Biology Chapter 22 Notes
Biology Chapter 22 Notes BIL 160
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Biology Chapter 22 Notes Concept 22.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species o Darwin’s ideas had deep historical roots o Darwin’s research As a boy and into adulthood, Charles Darwin had a consuming interest in nature Darwin first studied medicine (unsuccessfully), and then theology at Cambridge University After graduating, he took an unpaired position as naturalist and companion to Captain Robert Fitzroy for a 5-year around the world voyage on the Beagle o What Darwin knew before the voyage Cuvier (1769-1832) recognized that many fossils were extinct and speculated on catastrophic events influencing extinction, made many contributions to Comparative Anatomy (form and function) Paleontology is the study of fossils, and was largely developed by French scientist Georges Cuvier Cuvier speculated that the boundaries between strata represent catastrophic events o Ideas about change over time The study of fossils helped to lay the groundwork for Darwin’s ideas Fossils are remains or traces or organisms from the past, usually found in sedimentary rock, which appears in layers called strata Geologists James Hutton and Charles Lyell perceived that changes in Earth’s surface can result from slow continuous actions still operating today, and at the same rate This view strongly influenced Darwin’s thinking o Scala Naturae and Classification of Species The Greek philosopher Aristotle viewed species as fixed and arranged them on a scala naturae The Old Testament holds that species were individually designed by God and therefore perfect Aristotle’s “Scala naturae” or great chain of being – discredited idea that life can be arranged in one vertical dimension from simplest to most advanced Linnaeus – binomial nomenclature (two names) to identify species of living things Carolus Linnaeus interpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose Linnaeus was the founder of taxonomy, the branch of biology concerned with classifying organisms He developed the binomial format for naming species (Homo sapiens) Darwin also learned that scientists of his day had recognized structural correspondences (homologies) in the way different groups of animals were put together o What Darwin knew before the voyage Existence of vestigial structures: digits 2 and 5 of the pig never touch the ground…why did such useless structures exist? And, he knew that some aquatic organisms originated from land organisms Concept 22.2: Descent with modification by natural selection explains the adaptation of organisms and the unity and diversity of life o Some doubt about the permanence of species preceded Darwin’s ideas o Lamarck’s theory – inheritance of acquired characteristics – had little evidential support (later mostly discredited) – Darwin built an alternative theory o Lamarck’s Hypothesis of Evolution Lamarck believed in evolution had a different explanation of how the process worked He hypothesized that species evolve through use and disuse of body parts and the inheritance of acquired characteristics (changes acquired during the lifetime of an individual) The mechanisms Lamarck proposed are unsupported by evidence You can prune and train a tree into a miniaturized (bonsai) form, but those changes during its lifetime will not be passed along to its offspring via seeds (sexual reproduction) o Darwin’s Voyage on the Beagle Darwin’s interest in geographic distribution of species was kindled by a stop at the Galapagos Islands west of South America He hypothesized that species from South America had colonized the Galapagos and speciated on the islands Speciation – new species arise from existing speices; increase in the number of species During his voyage, Darwin observed many examples of adaptations Adaptations – inherited characteristics or organisms that enhance their survival and reproduction in specific environments “Darwin’s finches” – a number of bird species occurring in the Galapagos Islands, so different in their food preferences and their appearance that Darwin first thought they were not closely related to one another o Darwin realized that explaining such adaptations was essential to understanding evolution, so his explanation centered on natural selection Natural selection – a process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of their traits o In the Origin of Species, Darwin used the phrase “descent with modification” instead of evolution Three broad observations: The unity of life The diversity of life The match between organisms and their environment o Darwin proposed the mechanism of natural selection to explain the observable patterns of evolution First he discussed familiar examples of selective breeding of domesticated plants and animals Humans have modified other species over many generations by selecting and breeding individuals that possess desired traits, a process called artificial selection As a result of artificial selection, animals often bear little resemblance to their wild ancestors (creating different breeds of dogs) Darwin drew two inferences from two observations Observation #1: members of a population often vary in their inherited traits Observation #2: All species can produce more offspring than the environment can support, and many of these offspring fail to survive and reproduce Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations o Darwin applied Malthusian concepts If some heritable traits are advantageous, these will accumulate in a population over time, and this will increase the frequency of individuals with these traits This process explains the match between organisms and their environment o Natural selection: a summary Natural selection is a process in which individuals that