The Evolution Lab 101

The Evolution Lab EVOLUTION 101 You are about to play NOVA’s Evolution Lab—a game that will help you to understand the ways scientists piece together the tree of life. But before you begin Mission 1, “Training Trees,” watch the introductory video, “Evolution 101,” and answer questions 1–5 below. 1. According to the video, what are the two key ingredients to natural selection? a. b. c. d. Predation and the environment Reproduction and predation Reproduction and variation The environment and variation 2. What does “the fittest” mean in an evolutionary sense? a. b. c. d. The strongest The longest lived The most reproductively successful The best able to avoid being eaten 3. Evolution is: a. Fixed in one direction b. Completely random c. Neither entirely fixed nor entirely random 4. What is happening in this image? How does it help to illustrate the concept of natural selection? The bird is consuming the yellow insect rather than the green one. This is probably because the yellow one stood out more, while the green one blends in with the leaf. This is an example of The Evolution Lab MISSION 1 natural selection because a variation (green colored insect) is giving some of the insects an advantage that will help them to survive and reproduce more than the yellow colored insects. 5. According to the video, what is the goal of the tree of life? a. b. c. d. To summarize the fossil record To describe how natural selection works To be a library of all life that has ever lived To explain how all species are related to each other MISSION 1 Training Trees Introductory video: Watch the video to learn some tree basics and to get an overview for how the Build A Tree game works. Each level tasks you with building a phylogenetic tree—a small piece of the overall tree of life. A phylogenetic tree is a model of evolutionary relationships. Before you start the first level, “Red, green, and gecko,” use the tree below and the information in the introductory video to answer questions 1–5. A 1. What does the circled node represent? a. The common ancestor species of A and B b. A speciation event c. Both a and b B trait 4 branch tips trait 5 trait 2 trait 3 2. Which way does time run on this tree? a. From root to branch tip b. Across branch tips, from left to right C trait 1 root 3. Which lived more recently in time, the common ancestor species of A and B or the common ancestor species of B and C? The common ancestor of B and C 4. Which traits do A and B share? Which traits do B and C share? A and B: trait 1 B and C: trait 1 & 3 Use your answers to questions 3 and 4 to explain why B and C are more closely related to each other than A and C are. The Evolution Lab MISSION 1 B and C are more closely related than A and C because they share more traits. B and C share traits 1 and 2 while A and C only share trait 1. Red, green, and gecko: Your first question is simple: Is a fungus more closely related to an animal or a plant? At first glance, many people might be tempted to say plant—but be careful! First impressions can be misleading. In this level, be sure to read and follow the prompts. The prompts are there to help you get the hang of things. When you’re done, answer questions 6–9 below before you move on to the next level, “Familiar faces.” 5. Under a microscope, the cells of mushrooms, plants, and animals all have visible nuclei. This makes them all: a. Autotrophs b. Heterotrophs c. Eukaryotic d. Prokaryotic 6. What trait do the mushroom and gecko share that the tree lacks? They are heterotrophs 7. The pop-up question at the end of this level asks whether an animal or a plant is more closely related to a fungus. Why is the correct answer likely surprising to many people? The answer is surprising because mushrooms and plants look a lot more alike than mushrooms and animals. Familiar faces: Let’s take a look at some common animals—a dog, goldfish, snake, and stick insect. Think you know which ones share the most traits? Answer questions 10–11 below before you move on to the next level, “Tree of life: Vegetarian edition.” 