Evolution What We Now Know The “Theory” of Evolution Humans have come a long way! Have you ever stopped to wonder what mechanisms fueled our evolution? Why have we inherited some traits from our parents and lost others? Evolution is a hot topic in science. Everything is changing in our world. In this unit we will look at: Mechanisms of Evolution: Evidence of Evolution: - What caused the world to evolve into what we see now? - Mutations - Genetic drift - Gene Flow - Sexual Selection - Natural Selection -Good scientists want proof! -Geology -Fossil Record -Biogeography -Comparative Anatomy - Molecular Biology (DNA) History of Evolutionary Thought Creationism The early ideas about the natural world were heavily influenced by Plato and Aristotle. Early Christians built upon this idea, and concluded from the biblical account of creation that God had created each species individually. The traditional Judeo-Christian version of creationism was strongly reinforced by James Ussher , a 17th century Anglican archbishop of Armagh in Northern Ireland. By counting the generations of the Bible and adding them to modern history, he fixed the date of creation at October 23, 4004 B.C. Evolution vrs The Creation of Adam is a section of Michelangelo’s fresco on the ceiling of the Sistine Chapel painted in 1511. By the 18th century, the tide had begun to turn in favor of evolution. People were not quite sure how evolution happenedCharles Darwin and Alfred Russel Wallace had not thought of Natural Selection. Jean-Baptiste Lamarck’s inheritance of acquired traits was the most commonly accepted mechanism for evolutionary change. Early believers may have been wrong about how it happened but give them credit for at least understanding that it did happen. Evolution is the process in which significant changes in the inheritable traits (genetic makeup) of a species occur over time. What evidence supports this change of thinking? 1. Geology The earth is 4.6 billion years old. James Hutton – father of modern geology Hutton’s observations of geological processes led him to the concept of uniformitarianism (processes that operate today are the same processes that operated in the past) Charles Lyell popularized the principle of uniformitarianism. Lyell and Darwin were friends. Darwin’s musings on natural selection were influenced by the idea of uniformitarianism. Hutton and Lyell laid important groundwork for evolutionary thought. Geology and uniformitarianism were critical in showing that the earth had been around long enough for evolution to occur. Charles Lyell Proposed that the earth’s surface has changed and continues to change through similar gradual processes. 1851 visited Joggins Stratigraphy – the study of layers of rocks and sediments Ages of Rocks Relative Age – age of rocks and the relative age of fossils can be determined by the chronology of the rock layers. Oldest on bottom, youngest on top. Absolute Age – determined by radioactive decay (radioactive dating using half lives) C14 has a half life of 5730 y K 40 has a half life of 1.3 b.y. 2. Fossil Evidence - Fossils show evidence of organisms that were once alive. - It also shows the record of the extinction of many others. Fossil Evidence - Shows a record of the diversification of species What exactly is a fossil: - Any preserved remains or traces of an organism or its activity. - In 1669 Nicholas Steno detailed an impressive analysis of fossils showing that they were the remains of living organisms - fossils form in sedimentary rocks How does a fossil form? Organisms must die and then be rapidly buried to prevent scavengers or rapid decomposition (if there are only soft parts). There are two types of fossils: Body Fossils which are actual remains: Includes actual bones, shark’s tooth, petrified wood, frozen mammoth, insects in amber. Trace Fossils which include: Mold or Cast formed by replacement Or footprints, worm trails, coproliths, or stomach stones English geologist William Smith (1769-1839) realized that certain fossils always showed up in the same kinds of rocks, even if they were found in different locations. Smith called the predictable layering of fossils the Principle of Faunal Succession, because animals (fauna) in the layers always occurred in the same order (succession). Fossils in layers closest to the surface (youngest) most closely resemble living organisms where fossils in lower layers (older) look very different from living organisms. Some organisms in older layers no longer exist (extinct). Index Fossils Used to determine ages of rock layers Examples of index fossils: Short lived, easy to identify Mass Extinctions Why are mass extinctions important? They stimulate new biodiversity! No competition. Fossils show transitional forms. They show intermediate stages as an organism evolves from one thing into another. These transitional fossils provide direct evidence that life forms change over long periods of time. 3. Biogeographic distribution of living species gave scientists clues to the patterns of evolution If a group of related species all descended from a common ancestor, they should share many similarities even if they evolved different lifestyles. 