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Chapter 17 Lecture Conceptual Integrated Science Second Edition The Evolution of Life © 2013 Pearson Education, Inc. This lecture will help you understand: • • • • • • • • • • • • • • The Origin of Life Did Life on Earth Originate on Mars? Early Life on Earth Charles Darwin and The Origin of Species How Natural Selection Works Adaptation Staying Warm and Keeping Cool Evolution and Genetics How Species Form Evidence of Evolution Fossils: Earth's Tangible Evidence of Evolution The Evolution of Humans History of Science: The Peppered Moth Science and Society: Antibiotic-Resistant Bacteria © 2013 Pearson Education, Inc. The Origin of Life • For thousands of years, people believed that life was created through spontaneous generation, the sudden emergence of living organisms from nonliving materials. © 2013 Pearson Education, Inc. The Origin of Life • In 1862, Louis Pasteur demonstrated that life did not arise from nonlife. © 2013 Pearson Education, Inc. • He designed a flask that kept out dust and other airborne particles • He filled the flask with meat broth, and let it sit • No life emerged © 2013 Pearson Education, Inc. The Origin of Life • Life originated billions of years ago on a young Earth very different from the Earth of today. • The Miller and Urey experiment modeled the young Earth's atmosphere and oceans. • When Miller and Urey shot electric sparks through the model to simulate lightning, complex organic molecules formed. © 2013 Pearson Education, Inc. • Many complex organic molecules could have been formed – Including Amino Acids, Proteins, Sugars and Lipids • But many scientist question the validity of this experiment – Because the Earth’s atmosphere may have been different © 2013 Pearson Education, Inc. The Origin of Life • There are two alternative hypotheses for the origin of organic molecules on Earth: – Organic molecules came to Earth on incoming meteorites. – Organic molecules were synthesized in deepsea environments. • But, how do you get from organic molecules to cells? © 2013 Pearson Education, Inc. The Origin of Life • Liposomes form spontaneously when certain lipids are added to water. Liposomes – have double membranes similar to cell membranes. – can grow, shrink, and divide. – run chemical reactions inside their membranes. – control what molecules move into and out of them. – they are not alive. © 2013 Pearson Education, Inc. The Origin of Life • Living cells also need genes. • Scientists now believe that the first genes were made of RNA, not DNA. – Short strands of RNA can spontaneously assemble from individual RNA nucleotides. – RNA can replicate by itself. • Liposomes may have captured RNA "genes," forming the first primitive cells on Earth. © 2013 Pearson Education, Inc. Did Life on Earth Originate on Mars? • In 1996, scientists found what resembled tiny, fossilized bacteria in a Martian meteorite. • Mars may have once been a much warmer and wetter planet. • The supposed fossils may be too small to be fossilized bacteria. • NASA continues to explore the possibility of life on Mars. © 2013 Pearson Education, Inc. Early Life on Earth • The origin of autotrophs – Earth's earliest living organisms • were marine prokaryotes (3.5 billion years old). • lived with no free oxygen. • were heterotrophs that obtained energy and food from outside sources. – The evolution of autotrophs, organisms able to convert inorganic molecules into food and organic molecules, was a key event in the history of life. • Photosynthesizers use energy from the Sun. • Chemoautotrophs use energy from certain inorganic chemicals. © 2013 Pearson Education, Inc. Early Life on Earth • The oxygenation of the atmosphere – Cyanobacteria are photosynthetic bacteria that produce oxygen as a by-product of photosynthesis. – They arose 2.7 billion years ago. – They changed the environment. © 2013 Pearson Education, Inc. Early Life on Earth • The first eukaryotes – Eukaryotes appeared about 2 billion years ago. – The nucleus and most organelles most likely originated from inward foldings of the cell membrane. – According to the endosymbiotic theory, mitochondria and chloroplasts (have their own DNA) evolved from prokaryotes living inside the earliest eukaryotic cells. © 2013 Pearson Education, Inc. Charles Darwin and The Origin of Species • For thousands of years, people believed that species on Earth did not change. • But then what are fossils? © 2013 Pearson Education, Inc. Charles Darwin and The Origin of Species • Jean Baptiste