The Academy's Evolution Site
The concept of biological evolution is a fundamental concept in biology. The Academies have long been involved in helping those interested in science understand the theory of evolution and how it influences all areas of scientific research.
This site provides teachers, students and general readers with a range of learning re sources on evolution. It also includes important video clips from NOVA and WGBH produced science programs on DVD.
Tree of Life
The Tree of Life, an ancient symbol, represents the interconnectedness of all life. It appears in many cultures and spiritual beliefs as a symbol of unity and love. It has many practical applications as well, such as providing a framework for understanding the history of species, and how they react to changes in environmental conditions.
The first attempts to depict the biological world were built on categorizing organisms based on their physical and metabolic characteristics. These methods, based on the sampling of various parts of living organisms or on sequences of short fragments of their DNA, significantly expanded the diversity that could be included in a tree of life2. However, these trees are largely comprised of eukaryotes, and bacterial diversity is not represented in a large way3,4.
In avoiding the necessity of direct observation and experimentation genetic techniques have made it possible to depict the Tree of Life in a much more accurate way. Trees can be constructed using molecular techniques like the small-subunit ribosomal 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 particularly true of microorganisms, which can be difficult to cultivate and are typically only represented in a single sample5. A recent study of all genomes that are known has created a rough draft of the Tree of Life, including numerous bacteria and archaea that have not been isolated and whose diversity is poorly understood6.
The expanded Tree of Life is particularly useful in assessing the diversity of an area, which can help to determine whether specific habitats require special protection. The information can be used in a variety of ways, from identifying the most effective medicines to combating disease to enhancing crops. This information is also extremely valuable for conservation efforts. It can help biologists identify those areas that are most likely contain cryptic species with significant metabolic functions that could be at risk of anthropogenic changes. While funding to protect biodiversity are important, the most effective way to conserve the world's biodiversity is to equip more people in developing countries with the necessary knowledge to act locally and support conservation.
Phylogeny
A phylogeny (also called an evolutionary tree) depicts the relationships between organisms. By using molecular information similarities and differences in morphology or ontogeny (the course of development of an organism) scientists can construct a phylogenetic tree that illustrates the evolutionary relationships between taxonomic groups. The role of phylogeny is crucial in understanding biodiversity, genetics and evolution.
A basic phylogenetic tree (see Figure PageIndex 10 Identifies the relationships between organisms with similar traits and have evolved from an ancestor that shared traits. These shared traits can be either homologous or analogous. Homologous traits share their evolutionary origins while analogous traits appear like they do, but don't have the same origins. 에볼루션카지노 organize similar traits into a grouping known as a the clade. All members of a clade have a common characteristic, like amniotic egg production. They all derived from an ancestor that had these eggs. A phylogenetic tree is constructed by connecting the clades to identify the organisms which are the closest to each other.
Scientists make use of DNA or RNA molecular information to construct a phylogenetic graph that is more accurate and precise. This information is more precise and gives evidence of the evolution of an organism. Molecular data allows researchers to identify the number of species who share a common ancestor and to estimate their evolutionary age.
The phylogenetic relationships between organisms can be influenced by several factors, including phenotypic flexibility, a kind of behavior that alters in response to unique environmental conditions. This can cause a particular trait to appear more like a species another, clouding the phylogenetic signal. However, this problem can be solved through the use of methods such as cladistics which combine analogous and homologous features into the tree.
In addition, phylogenetics can help predict the time and pace of speciation. This information can aid conservation biologists to make decisions about the species they should safeguard from the threat of extinction. Ultimately, it is the preservation of phylogenetic diversity that will result in a complete and balanced ecosystem.
Evolutionary Theory
The main idea behind evolution is that organisms change over time as a result of their interactions with their environment. Several theories of evolutionary change have been developed by a wide variety of scientists, including the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who proposed that a living organism develop gradually according to its needs as well as the Swedish botanist Carolus Linnaeus (1707-1778) who conceived the modern hierarchical taxonomy, as well as Jean-Baptiste Lamarck (1744-1829) who suggested that the use or misuse of traits can cause changes that could be passed on to offspring.
In the 1930s and 1940s, concepts from various fields, such as genetics, natural selection and particulate inheritance, came together to form a modern evolutionary theory. This describes how evolution is triggered by the variations in genes within a population and how these variations alter over time due to natural selection. This model, known as genetic drift mutation, gene flow, and sexual selection, is the foundation of current evolutionary biology, and is mathematically described.
Recent developments in the field of evolutionary developmental biology have shown that genetic variation can be introduced into a species via genetic drift, mutation, and reshuffling of genes during sexual reproduction, as well as by migration between populations. These processes, along with other ones like directional selection and genetic erosion (changes in the frequency of the 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 the genotype in the individual).
Students can gain a better understanding of phylogeny by incorporating evolutionary thinking in all aspects of biology. In a study by Grunspan et al. It was found that teaching students about the evidence for evolution increased their understanding of evolution in an undergraduate biology course. To learn more about how to teach about evolution, read The Evolutionary Potential of All Areas of Biology and Thinking Evolutionarily: A Framework for Infusing Evolution into Life Sciences Education.
Evolution in Action
Traditionally scientists have studied evolution by looking back--analyzing fossils, comparing species, and studying living organisms. But evolution isn't just something that happened in the past; it's an ongoing process happening right now. Bacteria evolve and resist antibiotics, viruses evolve and are able to evade new medications and animals alter their behavior to the changing environment. The changes that occur are often apparent.
It wasn't until late 1980s that biologists understood that natural selection could be seen in action, as well. The reason is that different traits confer different rates of survival and reproduction (differential fitness) and can be transferred from one generation to the next.
In the past, if a certain allele - the genetic sequence that determines color - appeared in a population of organisms that interbred, it could become more prevalent than any other allele. As time passes, this could mean that the number of moths sporting black pigmentation in a group may 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 biologist Richard Lenski has been tracking twelve populations of E. bacteria that descend from a single strain; samples from each population are taken regularly, and over fifty thousand generations have been observed.
Lenski's research has shown that a mutation can dramatically alter the efficiency with which a population reproduces and, consequently the rate at which it alters. It also demonstrates that evolution takes time, something that is difficult for some to accept.
Microevolution can be observed in the fact that mosquito genes for pesticide resistance are more prevalent in areas where insecticides are used. This is due to the fact that the use of pesticides causes a selective pressure that favors individuals with resistant genotypes.
The rapidity of evolution has led to an increasing recognition of its importance, especially in a world shaped largely by human activity. 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 smarter decisions about the future of our planet as well as the life of its inhabitants.