small Population Size Immigration and Emigration Mutations Natural Selection Speciation Species – a population or group of populations whose members can interbreed and produce fertile offspring. Speciation – the formation of new species. Speciation There are four types of isolating mechanisms that can cause speciation. Speciation: Reproductive Isolation Reproductive Isolation – When the members of two populations cannot interbreed and cannot produce fertile offspring. Three ways that reproductive isolation can develop: Behavioral Isolation – different behaviors prevent interbreeding Geographic Isolation – populations are separated by geographic barriers Temporal Isolation – species reproduce at different times Speciation: Reproductive Isolation Reproductive Isolation Behavioral Isolation – two populations are capable of interbreeding but differences in courtship rituals or other types of behavior prevent them from mating. Speciation: Reproductive Isolation Reproductive Isolation Geographic Isolation – two populations are separated by geographic barriers (rivers, mountains or bodies of water) that prevent mating. Speciation: Reproductive Isolation Reproductive Isolation Temporal times. Isolation – Species reproduce at different Speciation: Adaptive Radiation Founder Effect – the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. Adaptive Radiation – a single species evolves into several different species usually in response to new environments. Galapagos Islands Darwin – 1835 – went to Galapagos aboard the HMS Beagle Speciation – Galapagos Finches 1. Founders arrive 2. Separation of Populations 3. Changes in Gene Pool 4. Reproductive Isolation 5. Ecological Competition 6. Continued Evolution Funky scardey cats run every Christmas! See figure 16-7 Speciation – Galapagos Finches MACROEVOLUTION Jigsaw Activity Macroevolution vs. Microevolution Microevolution – small scale, short time frame – within a single population or species Macroevolution – large scale, long time frame (millions to billions of years) – includes more than one species Both involve natural selection, mutations, genetic drift and migration Image Source: http://evolution.berkeley.edu/evolibrary/article/evoscales_01 Macroevolution Paleontologists study fossils to learn about the patterns of macroevolution. Fossils are classified into clades (group of organisms that consists of a common ancestor and all of its descendants, it is a branch on the tree of life) Image Source: http://evolution.berkeley.edu/evolibrary/search/imagedetail.php?id=260 Models of Evolution Evidence shows that evolution occurs at different rates for different organisms at different times throughout the history of the Earth. Two Models 1. Gradualism – Slow and steady evolution over time. Models of Evolution 2. Punctuated Equilibrium - slow and steady is not always the case. Most of the time the species are in equilibrium (structures don’t change even though genes may change). Then equilibrium is interrupted by brief periods of rapid change. Rapid on geologic time scale may be 1000s of years Types of Macroevolution Extinct – species dies off, no longer exists. Background extinction – natural rate of extinctions due to natural processes like natural selection. Mass extinction – event in which many species become extinct over a relatively short time period. 6 mass extinctions Types of Macroevolution Coevolution – two species evolve in response to changes in each other over time. Usually these two species can’t survive without each other. Ants and Acacia Types of Macroevolution Convergent Evolution – evolution produces similar structures and characteristics in very distantly related organisms because they evolve in very similar environments. Types of Macroevolution Speciation – one species evolves into two or more species. Types of Macroevolution Adaptive Radiation = rapid speciation - a single species or a small group of species evolves over a relatively short time frame into several different forms that live in different ways (different ecological niches).