10/2/2015 Name:______________________________ Objective: Describe the evidence of evolution including: fossils, homologous structures, vestigial structures, molecular similarities, and biogeography. Homology vs. Analogy (Station 1) Read the station notes. 2. How does each concept provide evidence to support evolution? 1. 3. Using the image below describe which wings are homologous and which are analogous? Moth Pterodactyl Bird Bat 3. The “wings” of sugar gliders and flying squirrels are analogous. What does that tell you about their evolutionary history? 4. The limbs above are homologous structures. What does that tell you about the evolutionary history of these organisms? Embryos (Station 2) 1. Read the station notes. 2. How is embryology important to the study of evolutionary relationships? What does it tell us about the evolutionary history of these organisms? (fish, salamander, tortoise, chicken, pig, rabbit, and human) 3. A naturalist cataloging species in a remote forest discovers two different varieties of beetles. Both have a large horn-like structure on their heads that they use to dig into the ground to find food, but they are otherwise not very similar. What conclusions can the naturalist draw from this comparison of traits? Fossils (Station 3) 1. 2. Read the station notes What are intermediate forms/transitional fossils? How do they provide evidence for evolution? 3. Discuss how different organisms living in different niches might have very different probabilities of being fossilized. 4. How does the layering of the Earth provide clues to the evolutionary history of organisms? Vestigial Structures (Station 4) Below are three different diagrams illustrating vestigial structures. Identify the vestigial structures and describe why it is considered a vestigial structure. Also state its evolutionary significance. 4. Vestigial Pelvis and Legs in Snakes 5. Use the tenets of natural selection to explain why fish species that live in completely dark caves have vestigial, non-functional eyes. Biogeography (Station 5) 1. Read the station notes. 2. Use the figures below to describe the concept of biogeography. How is this evidence supporting evolution? Molecular Biology (Station 6) 1. Why do humans and a banana share 50% of their DNA sequences? Listed below are the amino acid sequences of the Cytochrome-c protein for several organisms. 2. Why are we going to compare amino acid sequences? Dog D V E K K K I V Q K A Q T V E K G G K H T N H L F G K T K N K G I T G E E T L M E D I E K K K I V Q K S Q T V E K G G K H T N H L F G K T K N K G I T G E D T L M E Penguin Dog D V E K K K I V Q K A Q T V E K G G K H T N H L F G K T K N K G I T G E E T L M E D V E K K K I V Q K A Q T C E K G G K H V N Y L I G K T Q A A F S T D K N K G I T Frog Dog D V E K K K I V Q K A Q T V E K G G K H T N H L F G K T K N K G I T G E E T L M E N A E N K K I V Q R A Q T V E A G G K H V N H F Y G K T Q A P F S S N K A K G I T Silkworm 3. Using the sequences above, write the number of amino acid differences between the two species. Dog vs. Penguin ___________ Dog vs. Frog ________ Dog vs. Silkworm _________ 4. Based on the DNA data, which organism is most closely related to a dog? Explain your answer. ______________________________________________________________________________ ______________________________________________________________________________ 5. Based on the DNA data, which organism is most distantly related to a dog? Explain your answer. ______________________________________________________________________________ ______________________________________________________________________________ Homology vs. Analogy Homology Analog y Embryos Background: In the 1700s scientists were fascinated by the observation that different animals looked very similar in their early stages of development. They noticed that as different organisms develop they become less and less alike. Scientists today still compare the developmental stages of animals of different species to help identify evolutionary relationships. The study of the early developmental stages of living things is called embryology. An embryo is an early stage of a living thing. In most vertebrate animals, embryos develop inside the mother. Comparison of early embryos, particularly those of vertebrates, illustrates remarkable similarities. For example, early embryos of fish, reptiles, birds, and mammals all have tails and gill slits. Fish keep the gills as they develop, while the other vertebrates lose them. In humans, the tail disappears in later stages, but in other vertebrates such as fish, birds, and reptiles, the tail remains. Similarities in embryology of different living things suggest strong evolutionary relationships. Scientists often study the embryology of different organisms to help understand their evolutionary relationships. Embryological evidence suggests many animals share a common ancestry- the more closely associated the embryology of different organism, the closer their evolutionary relationship. Fossils Although it was Darwin, above all others, who first marshaled convincing evidence for biological evolution, earlier scholars had recognized that organisms on Earth had changed systematically