The Academy's Evolution Site
Biological evolution is one of the most central concepts in biology. The Academies have been for a long time involved in helping those interested in science understand the concept of evolution and how it affects all areas of scientific exploration.
This site provides a wide range of sources for students, teachers and general readers of evolution. 무료에볼루션 contains important video clips from NOVA and WGBH-produced science programs on DVD.
Tree of Life
The Tree of Life, an ancient symbol, symbolizes the interconnectedness of all life. It is a symbol of love and unity across many cultures. It also has important practical applications, like providing a framework to understand the history of species and how they respond to changes in environmental conditions.
The earliest attempts to depict the biological world focused on categorizing organisms into distinct categories which were distinguished by physical and metabolic characteristics1. These methods, which rely on the sampling of different parts of living organisms or small fragments of their DNA, significantly expanded the diversity that could be included in the tree of life2. The trees are mostly composed by eukaryotes and bacteria are largely underrepresented3,4.
Genetic techniques have greatly expanded our ability to depict the Tree of Life by circumventing the need for direct observation and experimentation. We can construct trees using molecular methods like the small-subunit ribosomal gene.
The Tree of Life has been dramatically expanded through genome sequencing. However, there is still much diversity to be discovered. This is particularly relevant to microorganisms that are difficult to cultivate and which are usually only present in a single sample5. A recent analysis of all genomes known to date has created a rough draft of the Tree of Life, including many archaea and bacteria that are not isolated and which are not well understood.
This expanded Tree of Life can be used to evaluate the biodiversity of a specific region and determine if specific habitats require special protection. This information can be used in a variety of ways, including finding new drugs, fighting diseases and improving the quality of crops. The information is also incredibly beneficial to conservation efforts. It helps biologists determine those areas that are most likely contain cryptic species with potentially important metabolic functions that could be at risk from anthropogenic change. While conservation funds are essential, the best method to protect the biodiversity of the world is to equip the people of developing nations with the information they require to act locally and promote conservation.
Phylogeny
A phylogeny (also known as an evolutionary tree) shows the relationships between species. Using molecular data as well as morphological similarities and distinctions, or ontogeny (the process of the development of an organism) scientists can construct a phylogenetic tree which illustrates the evolutionary relationship between taxonomic categories. 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 Identifies the relationships between organisms that have similar traits and evolved from an ancestor with common traits. These shared traits may be analogous, or homologous. Homologous traits are similar in terms of their evolutionary paths. Analogous traits might appear similar however they do not have the same ancestry. Scientists group similar traits into a grouping called a Clade. For example, all of the species in a clade have the characteristic of having amniotic eggs and evolved from a common ancestor which had eggs. The clades are then linked to create a phylogenetic tree to determine which organisms have the closest relationship to.
Scientists utilize DNA or RNA molecular data to build a phylogenetic chart that is more accurate and precise. This information is more precise and provides evidence of the evolutionary history of an organism. Molecular data allows researchers to determine the number of organisms who share an ancestor common to them and estimate their evolutionary age.
The phylogenetic relationships between organisms can be influenced by several factors, including phenotypic flexibility, 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 another, obscuring the phylogenetic signal. This problem can be addressed by using cladistics, which is a an amalgamation of homologous and analogous traits in the tree.
Furthermore, phylogenetics may aid in predicting the duration and rate of speciation. This information will assist conservation biologists in deciding which species to safeguard from the threat of extinction. In the end, it is the preservation of phylogenetic diversity that will result in an ecosystem that is balanced and complete.
Evolutionary Theory
The central theme of evolution is that organisms acquire various characteristics over time based on 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 proposed that a living organism develop gradually according to its requirements, the Swedish botanist Carolus Linnaeus (1707-1778) who developed modern hierarchical taxonomy, and Jean-Baptiste Lamarck (1744-1829) who suggested that the use or non-use of traits can cause changes that could be passed on to the offspring.
In the 1930s and 1940s, concepts from various areas, including genetics, natural selection and particulate inheritance, merged to form a modern synthesis of evolution theory. This describes how evolution is triggered by the variation of genes in the population and how these variations change with time due to natural selection. This model, which includes mutations, genetic drift, gene flow and sexual selection can be mathematically described.
Recent discoveries in the field of evolutionary developmental biology have revealed that variations can be introduced into a species via genetic drift, mutation, and reshuffling genes during sexual reproduction, as well as by migration between populations. These processes, as well as other ones like the directional selection process and the erosion of genes (changes to the frequency of genotypes over time) can result in evolution. Evolution is defined by changes in the genome over time and changes in the phenotype (the expression of genotypes in an individual).
Students can gain a better understanding of the concept of phylogeny through incorporating evolutionary thinking into all aspects of biology. In a study by Grunspan et al. It was found that teaching students about the evidence for evolution increased their acceptance of evolution during a college-level course in biology. For more details about how to teach evolution look up The Evolutionary Potency in All Areas of Biology or Thinking Evolutionarily as 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 observing living organisms. But evolution isn't just something that happened in the past; it's an ongoing process, happening right now. Bacteria transform and resist antibiotics, viruses re-invent themselves and elude new medications and animals change their behavior to the changing environment. The results are often visible.
It wasn't until the 1980s that biologists began realize that natural selection was also in play. The key is that various traits confer different rates of survival and reproduction (differential fitness) and are transferred from one generation to the next.
In the past, if one particular allele--the genetic sequence that determines coloration--appeared in a population of interbreeding species, it could rapidly become more common than other alleles. As time passes, this could mean that the number of moths sporting black pigmentation in a population could increase. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
Observing evolutionary change in action is much easier when a species has a rapid turnover of its generation, as with bacteria. Since 1988, Richard Lenski, a biologist, has been tracking twelve populations of E.coli that descend from a single strain. Samples from each population have been collected regularly and more than 50,000 generations of E.coli have passed.
Lenski's work has demonstrated that mutations can drastically alter the efficiency with which a population reproduces--and so the rate at which it evolves. It also demonstrates that evolution is slow-moving, a fact that some are unable to accept.
Microevolution is also evident in the fact that mosquito genes that confer resistance to pesticides are more common in populations where insecticides are used. This is because the use of pesticides causes a selective pressure that favors those 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 prevents many species from adapting. Understanding the evolution process can help us make better decisions regarding the future of our planet as well as the lives of its inhabitants.