8. What is an amniote, and which animals on this tree are amniotes? The Evolution Lab MISSION 1 An amniote is an animal whose embryos develop inside the protective membrane. The snake and dog are amniotes rest of tree dog cat 9. If you were to add a cat onto this tree, it would be placed so cat and dog are more closely related to each other than to anything else in the tree, as shown. What biological trait could you use in the spot that is The trait could be presence of hair that the marked? trait Tree of life: Vegetarian edition: We often use the terms fruit and vegetable to describe the plants we eat; however, not many people know the real difference between them. If you’re a botanist, a fruit isn’t something sweet and delicious—it’s the part of some plants that contains the seeds. This makes things like tomatoes, nuts, and squash fruits, technically! Any other part of a plant that we eat is called a vegetable. Some vegetables are roots, like carrots, and others are stems or leaves, like celery and lettuces. Being an animal yourself, it’s often easy to overlook plants and their many interesting traits. In this level, you’ll gain a new appreciation for some of the plants we eat. Things are getting more challenging now, so be sure to use the species and species compare tabs! Answer questions 12–13 before you move on to Mission 2, “Fossils—Rocking the Earth.” 10. What makes the seaweed different from all the other plants on this tree? a. It has leaves. b. It’s a vegetable. c. It uses spores to reproduce. d. It is a photosynthetic autotroph. 11. The pop-up question at the end of this level asks whether a banana is more closely related to a lemon or an onion. Why might the correct answer be surprising to many people? The Evolution Lab MISSION 1 The answer is surprising because both a banana and a lemon ae yellow colored fruits, which may lead people to think they are more closely related. However, the banana and onion are more closely related . The Evolution Lab MISSION 2 MISSION 2 Fossils: Rocking the Earth Introductory video: Fossils provide us with a historical record of life on Earth. There are many types of fossils, from extraordinary unaltered remains trapped in permafrost or amber, to subtle traces of past activities in the form of footprints and burrows. The fossils that we have found provide windows into the past and direct evidence of evolution. Before you start the first level in this mission, “Eating dinosaurs for dinner,” watch the introductory video and answer questions 1–2 below. 1. If these rock layers have been undisturbed, which layer is the oldest? Which layer is the youngest? Mark your answer on the figure. The upper most layer is the youngest and the bottom is the oldest 2. According to the video, fossils provide each of the following except: Examples of transitional species A complete record of past life on Earth Physical proof of extinction and speciation Evidence that evolutionary change tends to be gradual Eating dinosaurs for dinner: Has anyone ever told you that dinosaurs aren’t extinct? It’s true! They aren’t. But how can that be? There are no T. rexes at the zoo, or Triceratopses roaming the plains. This level holds the key to understanding where today’s dinosaurs are hiding—on our farms, in the trees, and on our dinner plates. Answer questions 3–5 below before you move on to the next level, “One small step.” a. b. c. d. The Evolution Lab MISSION 2 3. What is another name for the wishbone? a. b. c. d. Furcula Lucky bone Shoulder blade Sternum 4. Today, it’s widely accepted that all of the two-legged meat-eating dinosaurs known as theropods— including T. rex and Albertosaurus—had at least very simple fuzzy feathers covering their bodies. According to the tree you built, what distinguishes the feathers of modern birds and Archaeopteryx from the feathers of other theropods? a. Barbs b. Fibers c. Filaments 5 d. Shafts 3 2 5. A clade is a fancy word for any group in a phylogene tree that includes 4 1 an ancestor and all of its descendants. A simplified dinosaur tree is to the right. 1 Imagine that you have a pair of scissors and can cut the tree. 4 You can tell a group is a clade because it would only take one “snip” to make the group “fall off” the tree. Five different clades have been marked on the tree with brackets. The clade marked 1 is clade Aves—the birds. 3 5 The clade marked 2 is clade Theropoda—the theropods. Clades 2 and 3 are the two major groups of dinosaurs—clade Saurischia and clade Ornithischia. Finally, clade 5 is clade Dinosauria—the dinosaurs. 2 a. Mark on the tree using numbers 2–4 where you can “snip” off each clade. Numbers 1 and 5 have been done for you. b. Triceratops belongs to two of the marked clades on this tree: 4 and 5. This means that Triceratops is both an ornithischian (clade 4) and a dinosaur (clade 5). Which clades do birds belong to? Aves (clade 1), Theropoda (clade 2), Ornithischia (clade 3), Dinosauria (clade 5) The Evolution Lab c. MISSION 2 Use your answer to part b to explain why birds are dinosaurs. Birds are dinosaurs because they are part of the clade Dinosauria One small step: There have been a number of dramatic transitions over the history of life. After a few billion years of nothing but single-celled organisms, multicellular life developed. Organisms evolved tissues and organs. Plants developed spores, flowers, and seeds. Animals developed complex neurological systems and external and internal skeletons. And, of course, bacteria evolved novel methods to live just about everywhere on Earth. One of these great transitions is the subject of this level. Have you ever heard of an animal called Tiktaalik? How about Acanthostega? They are but two of the many remarkable fossils we have that document the transition of animal life from water to land. Answer questions 6–9 below before you move on to the next level, “Origin of whales.” 