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The Academy's Evolution Site Biology is one of the most fundamental concepts in biology. The Academies are involved in helping those interested in the sciences learn about the theory of evolution and how it is permeated across all areas of scientific research. This site provides teachers, students and general readers with a wide range of learning resources on evolution. It includes key video clip from NOVA and WGBH produced science programs on DVD. Tree of Life The Tree of Life is an ancient symbol of the interconnectedness of life. It is a symbol of love and harmony in a variety of cultures. It can be used in many practical ways as well, such as providing a framework to understand the history of species and how they react to changes in environmental conditions. The earliest attempts to depict the biological world focused on the classification of organisms into distinct categories which were distinguished by their physical and metabolic characteristics1. These methods, which are based on the sampling of different parts of organisms, or fragments of DNA, have significantly increased the diversity of a Tree of Life2. These trees are largely composed by eukaryotes and bacteria are largely underrepresented3,4. By avoiding the necessity for direct experimentation and observation, genetic techniques have enabled us to represent the Tree of Life in a more precise manner. Particularly, molecular methods allow us to build trees by using sequenced markers, such as the small subunit ribosomal gene. Despite ?????????? of the Tree of Life through genome sequencing, a large amount of biodiversity remains to be discovered. This is particularly true of microorganisms, which can be difficult to cultivate and are typically only present in a single sample5. A recent analysis of all genomes that are known has created a rough draft of the Tree of Life, including a large number of archaea and bacteria that have not been isolated and whose diversity is poorly understood6. This expanded Tree of Life can be used to evaluate the biodiversity of a particular area and determine if certain habitats require special protection. The information can be used in a variety of ways, from identifying new medicines to combating disease to improving crop yields. This information is also extremely useful to conservation efforts. It can help biologists identify areas that are likely to be home to species that are cryptic, which could perform important metabolic functions, and could be susceptible to the effects of human activity. While funds to protect biodiversity are important, the most effective way to conserve the world's biodiversity is to empower the people of developing nations with the knowledge they need to act locally and support conservation. Phylogeny A phylogeny (also called an evolutionary tree) illustrates the relationship between species. Scientists can create an phylogenetic chart which shows the evolutionary relationships between taxonomic groups based on molecular data and morphological differences or similarities. The phylogeny of a tree plays an important role in understanding biodiversity, genetics and evolution. A basic phylogenetic tree (see Figure PageIndex 10 Finds the connections between organisms that have similar traits and evolved from a common ancestor. These shared traits can be analogous, or homologous. Homologous traits are similar in their evolutionary paths. Analogous traits might appear similar but they don't have the same origins. Scientists arrange similar traits into a grouping referred to as a clade. For instance, all the organisms that make up a clade share the trait of having amniotic eggs and evolved from a common ancestor who had eggs. The clades are then linked to form a phylogenetic branch to determine the organisms with the closest connection to each other. Scientists make use of DNA or RNA molecular data to build a phylogenetic chart that is more accurate and precise. This information is more precise than morphological information and provides evidence of the evolutionary background of an organism or group. The analysis of molecular data can help researchers determine the number of species that share a common ancestor and to estimate their evolutionary age. The phylogenetic relationships of a species can be affected by a number of factors such as the phenomenon of phenotypicplasticity. This is a type behavior that alters in response to particular environmental conditions. This can cause a characteristic to appear more like a species another, clouding the phylogenetic signal. This issue can be cured by using cladistics. This is a method that incorporates the combination of homologous and analogous features in the tree. Additionally, phylogenetics aids predict the duration and rate of speciation. This information can aid conservation biologists in making choices about which species to protect from disappearance. In the end, it's the preservation of phylogenetic diversity that will result in an ecosystem that is complete and balanced. Evolutionary Theory The fundamental concept of evolution is that organisms develop different features over time as a result of their interactions with their environments. Many scientists have developed theories of evolution, such as the Islamic naturalist Nasir al-Din al-Tusi (1201-274), who believed that an organism would develop according to its own requirements as well as the Swedish taxonomist Carolus Linnaeus (1707-1778), who created the modern hierarchical taxonomy, as well as Jean-Baptiste Lamarck (1844-1829), who believed that the use or non-use of traits can cause changes that can be passed on to future generations. In the 1930s & 1940s, ideas from different fields, including natural selection, genetics & particulate inheritance, came together to create a modern synthesis of evolution theory. This describes how evolution happens through the variations in genes within a population and how these variations change over time as a result of natural selection. This model, which incorporates genetic drift, mutations as well as gene flow and sexual selection, can be mathematically described. Recent developments in the field of evolutionary developmental biology have demonstrated that variations can be introduced into a species via genetic drift, mutation, and reshuffling of genes during sexual reproduction, as well as through migration between populations. These processes, along with others such as directional selection and gene erosion (changes in frequency of genotypes over time) can result in evolution. Evolution is defined as changes in the genome over time and changes in phenotype (the expression of genotypes in individuals). Incorporating evolutionary thinking into all areas of biology education can increase students' understanding of phylogeny and evolutionary. A recent study conducted by Grunspan and colleagues, for example, showed that teaching about the evidence for evolution helped students accept the concept of evolution in a college-level biology course. To learn more about how to teach about evolution, read The Evolutionary Potential of All Areas of Biology and Thinking Evolutionarily A Framework for Infusing Evolution in Life Sciences Education. Evolution in Action Scientists have traditionally studied evolution by looking in the past, analyzing fossils and comparing species. They also observe living organisms. But evolution isn't just something that happened in the past, it's an ongoing process, that is taking place today. Bacteria transform and resist antibiotics, viruses evolve and elude new medications, and animals adapt their behavior in response to a changing planet. The results are often evident. However, it wasn't until late 1980s that biologists understood that natural selection could be seen in action, as well. The key is the fact that different traits result in the ability to survive at different rates and reproduction, and can be passed on from one generation to the next. In the past, if one allele - the genetic sequence that determines color - appeared in a population of organisms that interbred, it could become more common than other allele. As time passes, that could mean the number of black moths within a population could increase. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms. The ability to observe evolutionary change is easier when a particular species has a rapid turnover of its generation, as with bacteria. Since 1988 biologist Richard Lenski has been tracking twelve populations of E. Coli that descended from a single strain; samples of each population are taken regularly and over fifty thousand generations have been observed. Lenski's work has shown that mutations can alter the rate of change and the efficiency of a population's reproduction. It also demonstrates that evolution takes time, something that is difficult for some to accept. Another example of microevolution is that mosquito genes for resistance to pesticides show up more often in areas where insecticides are employed. This is because the use of pesticides causes a selective pressure that favors people who have resistant genotypes. The rapidity of evolution has led to a greater recognition of its importance especially in a planet that is largely shaped by human activity. This includes the effects of climate change, pollution and habitat loss, which prevents many species from adapting. Understanding evolution will help you make better decisions regarding the future of the planet and its inhabitants.
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