The Academy's Evolution Site
Biological evolution is a central concept in biology. The Academies are committed to helping those who are interested in the sciences learn about the theory of evolution and how it is incorporated across all areas of scientific research.
This site provides students, teachers and general readers with a variety of learning resources on evolution. It has important video clips from NOVA and WGBH's science programs on DVD.
Tree of Life
The Tree of Life is an ancient symbol of the interconnectedness of life. 에볼루션 슬롯 is seen in a variety of spiritual traditions and cultures as an emblem of unity and love. It has many practical applications in addition to providing a framework to understand 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 were identified by their physical and metabolic characteristics1. These methods, which are based on the sampling of different parts of organisms, or fragments of DNA have greatly increased the diversity of a tree of Life2. However these trees are mainly made up of eukaryotes. Bacterial diversity remains vastly underrepresented3,4.
Genetic techniques have greatly broadened our ability to represent the Tree of Life by circumventing the need for direct observation and experimentation. Trees can be constructed using molecular methods such as the small subunit ribosomal gene.
The Tree of Life has been dramatically expanded through genome sequencing. However, there is still much diversity to be discovered. This is particularly the case for microorganisms which are difficult to cultivate and are typically found in a single specimen5. A recent study of all known genomes has produced a rough draft version of the Tree of Life, including a large number of bacteria and archaea that have not been isolated and which are not well understood.
The expanded Tree of Life can be used to assess the biodiversity of a specific region and determine if particular habitats require special protection. This information can be used in many ways, including identifying new drugs, combating diseases and improving the quality of crops. The information is also useful for conservation efforts. It can aid biologists in identifying areas that are likely to have cryptic species, which may have important metabolic functions, and could be susceptible to changes caused by humans. While funds to protect biodiversity are crucial, ultimately the best way to preserve 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 called an evolutionary tree) illustrates the relationship between species. Using molecular data similarities and differences in morphology, or ontogeny (the process of the development of an organism), scientists can build a phylogenetic tree which illustrates the evolutionary relationship between taxonomic categories. Phylogeny is essential in understanding biodiversity, evolution and genetics.
A basic phylogenetic Tree (see Figure PageIndex 10 ) is a method of identifying the relationships between organisms that share similar traits that evolved from common ancestral. These shared traits can be homologous, or analogous. Homologous traits are identical in their underlying evolutionary path and analogous traits appear like they do, but don't have the same origins. Scientists group similar traits together into a grouping known as a clade. For example, all of the species in a clade share the characteristic of having amniotic eggs 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 each other.
For a more precise and accurate phylogenetic tree, scientists rely on molecular information from DNA or RNA to determine the relationships among organisms. This data is more precise than morphological information and provides evidence of the evolutionary history of an organism or group. The use of molecular data lets researchers determine the number of species who share the same ancestor and estimate their evolutionary age.
The phylogenetic relationships of a species can be affected by a number of factors, including phenotypicplasticity. This is a type behavior that alters as a result of particular environmental conditions. This can cause a trait to appear more similar in one species than another, obscuring the phylogenetic signal. However, this issue can be reduced by the use of methods such as cladistics which incorporate a combination of homologous and analogous features into the tree.
Additionally, phylogenetics can aid in predicting the duration and rate of speciation. This information can aid conservation biologists to make decisions about which species to protect from extinction. In the end, it is the conservation of phylogenetic diversity that will lead to an ecosystem that is balanced and complete.
Evolutionary Theory
The main idea behind evolution is that organisms change over time as a result of their interactions with their environment. Many scientists have proposed theories of evolution, such as the Islamic naturalist Nasir al-Din al-Tusi (1201-274), who believed that an organism would evolve according to its own needs, the Swedish taxonomist Carolus Linnaeus (1707-1778) who conceived the modern hierarchical taxonomy and Jean-Baptiste Lamarck (1844-1829), who believed that the use or non-use of certain traits can result in changes that are passed on to the next generation.
In the 1930s and 1940s, theories from a variety of fields -- including natural selection, genetics, and particulate inheritance - came together to create the modern evolutionary theory, which defines how evolution happens through the variation of genes within a population, and how these variants change in time due to natural selection. This model, which encompasses mutations, genetic drift in gene flow, and sexual selection can be mathematically described mathematically.
Recent developments in the field of evolutionary developmental biology have shown that variation can be introduced into a species through mutation, genetic drift, and reshuffling of genes in sexual reproduction, and also by migration between populations. These processes, as well as others such as directional selection or genetic erosion (changes in the frequency of a genotype over time) can lead to evolution, which is defined by changes in the genome of the species over time, and the change in phenotype as time passes (the expression of the genotype in an individual).
Incorporating evolutionary thinking into all areas of biology education can increase student understanding of the concepts of phylogeny and evolution. A recent study by Grunspan and colleagues, for instance demonstrated that teaching about the evidence for evolution increased students' understanding of evolution in a college biology course. To find out more about how to teach about evolution, please 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 observing living organisms. Evolution is not a past event, but an ongoing process. The virus reinvents itself to avoid new medications and bacteria mutate to resist antibiotics. Animals alter their behavior as a result of a changing world. The resulting changes are often evident.
It wasn't until the 1980s that biologists began realize that natural selection was also at work. The key is the fact that different traits result in a different rate of survival as well as reproduction, and may be passed on from one generation to the next.
In the past, if a certain allele - the genetic sequence that determines colour - was found in a group of organisms that interbred, it might become more common than other allele. Over time, that would mean that the number of black moths in a particular population could rise. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
It is easier to observe evolutionary change when an organism, like bacteria, has a high generation turnover. Since 1988, biologist Richard Lenski has been tracking twelve populations of E. bacteria that descend from a single strain. samples of each population are taken every day and more than 500.000 generations have passed.
Lenski's work has demonstrated that a mutation can profoundly alter the rate at which a population reproduces--and so, the rate at which it evolves. It also shows that evolution takes time, a fact that is hard for some to accept.
Microevolution can be observed in the fact that mosquito genes for pesticide resistance are more prevalent in populations that have used insecticides. That's because the use of pesticides causes a selective pressure that favors people with resistant genotypes.
The rapid pace at which evolution takes place has led to a growing recognition of its importance in a world that is shaped by human activity, including climate change, pollution and the loss of habitats that prevent many species from adjusting. Understanding the evolution process will help us make better decisions regarding the future of our planet, and the life of its inhabitants.