Lamarck argued that modern species were descended from ancestors that had evolved to become better adapted to their environments. • Lamarck believed that organisms acquired new traits over their lifetimes and then passed these traits to their offspring. He called this the inheritance of acquired characteristics. © 2013 Pearson Education, Inc. Charles Darwin and The Origin of Species • Charles Darwin argued that evolution—inherited changes in populations of organisms over time—had produced all the living forms on Earth. © 2013 Pearson Education, Inc. Lamarck's Evolution Hypotheses Lamarck's Evolution Hypotheses Jean-Baptiste Lamarck recognized that: – living things have changed over time. – all species were descended from other species. – organisms were adapted to their environments. Copyright Pearson Prentice Hall Lamarck's Evolution Hypotheses Lamarck proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. These traits could then be passed on to their offspring. Over time, this process led to change in a species. Flaws: Tendency toward perfection Use and Disuse Copyright Pearson Prentice Hall Lamarck's Evolution Hypotheses A male fiddler crab uses its front claw to ward off predators and to attract mates. Lamarck's Hypothesis Copyright Pearson Prentice Hall Lamarck's Evolution Hypotheses Because the front claw is used repeatedly, it becomes larger. Lamarck's Hypothesis This characteristic (large claw) is passed onto its offspring. Copyright Pearson Prentice Hall Lamarck's Evolution Hypotheses Evaluating Lamarck's Hypotheses Lamarck’s hypotheses of evolution are incorrect in several ways. Lamarck did not know: – how traits are inherited. – that an organism’s behavior has no effect on its heritable characteristics. However, he paved the way for the work of later biologists. Copyright Pearson Prentice Hall Voyage of the Beagle Voyage of the Beagle In 1831, Darwin set sail from England aboard the H.M.S. Beagle for a voyage around the world. Copyright Pearson Prentice Hall Voyage of the Beagle During his travels, Darwin made numerous observations and collected evidence that led him to propose a hypothesis about the way life changes over time. That hypothesis has become the theory of evolution (aka theory of natural selection). Copyright Pearson Prentice Hall Darwin's Observations Darwin's Observations • He observed many plants and animals were well suited to the environments they inhabited. • He was impressed by the ways in which organisms survived and produced offspring. • Darwin was puzzled by where different species lived and did not live. Copyright Pearson Prentice Hall Darwin's Observations • Living Organisms and Fossils • Darwin collected the preserved remains of ancient organisms, called fossils. • Some of those fossils resembled organisms that were still alive. • Others looked completely unlike any creature he had ever seen. Copyright Pearson Prentice Hall Charles Darwin and The Origin of Species • Darwin was inspired by the observations he made as the naturalist aboard the H.M.S. Beagle as it sailed around South America from 1831 to 1836. • For example, the 13 species of finches on the Galápagos Islands varied in beak size and shape, depending on their diet. How had the beaks of the finches come to vary in this way? © 2013 Pearson Education, Inc. Charles Darwin and The Origin of Species • Darwin was also inspired by – the work of geologist Charles Lyell, who argued that Earth's geologic features were built by gradual processes over millennia. – the work of economist Thomas Malthus, who wrote about famine and the struggle of humans over resources. – Malthus reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone. © 2013 Pearson Education, Inc. An Ancient, Changing Earth • Lyell's Principles of Geology • Lyell stressed that scientists must explain past events in terms of processes that they can actually observe. • The processes that shaped the Earth millions of years earlier continue in the present. An Ancient, Changing Earth This understanding of geology influenced Darwin: • If the Earth could change over time, life might change as well. • It would have taken many years for life to change in the way Lyell suggested. This would have been possible only if the Earth were extremely old. How Natural Selection Works • In any population of organisms, individuals have many traits that show variation. • Traits that are determined at least partly by genes are heritable, passed from parents to offspring. • Organisms that possess variable heritable traits that are