The Academy's Evolution Site
Biology is a key concept in biology. The Academies are involved in helping those interested in the sciences understand evolution theory and how it can be applied in all areas of scientific research.
This site provides teachers, students and general readers with a variety of learning resources about evolution. It includes key video clips from NOVA and WGBH's science programs on DVD.
Tree of Life
The Tree of Life, an ancient symbol, represents the interconnectedness of all life. It appears in many religions and cultures as an emblem of unity and love. It also has practical uses, like providing a framework for understanding the history of species and how they respond to changing environmental conditions.
Early approaches to depicting the biological world focused on separating organisms into distinct categories which were distinguished by physical and metabolic characteristics1. These methods rely on the collection of various parts of organisms or fragments of DNA, have greatly increased the diversity of a tree of Life2. However, these trees are largely comprised of eukaryotes, and bacterial diversity remains vastly underrepresented3,4.
By avoiding the necessity for direct experimentation and observation, genetic techniques have enabled us to represent the Tree of Life in a more precise manner. Particularly, molecular methods allow us to build trees using sequenced markers such as the small subunit ribosomal RNA gene.
The Tree of Life has been significantly expanded by genome sequencing. However there is a lot of biodiversity to be discovered. This is especially relevant to microorganisms that are difficult to cultivate and are usually found in one sample5. A recent analysis of all genomes has produced a rough draft of the Tree of Life. click through the following post includes a large number of archaea, bacteria and other organisms that have not yet been isolated or the diversity of which is not fully understood6.
This expanded Tree of Life is particularly beneficial in assessing the biodiversity of an area, which can help to determine if certain habitats require protection. The information is useful in many ways, including finding new drugs, fighting diseases and improving the quality of crops. It is also valuable to conservation efforts. It can help biologists identify areas most likely to have cryptic species, which may perform important metabolic functions, and could be susceptible to the effects of human activity. Although funding to protect biodiversity are essential, ultimately the best way 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 known as an evolutionary tree) shows the relationships between different organisms. Scientists can build an phylogenetic chart which shows the evolutionary relationships between taxonomic groups using molecular data and morphological differences or similarities. The phylogeny of a tree plays an important role in understanding biodiversity, genetics and evolution.
A basic phylogenetic Tree (see Figure PageIndex 10 Determines the relationship between organisms with similar traits and have evolved from a common ancestor. These shared traits are either homologous or analogous. Homologous traits are the same in terms of their evolutionary paths. Analogous traits could appear similar however they do not share the same origins. Scientists combine similar traits into a grouping known as a clade. For example, all of the organisms that make up a clade have the characteristic of having amniotic eggs. They evolved from a common ancestor that had eggs. The clades are then connected to form a phylogenetic branch to identify organisms that have the closest connection to each other.
Scientists make use of DNA or RNA molecular data to build a phylogenetic chart which is more precise and precise. This data is more precise than morphological information and gives evidence of the evolutionary history of an organism or group. The analysis of molecular data can help researchers identify the number of species that share an ancestor common to them and estimate their evolutionary age.
The phylogenetic relationships between species can be affected by a variety of factors, including phenotypic plasticity a type of behavior that changes in response to unique environmental conditions. This can cause a particular trait to appear more similar in one species than other species, which can obscure the phylogenetic signal. This problem can be addressed by using cladistics, which incorporates the combination of analogous and homologous features in the tree.
Furthermore, phylogenetics may help predict the length and speed of speciation. This information can help conservation biologists make decisions about the species they should safeguard from the threat of extinction. In the end, it's the conservation of phylogenetic variety that will lead to an ecosystem that is complete and balanced.
Evolutionary Theory
The central theme in evolution is that organisms change over time as a result of their interactions with their environment. Many theories of evolution have been developed by a variety of scientists, including the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who envisioned an organism developing slowly in accordance with its needs, the Swedish botanist Carolus Linnaeus (1707-1778) who developed the modern hierarchical taxonomy Jean-Baptiste Lamarck (1744-1829) who suggested that use or disuse of traits can cause changes that can be passed on to the offspring.
In the 1930s and 1940s, concepts from a variety of fields -- including genetics, natural selection and particulate inheritance - came together to form the modern synthesis of evolutionary theory that explains how evolution is triggered by the variation of genes within a population, and how those variations change over time as a result of natural selection. This model, called genetic drift or mutation, gene flow and sexual selection, is the foundation of modern evolutionary biology and is mathematically described.
Recent developments in the field of evolutionary developmental biology have demonstrated that variation can be introduced into a species through mutation, genetic drift and reshuffling genes during sexual reproduction, as well as through migration between populations. These processes, along with other ones like directional selection and genetic erosion (changes in the frequency of an individual's genotype over time), can lead to evolution that is defined as change in the genome of the species over time, and also the change in phenotype as time passes (the expression of that genotype within the individual).
Students can better understand the concept of phylogeny by using evolutionary thinking throughout all areas of biology. In a recent study by Grunspan and colleagues. It was found that teaching students about the evidence for evolution boosted their understanding of evolution in a college-level course in biology. For more details on how to teach about evolution look up The Evolutionary Power of Biology in All Areas of Biology or Thinking Evolutionarily as a Framework for Integrating Evolution into Life Sciences Education.
Evolution in Action
Scientists have studied evolution by looking in the past--analyzing fossils and comparing species. They also observe living organisms. Evolution is not a past event; it is an ongoing process. Bacteria mutate and resist antibiotics, viruses evolve and are able to evade new medications and animals change their behavior to a changing planet. The resulting changes are often easy to see.
It wasn't until the late 1980s when biologists began to realize that natural selection was also at work. The key is that various traits confer different rates of survival and reproduction (differential fitness) and can be transferred from one generation to the next.
In the past, if an allele - the genetic sequence that determines color - appeared in a population of organisms that interbred, it might become more common than any other allele. In time, this could mean that the number of moths sporting 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.
It is easier to observe evolutionary change when an organism, like bacteria, has a rapid 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 regularly, and over 50,000 generations have now been observed.
Lenski's research has demonstrated that mutations can alter the rate of change and the rate of a population's reproduction. It also shows evolution takes time, a fact that is difficult for some to accept.
our homepage of microevolution is how mosquito genes that are resistant to pesticides appear more frequently in areas where insecticides are used. This is because pesticides cause an enticement that favors those with resistant genotypes.
The speed at which evolution can take place has led to a growing recognition of its importance in a world shaped by human activity--including climate changes, pollution and the loss of habitats that hinder many species from adjusting. Understanding evolution will assist you in making better choices about the future of our planet and its inhabitants.