over long periods of time. For example, in 1799 an engineer named William Smith reported that, in undisrupted layers of rock, fossils occurred in a definite sequential order, with more modern-appearing ones closer to the top. Because bottom layers of rock logically were laid down earlier and thus are older than top layers, the sequence of fossils also could be given a chronology from oldest to youngest. His findings were confirmed and extended in the 1830s by the paleontologist William Lonsdale, who recognized that fossil remains of organisms from lower strata were more primitive than the ones above. Today, many thousands of ancient rock deposits have been identified that show corresponding successions of fossil organisms. Thus, the general sequence of fossils had already been recognized before Darwin conceived of descent with modification. But the paleontologists and geologists before Darwin used the sequence of fossils in rocks not as proof of biological evolution, but as a basis for working out the original sequence of rock strata that had been structurally disturbed by earthquakes and other forces. In Darwin's time, paleontology was still a rudimentary science. Large parts of the geological succession of stratified rocks were unknown or inadequately studied. Darwin, therefore, worried about the rarity of intermediate forms between some major groups of organisms. Today, many of the gaps in the paleontological record have been filled by the research of paleontologists. Hundreds of thousands of fossil organisms, found in well-dated rock sequences, represent successions of forms through time and manifest many evolutionary transitions. As mentioned earlier, microbial life of the simplest type was already in existence 3.5 billion years ago. The oldest evidence of more complex organisms (that is, eukaryotic cells, which are more complex than bacteria) has been discovered in fossils sealed in rocks approximately 2 billion years old. Multicellular organisms, which are the familiar fungi, plants, and animals, have been found only in younger geological strata. The following list presents the order in which increasingly complex forms of life appeared: So many intermediate forms have been discovered between fish and amphibians, between amphibians and reptiles, between reptiles and mammals, and along the primate lines of descent that it often is difficult to identify categorically when the transition occurs from one to another particular species. Actually, nearly all fossils can be regarded as intermediates in some sense; they are life forms that come between the forms that preceded them and those that followed. The fossil record thus provides consistent evidence of systematic change through time—of descent with modification. From this huge body of evidence, it can be predicted that no reversals will be found in future paleontological studies. That is, amphibians will not appear before fishes, nor mammals before reptiles, and no complex life will occur in the geological record before the oldest eukaryotic cells. This prediction has been upheld by the evidence that has accumulated until now: no reversals have been found. Vestigial Structures Background: Some living things, including humans, have organs or structures with no apparent function. For example, some snakes possess the remnants of hind legs and a pelvis embedded in their body. Manatees are animals which live their lives in the water, but retain the bones of a pelvis that are found in land dwelling vertebrates. These are just a couple examples of what scientists call vestigial structures. A vestigial structure is a body part of an organism that tends to be reduced in size and does not seem to have a function. It is thought that vestigial structures are parts or organs that once functioned in the ancestors of organisms. While the part had an important function in the ancestor, it lost its usefulness in the new organism. For this reason, vestigial structures are considered a valuable piece of evolutionary evidence. Vestigial Pelvis and Legs in Snakes Biogeography The field of biogeography is concerned with the distribution of species in relation both to geography and to other species. Biogeography comprises two disciplines: historical biogeography, which is concerned with the origins and evolutionary histories of species on a long time scale, and ecological biogeography, which deals with the current interactions of species with their environments and each other on a much shorter time scale. Historical Biogeography Historical biogeographers also make use of a tool called an area cladogram. This diagram is made by taking a taxonomic tree, which shows various species and their relatedness, and replacing the species names with the geographic location in which those species are found. This new tree allows scientists to determine how the differences in environments have affected the evolutionary history of different species of common origin. A sample area cladogram is shown in. Ecological Biogeography Unlike historical biogeographers, ecological biogeographers make extensive use of current population information. They study the ways in which species develop and interact in the presence of other