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Evolution and Adaptation Notes

Evolution and Adaptation Notes. http:// www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html - vid eo 7. What is Evolution??. Evolution. Evolution - Change in a kind of organism over time ; process by which modern organisms have descended from ancient organisms.

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Evolution and Adaptation Notes

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  1. Evolution and Adaptation Notes http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html - video 7

  2. What is Evolution??

  3. Evolution • Evolution - Change in a kind of organism over time; process by which modern organisms have descended from ancient organisms.

  4. What is a Theory versus a Hypothesis?http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html - video 1 Hypothesis Theory An educated guess that has to be testable by scientific methods Has to be well-supported and has been tested over and over Is an explanation of a phenomena that has occurred in the natural world.

  5. Origins of Evolutionary Thought • 1785 - James Hutton: Proposes that earth is shaped by geological forces that took place over extremely long periods of time. He estimates Earth to be millions – not thousands – of years old. • 1798 – Thomas Malthus: Predicts that the human population will grow faster than the space and food supplies needed to sustain it.

  6. Origins of Evolutionary Thought • 1809 – Jean-Baptiste Lamarck: Published his hypotheses of the inheritance of acquired traits. His ideas are flawed, but he is one of the first to propose a new mechanism explaining how organisms change over time. • 1833 – Charles Lyell: In his final volume of Principles of Geology, he explained that processes occurring now have shaped Earth’s geological features over long periods of time.

  7. Charles Darwin • In 1831, Darwin joined the crew of the Beagle and set sail from England for a voyage around the world. • Darwin made numerous observations and collected evidence (fossils) that led him to propose a revolutionary hypothesis about the way life changes over time. • That hypothesis, now supported by a huge body of evidence, has become the theory of evolution.

  8. The Galápagos Islands  • Although they were close together, the islands had very different climates. • Darwin observed that the characteristics of many animals and plants varied noticeably among the different islands of the Galápagos. • Giant tortoises: The shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited. • Birds varied: differently shaped beaks.

  9. Darwin Presents His Case • Eighteen months later, in 1859, Darwin published the results of his work, On the Origin of Species. • He proposed a mechanism for evolution that he called natural selection. • He then presented evidence that evolution has been taking place for millions of years – and continues in all living things. • His worked caused a sensation – many considered him brilliant and many strongly opposed.

  10. Some of Darwin’s Most Important Insights • One of Darwin’s most important insights was that members of each species vary from one another in important ways. • Variation existed both in nature and on farms. • Darwin argued that this variation mattered. This was a revolutionary idea, because in Darwin’s day, variations were thought to be unimportant, minor defects. • He noted that plant and animal breeders used heritable variation – what we now call genetic variation- to improve crops and livestock. They would select for breeding only the largest hogs, the fastest horses, or the cows that produced the most milk. Darwin termed this process artificial selection. • Artificial selection – Nature provided the variation, and humans selected those variations that they found useful.

  11. Darwin’s Conclusions Evolution Occurs by Natural Selection • Struggle for existence exists in nature • Competition among members of a species exist for food, living space, and the other necessities of life. • Survival of the Fittest – Individuals that are better suited to their environment – that it, with adaptations that enable fitness – survive and reproduce more successfully; Darwin referred to this as natural selection • Fitness - Ability of an organism to survive and reproduce in its environment. • Adaptation - Inherited characteristic that increases an organism's chance of survival • http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html- video 4

  12. Natural Selection • Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species' fitness in its environment. • Takes place without human control or direction. • Natural selection cannot be seen directly; it can only be observed as changes in a population over many successive generations. http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html - video 6

  13. Descent with Modification • Darwin proposed that over long periods, natural selection produces organisms have different structures, establish different niches, or occupy different habitats. • As a result, species today look different from their ancestors. • Each living species has descended, with changes, from other species over time. • Darwin referred to this principle as descent with modification

  14. How Common Is Genetic Variation? • Many genes have at least two genes or alleles. • Animals such as dogs, horses, and mice often have several alleles for traits such as body size or coat color. • All organisms have additional genetic variation that is “invisible” because it involves small differences in biochemical processes. • An organism can be heterozygous for many genes. • An insect can be heterozygous for as many as 15% of its genes. • Individual fishes, reptiles, and mammals are typically heterozygous for between 4–8% of their genes. Hh

  15. Biodiversity • Another word for variety is diversity. • Biodiversity – Biological diversity; Sum total of the genetically based variety of all organisms in the biosphere.

  16. Variation and Gene Pools • Genetic variation is studied in populations. • A population is a group of individuals of the same species that interbreed. • Because members of a population interbreed, they share a common group of genes called a gene pool. • Gene Pool - Consists of all genes, including all the different alleles, that are present in a population.

