Download 7A - gcisd

Rhonda Alexander IC Science Robert E. Lee
7.A analyze and evaluate how evidence of common ancestry among groups is provided by the fossil record, biogeography, and homologies, including anatomical, molecular, and developmental The Theory of Evolution In science, theories are statements or models that have been tested and confirmed many times.  Theories have some important properties:  They explain a wide variety of data and observations  They can be used to make predictions  They are not absolute, they serve as a model of understanding the world and can be changed as the world view changes In science, the term “Theory” does not express doubt. In science, the term theory is used to represent ideas and explanations that have been confirmed through tests and observations The theory of evolution remains one of the most useful theories in biology because it explains many questions and observations. Some questions that can be answered by evolution.  Why do so many different animals have the same structures, the arm bones in a human are the same bones as a flipper in a whale?  Why do organisms have structures they no longer use, like the appendix in a human? Non functioning wings in penguins  Why are there bones and fossil evidence of creatures that no longer exist? What happened to these creatures?  Why do so many organisms’ morphology and anatomy follow the same plan?  Why is the sequence of DNA very similar in some groups of organisms but not in others?  Why do the embryos of animals look very similar at an early stage? The Theory of Evolution is considered a Unifying Theory of Biology, because it answers many of these questions and offers and explanation for the data. Lamarke’s Theory of Acquired Characteristics Some thought that you would gain or lose features if you overused or didn’t use them, and you could pass these new traits onto your offspring. This was known as the Inheritance of Acquired Characteristics A lizard that didn’t use it legs would eventually not have legs and its offspring wouldn’t have legs A giraffe stretched its neck to reach higher leaves, and this stretched neck would be a trait inherited by its offspring Lamarke’s Theory was eventually discarded – PROVEN TO BE WRONG! Why? Logically it doesn’t work. Imagine if you were in a car accident and had a leg amputed. This does not mean that your children will only have one leg. Features gained during life are not passed on to children. Darwin’s Theory of Evolution by Natural Selection Darwin was a naturalist who observed many species. He is famous for his trips to the Galapagos Islands, his observations of the finches (and other animals) and the book he wrote: “The Origin of Species: 1. Variation exists among individuals in a species. 2. Individuals of species will compete for resources (food and space) 3. Some competition would lead to the death of some individuals while others would survive 4. Individuals that had advantageous variations are more likely to survive and reproduce. This process he describes came to be known as Natural Selection The favorable variations are called Adaptations Darwin’s Finches: Darwin noted that all the finches on the Galapagos Island looked about the same except for the shape of their beak. His observations lead to the conclusion that all the finches were descendants of the same original population. The shape of the beaks were adaptations for eating a particular type of food (Ex. long beaks were used for eating insects, short for seeds) Paleontology is key to the study of evolution for two reasons. 1. The discovery of fossils showing forms of animals that had never previously been seen began to cast serious doubt upon creationist theories. 2. Fossils provide the only direct evidence of the history of evolution. Taken together, fossils can be used to construct a fossil record, which is a timeline of fossils reaching back through history. Several factors must be taken into account when constructing such a record. The strata of rock in which fossils are found give us clues about their relative ages. Similarly, new technological techniques such as radioactive carbon dating help determine the absolute ages of fossils. In addition to supplying a fossil's relative age, rock strata can also give clues about the environments in which an animal or plant lived. The chemical make‐up of these strata can tell us the balance of gases in ancient atmospheres. Major cataclysmic events such as eruptions and meteor strikes also leave their mark on the fossil record. There are, however, limitations on the information fossils can supply. Fossilization is an improbable event. Most often, bones and other materials are crushed or consumed before they can be fossilized. In addition, fossils can only form in areas where sedimentary rock is formed, such as ocean floors. Organisms that live in these environments are therefore more likely to be fossilized. Erosion of exposed rock faces or through the crushing action of geological movements can destroy fossils even after they are formed. All of these conditions lead to large and numerous gaps in the fossil record Paleontology supports the theory of evolution because it shows a descent of modern organisms from common ancestors. Paleontology indicates that fewer kinds of organisms existed in past eras, and the organisms were probably less complex. As paleontologists descend deeper and deeper into layers of rock, the variety and complexity of fossils decreases. The fossils from the uppermost rock layers are most like current forms. Fossils from the deeper layers are the ancestors of modern forms. Comparative anatomy Homologous Structures: More evidence for evolution is offered by comparative anatomy). As Darwin pointed out, the forelimbs of such animals as humans, whales, bats, and other creatures are strikingly similar, even though the forelimbs are used for different purposes (that is, lifting, swimming, and flying). Darwin proposed that similar forelimbs have similar origins, and he used this evidence to point to a common ancestor for modern forms. He suggested that various modifications are nothing more than adaptations to the special