The Academy's Evolution Site
Biology is a key concept in biology. The Academies have been for a long time involved in helping people who are interested in science understand the concept of evolution and how it affects all areas of scientific research.
This site provides students, teachers and general readers with a range of learning resources about evolution. It contains key video clips from NOVA and WGBH produced science programs on DVD.
Tree of Life
The Tree of Life is an ancient symbol that symbolizes the interconnectedness of all life. It is seen in a variety of religions and cultures as an emblem of unity and love. It also has many practical applications, like providing a framework to understand the evolution of species and how they react to changes in the environment.
Early attempts to represent the biological world were founded on categorizing organisms on their metabolic and physical characteristics. These methods, which relied on the sampling of various parts of living organisms, or sequences of small fragments of their DNA greatly increased the variety of organisms that could be represented in 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 depict 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.
Despite the massive expansion of the Tree of Life through genome sequencing, much biodiversity still is waiting to be discovered. This is particularly true for microorganisms that are difficult to cultivate and are typically found in a single specimen5. Recent analysis of all genomes has produced an unfinished draft of a Tree of Life. This includes a wide range of bacteria, archaea 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 useful in assessing the diversity of an area, assisting to determine if specific habitats require special protection. This information can be used in a variety of ways, such as finding new drugs, fighting diseases and improving crops. It is also beneficial to 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 funds to protect biodiversity are important, the most effective way to conserve the biodiversity of the world is to equip more people in developing countries with the knowledge they need to act locally and promote conservation.
Phylogeny
A phylogeny, also known as an evolutionary tree, illustrates the relationships between different groups of 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 groups. The phylogeny of a tree plays an important role in understanding genetics, biodiversity and evolution.
A basic phylogenetic tree (see Figure PageIndex 10 Identifies the relationships between organisms that have similar traits and have evolved from a common ancestor. These shared traits could be either analogous or homologous. Homologous traits are identical in their evolutionary origins and analogous traits appear similar, but do not share the identical origins. Scientists put similar traits into a grouping called a clade. All organisms in a group have a common characteristic, like amniotic egg production. They all evolved from an ancestor with these eggs. 에볼루션 무료 바카라 are then connected to form a phylogenetic branch that can determine the organisms with the closest relationship.
To create a more thorough and precise phylogenetic tree scientists make use of molecular data from DNA or RNA to determine the relationships between organisms. This data is more precise than the morphological data and gives evidence of the evolutionary background of an organism or group. Molecular data allows researchers to determine the number of organisms that have the same ancestor and 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 characteristic to appear more similar to one species than another which can obscure the phylogenetic signal. This problem can be mitigated by using cladistics, which is a a combination of homologous and analogous traits in the tree.
Additionally, phylogenetics aids determine the duration and speed at which speciation takes place. This information can assist conservation biologists make decisions about the species they should safeguard from the threat of extinction. In the end, it is the preservation of phylogenetic diversity that will result in an ecosystem that is complete and balanced.
Evolutionary Theory
The central theme in evolution is that organisms change over time due to their interactions with their environment. A variety of theories about evolution have been proposed by a wide range of scientists including the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who believed that an organism would evolve slowly according to its requirements and needs, the Swedish botanist Carolus Linnaeus (1707-1778) who developed the modern hierarchical taxonomy, as well as Jean-Baptiste Lamarck (1744-1829) who suggested that the use or misuse of traits causes changes that can be passed onto offspring.
In the 1930s and 1940s, ideas from a variety of fields--including genetics, natural selection and particulate inheritance - came together to form the current evolutionary theory, which defines how evolution is triggered by the variations of genes within a population and how these variants change in time as a result of natural selection. This model, called genetic drift or mutation, gene flow and sexual selection, is the foundation of current evolutionary biology, and can be mathematically described.
Recent discoveries in the field of evolutionary developmental biology have demonstrated how variations can be introduced to a species through genetic drift, mutations, reshuffling genes during sexual reproduction and the movement 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 result in evolution which is defined by changes in the genome of the species over time, and the change in phenotype over time (the expression of the genotype within the 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 instance demonstrated that teaching about the evidence for evolution increased students' acceptance of evolution in a college-level biology course. For more information on how to teach about evolution, please see The Evolutionary Potential in All Areas of Biology and Thinking Evolutionarily A Framework for Infusing Evolution in Life Sciences Education.
Evolution in Action
Scientists have traditionally looked at evolution through the past--analyzing fossils and comparing species. They also observe living organisms. Evolution is not a distant event; it is an ongoing process. Bacteria evolve and resist antibiotics, viruses evolve and are able to evade new medications and animals alter their behavior in response to a changing planet. The changes that result are often evident.
However, it wasn't until late 1980s that biologists understood that natural selection could be seen in action, as well. The main reason is that different traits result in an individual rate of survival as well as reproduction, and may be passed down from one generation to another.
In the past, if one allele - the genetic sequence that determines colour - was found in a group of organisms that interbred, it could be more prevalent than any other allele. Over time, this would mean that the number of moths with black pigmentation may increase. Read Significantly more is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
The ability to observe evolutionary change is much easier when a species has a rapid generation turnover like bacteria. Since 1988, Richard Lenski, a biologist, has been tracking twelve populations of E.coli that descend from one strain. Samples from each population have been collected regularly, and more than 50,000 generations of E.coli have passed.
Lenski's research has revealed that mutations can alter the rate of change and the effectiveness at which a population reproduces. It also demonstrates that evolution takes time, a fact that some people find hard to accept.
Microevolution can also be seen in the fact that mosquito genes for pesticide resistance are more prevalent in areas where insecticides have been used. This is due to pesticides causing an enticement that favors individuals who have resistant genotypes.
The speed at which evolution takes place has led to an increasing awareness of its significance in a world that is shaped by human activity, including climate change, pollution, and the loss of habitats which prevent many species from adjusting. Understanding the evolution process can help us make better choices about the future of our planet, and the life of its inhabitants.