The Academy's Evolution Site
The concept of biological evolution is a fundamental concept in biology. The Academies are committed to helping those interested in the sciences understand evolution theory and how it is incorporated in all areas of scientific research.
This site provides students, teachers and general readers with a wide range of learning resources on evolution. It includes important video clips from NOVA and WGBH's science programs on DVD.
Tree of Life
The Tree of Life is an ancient symbol that symbolizes the interconnectedness of life. It is seen in a variety of spiritual traditions and cultures as symbolizing unity and love. It has many practical applications as well, including providing a framework to understand the evolution of species and how they respond to changing environmental conditions.
Early attempts to represent the biological world were founded on categorizing organisms on their physical and metabolic characteristics. These methods, which rely on the sampling of different parts of living organisms or on short DNA fragments, greatly increased the variety of organisms that could be represented in the tree of life2. These trees are mostly populated by eukaryotes and the diversity of bacterial species is greatly underrepresented3,4.
Genetic techniques have greatly broadened our ability to visualize the Tree of Life by circumventing the requirement for direct observation and experimentation. We can construct trees using molecular techniques such as the small subunit ribosomal gene.
Despite the dramatic expansion of the Tree of Life through genome sequencing, a large amount of biodiversity awaits discovery. This is especially the case for microorganisms which are difficult to cultivate, and which are usually only present in a single sample5. A recent analysis of all known genomes has produced a rough draft version of the Tree of Life, including a large number of archaea and bacteria that have not been isolated, and whose diversity is poorly understood6.
This expanded Tree of Life is particularly useful for assessing the biodiversity of an area, helping to determine if specific habitats require special protection. This information can be used in a variety of ways, such as identifying new drugs, combating diseases and improving the quality of crops. The information is also incredibly valuable to conservation efforts. It can aid biologists in identifying the areas that are most likely to contain cryptic species with potentially important metabolic functions that may 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 the people of developing nations with the information they require to take action locally and encourage conservation.
Phylogeny
A phylogeny, also called an evolutionary tree, shows the connections between various groups of organisms. Using molecular data similarities 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 categories. 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 that share similar traits that have evolved from common ancestors. These shared traits can be either analogous or homologous. Homologous traits are similar in their evolutionary roots, while analogous traits look like they do, but don't have the same origins. Scientists organize similar traits into a grouping called a the clade. All members of a clade share a characteristic, like amniotic egg production. They all came from an ancestor that had these eggs. A phylogenetic tree is then built by connecting the clades to identify the species that are most closely related to one another.
For a more detailed and accurate phylogenetic tree, scientists rely on molecular information from DNA or RNA to determine the relationships between organisms. This information is more precise and gives evidence of the evolution history of an organism. Researchers can utilize Molecular Data to estimate the age of evolution of living organisms and discover how many species have a common ancestor.
The phylogenetic relationships between species can be influenced by several factors, including phenotypic plasticity a type of behavior that changes in response to specific environmental conditions. This can cause a characteristic to appear more similar to one species than to the other and obscure the phylogenetic signals. This problem can be addressed by using cladistics, which is a the combination of homologous and analogous features in the tree.
Additionally, phylogenetics can help determine the duration and rate at which speciation occurs. This information can help conservation biologists decide which species to protect from the threat of extinction. In the end, it is the conservation of phylogenetic diversity that will lead to an ecosystem that is complete and balanced.
Evolutionary Theory
The main idea behind evolution is that organisms acquire various characteristics over time based on their interactions with their surroundings. Many theories of evolution have been proposed by a 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, the Swedish botanist Carolus Linnaeus (1707-1778) who conceived modern hierarchical taxonomy, and Jean-Baptiste Lamarck (1744-1829) who suggested that use or disuse of traits cause changes that can be passed onto offspring.
In the 1930s and 1940s, concepts from various fields, such as genetics, natural selection, and particulate inheritance, were brought together to form a contemporary theorizing of evolution. This describes how evolution occurs by the variation in genes within a population and how these variants change over time as a result of natural selection. This model, which incorporates genetic drift, mutations, gene flow and sexual selection, can be mathematically described.
Recent developments in the field of evolutionary developmental biology have revealed the ways in which variation can be introduced to a species by genetic drift, mutations and reshuffling of genes during sexual reproduction, and even migration between populations. These processes, as well as others, such as directional selection and gene erosion (changes in the frequency of genotypes over time) can lead to evolution. Evolution is defined by changes in the genome over time, as well as changes in phenotype (the expression of genotypes within individuals).
Incorporating evolutionary thinking into all aspects of biology education can improve students' understanding of phylogeny and evolutionary. A recent study by Grunspan and colleagues, for example revealed that teaching students about the evidence that supports evolution increased students' acceptance of evolution in a college biology class. For more details about how to teach evolution read The Evolutionary Potential in all Areas of Biology or Thinking Evolutionarily A Framework for Integrating Evolution into Life Sciences Education.
Evolution in Action
Traditionally scientists have studied evolution through looking back, studying fossils, comparing species, and studying living organisms. Evolution is not a distant event, but an ongoing process that continues to be observed today. 에볼루션 사이트 transform and resist antibiotics, viruses re-invent themselves and elude new medications and animals alter their behavior in response to the changing environment. The changes that result are often apparent.
It wasn't until the 1980s that biologists began realize that natural selection was also at work. The main reason is that different traits confer the ability to survive at different rates as well as reproduction, and may be passed on from one generation to another.
In the past, if one particular allele - the genetic sequence that determines coloration--appeared in a group of interbreeding species, it could quickly become more prevalent than other alleles. Over time, this would mean that the number of moths that have 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.
The ability to observe evolutionary change is much easier when a species has a rapid turnover of its generation, as with bacteria. Since 1988, Richard Lenski, a biologist, has tracked twelve populations of E.coli that are descended from a single strain. The samples of each population have been taken regularly, and more than 500.000 generations of E.coli have passed.
Lenski's research has revealed that a mutation can dramatically alter the speed at which a population reproduces--and so, the rate at which it evolves. It also demonstrates that evolution takes time, a fact that some people find hard to accept.
Another example of microevolution is 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 people with resistant genotypes.
The rapidity of evolution has led to a growing appreciation of its importance, especially in a world that is largely shaped by human activity. This includes the effects of climate change, pollution and habitat loss that prevents many species from adapting. Understanding evolution can assist you in making better choices about the future of our planet and its inhabitants.