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The Academy's Evolution Site Biological evolution is a central concept in biology. The Academies have long been 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 teachers, students and general readers with a wide range of educational resources 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 that represents the interconnectedness of life. It is used in many spiritual traditions and cultures as a symbol of unity and love. It also has many practical applications, such as providing a framework for understanding the history of species and how they react to changing environmental conditions. Early approaches to depicting the world of biology focused on categorizing organisms into distinct categories that had been identified by their physical and metabolic characteristics1. These methods, based on sampling of different parts of living organisms, or short DNA fragments, significantly increased the variety that could be represented in a tree of life2. However, these trees are largely composed of eukaryotes; bacterial diversity is still largely unrepresented3,4. In avoiding the necessity of direct experimentation and observation genetic techniques have allowed us to represent the Tree of Life in a much more accurate way. In particular, molecular methods enable us to create trees by using sequenced markers such as the small subunit ribosomal gene. Despite the dramatic expansion of the Tree of Life through genome sequencing, a large amount of biodiversity awaits discovery. This is especially relevant to microorganisms that are difficult to cultivate, and which are usually only found in a single specimen5. A recent analysis of all genomes resulted in a rough draft of a Tree of Life. This includes a large number of bacteria, archaea and other organisms that haven't yet been isolated or whose diversity has not been well understood6. The expanded Tree of Life can be used to assess the biodiversity of a specific region and determine if specific habitats require special protection. This information can be used in a range of ways, from identifying the most effective treatments to fight disease to enhancing crop yields. The information is also useful to conservation efforts. It helps biologists discover areas most likely to have species that are cryptic, which could perform important metabolic functions and be vulnerable to the effects of human activity. Although funds to protect biodiversity are essential however, the most effective method to protect the world's biodiversity is for more people in developing countries to be empowered with the knowledge to act locally to promote conservation from within. Phylogeny A phylogeny (also known as an evolutionary tree) illustrates the relationship between species. Utilizing molecular data as well as morphological similarities and distinctions or ontogeny (the process of the development of an organism), scientists can build an phylogenetic tree that demonstrates the evolution of taxonomic categories. The concept of phylogeny is fundamental to understanding biodiversity, evolution and genetics. A basic phylogenetic tree (see Figure PageIndex 10 ) identifies the relationships between organisms with similar traits that have evolved from common ancestors. These shared traits can be either analogous or homologous. Homologous traits are similar in their underlying evolutionary path while analogous traits appear like they do, but don't have the same origins. Scientists combine similar traits into a grouping called a clade. For instance, all of the species in a clade have the characteristic of having amniotic egg and evolved from a common ancestor who had these eggs. A phylogenetic tree is constructed by connecting the clades to identify the species who are the closest to one another. Scientists make use of molecular DNA or RNA data to create a phylogenetic chart that is more accurate and precise. This data is more precise than the morphological data and provides evidence of the evolution history of an organism or group. The analysis of molecular data can help researchers identify the number of species that have the same ancestor and estimate their evolutionary age. The phylogenetic relationships of organisms can be influenced by several factors, including phenotypic flexibility, a type of behavior that alters in response to specific 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 problem can be cured by the use of methods such as cladistics which include a mix of similar and homologous traits into the tree. Additionally, phylogenetics can help determine the duration and speed of speciation. This information can aid conservation biologists in deciding which species to safeguard from disappearance. In the end, it's the preservation of phylogenetic diversity which will result in an ecologically balanced and complete ecosystem. Evolutionary Theory The fundamental concept of evolution is that organisms develop distinct characteristics over time due to their interactions with their environment. Several theories of evolutionary change have been developed by a wide range of scientists such as the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who believed that an organism would evolve slowly in accordance with its needs and needs, the Swedish botanist Carolus Linnaeus (1707-1778) who designed modern hierarchical taxonomy, and Jean-Baptiste Lamarck (1744-1829) who suggested that the use or misuse of traits cause changes that can be passed on to offspring. In the 1930s & 1940s, theories from various fields, including genetics, natural selection and particulate inheritance, came together to create a modern evolutionary theory. This describes how evolution occurs by the variation of genes in 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 the current evolutionary biology and is mathematically described. Recent developments in the field of evolutionary developmental biology have shown that variation can be introduced into a species via genetic drift, mutation, and reshuffling genes during sexual reproduction, and also through the movement of populations. These processes, along with other ones like directional selection and gene erosion (changes to the frequency of genotypes over time) can result in evolution. Evolution is defined as changes in the genome over time, as well as changes in the phenotype (the expression of genotypes within individuals). Incorporating evolutionary thinking into all areas of biology education can improve students' understanding of phylogeny as well as evolution. A recent study by Grunspan and colleagues, for example demonstrated that teaching about the evidence that supports evolution helped students accept the concept of evolution in a college-level biology course. To learn more about how to teach about evolution, please look up The Evolutionary Potential of all Areas of Biology and Thinking Evolutionarily: A Framework for Infusing Evolution in Life Sciences Education. evolutionkr in Action Scientists have studied evolution through looking back in the past, analyzing fossils and comparing species. They also observe living organisms. But evolution isn't just something that occurred in the past; it's an ongoing process that is taking place today. Bacteria mutate and resist antibiotics, viruses re-invent themselves and are able to evade new medications and animals alter their behavior to the changing environment. The resulting changes are often evident. It wasn't until the 1980s when biologists began to realize that natural selection was also in action. The key to this is that different traits confer an individual rate of survival as well as reproduction, and may be passed down from one generation to the next. In the past, if an allele – the genetic sequence that determines colour – was present in a population of organisms that interbred, it might become more common than other allele. 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. It is easier to track evolution when an organism, like bacteria, has a high generation turnover. Since 1988 the biologist Richard Lenski has been tracking twelve populations of E. coli that descended from a single strain; samples from each population are taken every day, and over fifty thousand generations have been observed. Lenski's research has revealed that a mutation can dramatically alter the efficiency with which a population reproduces—and so, the rate at which it alters. It also proves that evolution takes time—a fact that some find difficult to accept. Microevolution can also be seen in the fact that mosquito genes that confer resistance to pesticides are more prevalent in areas that have used insecticides. Pesticides create a selective pressure which favors individuals who have resistant genotypes. The rapidity of evolution has led to a greater appreciation of its importance especially in a planet which is largely shaped by human activities. This includes pollution, climate change, and habitat loss that prevents many species from adapting. Understanding the evolution process can help us make better decisions about the future of our planet and the life of its inhabitants.