advantageous leave more offspring than organisms without the advantageous traits. This is natural selection. • Advantageous traits become more common in a population, resulting in adaptation. © 2013 Pearson Education, Inc. How Natural Selection Works © 2013 Pearson Education, Inc. Adaptation • Adaptations are traits that make organisms well suited to living and reproducing in their environments. • Adaptations can relate to various aspects of an organism's life: – Survival adaptations (acquire resources) – Sexual selection, which leads to the evolution of adaptations that help organisms acquire mates – Bearing and raising young © 2013 Pearson Education, Inc. Staying Warm and Keeping Cool • Mammals thermoregulate, maintaining a fairly constant body temperature. • The surface-area-to-volume ratio is an important factor in thermoregulation. It affects the size and shape of animals. – Size: Animals found in cold habitats are often larger than related species living in warm habitats. – Shape: Animals found in cold habitats tend to have short legs and small ears. Animals found in warm habitats have long legs and large ears. © 2013 Pearson Education, Inc. Evolution and Genetics • The incorporation of modern genetics into Darwin's theory of evolution took place in the middle of the 20th century. • This led to a focus on evolution as changes in the allele frequencies of genes over time. • Allele frequencies describe how common different alleles for a gene are in the population. © 2013 Pearson Education, Inc. History of Science: The Peppered Moth © 2013 Pearson Education, Inc. History of Science: The Peppered Moth • Peppered moths in England had always been light with a scattering of peppery flakes. This made them well camouflaged from birds (their main predators) in a habitat of lichen-covered trees. • During the Industrial Revolution, pollution caused trees to become darkened with soot. • More and more dark moths were seen in the peppered moth population. • After antipollution laws were passed, the soot disappeared. • Light moths increased in number. The dark moths have all but disappeared. © 2013 Pearson Education, Inc. History of Science: The Peppered Moth • Kettlewell's experiments confirmed that natural selection was responsible for changes in coloration in peppered moth populations. • Kettlewell released and recaptured marked moths. He recaptured more dark moths in polluted habitats and more light moths in unpolluted habitats. • Kettlewell also placed moths on trees and filmed birds eating the moths. Birds ate more light moths in polluted habitats and more dark moths in unpolluted habitats. • Challenges to Kettlewell's work resulted in his experiments being repeated by Michael Majerus. Kettlewell's results were confirmed. © 2013 Pearson Education, Inc. Science and Society: Antibiotic-Resistant Bacteria • Antibiotic resistance has become a serious health issue. • Antibiotic resistance is the result of natural selection. • When a patient takes a course of antibiotics, a few naturally resistant bacteria may survive the treatment. These reproduce. Eventually, strains of bacteria exist that cannot be controlled by the antibiotic. • All antibiotic use contributes to antibiotic resistance. • We must learn to take antibiotics only for bacterial infections, and then to complete the course of treatment. • Antibiotics should not be used to promote the growth of livestock. © 2013 Pearson Education, Inc. Science and Society: Antibiotic-Resistant Bacteria • Ways to slow the development of antibiotic resistance in bacteria: – Take antibiotics only when needed. – Take the entire course of antibiotics. – Use antibiotics responsibly in agriculture. © 2013 Pearson Education, Inc. • Notice that, although natural selection affects genes and allele frequencies, it does not act directly on genes. – Natural Selection acts on the organisms phenotype (traits), not on its genotype (genes). © 2013 Pearson Education, Inc. Evolution and Genetics • Mechanisms of Evolution – Natural selection • A specific allele may be advantageous and allow organisms with the allele to reproduce more than organisms with a different allele. • More copies of the advantageous allele are passed to the next generation, and the frequency of the advantageous allele increases in the population. © 2013 Pearson Education, Inc. Evolution and Genetics • Mechanisms of Evolution (continued) – Mutation pressure • A genetic mutation may be more likely to turn one allele into a second allele than vice versa. • Like the previous moth example – Genetic drift • Genetic drift is the evolution of populations due to chance. • Genetic drift is particularly important in small populations. • Ex – a worm wipes out ½ the moth population © 2013 Pearson Education, Inc. – By chance the light ones survive – This is not natural selection it is evolution by chance • Flipping the coin 10 times vs 100 times gives a different result. © 2013 Pearson Education, Inc. Evolution and Genetics • Mechanisms of Evolution (continued) – Gene flow • Changes in allele frequency result from the movement of alleles into or out of a population, such as through migration. © 2013 Pearson Education, Inc. Variation • Natural selection cannot happen without variation. • Populations with more variation have a better chance of adapting to a changing environment. – Ex – The moths • What if there were only light moths and not dark moths • Would they have survived if the habitat shifted to favor dark coloration? © 2013 Pearson Education, Inc. How Species Form • A species is a group of organisms whose members can breed with one another but not with members of other species. • Speciation is the formation of new species. • The key to speciation is the evolution of reproductive barriers that prevent two groups of organisms from interbreeding. © 2013 Pearson Education, Inc. How Species Form • There are two kinds of reproductive barriers: – Prezygotic reproductive barriers (before fertilization) prevent individuals of different species from mating or prevent fertilization from occurring if they do mate. • When, where they breed, sex organs may not fit appropriately and courtship rituals – Postzygotic reproductive barriers (after fertilization) occur when mating results in hybrids that do not survive or are sterile, unable to reproduce. © 2013 Pearson Education, Inc. How Species Form CHECK YOUR NEIGHBOR • Is a mule a demonstration of a prezygotic reproductive barrier or a postzygotic reproductive barrier? • Explain your answer to your neighbor. © 2013 Pearson Education, Inc. How Species Form • Two ways speciation can occur: – In allopatric speciation, speciation occurs after a geographic barrier divides a population into two isolated populations. • Mountain range, river, ocean, canyon © 2013 Pearson Education, Inc. © 2013 Pearson Education, Inc. • Adaptive Radiation – type of allopatric speciation – Where many new species, each adapted to a distinct way of life, evolved from a single ancestor. © 2013 Pearson Education, Inc. How Species Form • Two ways speciation can occur (continued): – In sympatric speciation, speciation occurs without a geographic barrier. • Examples: hybridization and chromosomal changes such as polyploidy (in plants, it is deadly in animals). © 2013 Pearson Education, Inc. Evidence of Evolution • Observations of natural selection in action – Resistance to myxoma virus in Australian rabbits – Peppered moth coloration and camouflage – Antibiotic-resistant bacteria – Evolution of the beaks of Darwin's finches after a drought – Many other documented examples © 2013 Pearson Education, Inc. Evidence of Evolution • Artificial selection – In domesticated animals and crops, such as dogs, racehorses, and corn • Similarities in body structures © 2013 Pearson Education, Inc. Evidence of Evolution • Vestigial organs • DNA and molecular evidence – Similar DNA sequences in related species • Patterns of development © 2013 Pearson Education, Inc. Evidence of Evolution • Hierarchical organization of living things – Nested groups, or "groups within groups" • Biogeography – The study of how species are distributed on Earth – Organisms evolved in a certain place and then left descendants in the places where they were able to spread. © 2013 Pearson Education, Inc. Fossils: Earth's Tangible Evidence of Evolution • Fossils allow us to follow the evolution of certain groups of organisms over time. • The evolution of the whale blowhole © 2013 Pearson Education, Inc. Fossils: Earth's Tangible Evidence of Evolution • The evolution and loss of whale hind legs © 2013 Pearson Education, Inc. Fossils: Earth's Tangible Evidence of Evolution • Archaeopteryx, an early bird evolved from dinosaur ancestors © 2013 Pearson Education, Inc. The Evolution of Humans • Humans are – primates—we share an ancestry with monkeys and apes. – hominids—the primate group that includes Homo sapiens and extinct relatives. © 2013 Pearson Education, Inc. The Evolution of Humans • The fossil record has allowed us to document some aspects of human evolution. © 2013 Pearson Education, Inc.