  17. Sources of Genetic Variation • The two main sources of genetic variation are: • Mutations – Any change in a sequence of DNA. • Can occur because of mistakes in the replication of DNA or as a result of radiation or chemicals in the environment. • Recombination - The natural formation in offspring of genetic combinations not present in parents. • Independent assortment occurs during the production of gametes – each homologous pair moves independently during meiosis. As a result the 23 pairs of chromosomes found in humans can produce 8.4 billion different combinations of genes. • Crossing over during meiosis further increases variation.

  18. Gene Pools and Evolution • The relative frequency of an allele is the number of times that the allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur. • In genetic terms, evolution is any change in the relative frequency of alleles in a population.

  19. Natural Selection on Single-Gene Traits • Natural selection on single-gene traits can lead to changes in allele frequencies and thus to evolution. • Example – A population of lizards is normally brown, but experiences a mutation that produces red and black forms. • If red lizards are more visible to predators, they might be less likely to survive and reproduce, and the allele for red coloring might not become so common.

  20. Natural Selection on Polygenic Traits • When traits are controlled by more than one gene, the effects of natural selection are more complex. • The action of multiple alleles on traits such as height produces a range of phenotypes that often fit a bell curve. • Fitness of individuals close to one another on the curve will not be very different. • Fitness can vary a great deal from one end of such a curve to another. • Where fitness varies, natural selection can act.

  21. Natural Selection on Polygenic Traits • Natural selection can affect the distributions of phenotypes in any of three ways: • Directional Selection • Stabilizing Selection • Disruptive Selection

  22. Directional Selection • Directional Selection – Takes place when individuals at one end of the curve have higher fitness than individuals in the middle or at the other end. • The range of phenotypes shift as some individuals fail to survive and reproduce while others succeed.

  23. Stabilizing Selection • Stabilizing Selection – Takes place when individuals near the center of the curve have higher fitness than individuals at either end of the curve. • This situation keeps the center of the curve at its current position, but it narrows the overall graph. • Example: The weight of human infants – smaller than average babies are likely to be less healthy and larger than average babies are likely to have difficulty being born.

  24. Disruptive Selection • Disruptive Selection– Takes place when individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle. • In such situations, selection acts most strongly against individuals of an intermediate type. • If the pressure of natural selection is strong enough and lasts long enough, this situation can cause the single curve to split into two (can create two distinct phenotypes).

  25. The Process of Speciation • Factors such as natural selection and chance events can change the relative frequencies of alleles in a population. • But how do these changes lead to the formation of new species, or speciation? • Species - Group of organisms that breed with one another and produce fertile offspring

  26. Speciation & Reproductive Isolation • The gene pools of two populations must become separated for them to become new species. • As new species evolve, populations become reproductively isolated from each other. • Reproductive Isolation - When the members of two populations cannot interbreed and produce fertile offspring.

  27. Reproductive Isolation Reproductive isolation can occur in a variety of ways, including: • Behavioral Isolation • Geographic Isolation • Temporal Isolation

  28. Behavioral Isolation • Behavioral Isolation - Two populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior. • Example: Eastern and Western Meadowlarks • Members of the two species will not mate with each other partly because they use different songs to attract mates. • Eastern meadowlarks will not respond to western meadowlark songs, and vice versa.

  29. Geographic Isolation • With geographic isolation, two populations are separated by geographic barriers such as rivers, mountains, or bodies of water. • Example: The Abert & Kaibab Squirrel • About 10,000 years ago, the Colorado River split the species into two separate populations. • Two separate gene pools formed. • Natural selection worked separately on each group and led to the formation of a distinct subspecies, the Kaibab squirrel.

  30. Temporal Isolation • Temporal Isolation - Form of reproductive isolation in which two populations reproduce at different times. • Example: • Three similar species of orchid all live in the same rain forest. • Each species releases pollen only on a single day. • Because the three species release pollen on different days, they cannot pollinate one another.

  31. Genetic Drift • Natural selection is not the only source of evolutionary change. In small populations, an allele can become more or less common simply by chance. • Genetic Drift- Random change in allele frequencies that occurs in small populations. • The smaller a population is, the farther the results may be from what the laws of probability predict. • Unlike natural selection because: • It happens by chance - such as random mating or a natural disaster (fire, landslide or lightning strike). • Doesn’t work to produce adaptations like natural selection does.

  32. How Does Genetic Drift Occur? • In each generation, some individuals may, just by chance, leave behind a few more descendants (and genes, of course) than other individuals. • The genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better” individuals. • It happens to all populations – there’s no avoiding the vagaries of chance.

  33. Gene Flow • Gene Flow - The transfer of alleles or genes from one population to another; also known as gene migration. • Affected by: • Mobility • Barriers

  34. Evolution vs. Genetic Equilibrium • To clarify how evolutionary change operates, scientists often find it helpful to determine what happens when no change takes place. • So biologists ask: Are there any conditions under which evolution will not occur? • The answers to those questions are provided by the Hardy-Weinberg principle.

