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The Academy's Evolution Site Biological evolution is one of the most fundamental concepts in biology. The Academies are committed to helping those who are interested in science to learn about the theory of evolution and how it can be applied throughout all fields of scientific research. This site provides a wide range of resources for teachers, students, and general readers on evolution. It contains key 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 appears in many religions and cultures as symbolizing unity and love. It also has many practical applications, such as providing a framework for understanding the history of species and how they respond to changes in environmental conditions. The first attempts to depict the biological world were built on categorizing organisms based on their metabolic and physical characteristics. These methods, based on the sampling of various parts of living organisms, or sequences of short DNA fragments, greatly increased the variety of organisms that could be represented in the tree of life2. However these trees are mainly comprised of eukaryotes, and bacterial diversity remains vastly underrepresented3,4. Genetic techniques have significantly expanded our ability to depict the Tree of Life by circumventing the requirement for direct observation and experimentation. In particular, molecular methods enable us to create trees using sequenced markers, such as the small subunit ribosomal RNA gene. The Tree of Life has been greatly expanded thanks to genome sequencing. However, there is still much diversity to be discovered. This is especially true for microorganisms that are difficult to cultivate and which are usually only found in one sample5. A recent analysis of all known genomes has created a rough draft of the Tree of Life, including a large number of bacteria and archaea that are not isolated and which are not well understood. This expanded Tree of Life is particularly beneficial in assessing the biodiversity of an area, which can help to determine if certain habitats require special protection. This information can be utilized in a variety of ways, including finding new drugs, battling diseases and improving the quality of crops. The information is also valuable to conservation efforts. It helps biologists determine the areas most likely to contain cryptic species with significant metabolic functions that could be at risk of anthropogenic changes. While conservation funds are essential, the best way to conserve the world's biodiversity is to equip more people in developing countries with the knowledge they need to act locally and support conservation. Phylogeny A phylogeny, also called an evolutionary tree, illustrates the relationships between groups of organisms. Scientists can construct a phylogenetic chart that shows the evolutionary relationship of taxonomic groups based on molecular data and morphological similarities or differences. The phylogeny of a tree plays an important role in understanding genetics, biodiversity and evolution. A basic phylogenetic tree (see Figure PageIndex 10 Determines the relationship between organisms that have similar traits and have evolved from an ancestor that shared traits. These shared traits could be either homologous or analogous. Homologous traits are similar in their evolutionary path. Analogous traits may look similar however they do not have the same ancestry. Scientists group similar traits together into a grouping called a clade. All organisms in a group share a trait, such as amniotic egg production. They all derived from an ancestor who had these eggs. A phylogenetic tree is then constructed by connecting clades to identify the species that are most closely related to one another. For a more detailed and accurate phylogenetic tree scientists rely on molecular information from DNA or RNA to identify the relationships between organisms. This information is more precise and provides evidence of the evolution history of an organism. Researchers can utilize Molecular Data to calculate the age of evolution of organisms and determine how many species have a common ancestor. The phylogenetic relationship can be affected by a variety of factors that include the phenomenon of phenotypicplasticity. This is a kind of behaviour that can change in response to specific environmental conditions. This can cause a characteristic to appear more similar to one species than another, obscuring the phylogenetic signal. However, this problem can be reduced by the use of techniques such as cladistics that include a mix of homologous and analogous features into the tree. Additionally, phylogenetics can help predict the duration and rate of speciation. This information can assist conservation biologists in making decisions about which species to protect from disappearance. It is ultimately the preservation of phylogenetic diversity that will lead to an ecologically balanced and complete ecosystem. Evolutionary Theory The central theme of evolution is that organisms develop distinct characteristics over time based on their interactions with their environments. A variety of theories about evolution have been developed by a wide range of scientists including the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who proposed that a living organism develop slowly according to its requirements and needs, the Swedish botanist Carolus Linnaeus (1707-1778) who developed the modern hierarchical taxonomy Jean-Baptiste Lamarck (1744-1829) who suggested that the use or non-use of traits can cause changes that could be passed on to the offspring. In the 1930s and 1940s, concepts from various fields, such as natural selection, genetics & particulate inheritance, were brought together to form a modern evolutionary theory. This explains how evolution happens through the variation in genes within a population and how these variations alter over time due to natural selection. ?????????? , which includes genetic drift, mutations, gene flow and sexual selection can be mathematically described. Recent developments in the field of evolutionary developmental biology have revealed the ways in which variation can be introduced to a species via mutations, genetic drift and reshuffling of genes during sexual reproduction and migration between populations. These processes, as well as other ones like the directional selection process and the erosion of genes (changes in frequency of genotypes over time) can lead to evolution. Evolution is defined by changes in the genome over time, as well as changes in phenotype (the expression of genotypes in an individual). Students can better understand the concept of phylogeny by using evolutionary thinking in all areas of biology. A recent study conducted by Grunspan and colleagues, for instance demonstrated that teaching about the evidence for evolution increased students' understanding of evolution in a college-level biology course. To learn more about how to teach about evolution, read The Evolutionary Potential in All Areas of Biology and Thinking Evolutionarily: A Framework for Infusing Evolution in Life Sciences Education. Evolution in Action Traditionally, scientists have studied evolution through looking back--analyzing fossils, comparing species, and studying living organisms. However, evolution isn't something that occurred in the past. It's an ongoing process that is happening right now. Bacteria transform and resist antibiotics, viruses evolve and elude new medications and animals alter their behavior to the changing environment. The changes that occur are often evident. It wasn't until the late 1980s that biologists began to realize that natural selection was at work. The key is that different traits have different rates of survival and reproduction (differential fitness) and can be passed down from one generation to the next. In the past, if one particular allele - the genetic sequence that determines coloration--appeared in a group of interbreeding organisms, it could rapidly become more common than other alleles. In time, this could mean that the number of black moths in the population could increase. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms. Observing evolutionary change in action is easier when a particular species has a fast generation turnover, 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 every day, and over fifty thousand generations have passed. Lenski's work has demonstrated that mutations can drastically alter the efficiency with which a population reproduces--and so the rate at which it evolves. It also shows evolution takes time, a fact that is difficult for some to accept. Another example of microevolution is that mosquito genes that are resistant to pesticides are more prevalent in populations where insecticides are employed. That's because the use of pesticides creates a pressure that favors those who have resistant genotypes. The speed at which evolution takes place has led to a growing appreciation of its importance in a world shaped by human activities, including climate changes, pollution and the loss of habitats that hinder many species from adapting. Understanding evolution can help us make better choices about the future of our planet, and the life of its inhabitants.
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