6. For an animal that lives in shallow water, what is the advantage of having eyes on the top of its head? It helps them to see and catch prey above them in the water 7. We know that Tiktaalik is more closely related to Acanthostega than it is to Eusthenopteron because Tiktaalik and Acanthostega: a. Both lacked digits b. Both lacked strong forearms c. Both had a humerus, radius, and ulna d. Both had eyes on the top of their heads 8. Animals commonly called reptiles, amphibians, birds, and mammals are all tetrapods—a term that means “four feet.” The transition from water to land is fascinating to scientists in part because it’s our history—the transition documents the evolution of tetrapods, and humans are tetrapods. Tetrapods form a clade. Which of the following is true of tetrapods? a. Tetrapods are more complex than non-tetrapods. b. Tetrapods are more evolved than non-tetrapods. c. Tetrapods are more closely related to each other than to non-tetrapods. d. All of the above e. The Evolution Lab MISSION 2 Origin of whales: In the previous level, you looked at the transition from water to land and the evolution of tetrapods. Several groups of tetrapods went on to make the reverse trip—they headed back to the water. In this level, you’ll put together a tree that summarizes some of the changes that occurred as a group of mammals, closely related to the modern-day hippopotamus, returned to the sea. Answer questions 10–12 below before you move on to Mission 3, “DNA Spells Evolution.” 9. When did whale ancestors begin living full time in the water? a. b. c. d. After they nursed under water After they lost their hind legs Before they evolved gills Before they began eating a carnivorous diet 10. Whales are tetrapods—but living whales do not have four limbs. What is a more accurate way to describe tetrapods? a. Animals that have at least two limbs b. Animals that descended from a four-limbed ancestor c. Animals that have four limbs at some point in their lives d. Animals that evolved the ability to survive without limbs 11. When two groups of organisms independently evolve similar adaptations, it’s called convergent evolution. Sharks and whales both have streamlined bodies and tail flukes. How do we know that these similarities are because of convergent evolution? Hint: Whales are tetrapods. Are sharks? This is convergent evolution because sharks and whales are not closely related and do not share a common ancestor. Whales evolved from tetrapods and sharks did not. The Evolution Lab MISSION 3 MISSION 3 DNA Spells Evolution Introductory video: Since its discovery in 1953, DNA has revolutionized the study of evolutionary relationships. Darwin didn’t know about DNA. He couldn’t explain how traits were passed from one generation to the next—he just knew that they were. Were Darwin alive today, he’d no doubt be astonished at how much we can learn about the natural world without even leaving the lab. Before you start the first level in this mission, “Frog legs and fish eggs,” watch the introductory video and answer questions 1–5 below. 1. For a mutation to affect evolution, it must: a. b. c. d. Provide a benefit to the organism Involve more than one chromosome Be able to get passed from parent or offspring Be neutral—neither help nor harm the organism 2. What is evolution? a. b. c. d. An increase in complexity over time The tendency of species to improve over time Any change to the genetic composition of a population All of the above 3. “An organism that is closely related to the group you’re interested in, but not a part of it. A way to establish a basis of comparison for an trait analysis.” This is a definition of: a. An ancestor b. A marker c. An outgroup d. A stem group 4. When you compare the DNA of two closely related organisms, would you expect their DNA to be more similar or less similar than the DNA of two distantly related organisms? Explain your answer. The DNA would be more similar if the two organisms are more closely related. This is because less time has passed since they split from a common ancestor so fewer mutations will have occurred. 