Near an agricultural town lived a species of moth. The moth spent much of its time perched on the lichen-covered bark of trees of the area. Most of the moths were of a pepper color, though a few were black. When the pepper-color moths were attached to the lichen-covered bark of the trees in the region, it was quite difficult for predators to see them. The black moths were easy to spot against the black-and-white speckled trunks. The nearby city, however, slowly became industrialized. Smokestacks and foundries in the town puffed out soot and smoke into the air. In a fairly short time, the soot settled on everything, including the trees, and killed much of the lichen.
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In 1859, he published his theory of natural selection and the evolution it produced. Darwin explained his theory through four basic points: Each species produces more offspring than can survive. The individual organisms that make up a larger population are born with certain variations. The overabundance of offspring creates a competition for survival among individual organisms. The individuals that have the most favorable variations will survive and reproduce, while those with less favorable variations are less likely to friends survive and reproduce. Variations are passed down from parent to offspring. Natural selection creates change within a species through competition, or the struggle for life. Members of a species compete with each other and with other species for resources. In this competition, the individuals that are the most fit —the individuals that have certain variations that make them better adapted to their environments—are the most able to survive, reproduce, and pass their traits on to their offspring. The competition that Darwins theory describes is one sometimes called the survival of the fittest. Natural Selection in Action One of the best examples of natural selection is a true story that took place in England around the turn of the century.
Lamarcks theory has been proven wrong in both of its basic premises. First, an organism cannot fundamentally change its structure through use or disuse. A giraffes neck will not become longer or shorter by stretching for leaves. Second, modern genetics shows that it is impossible to pass on acquired traits; the traits that an organism can pass on are determined by the genotype of its sex cells, which does not change according to changes in phenotype. Darwin: Natural Selection lab While sailing aboard the hms beagle, the Englishman Charles Darwin had the opportunity to study the wildlife of the galápagos Islands. On the islands, he was amazed by the great diversity of life. Most particularly, he took interest in the islands various finches, whose beaks were all highly adapted to their particular lifestyles. He hypothesized that there must be some process that created such diversity and adaptation, and he spent much of his time trying to puzzle out just what the process might.
His theory is referred to party as the theory of transformation or Lamarckism. The classic example used to explain Lamarckism is the elongated neck of the giraffe. According to lamarcks theory, a given giraffe could, over a lifetime of straining to reach high branches, develop an elongated neck. This vividly illustrates Lamarcks belief that use could amplify or enhance a trait. Similarly, he believed that disuse would cause a trait to become reduced. According to lamarcks theory, the wings of penguins, for example, were understandably smaller than the wings of other birds because penguins did not use their wings to fly. The second part of Lamarcks mechanism for evolution involved the inheritance of acquired traits. He believed that if an organisms traits changed over the course of its lifetime, the organism would pass these traits along to its offspring.
Cytochrome c, a protein that plays an important role in aerobic respiration, is an example of a protein commonly used as a molecular clock. Theories of evolution In the nineteenth century, as increasing evidence suggested that species changed over time, scientists began to develop theories to explain how these changes arise. During this time, there were two notable theories of evolution. The first, proposed by lamarck, turned out to be incorrect. The second, developed by darwin, is the basis of all evolutionary theory. Lamarck: Use and Disuse The first notable theory of evolution was proposed by jean-Baptiste lamarck (17441829). He described a two-part mechanism by which evolutionary change was gradually introduced into the species and passed down through generations.
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Comparative embryology homologous structures not present in adult organisms often do appear in some form during embryonic development. Species that bear little resemblance to each other in their adult forms may have strikingly similar embryonic stages. In some ways, it is almost as if the embryo passes through many evolutionary stages to produce the mature organism. For example, for a large portion of its development, the human embryo possesses a tail, much like those of our close primate relatives. This tail is usually reabsorbed before birth, but occasionally children are born with the ancestral android structure intact. Even though they are not generally present in the adult organism, tails could be considered homologous traits between humans and primates.
In general, the more closely related two species are, the more their embryological processes of development resemble each other. Molecular evolution Just as comparative anatomy is used to determine the anatomical relatedness of species, molecular biology can be used to determine evolutionary relationships at the molecular level. Two species that are closely related will have fewer genetic or protein differences between them than two species that are distantly related and split in evolutionary development long in the past. Certain genes or proteins in organisms change at a constant rate over time. These genes and proteins, called molecular clocks because they are so constant in their rate of change, are especially useful in comparing the molecular evolution of different species. Scientists can use the rate of change in the gene or protein to calculate rowling the point at which two species last shared a common ancestor. For example, ribosomal rna has a very slow rate of change, so it is commonly used as a molecular clock to determine relationships between extremely ancient species.