4. Structures – Homologous and Analogous Homologous- structures that share a common origin but may serve different functions in modern species Long bone Two short bones 1) Salamander, 2) Frog, 3) Turtle, 4) Aetosaurus, 5)Pleisiosaurus, 6) Ichthyosaurus, 7) Mesosaurus, 8) Duck. Example of Homology: the tetrapod limb The wing of a dragonfly and the wing of a butterfly are homologous — they were both inherited from an ancient flying insect. Not all homologies are obvious if they have been adapted for different roles. For example, the chomping front teeth of a beaver look quite different than the tusks of an elephant. Each is a modification of the basic incisor tooth structure Homologies show that Divergent Evolution takes place Divergent Evolution: A common ancestor evolves into new species, which continue to evolve and become less and less alike over time due to differences in the demands driven by the environment. Brown Bears and Polar Bears illustrate divergent evolution. Scientists think that a long time ago a group of Brown Bears became geographically separated from the rest. This isolated group acquired new characteristics, such as the ability to eat meat, blubber to keep warm in snowy weather, and a white coat for camouflage. They slowly evolved into Polar Bears Analogous – structures similar in function but not in origin So what about ANALOGY?? Consider the following example.... Both are extinct animals and both of them have saberteeth...but are they homologous?? (Consider that Australia had separated from the Supercontinent a loooooong time ago) Thylacosmilus, a marsupial mammal Smilodon, the saber-toothed cat, which is a placental mammal analogy similarity due to convergent evolution not common ancestry CONVERGENT Evolution: When two separate groups of animals evolve to have similar structures How do analogies evolve? Often, two species face a similar problem or challenge. Evolution may then shape both of them in similar ways — resulting in analogous structures.....like the saber teeth. Another good example of Analogous structures...... While sugar gliders (marsupials) superficially resemble the placental flying squirrels of North America, the ability to glide through the air evolved independently in these unrelated mammals. So there you have it..... HOMOLOGY vs. ANALOGY 5. Embryonic Development – Embryos of different organisms can have homologous features Human embryos have a tail 6. Vestigial Features- Structures which serve no useful function in a living organism Digits (dogs) Hipbones (whales) 7. Molecular Biology The tools of modern molecular biology were not available to early evolutionary thinkers. We know that similar chemistry, structures and processes underlie all cells. (All cells have mitochondria). All cells have ribosomes which assemble proteins based on genetic code. Molecular biology shows the degrees of relatedness between different organisms. By sequencing certain genes and comparing them in different organisms, scientists can figure out who is more closely related. For aficionados of gigantic Ice Age mammals, woolly mammoths provide a cool example of how gene sequencing reveals information about the evolution of elephants and their relatives. In 2006 an international group of scientists sequenced genes from extinct wooly mammoths—itself a remarkable feat. Mammoths are often found in permafrost, extremely cold soil, which provides ideal conditions for preserving DNA. The research team compared mammoth gene sequences to two different kinds of elephants living today: modern Asian and African elephants. They discovered that the closest living relatives of mammoths are Asian elephants. In other words, mammoths and Asian elephants share more of their DNA and a more recent common ancestor than modern Asian and African elephants. A Special Note About Mutations: Mutations occur every time our genetic material is replicated; it doesn't happen very often, but every once in a while a base pair might be added, deleted, or changed. It is estimated that 300 new mutations are introduced into the human genome every generation—that is, you have 300 new mutations compared to your mom and dad! Assuming these mutations occur at a somewhat constant, predictable rate, we can reason that the more time that has passed since two organisms diverged from each other, the more different their DNA will be. Just think, taking into account 300 new mutations every generation, your child would have 600 new mutations compared to your parents and your grandchild would have 900 new mutations. Over time, these accumulate in the genome, adding to the differences observed between organisms. In other words, more similar DNA sequences can mean that two organisms are closely related, and very different sequences indicate that they split from each other a longer time ago.