The Academy's Evolution Site
The concept of biological evolution is among the most important concepts in biology. The Academies are committed to helping those interested in the sciences learn about the theory of evolution and how it can be applied throughout all fields of scientific research.
This site provides a range of tools for teachers, students and general readers of evolution. It includes key video clip 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. It is a symbol of love and unity across many cultures. It has numerous practical applications in addition to providing a framework for understanding the history of species and how they react to changes in environmental conditions.
The earliest attempts to depict the biological world focused on categorizing organisms into distinct categories which had been distinguished by physical and metabolic characteristics1. These methods, based on the sampling of different parts of living organisms, or sequences of short fragments of their DNA significantly increased the variety that could be represented in a tree of life2. However the trees are mostly comprised of eukaryotes, and bacterial diversity remains vastly underrepresented3,4.
Genetic techniques have greatly expanded our ability to represent the Tree of Life by circumventing the requirement for direct observation and experimentation. Particularly, molecular techniques allow us to build 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 a lot of biodiversity to be discovered. This is especially true of microorganisms that are difficult to cultivate and are often only found in a single sample5. Recent analysis of all genomes resulted in a rough draft of a Tree of Life. This includes a wide range of archaea, bacteria and other organisms that haven't yet been identified or whose diversity has not been fully understood6.
This expanded Tree of Life can be used to determine the diversity of a specific region and determine if certain habitats need special protection. This information can be utilized in a variety of ways, from identifying the most effective treatments to fight disease to enhancing crop yields. This information is also extremely useful for conservation efforts. It can aid biologists in identifying those areas that are most likely contain cryptic species with significant metabolic functions that could be vulnerable to anthropogenic change. While funding to protect biodiversity are important, the best way to conserve the world's biodiversity is to equip more people in developing nations with the necessary knowledge to take action locally and encourage conservation.
Phylogeny
A phylogeny (also known as an evolutionary tree) shows the relationships between different organisms. Using molecular data similarities and differences in morphology, or ontogeny (the process of the development of an organism) scientists can create an phylogenetic tree that demonstrates the evolution of taxonomic categories. The concept of phylogeny is fundamental to understanding the evolution of biodiversity, evolution and genetics.
A basic phylogenetic tree (see Figure PageIndex 10 Identifies the relationships between organisms that have similar characteristics and have evolved from an ancestor with common traits. These shared traits can be either analogous or homologous. Homologous traits are similar in their evolutionary paths. Analogous traits could appear like they are however they do not have the same ancestry. Scientists group similar traits into a grouping called a Clade. For instance, all the organisms in a clade share the characteristic of having amniotic eggs and evolved from a common ancestor which had these eggs. A phylogenetic tree can be constructed by connecting clades to determine the organisms who are the closest to each other.
To create a more thorough and precise phylogenetic tree scientists rely on molecular information from DNA or RNA to determine the relationships among organisms. This information is more precise and provides evidence of the evolution history of an organism. Molecular data allows researchers to determine the number of organisms that have an ancestor common to them and estimate their evolutionary age.
The phylogenetic relationship can be affected by a variety of factors that include the phenotypic plasticity. This is a kind of behaviour that can change as a result of specific environmental conditions. This can cause a trait to appear more similar to a species than another and obscure the phylogenetic signals. However, this problem can be reduced by the use of methods such as cladistics that include a mix of similar and homologous traits into the tree.
Furthermore, phylogenetics may aid in predicting the duration and rate of speciation. This information will assist conservation biologists in deciding which species to protect from the threat of extinction. Ultimately, it is the preservation of phylogenetic diversity which will create a complete and balanced ecosystem.
Evolutionary Theory
The main idea behind evolution is that organisms change over time due to their interactions with their environment. Many theories of evolution have been developed by a wide variety of scientists such as the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who believed that an organism would evolve gradually according to its needs as well as the Swedish botanist Carolus Linnaeus (1707-1778) who designed modern hierarchical taxonomy, and Jean-Baptiste Lamarck (1744-1829) who suggested that the use or non-use of traits cause changes that could be passed on to offspring.
In the 1930s & 1940s, concepts from various areas, including genetics, natural selection, and particulate inheritance, came together to create a modern theorizing of evolution. This explains how evolution occurs by the variation in genes within the population and how these variations change over time as a result of natural selection. This model, which incorporates genetic drift, mutations, gene flow and sexual selection is mathematically described mathematically.
Recent discoveries in the field of evolutionary developmental biology have demonstrated how variation can be introduced to a species by genetic drift, mutations or reshuffling of genes in sexual reproduction, and even migration between populations. These processes, along with other ones like directional selection and genetic erosion (changes in the frequency of a genotype over time) can lead to evolution that is defined as change in the genome of the species over time, and the change in phenotype as time passes (the expression of the genotype in an individual).
Students can better understand the concept of phylogeny by using evolutionary thinking in all aspects of biology. A recent study conducted by Grunspan and colleagues, for example revealed that teaching students about the evidence supporting evolution increased students' acceptance of evolution in a college-level biology course. For more information about how to teach evolution, see The Evolutionary Potency in All Areas of Biology or Thinking Evolutionarily A Framework for Infusing Evolution into Life Sciences Education.
Evolution in Action
Scientists have traditionally studied evolution by looking in the past, studying fossils, and comparing species. They also study living organisms. But evolution isn't just something that happened in the past, it's an ongoing process taking place in the present. Viruses evolve to stay away from new drugs and bacteria evolve to resist antibiotics. Animals alter their behavior in the wake of a changing environment. The changes that result are often visible.
It wasn't until late 1980s that biologists realized that natural selection could be observed in action as well. The main reason is that different traits can confer an individual rate of survival and reproduction, and they can be passed down from one generation to the next.
In the past, if one allele - the genetic sequence that determines color - appeared in a population of organisms that interbred, it could be more common than other allele. Over time, that would mean that the number of black moths within 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 evolutionary change when an organism, like bacteria, has a high generation turnover. Since 1988, biologist Richard Lenski has been tracking twelve populations of E. coli that descended from a single strain; samples from each population are taken regularly, and over 500.000 generations have been observed.
Lenski's work has demonstrated that a mutation can dramatically alter the rate at which a population reproduces--and so the rate at which it changes. It also shows that evolution takes time, a fact that some people find difficult to accept.
Microevolution is also evident in the fact that mosquito genes that confer resistance to pesticides are more common in populations where insecticides have been used. Pesticides create an exclusive pressure that favors those who have resistant genotypes.
무료 에볼루션 at which evolution takes place has led to a growing recognition of its importance in a world that is shaped by human activities, including climate change, pollution and the loss of habitats which prevent many species from adapting. Understanding evolution will aid you in making better decisions about the future of the planet and its inhabitants.