have certain heritable traits survive and reproduce at a higher rate than other individuals because of those traits Over time, natural selection can increase the match between organisms and their environment If an environment changes, or if individuals move to a new environment, natural selection may result in adaptation to these new conditions, sometimes giving rise to new species Individuals do not evolve, it is a population that evolves over time o Final points from the reading An organism’s heritable traits can influence not only its own performance, but also how well its offspring cope for environmental challenge Artificial selection can bring about dramatic change in a relatively short period of time, then natural selection should be capable of substantial modification of species over many hundreds of generations Concept 22.3: Evolution is supported by an overwhelming amount of scientific evidence o Four types of data that document the pattern of evolution Direct observations Homology The fossil record Biogeography o Direct observations of evolutionary change Natural selection in response to introduced plant species Soapberry bugs use their “beak” to feed on seeds within fruits Feeding is most effective when beak length is closely matched to seed depth within the fruit In southern Florida, soapberry bugs feed on the native balloon vine with larger fruit, they have longer beaks In central Florida, they feed on the introduced goldenrain tree with smaller fruit, they have shorter beaks Correlation between fruit size and beak size has also been observed in Louisiana, Oklahoma, and Australia In all cases, beak size has evolved in populations that feed on introduced plants with fruits that are smaller or larger than the native fruits (took less than 35 years in Florida) Evolution of drug-resistant bacteria One strain of bacterium MRSA is a dangerous pathogen Resistance to penicillin and methicillin evolved in 1945 and 1961 respectively, each two years after it was first widely used Methicillin works by inhibiting a protein used by bacteria to produce cell walls MRSA bacteria use a different protein in cell wall production When exposed to methicillin, MRSA strains are more likely to survive and reproduce than nonresistant strains MRSA strains are now resistant to many antibiotics o Natural selection does not create new traits, but edits or selects for traits already present in the population o The current, local environment determines which traits will be selected for or selected against in any specific population o Homology is similarity resulting from common ancestry This is the evolutionary interpretation of the structural correspondence that was first observed by comparative anatomists Anatomical and molecular homologies Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor Vestigial structures are remnants of features that served important functions in the organism’s ancestors Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor o Homologies and “tree thinking” Evolutionary trees are hypotheses about the relationships amount different groups Homologies form nested patterns in evolutionary trees Evolutionary trees can be made using different types of data (anatomical and DNA sequence data) o A different cause for resemblance – convergent evolution Convergent evolution is the evolution of similar (or analogous) features in distantly related groups Analogous traits arise when groups independently adapt to similar environments in similar ways Convergent evolution does not provide information about ancestry o The fossil record The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time Fossils can document important transitions The transition from land to sea in the ancestors of cetaceans o Biogeography – the scientific study of the geographic distribution of species, provides evidence of evolution Earth’s continents were formerly united in a single large continent called Pangaea, but have since separated by continental drift An understanding of continent movement and modern distribution of species allows us to predict when and where different groups evolved Endemic species are species that are not found anywhere else in the world Islands have many endemic species that are often closely related to species on the nearest mainland or island Darwin explained that species from the mainland colonized islands and give rise to new species as they adapted to new environments o What is theoretical about Darwin’s view of life? In science, a theory accounts for many observations and data and attempts to explain and integrate a great variety of phenomena Darwin’s theory of evolution by natural selection integrates diverse areas of biological study and stimulates many new research questions Ongoing research adds to our understanding of evolution o Genetics – the science of heredity and variation How information is inherited from parents and passed on to offspring in living things Breeding studies, molecular biology, developmental genetics o Gene – basic unit of heredity (information that specifies or influences a trait) Traits are what we observe, genes are underlying information that is inherited Genes must be able to be replicated (in different cells of organisms and in offspring) Errors in DNA replication can lead to mutations (heritable changes in the DNA sequence and/or in the traits Different colors are caused by different variants of a gene, called alleles Example: R vs. r The locus is the location of a gene on a chromosome (DNA molecule) o Microevolution – evolutionary change within a species – and the genetic basis of variation in populations Evolution as genetic change (in which alleles are present and/or in frequencies of alleles) in a population, from generation to generation
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