needs of modern organisms. H Figure 1 The forelimbs of a human and four animals showing the similarity in construction. This similarity was offered by Darwin as evidence that evolution has occurred. Darwin also observed that animals have structures they do not use. Often these structures degenerate and become undersized compared with similar organs in other organisms. The useless organs are called vestigial organs. In humans, they include the appendix, the fused tail vertebrae, the wisdom teeth, and muscles that move the ears and nose. Darwin maintained that vestigial organs may represent structures that have not quite disappeared. Perhaps an environmental change made the organ unnecessary for survival, and the organ gradually became nonfunctional and reduced in size. For example, the appendix in human ancestors may have been an organ for digesting certain foods, and the coccyx at the tip of the vertebral column may be the remnants of a tail possessed by an ancient ancestor. Do not confuse homologous structures with analogous structures. Homologous structures ‐ structures in organisms that are derived from the same ancestral structure. For example, cat paws and human hands. Analogous structures are structures in different organisms that look similar, or perform similar functions, but are not derived from the same ancestral source. For example bat wings and bird wings, though looking similar and performing similar functions evolved separately. Embryology Darwin noted the striking similarity among embryos of complex animals such as humans, chickens, frogs, reptiles, and fish. He wrote that the uniformity is evidence for evolution. He pointed out that human embryos pass through a number of embryonic stages inherited from their ancestors because they have inherited the developmental mechanisms from a common ancestor. These mechanisms are modified in a way that is unique to an organism's way of life. The similarities in comparative embryology are also evident in the early stages of development. For example, fish, bird, rabbit, and human embryos are similar in appearance in the early stages. They all have gill slits, a two‐chambered heart, and a tail with muscles to move it. Later on, as the embryos grow and develop, they become less and less similar. Domestic breeding From observing the domestic breeding experiments of animal and plant scientists, Darwin developed an idea about how evolution takes place. Domestic breeding brings about new forms that differ from ancestral stock. For example, pigeon fanciers have developed many races of pigeons through domestic breeding experiments. In effect, evolution has taken place under the guidance of human hands. The development of new agricultural crops by farmers and botanists provides more evidence for directed evolution. Geographic distribution Darwin was particularly interested in the life forms of the Galapagos Islands. He noticed how many of the birds and other animals on the islands were found only there. The finches were particularly puzzling because Darwin found 13 species of finches not found anywhere else in the world, as far as he knew. He concluded that the finches had evolved from a common ancestor that probably reached the island many generations earlier. In the isolation of the Galapagos Islands, the original finches had probably evolved into the 13 species. Other geographic distributions also help to explain evolution. For instance, alligators are located only in certain regions of the world, presumably because they have evolved in those regions. The islands of Australia and New Zealand have populations of animals found nowhere else in the world because of their isolated environments. In allopatric speciation, an ancestral population is geographically isolated, resulting in the evolution of separate species largely due to genetic drift. The additive effect of differences due to genetic drift can eventually result in behavioral isolation (refusal to mate) if the two groups were to meet again in the future. If they refused to interbreed, they would be considered separate species Comparative biochemistry Although the biochemistry of organisms was not well known in Darwin's time, modern biochemistry indicates there is a biochemical similarity in all living things. For example, the same mechanisms for trapping and transforming energy and for building proteins from amino acids are nearly identical in almost all living systems. DNA and RNA are the mechanisms for inheritance and gene activity in all living organisms. The structure of the genetic code is almost identical in all living things. This uniformity in biochemical organization underlies the diversity of living things and points to evolutionary relationships. Immunological studies provide a method of indirectly estimating the degree of similarity of proteins in different species. If differences exist in the proteins, then there must also be differences in the DNA that codes for them . The evolutionary relationships of a large number of different animal groups have been established on the basis of immunology. The results support the phylogenies developed from other areas: biogeography, comparative anatomy, and fossil evidence. Amino Acid Sequences Each of our proteins has a specific number of amino acids arranged in a specific order. Any differences in the sequence reflect changes in the DNA sequence. The hemoglobin beta chain has been used as a standard molecule for comparing the precise sequence of amino acids in different species. Hemoglobin is the protein in our red blood cells that is responsible for carrying oxygen around our bodies. The hemoglobin in adults is made up of four polypeptide chains: 2 alpha chains and 2 beta chains. Each is coded for by a separate gene. . Example right: When the sequence of human hemoglobin, which is 146 amino acids long, was compared with that of 5 other primate species it was found that chimpanzees had an identical sequence while those that were already considered less closely related had a greater number of differences. This suggests a very close genetic relationship between humans, chimpanzees and gorillas, but less with the other primates