The Academy's Evolution Site
Biology is a key concept in biology. The Academies are committed to helping those interested in science learn about the theory of evolution and how it can be applied in all areas of scientific research.
This site provides a range of resources for students, teachers, and general readers on evolution. It contains important video clips from NOVA and WGBH-produced science programs on DVD.
Tree of Life
The Tree of Life, an ancient symbol, symbolizes the interconnectedness of all life. 에볼루션코리아 appears in many religions and cultures as a symbol of unity and love. It has many practical applications as well, such as providing a framework to understand the history of species, and how they react to changes in environmental conditions.
The first attempts at depicting the biological world focused on the classification of organisms into distinct categories which were distinguished by their physical and metabolic characteristics1. These methods are based on the collection of various parts of organisms or short fragments of DNA have significantly increased the diversity of a Tree of Life2. These trees are largely composed by eukaryotes, and the diversity of bacterial species is greatly underrepresented3,4.
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 allow us to construct trees by using sequenced markers like the small subunit ribosomal RNA gene.
Despite the massive expansion of the Tree of Life through genome sequencing, a lot of biodiversity remains to be discovered. This is particularly true of microorganisms, which can be difficult to cultivate and are often only represented in a single sample5. Recent analysis of all genomes resulted in an initial draft of a Tree of Life. This includes a large number of bacteria, archaea and other organisms that have not yet been identified or the diversity of which is not fully understood6.
The expanded Tree of Life can be used to determine the diversity of a specific region and determine if certain habitats need special protection. The information can be used in a variety of ways, from identifying the most effective remedies to fight diseases to enhancing the quality of crops. This information is also extremely useful to conservation efforts. It can aid biologists in identifying the areas that are most likely to contain cryptic species with important metabolic functions that may be at risk of anthropogenic changes. 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 in order to promote conservation from within.
Phylogeny
A phylogeny, also called an evolutionary tree, reveals the relationships between groups of organisms. Scientists can build an phylogenetic chart which shows the evolutionary relationship of taxonomic categories using molecular information 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 have similar traits and evolved from a common ancestor. These shared traits can be analogous or homologous. Homologous traits are identical in their underlying evolutionary path, while analogous traits look similar but do not have the identical origins. Scientists organize similar traits into a grouping known as a Clade. All members of a clade share a trait, such as amniotic egg production. They all evolved from an ancestor that had these eggs. A phylogenetic tree is constructed by connecting the clades to determine the organisms which are the closest to each other.
For a more detailed and precise phylogenetic tree scientists make use of molecular data from DNA or RNA to identify the relationships between organisms. This data is more precise than morphological information and provides evidence of the evolution history of an individual or group. The use of molecular data lets researchers determine the number of species that have the same ancestor and estimate their evolutionary age.
The phylogenetic relationship can be affected by a variety of factors, including the phenotypic plasticity. This is a type behaviour that can change due to particular environmental conditions. This can cause a trait to appear more similar to one species than another, obscuring the phylogenetic signal. This problem can be addressed by using cladistics, which incorporates the combination of homologous and analogous features in the tree.
Additionally, phylogenetics can help predict the length and speed of speciation. This information can aid conservation biologists to make decisions about which species to protect from extinction. In the end, it's the conservation of phylogenetic diversity that will lead to an ecosystem that is complete and balanced.
Evolutionary Theory
The main idea behind evolution is that organisms acquire distinct characteristics over time based on their interactions with their surroundings. Many scientists have come up with theories of evolution, including the Islamic naturalist Nasir al-Din al-Tusi (1201-274), who believed that an organism would develop according to its own needs, the Swedish taxonomist Carolus Linnaeus (1707-1778) who conceived the modern hierarchical system of taxonomy, as well as Jean-Baptiste Lamarck (1844-1829), who suggested that the use or non-use of traits can cause changes that can be passed on to future generations.
In the 1930s and 1940s, ideas from a variety of fields--including natural selection, genetics, and particulate inheritance - came together to form the current evolutionary theory that explains how evolution is triggered by the variation of genes within a population, and how those variants change in time due to natural selection. This model, which incorporates genetic drift, mutations as well as gene flow and sexual selection can be mathematically described.
Recent developments in evolutionary developmental biology have revealed how variation can be introduced to a species through genetic drift, mutations, reshuffling genes during sexual reproduction and migration between populations. These processes, in conjunction with other ones like directionally-selected selection and erosion of genes (changes in the frequency of genotypes over time), can lead towards evolution. Evolution is defined by changes in the genome over time and changes in the phenotype (the expression of genotypes in individuals).
Students can gain a better understanding of phylogeny by incorporating evolutionary thinking in all areas of biology. In a recent study by Grunspan and co., it was shown that teaching students about the evidence for evolution increased their understanding of evolution in an undergraduate biology course. For more details on how to teach about evolution look up The Evolutionary Potential in all Areas of Biology or Thinking Evolutionarily A Framework for Integrating Evolution into Life Sciences Education.
Evolution in Action
Traditionally scientists have studied evolution through looking back--analyzing fossils, comparing species and observing living organisms. But evolution isn't just something that happened in the past. It's an ongoing process, taking place today. Viruses evolve to stay away from new antibiotics and bacteria transform to resist antibiotics. Animals adapt their behavior because of a changing environment. The changes that result are often visible.
But it wasn't until the late-1980s that biologists realized that natural selection can be seen in action, as well. The key is that various characteristics result in different rates of survival and reproduction (differential fitness) and are transferred from one generation to the next.
In the past, if a certain allele - the genetic sequence that determines colour - appeared in a population of organisms that interbred, it might become more prevalent than any other allele. Over time, this would mean that the number of moths that have black pigmentation in a population may 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 fast generation turnover such as bacteria. Since 1988, biologist Richard Lenski has been tracking twelve populations of E. bacteria that descend from a single strain. samples from each population are taken on a regular basis, and over fifty thousand generations have passed.
Lenski's work has shown that mutations can alter the rate at which change occurs and the efficiency at which a population reproduces. It also demonstrates that evolution is slow-moving, a fact that some people are unable to accept.
Another example of microevolution is that mosquito genes for resistance to pesticides are more prevalent in areas where insecticides are used. Pesticides create an exclusive pressure that favors those with resistant genotypes.
The rapidity of evolution has led to a greater appreciation of its importance particularly in a world shaped largely by human activity. This includes climate change, pollution, and habitat loss that prevents many species from adapting. Understanding the evolution process will help us make better decisions about the future of our planet, and the life of its inhabitants.