The Academy's Evolution Site Biological evolution is a central concept in biology. The Academies have been active for a long time in helping those interested in science comprehend the concept of evolution and how it affects all areas of scientific exploration. This site provides teachers, students and general readers with a variety of learning resources on evolution. It contains the most important video clips from NOVA and the WGBH-produced science programs on DVD. Tree of Life The Tree of Life is an ancient symbol that represents the interconnectedness of all life. It is seen in a variety of spiritual traditions and cultures as a symbol of unity and love. It also has important practical applications, like providing a framework to understand the history of species and how they respond to changes in environmental conditions. The earliest attempts to depict the world of biology focused on categorizing species into distinct categories that were identified by their physical and metabolic characteristics1. These methods, which are based on the sampling of different parts of organisms or short fragments of DNA have significantly increased the diversity of a Tree of Life2. These trees are mostly populated by eukaryotes, and bacteria are largely underrepresented3,4. In avoiding the necessity of direct experimentation and observation genetic techniques have enabled us to depict the Tree of Life in a more precise manner. In particular, molecular methods allow us to construct trees using sequenced markers such as the small subunit of ribosomal RNA gene. The Tree of Life has been dramatically expanded through genome sequencing. However, there is still much diversity to be discovered. This is particularly true for microorganisms, which are difficult to cultivate and are often only represented in a single specimen5. A recent study of all genomes that are known has produced a rough draft version of the Tree of Life, including many archaea and bacteria that have not been isolated, and whose diversity is poorly understood6. This expanded Tree of Life can be used to determine the diversity of a particular area and determine if particular habitats require special protection. This information can be utilized in a range of ways, from identifying new remedies to fight diseases to improving crop yields. ???? ??? ???? is also extremely valuable to conservation efforts. It can aid biologists in identifying areas most likely to have cryptic species, which may perform important metabolic functions and are susceptible to human-induced change. Although funding to safeguard biodiversity are vital, ultimately the best way to protect the world's biodiversity is for more people in developing countries to be equipped with the knowledge to take action locally to encourage conservation from within. Phylogeny A phylogeny, also known as an evolutionary tree, illustrates the relationships between groups of organisms. Scientists can create a phylogenetic diagram that illustrates the evolution of taxonomic groups using molecular data and morphological differences or similarities. Phylogeny is crucial in understanding biodiversity, evolution and genetics. A basic phylogenetic Tree (see Figure PageIndex 10 ) identifies the relationships between organisms that share similar traits that evolved from common ancestral. These shared traits could be either analogous or homologous. Homologous traits are similar in their evolutionary journey. Analogous traits may look like they are but they don't have the same origins. Scientists combine similar traits into a grouping known as a the clade. All members of a clade share a characteristic, like amniotic egg production. They all evolved from an ancestor that had these eggs. A phylogenetic tree can be constructed by connecting clades to identify the organisms who are the closest to each other. For a more detailed and accurate phylogenetic tree scientists use molecular data from DNA or RNA to determine the connections between organisms. This information is more precise and gives evidence of the evolution history of an organism. Researchers can utilize Molecular Data to determine the age of evolution of organisms and determine how many species share the same ancestor. The phylogenetic relationships of organisms can be affected by a variety of factors, including phenotypic flexibility, an aspect of behavior that alters in response to unique environmental conditions. This can cause a trait to appear more like a species another, clouding the phylogenetic signal. However, this problem can be reduced by the use of techniques such as cladistics which include a mix of similar and homologous traits into the tree. In addition, phylogenetics helps predict the duration and rate at which speciation takes place. This information can aid conservation biologists in making choices about which species to save from disappearance. Ultimately, it is the preservation of phylogenetic diversity which will lead to a complete and balanced ecosystem. Evolutionary Theory The main idea behind evolution is that organisms alter over time because of their interactions with their environment. Many theories of evolution have been developed by a variety of scientists, including the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who proposed that a living organism develop gradually according to its needs as well as the Swedish botanist Carolus Linnaeus (1707-1778) who conceived modern hierarchical taxonomy, and Jean-Baptiste Lamarck (1744-1829) who suggested that the use or misuse of traits causes changes that could be passed on to offspring. In the 1930s and 1940s, ideas from different fields, including natural selection, genetics & particulate inheritance, merged to form a modern synthesis of evolution theory. This explains how evolution is triggered by the variations in genes within a population and how these variations alter over time due to natural selection. This model, which includes mutations, genetic drift, gene flow and sexual selection, can be mathematically described mathematically. Recent developments in the field of evolutionary developmental biology have revealed that variation can be introduced into a species via mutation, genetic drift, and reshuffling of genes during sexual reproduction, as well as through the movement of populations. These processes, in conjunction with others such as directionally-selected selection and erosion of genes (changes in the frequency of genotypes over time), can lead towards evolution. Evolution is defined as changes in the genome over time and changes in phenotype (the expression of genotypes in an individual). Incorporating evolutionary thinking into all areas of biology education can increase students' understanding of phylogeny and evolution. A recent study by Grunspan and colleagues, for instance demonstrated that teaching about the evidence that supports evolution increased students' acceptance of evolution in a college-level biology class. To find out more about how to teach about evolution, look up 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 through looking back--analyzing fossils, comparing species and studying living organisms. Evolution is not a past event, but an ongoing process that continues to be observed today. Viruses reinvent themselves to avoid new antibiotics and bacteria transform to resist antibiotics. Animals adapt their behavior because of the changing environment. The results are often evident. However, it wasn't until late 1980s that biologists understood that natural selection can be seen in action, as well. The key is the fact that different traits can confer the ability to survive at different rates as well as reproduction, and may be passed on from generation to generation. In the past, if one particular allele--the genetic sequence that determines coloration--appeared in a population of interbreeding species, it could quickly become more prevalent than all other alleles. Over time, that would mean that the number of black moths in a 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 species has a rapid turnover of its generation such as bacteria. Since 1988, Richard Lenski, a biologist, has studied twelve populations of E.coli that are descended from one strain. Samples from each population were taken regularly and more than 50,000 generations of E.coli have passed. Lenski's research has revealed that mutations can alter the rate at which change occurs and the rate at which a population reproduces. It also shows that evolution takes time, which is hard for some to accept. Another example of microevolution is that mosquito genes for resistance to pesticides are more prevalent in populations where insecticides are used. Pesticides create an exclusive pressure that favors individuals who have resistant genotypes. The rapidity of evolution has led to a growing awareness of its significance, especially in a world which is largely shaped by human activities. This includes climate change, pollution, and habitat loss that hinders many species from adapting. Understanding the evolution process will help us make better choices about the future of our planet as well as the lives of its inhabitants.
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