  35. The Hardy-Weinberg Principle • Hardy-Weinberg Principle – Allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change. • Genetic Equilibrium - Situation in which allele frequencies remain constant. • If the allele frequencies do not change, the population will not evolve. Hardy Weinberg Equation: p2 + 2pq + q2 = 1 p + q = 1

  36. Hardy-Weinberg Principle • Five conditions are required to maintain genetic equilibrium from generation to generation: • There must be random mating. • All members of the population must have an equal opportunity to produce offspring, which ensures that each individual has an equal chance of passing on its alleles to offspring. • The population must be very large. • Genetic drift has less effect on large populations than on small ones. • There can be no movement into or out of the population. • Individuals may bring new alleles into a population. • There can be no mutations. • If genes mutate from one form into another, new alleles may be introduced into the population, and allele frequencies will change. • There can be no natural selection. • No phenotype can have a selective advantage over another.

  37. The Hardy-Weinberg Equation p2 = Frequency of AA 2pq = Frequency of Aa q2 = Frequency of aa p = Frequency of A q = Frequency of a For example: If the frequency of two alleles in a gene pool is 90% A , and 10% a, what is the frequency of individuals in the population with the genotype Aa? Solve: p = frequency of A, which is .9 (90%) q = frequency of a, which is .1 (10%) 2pq = frequency of Aa= 2(.9)(.1) = .18 Therefore, the frequency of individuals with genotypeAawould be .18

  38. Evidence of Evolutioncomes primarily from these sources….http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html - video 3 • Fossil record • Geographical distribution of living species • Structural similarities of related life forms • Chemical similarities in DNA • Embryology

  39. Evidence of Evolution: Fossil Record • Darwin argued that the fossil record provided evidence that living things have been evolving for millions of years. • Noticed that the sizes, shapes, and varieties of related organisms preserved in the fossil record changed over time. • Example: Cephalopods

  40. Evidence of Evolution: Fossil Record • Fossils are direct or indirect remnants of the past. • The fossil record provides evidence about the history of life on Earth. It also shows how different groups of organisms, including species, have changed over time, that life on Earth has changed. • The fossil record is not complete- there are gaps but they are being filled as we speak!!! • 99% of living species are now extinct Fossil record of horses

  41. In 1974 remains of this skeleton were found in Ethiopia and lived 3-3.9 million yrs ago. She was 3 ft. 8 in tall and weighed ~65 lbs. Because of her pelvis she was one of the first to show upright walking. She has a really small skull but front teeth like a human. “Lucy’s baby” – in 2006 they found the oldest earliest child fossil in Ethiopia – about 3 yrs old, female, skull, milk teeth, tiny fingers, torso, foot and kneecap (no bigger than a dried pea) – more complete than Lucy and 120,000thousands of years older even.

  42. Age of Fossils • Paleontologists determine the age of fossils using two techniques: • Relative dating • Radioactive dating Relative Dating Radioactive Dating

  43. Relative Dating • In relative dating, the age of a fossil is determined by comparing its placement with that of fossils in other layers of rock. • Paleontologists estimate the age based on the age of other fossils found near it. • It’s not absolute and doesn’t tell the age in years.. • The rock layers form in order by age: • The oldest layers on the bottom • More recent layers on top (closer to Earth's surface)

  44. Radioactive Dating • Scientists use radioactive decay to assign absolute ages to rocks. • Some elements (C, K, Ar) found in rocks are radioactive. • Radioactive elements decay, or break down, into nonradioactive elements at a steady rate, which is measured in a unit called a half-life. • In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains.

  45. Radioactive Decay • A half-life is the length of time required for half of the radioactive atoms in a sample to decay. • After 1 half-life - Half of the original radioactive atoms in a sample have decayed. • Of those remaining atoms, half again are decayed after another half-life.

  46. Evidence of Evolution: The Geographical Distribution of Living Species • Similar, but unrelated species exist. Similar animals in different locations were the product of different lines of evolutionary descent. • Some animals on each continent live under similar ecological conditions. • Are exposed to similar pressures of natural selection. • Because of these similar selection pressures, different animals ended up evolving certain striking features in common.

  47. Evidence of Evolution: Structural Similarities of Living Things • Homologous Structures • Analogous Structures • Vestigial Structures

  48. Homologous Structures of Living Organisms • Researchers had noticed striking anatomical similarities among the body parts of animals with backbones. • Example: The arms of reptiles, wings of birds, and legs of mammals vary greatly in form and function. Yet, they are all constructed from the same basic bones.

  49. Homologous Structures • Homologous Structures - Structures that have different mature forms in different organisms but develop from the same embryonic tissues. • Same development - different function. • Provide strong evidence that all four-limbed vertebrates have descended, with modifications, from common ancestors.

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