But the bone structure of each is surprisingly similar, suggesting that whales and humans have a common ancestor way back in prehistory. Anatomical features in different species that point to a common ancestor are called homologous structures. However, comparative anatomists cannot just assume that every similar structure points to a common evolutionary origin. A hasty and reckless comparative anatomist might assume that bats and insects share a common ancestor, since both have wings. But a closer look at the structure of the wings shows that there is very little in common between them besides their function. In fact, the bat wing is much closer in structure to the arm of a man and the fin of a whale than it is to the wings of an insect.
In other words, bats and insects evolved their ability to fly along two very separate evolutionary paths. These sorts of structures, which have superficial similarities because of similarity of function but do not result from a common ancestor, are called analogous structures. In addition to homologous and analogous structures, vestigial structures, which serve no apparent modern function, can help determine how an organism may have evolved over time. In humans the appendix is useless, but in cows and other mammalian herbivores a similar structure is used to digest cellulose. The existence of the appendix suggests that humans share a common evolutionary ancestry with other mammalian herbivores. The fact that the appendix now serves no purpose in humans demonstrates that humans and mammalian herbivores long ago diverged in their evolutionary paths.
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Most often, remains and other traces of organisms are crushed or consumed before they can be fossilized. Additionally, fossils can only form in areas with sedimentary rock, such as ocean floors. Organisms that live in these environments house are therefore more likely to become fossils. Finally, erosion of exposed surfaces or geological movements such as earthquakes can destroy already formed fossils. All of these conditions lead to large and numerous gaps in the fossil record. Comparative anatomy Scientists often try to determine the relatedness of two organisms by comparing external and internal structures. The study report of comparative anatomy is an extension of the logical reasoning that organisms with similar structures must have acquired these traits from a common ancestor. For example, the flipper of a whale and a human arm seem to be quite different when looked at on the outside.
Fossils of prehistoric life can business be bones, shells, or teeth that are buried in rock, and they can also be traces of leaves or footprints left behind by organisms. Together, fossils can be used to construct a fossil record that offers a timeline of fossils reaching back through history. To puzzle together the fossil record, scientists have to be able to date the fossils to a certain time period. The strata of rock in which fossils are found give clues about their relative ages. If two fossils are found in the same geographic location, but one is found in a layer of sediment that is beneath the other layer, it is likely that the fossil in the lower layer is from an earlier era. After all, the first layer of sediment had to already be on the ground in order for the second layer to begin to build up on top. In addition to sediment layers, new techniques such as radioactive decay or carbon dating can also help determine a fossils age. There are, however, limitations to the information fossils can supply. First of all, fossilization is an improbable event.
about 6,000 years ago in a mass creation event. Proponents of creationism support the genesis account and state that species were created exactly as they are currently found in nature. This oldest formal conception of the origin of life still has proponents today. However, about 200 years ago, scientific evidence began to cast doubt on creationism. This evidence comes in a variety of forms. Rock and Fossil Formation, fossils provide the only direct evidence of the history of evolution. Fossil formation occurs when sediment covers some material or fills an impression. Very gradually, heat and pressure harden the sediment and surrounding minerals replace it, creating fossils.
These cells were heterotrophs, which could not produce their own food and instead fed on the organic material from the primordial soup. (These feasibility heterotrophs give this theory its name.). The anaerobic metabolic processes of the heterotrophs released carbon dioxide into the atmosphere, which allowed for the evolution of photosynthetic autotrophs, which could use light and CO2 to produce their own food. The autotrophs released oxygen into the atmosphere. For most of the original anaerobic heterotrophs, oxygen proved poisonous. The few heterotrophs that survived the change in environment generally evolved the capacity to carry out aerobic respiration. Over the subsequent billions of years, the aerobic autotrophs and heterotrophs became the dominant life-forms on the planet and evolved into all of the diversity of life now visible on Earth. Evidence of evolution, humankind has always wondered about its origins and the origins of the life around.
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Origin of Life: The heterotroph Hypothesis. Life on Earth began about.5 billion years ago. At that point in the development of the earth, the atmosphere was very different from what it is today. As opposed to the current atmosphere, which is mostly nitrogen and oxygen, the early earth atmosphere contained mostly hydrogen, water, ammonia, and methane. In experiments, scientists have showed that the electrical discharges of lightning, radioactivity, and ultraviolet light caused the elements in the early earth atmosphere to form the basic molecules of biological chemistry, such as nucleotides, simple proteins, and. It seems likely, then, that the earth was covered in a hot, thin soup of water and organic materials. Over time, the molecules became more complex and began to collaborate to run metabolic processes. Eventually, the first cells came into being.