The Academy's Evolution Site
Biology is one of the most important concepts in biology. The Academies have been for a long time involved in helping people who are interested in science understand the theory of evolution and how it influences every area of scientific inquiry.
This site provides students, teachers and general readers with a variety of learning resources about evolution. It includes key video clip from NOVA and WGBH produced science programs on DVD.
Tree of Life
The Tree of Life is an ancient symbol of the interconnectedness of life. It is a symbol of love and unity in many cultures. It has many practical applications in addition to providing a framework for understanding the history of species and how they react to changing environmental conditions.
The first attempts to depict the world of biology were founded on categorizing organisms on their metabolic and physical characteristics. These methods, which rely on the sampling of various parts of living organisms or sequences of short DNA fragments, greatly increased the variety of organisms that could be included in the tree of life2. However these trees are mainly made up of eukaryotes. Bacterial diversity remains vastly underrepresented3,4.
By avoiding the necessity for direct observation and experimentation, genetic techniques have enabled us to represent the Tree of Life in a more precise manner. 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 still much diversity to be discovered. This is particularly the case for microorganisms which are difficult to cultivate and are typically found in one sample5. A recent analysis of all genomes resulted in an initial draft of a Tree of Life. This includes a variety of bacteria, archaea and other organisms that have not yet been isolated, or whose diversity has not been well understood6.
This 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. This information can be used in many ways, including finding new drugs, fighting diseases and enhancing crops. This information is also extremely valuable 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 funds to protect biodiversity are important, the best method to preserve the world's biodiversity is to equip more people in developing nations with the necessary knowledge to act locally and support conservation.
Phylogeny
A phylogeny (also called an evolutionary tree) depicts the relationships between different organisms. Using 에볼루션 바카라 체험 and differences in morphology or ontogeny (the course of development of an organism) scientists can create a phylogenetic tree which illustrates the evolution of taxonomic groups. The phylogeny of a tree plays an important role in understanding the relationship between genetics, biodiversity and evolution.
A basic phylogenetic tree (see Figure PageIndex 10 ) is a method of identifying the relationships between organisms with similar traits that have evolved from common ancestral. These shared traits can be either analogous or homologous. Homologous characteristics are identical in their evolutionary journey. Analogous traits could appear like they are, but they do not have the same origins. Scientists organize similar traits into a grouping called a Clade. For example, all of the organisms that make up a clade share the characteristic of having amniotic eggs. They evolved from a common ancestor which had these eggs. A phylogenetic tree is then built by connecting the clades to identify the organisms which are the closest to one another.
For a more precise and accurate phylogenetic tree scientists use molecular data from DNA or RNA to establish the relationships between organisms. This information is more precise than the morphological data and provides evidence of the evolution history of an organism or group. The use of molecular data lets researchers determine the number of organisms that have an ancestor common to them and estimate their evolutionary age.
The phylogenetic relationships of organisms can be affected by a variety of factors, including phenotypic plasticity an aspect of behavior that alters in response to unique environmental conditions. This can cause a characteristic to appear more similar to a species than to the other which can obscure the phylogenetic signal. However, this problem can be cured by the use of methods such as cladistics that combine analogous and homologous features into the tree.
Additionally, phylogenetics aids predict the duration and rate at which speciation occurs. This information can aid conservation biologists in deciding which species to safeguard from extinction. It is ultimately the preservation of phylogenetic diversity which will result in an ecosystem that is complete and balanced.
Evolutionary Theory
The central theme of evolution is that organisms acquire distinct characteristics over time as a result of their interactions with their environments. 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 proposed that a living organism develop gradually 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 non-use of traits can cause changes that could be passed on to offspring.
In the 1930s & 1940s, ideas from different fields, including natural selection, genetics & particulate inheritance, merged to create a modern synthesis of evolution theory. This defines how evolution occurs by the variations in genes within the population and how these variants change over time as a result of natural selection. This model, which incorporates genetic drift, mutations as well as gene flow and sexual selection, can be mathematically described.
Recent advances in the field of evolutionary developmental biology have demonstrated the ways in which variation can be introduced to a species by mutations, genetic drift, reshuffling genes during sexual reproduction, and even migration between populations. These processes, as well as others such as directional selection or genetic erosion (changes in the frequency of the genotype over time), can lead to evolution which is defined by change in the genome of the species over time and the change in phenotype as time passes (the expression of that genotype in the individual).
Students can gain a better understanding of the concept of phylogeny through incorporating evolutionary thinking throughout all aspects of biology. A recent study conducted by Grunspan and colleagues, for instance, showed that teaching about the evidence that supports evolution increased students' acceptance of evolution in a college-level biology class. To learn more about how to teach about evolution, please read The Evolutionary Potential in All Areas of Biology and Thinking Evolutionarily A Framework for Infusing Evolution into Life Sciences Education.
Evolution in Action
Traditionally scientists have studied evolution through looking back--analyzing fossils, comparing species and studying living organisms. Evolution isn't a flims moment; it is a process that continues today. Viruses reinvent themselves to avoid new medications and bacteria mutate to resist antibiotics. Animals adapt their behavior because of the changing environment. The changes that occur are often apparent.
It wasn't until the 1980s that biologists began to realize that natural selection was also in play. The key is the fact that different traits confer a different rate of survival and reproduction, and can be passed down from generation to generation.
In the past, if an allele - the genetic sequence that determines color - was present in a population of organisms that interbred, it could be more common than any other allele. As time passes, that could mean 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 see evolution when an organism, like bacteria, has a high generation turnover. Since 1988, Richard Lenski, a biologist, has tracked twelve populations of E.coli that are descended from one strain. The samples of each population have been taken regularly, and more than 50,000 generations of E.coli have passed.
Lenski's work has shown that mutations can alter the rate at which change occurs and the effectiveness at which a population reproduces. It also shows that evolution takes time--a fact that many find difficult to accept.
Microevolution can be observed in the fact that mosquito genes for resistance to pesticides are more prevalent in populations where insecticides are used. That's because the use of pesticides creates a pressure that favors individuals with 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 climate change, pollution, and habitat loss that prevents many species from adapting. Understanding evolution can help us make better choices about the future of our planet and the lives of its inhabitants.