5. Fossils almost never contain DNA. So how can we know how closely or distantly related fossil organisms are to living organisms? The Evolution Lab MISSION 3 Frog legs and fish eggs: When scientists compare DNA, there are usually thousands upon thousands—or even millions—of nucleotide bases involved. A computer then scans the sequences and aligns them in the way that provides the best match. In some cases, the computer will add “blank” spaces to improve alignment. Such spaces represent nucleotides that were added or deleted as opposed to changed in one or more lineages. In this level, you’ll get the hang of analyzing DNA by looking at a tiny 4-base snippet. A dash (–) represents either a blank space added to improve alignment or a position that is not important for the analysis you’ve been asked to do. To make things easier, the information from the species compare tab is shown below. However, don’t forget to read the species tabs—they might help you. Answer questions 6–7 below before moving on to the next mission, “One fish, two fish, red fish, lungfish.” 6. True or false: “The change from a T to a C at position 3 caused all of the changes that exist between the cichlid and coelacanth/frog.” Explain your answer. One nucleotide change isn’t enough to generate all the changes. Typically one nucleotide will have no effect on an organism One fish, two fish, red fish, lungfish: For a long time, scientists though that coelacanths were the closest living relatives to amphibians. Coelacanths have big fleshy fins and hinged jaws, two traits they share with fossils of ancestral amphibians. When they went to analyze the DNA, however, they got a surprise. Take a look at the data yourself and see what you come up with. Answer questions 8–10 below before you move on to the next level, “Where the tiny wild things are.” position 1 2 3 4 5 6 7 8 9 10 Great white shark (outgroup) C – C T – – – – – T Midas cichlid S. American lungfish W. Indian coelacanth Western clawed frog C T T T – – – – C C C C C C C C – – – – – – – – – – – – – – – – – – – – T A T A 7. Does the DNA support the hypothesis that the coelacanth is the closest living relative to amphibians, such as frogs? If it does, explain how. If it does not, provide an alternative hypothesis suggested by the DNA data. No. The DNA data suggests that the lungfish is the closest living relative to the amphibians 8. Which do you consider more convincing evidence, DNA or physical features? Why? I consider DNA to be more convincing evidence. This is because physical features that are similar may mislead people to think two organisms are more closely related when they are not. The Evolution Lab MISSION 3 9. To which organism(s) on the tree is the coelacanth most closely related? a. Frog b. Lungfish c. Cichlid and shark equally d. Frog and lungfish equally Where the tiny wild things are: Even with a microscope, most people can’t tell the difference between an archaea and a bacterium. Crack open their DNA, however, and the differences become pretty obvious—and you don’t even need a microscope, just a computer to crunch the data. We’ve kept things pretty simple in this level, though, so you’ll only need your eyes and some brainpower. There is no outgroup on this level, so pay extra attention to the comparison data provided. Answer questions 11–14 below before you move on to the next mission, “Biogeography —Where Life Lives.” position 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 A. vinosum D. radiodurans M. acetivorans P. aerophilium S. solfataricus T. thermophilus – – – – – – G G G G G G – – – – – – – – – – – – – – – – – – – – – – – – T G C C C – T C A G A C – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – T T G C C T 10. What distinguishes bacteria from archaea? a. b. c. d. All archaea live in extreme environments, and bacteria do not. All archaea are unicellular, and some bacteria are multicellular. Archaean DNA is made up a different set of nucleotide bases than is bacterial DNA. Archaean cell walls are made up of different compounds than are bacterial cell walls. 11. A. vinosum is most closely related to which organism(s)? T. thermophilus and D. radiodurans 12. Can you tell from this tree whether a C at position 15 evolved before or after a T at position 15? Explain your answer. No. You can only discern the relative timing of changes along a single lineage. You don’t know from the data whether it evolved before or after the T at position 17 in the bacteria lineage. The Evolution Lab MISSION 3 13. The pop-up question at the end of this level asks why examining DNA is better than considering physical traits. However, remember that it’s not always possible. When do you have to rely on physical traits instead of DNA? You rely on physical traits instead of DNA when fossil organisms are part of the group your studying.