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 understand the concept of evolution and how it affects every area of scientific inquiry.
This site provides teachers, students and general readers with a wide range of educational resources on evolution. It contains the most 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 all life. It is an emblem of love and unity across many cultures. It also has many practical uses, like providing a framework to understand the evolution of species and how they respond to changes in the environment.
The first attempts to depict the world of biology were built on categorizing organisms based on their metabolic and physical characteristics. These methods, which rely on the sampling of different parts of organisms, or DNA fragments have significantly increased the diversity of a Tree of Life2. However these trees are mainly made up of eukaryotes. Bacterial diversity is still largely unrepresented3,4.
click through the next site have significantly expanded our ability to depict the Tree of Life by circumventing the need for direct observation and experimentation. We can construct trees using molecular methods such as the small subunit ribosomal gene.
Despite the massive growth of the Tree of Life through genome sequencing, a lot of biodiversity remains to be discovered. This is particularly true of microorganisms, which are difficult to cultivate and are typically only represented in a single sample5. Recent analysis of all genomes has produced an initial draft of the Tree of Life. This includes a large number of archaea, bacteria and other organisms that haven't yet been isolated, or the diversity of which is not well understood6.
The expanded Tree of Life is particularly beneficial in assessing the biodiversity of an area, which can help to determine whether specific habitats require protection. This information can be used in a range 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 helps biologists discover areas that are likely to have cryptic species, which may perform important metabolic functions, and could be susceptible to changes caused by humans. Although funds to protect biodiversity are essential, ultimately the best way to protect the world's biodiversity is for more people living in developing countries to be equipped with the knowledge to act locally to promote conservation from within.
Phylogeny
A phylogeny (also called an evolutionary tree) illustrates the relationship between different organisms. Scientists can build an phylogenetic chart which shows the evolutionary relationship of taxonomic groups using molecular data and morphological differences or similarities. Phylogeny is essential in understanding evolution, biodiversity and genetics.
A basic phylogenetic tree (see Figure PageIndex 10 Identifies the relationships between organisms that have similar traits and have evolved from an ancestor with common traits. These shared traits can be either homologous or analogous. Homologous traits are similar in their evolutionary roots while analogous traits appear like they do, but don't have the identical origins. Scientists organize similar traits into a grouping known as a clade. For example, all of the organisms in a clade share the characteristic of having amniotic eggs. They evolved from a common ancestor that had eggs. The clades then join to form a phylogenetic branch that can determine which organisms have the closest relationship.
Scientists make use of molecular DNA or RNA data to build a phylogenetic chart that is more accurate and precise. This information is more precise than morphological information and provides evidence of the evolutionary history of an organism or group. Molecular data allows researchers to determine the number of organisms that share a common ancestor and to estimate their evolutionary age.
Phylogenetic relationships can be affected by a number of factors that include the phenomenon of phenotypicplasticity. This is a kind of behaviour that can change due to particular environmental conditions. This can cause a particular trait to appear more similar to one species than other species, which can obscure the phylogenetic signal. This problem can be mitigated by using cladistics, which incorporates the combination of homologous and analogous traits in the tree.
Additionally, phylogenetics can help determine the duration and speed at which speciation occurs. This information can assist conservation biologists in making choices about which species to protect from the threat of extinction. In the end, it's the preservation of phylogenetic diversity which will result in 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 scientists have proposed theories of evolution, such as the Islamic naturalist Nasir al-Din al-Tusi (1201-274) who believed that an organism could evolve according to its individual requirements, the Swedish taxonomist Carolus Linnaeus (1707-1778), who created the modern taxonomy system that is hierarchical, as well as Jean-Baptiste Lamarck (1844-1829), who believed that the use or absence of traits can lead to changes that can be passed on to future generations.
In the 1930s and 1940s, ideas from a variety of fields -- including genetics, natural selection and particulate inheritance -- came together to form the current synthesis of evolutionary theory that explains how evolution is triggered by the variation of genes within a population, and how these variants change in time due to natural selection. This model, which includes mutations, genetic drift as well as gene flow and sexual selection, can be mathematically described mathematically.
Recent developments in evolutionary developmental biology have demonstrated how variations can be introduced to a species via genetic drift, mutations and reshuffling of genes during sexual reproduction and migration between populations. These processes, in conjunction with others such as directional selection and gene erosion (changes in the frequency of genotypes over time) can lead to evolution. Evolution is defined as changes in the genome over time, as well as changes in the phenotype (the expression of genotypes in individuals).
Students can gain a better understanding of the concept of phylogeny through incorporating evolutionary thinking into all areas of biology. A recent study conducted by Grunspan and colleagues, for example revealed that teaching students about the evidence supporting evolution increased students' understanding of evolution in a college biology course. For more details on how to teach evolution read The Evolutionary Power of Biology in All Areas of Biology or Thinking Evolutionarily A Framework for Infusing Evolution into Life Sciences Education.
Evolution in Action
Traditionally, scientists have studied evolution through studying fossils, comparing species, and studying living organisms. Evolution isn't a flims event, but an ongoing process that continues to be observed today. Viruses evolve to stay away from new drugs and bacteria evolve to resist antibiotics. Animals adapt their behavior because of a changing environment. The changes that result are often apparent.
However, it wasn't until late 1980s that biologists understood that natural selection could be seen in action, as well. The key is the fact that different traits can confer a different rate of survival and reproduction, and can be passed down from one generation to the next.
In the past when one particular allele--the genetic sequence that controls coloration - was present in a group of interbreeding organisms, it might quickly become more prevalent than other alleles. As time passes, this could mean that the number of moths sporting black pigmentation in a group could increase. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
It is easier to see evolutionary change when a species, such as bacteria, has a high generation turnover. Since 1988, Richard Lenski, a biologist, has been tracking twelve populations of E.coli that are descended from a single strain. The samples of each population have been collected regularly and more than 50,000 generations of E.coli have passed.
Lenski's research has demonstrated that mutations can alter the rate of change and the efficiency at which a population reproduces. It also shows that evolution takes time, a fact that is difficult for some to accept.
Microevolution is also evident in the fact that mosquito genes for resistance to pesticides are more common in populations that have used insecticides. This is because pesticides cause a selective pressure which favors those who have resistant genotypes.
The rapidity of evolution has led to an increasing awareness of its significance particularly in a world which is largely shaped by human activities. This includes the effects of climate change, pollution and habitat loss that hinders many species from adapting. Understanding the evolution process can help us make better choices about the future of our planet, and the lives of its inhabitants.