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The Academy's Evolution Site Biological evolution is a central concept in biology. The Academies have been for a long time involved in helping people who are interested in science comprehend the concept of evolution and how it permeates every area of scientific inquiry. This site provides a range of sources for students, teachers as well as general readers about evolution. It contains the most important video clips from NOVA and WGBH-produced science programs on DVD. Tree of Life The Tree of Life is an ancient symbol of the interconnectedness of all life. It is a symbol of love and unity across many cultures. It also has practical applications, such as providing a framework for understanding the history of species and how they respond to changes in the environment. Early attempts to describe the world of biology were founded on categorizing organisms on their physical and metabolic characteristics. These methods, which rely on the sampling of different parts of organisms or short DNA fragments, have significantly increased the diversity of a Tree of Life2. However, these trees are largely composed of eukaryotes; bacterial diversity is not represented in a large way3,4. In avoiding the necessity of direct observation and experimentation, genetic techniques have allowed us to represent the Tree of Life in a more precise manner. We can construct trees using molecular methods like the small-subunit ribosomal gene. Despite the dramatic expansion of the Tree of Life through genome sequencing, a lot of biodiversity remains to be discovered. This is particularly relevant to microorganisms that are difficult to cultivate and which are usually only present in a single sample5. A recent study of all genomes known to date has produced a rough draft of the Tree of Life, including numerous archaea and bacteria that have not been isolated, and their diversity is not fully understood6. This expanded Tree of Life can be used to assess the biodiversity of a specific area and determine if specific habitats require special protection. The information is useful in a variety of ways, such as finding new drugs, fighting diseases and enhancing crops. The information is also incredibly useful in conservation efforts. It can aid biologists in identifying areas that are likely to be home to cryptic species, which could have important metabolic functions, and could be susceptible to human-induced change. While funds to safeguard biodiversity are vital, ultimately the best way to ensure the preservation of biodiversity around the world is for more people in developing countries to be empowered with the knowledge to act locally in order to promote conservation from within. Phylogeny A phylogeny, also known as an evolutionary tree, shows the connections between groups of organisms. Utilizing molecular data similarities and differences in morphology or ontogeny (the course of development of an organism), scientists can build an phylogenetic tree that demonstrates the evolutionary relationship between taxonomic categories. The phylogeny of a tree plays an important role in understanding biodiversity, genetics and evolution. A basic phylogenetic tree (see Figure PageIndex 10 Identifies the relationships between organisms that have similar characteristics and have evolved from a common ancestor. These shared traits may be analogous or homologous. Homologous traits are similar in their evolutionary journey. Analogous traits might appear like they are but they don't share the same origins. Scientists combine similar traits into a grouping called a the clade. All members of a clade share a characteristic, for example, amniotic egg production. They all evolved from an ancestor who had these eggs. The clades are then linked to form a phylogenetic branch to identify organisms that have the closest connection to each other. Scientists make use of DNA or RNA molecular information to construct a phylogenetic graph that is more precise and detailed. This information is more precise and provides evidence of the evolutionary history of an organism. Researchers can use Molecular Data to calculate the age of evolution of organisms and determine how many organisms have the same ancestor. The phylogenetic relationships of organisms are influenced by many factors, including phenotypic plasticity a kind of behavior that alters in response to unique environmental conditions. This can cause a characteristic to appear more resembling to one species than to another which can obscure the phylogenetic signal. However, this issue can be cured by the use of techniques such as cladistics that include a mix of analogous and homologous features into the tree. Additionally, phylogenetics can help determine the duration and speed at which speciation takes place. This information can help conservation biologists make decisions about the species they should safeguard from the threat of extinction. In the end, it is the conservation of phylogenetic diversity that will result in an ecosystem that is balanced and complete. Evolutionary Theory The central theme in evolution is that organisms change over time as a result of their interactions with their environment. Many scientists have come up with theories of evolution, such as the Islamic naturalist Nasir al-Din al-Tusi (1201-274), who believed that an organism could develop according to its own requirements and needs, the Swedish taxonomist Carolus Linnaeus (1707-1778), who created the modern taxonomy system that is hierarchical and Jean-Baptiste Lamarck (1844-1829), who believed that the use or non-use of traits can cause changes that are passed on to the next generation. In the 1930s and 1940s, ideas from various fields, including genetics, natural selection, and particulate inheritance -- came together to form the current evolutionary theory synthesis that explains how evolution happens through the variation of genes within a population and how these variants change over time as a result of natural selection. This model, which is known as genetic drift, mutation, gene flow and sexual selection, is a cornerstone of modern evolutionary biology and can be mathematically described. Recent discoveries in the field of evolutionary developmental biology have revealed that variation can be introduced into a species through genetic drift, mutation, and reshuffling of genes in sexual reproduction, and also through migration between populations. These processes, along with others such as directional selection or genetic erosion (changes in the frequency of the genotype over time) can result in evolution, which is defined by changes in the genome of the species over time, and also by changes in phenotype as time passes (the expression of that genotype in the individual). Incorporating evolutionary thinking into all aspects of biology education can improve student understanding of the concepts of phylogeny as well as evolution. A recent study conducted by Grunspan and colleagues, for example, showed that teaching about the evidence for evolution increased students' understanding of evolution in a college-level biology class. To find out more about how to teach about evolution, please read The Evolutionary Potential in All Areas of Biology and Thinking Evolutionarily: A Framework for Infusing the Concept of Evolution into Life Sciences Education. Evolution in Action Traditionally, scientists have studied evolution by studying fossils, comparing species and studying living organisms. Evolution is not a distant event; it is an ongoing process that continues to be observed today. Bacteria mutate and resist antibiotics, viruses evolve and escape new drugs and animals change their behavior to a changing planet. The changes that occur are often evident. But it wasn't until the late 1980s that biologists realized that natural selection could be observed in action as well. The reason is that different characteristics result in different rates of survival and reproduction (differential fitness) and are transferred from one generation to the next. In the past, if an allele - the genetic sequence that determines colour - was found in a group of organisms that interbred, it might become more prevalent than any other allele. As time passes, that could mean the number of black moths in a population could increase. my website is true for many other characteristics--including morphology and behavior--that vary among populations of organisms. Monitoring evolutionary changes in action is easier when a species has a fast generation turnover such as bacteria. Since 1988, Richard Lenski, a biologist, has studied twelve populations of E.coli that descend from a single strain. Samples of each population were taken regularly and more than 500.000 generations of E.coli have been observed to have passed. Lenski's work has demonstrated that mutations can drastically alter the rate at the rate at which a population reproduces, and consequently, the rate at which it alters. It also demonstrates that evolution takes time, a fact that is difficult for some to accept. Microevolution can also be seen in the fact that mosquito genes for pesticide resistance are more common in populations that have used insecticides. This is because the use of pesticides creates a selective pressure that favors individuals who have resistant genotypes. The rapid pace at which evolution can take place has led to a growing recognition of its importance in a world shaped by human activity, including climate changes, pollution and the loss of habitats that hinder many species from adapting. Understanding the evolution process can help us make better decisions regarding the future of our planet as well as the life of its inhabitants.
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