species and different environments. Many ecological biogeographers mimic Darwin: they study island communities as a type of experimental system to test hypotheses about species development. Much of ecological biogeography is concerned with species richness, the number of different species an area supports. In specific, ecological biographers have developed the species richness equilibrium model. The model begins with an uninhabited "island" that can be either a literal island or an area of like habitats completely surrounded by unlike habitats. All species available to colonize the new area are called the "species pool." As more and more new species enter the new area, the species pool becomes smaller and smaller, and the immigration rate (the probability that any given species moving into the area will be a new species) decreases. At the same time, the island becomes more and more crowded and supplies become scarce, causing the extinction rate to increase. The point at which the extinction rate and the immigration rate balance is called the equilibrium point. The model predicts that changes in extinction and immigration rates will tend toward the equilibrium point, which is different for every island, depending on resources and degree of separation from other areas. This is shown graphically in the figure below. Molecular Biology Since Darwin's day, science has made astounding advances in the ways in which it can study organisms. One of the most useful advances has been the development of molecular biology. In this field, scientists look at the proteins and other molecules that control life processes. While these molecules can evolve just as an entire organism can, some important molecules are highly conserved among species. The slight changes that occur over time in these conserved molecules, which are often called molecular clocks, can help shed light on past evolutionary events. Molecular Clocks The key to using biological molecules as molecular clocks is the hypothesis of neutral evolution. This hypothesis states that most of the variability in molecular structure does not affect the molecule's functionality. This is because most of the variability occurs outside of the functional regions of the molecule. Changes that do not affect functionality are called "neutral substitutions" and their accumulation is not affected by natural selection. As a result, neutral substitutions occur at a fairly regular rate, though that rate is different for different molecules. Not every molecule makes a good molecular clock, however. To serve as a molecular clock, a molecule must meet two requirements: 1) it must be present in all of the organisms being studied; 2) it must be under strong functional constraint so that the functional regions are highly conserved. Examples of molecules that have been used to study evolution are cytochrome c, which is vital to the respiratory pathway, and ribosomal RNA, which performs protein synthesis. Once a good molecular clock is identified, using it to compare species is fairly simple. The most complicated step is the comparison of molecular sequences. The sequences of the molecule in the different species must be compared so that the number of amino acid or nucleic acid bases that differ can be counted. This number is then plotted against the rate at which the molecule is known to undergo neutral base pair substitutions to determine the point at which two species last shared a common ancestor. Depending on the rate of substitution, molecules may be used to determine ancient relationships or relatively recent ones. Ribosomal RNA has a very slow rate of substitution, so it is most commonly used in conjunction with fossil information to determine relationships between extremely ancient species. Molecular Biology Cytochrome c is part of the electron transport chain down which electrons are passed to oxygen during cellular respiration. Cytochrome c is found in the mitochondria of every aerobic eukaryote — animal, plant, and protist. The amino acid sequences of many of these have been determined, and comparing them shows that they are related. Human cytochrome c contains 104 amino acids, and 37 of these have been found at equivalent positions in every cytochrome c that has been sequenced. We assume that each of these molecules has descended from a precursor cytochrome in a primitive microbe that existed over 2 billion years ago. In other words, these molecules are homologous. The first step in comparing cytochrome c sequences is to align them to find the maximum number of positions that have the same amino acid. Sometimes gaps are introduced to maximize the number of identities in the alignment. Gaps correct for insertions and deletions that occurred during the evolution of the molecule. We assume that the more identities there are between two molecules, the more recently they have evolved from a common ancestral molecule and thus the closer the kinship of their owners. Thus the cytochrome c of the rhesus monkey is identical to that of humans except for one amino acid, whereas yeast cytochrome c differs from that of humans at 44 positions. (There are no differences between the cytochrome c of humans and that of chimpanzees.)