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 affects all areas of scientific exploration.
This site provides a wide range of sources for teachers, students as well as general readers about evolution. 에볼루션 사이트 includes important video clips from NOVA and WGBH's science programs on DVD.
Tree of Life
The Tree of Life, an ancient symbol, symbolizes the interconnectedness of all life. It appears in many cultures and spiritual beliefs as a symbol of unity and love. It also has practical uses, like providing a framework to understand the evolution of species and how they react to changes in environmental conditions.
Early attempts to describe the world of biology 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 fragments of their DNA significantly increased the variety that could be represented in a tree of life2. The trees are mostly composed by eukaryotes and bacterial diversity is vastly underrepresented3,4.
Genetic techniques have greatly expanded our ability to visualize the Tree of Life by circumventing the need for direct observation and experimentation. We can construct trees using molecular methods, such as the small-subunit ribosomal gene.
Despite the rapid growth of the Tree of Life through genome sequencing, much biodiversity still remains to be discovered. This is particularly true for microorganisms, which can be difficult to cultivate and are typically only present in a single specimen5. Recent analysis of all genomes produced an unfinished draft of a Tree of Life. This includes a variety of bacteria, archaea and other organisms that haven't yet been isolated or the diversity of which is not well understood6.
This expanded Tree of Life can be used to evaluate the biodiversity of a specific area and determine if certain habitats need special protection. The information is useful in many ways, including finding new drugs, battling diseases and improving the quality of crops. It is also useful to conservation efforts. It can help biologists identify the areas most likely to contain cryptic species with potentially significant metabolic functions that could be at risk from anthropogenic change. While conservation funds are important, the most effective method to preserve the biodiversity of the world is to equip more people in developing nations with the necessary knowledge to act locally and support conservation.
Phylogeny
A phylogeny (also known as an evolutionary tree) depicts the relationships between organisms. Using molecular data, morphological similarities and differences or ontogeny (the process of the development of an organism), scientists can build an phylogenetic tree that demonstrates the evolutionary relationships between taxonomic categories. The role of phylogeny is crucial in understanding the relationship between genetics, biodiversity and evolution.
A basic phylogenetic tree (see Figure PageIndex 10 Identifies the relationships between organisms with similar traits and have evolved from an ancestor with common traits. These shared traits may be analogous, or homologous. Homologous characteristics are identical in their evolutionary journey. Analogous traits might appear similar but they don't have the same ancestry. Scientists group similar traits into a grouping called a clade. Every organism in a group have a common characteristic, like amniotic egg production. They all evolved from an ancestor who had these eggs. The clades are then connected to form a phylogenetic branch to identify organisms that have the closest connection to each other.
To create a more thorough and accurate phylogenetic tree, scientists rely on molecular information from DNA or RNA to establish the relationships among organisms. This information is more precise than morphological data and gives evidence of the evolutionary history of an organism or group. The use of molecular data lets researchers identify the number of organisms who share an ancestor common to them and estimate their evolutionary age.
The phylogenetic relationships between species can be affected by a variety of factors, including phenotypic plasticity a type of behavior that changes in response to specific environmental conditions. This can cause a characteristic to appear more resembling to one species than to another which can obscure the phylogenetic signal. This problem can be addressed by using cladistics, which is a the combination of analogous and homologous features in the tree.
Furthermore, phylogenetics may help predict the length and speed of speciation. This information can help conservation biologists make decisions about which species they should protect from extinction. In the end, it's the preservation of phylogenetic diversity which will lead to an ecologically balanced and complete ecosystem.
Evolutionary Theory
The central theme of evolution is that organisms acquire distinct characteristics over time based on their interactions with their surroundings. Several theories of evolutionary change have been developed 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 needs and needs, the Swedish botanist Carolus Linnaeus (1707-1778) who conceived the modern hierarchical taxonomy 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, theories from various fields, including natural selection, genetics, and particulate inheritance - came together to create the modern synthesis of evolutionary theory that explains how evolution happens through the variation of genes within a population, and how those variations change in time due to natural selection. This model, which includes genetic drift, mutations, gene flow and sexual selection, can be mathematically described.
Recent discoveries in the field of evolutionary developmental biology have demonstrated the ways in which variation can be introduced to a species through mutations, genetic drift or reshuffling of genes in sexual reproduction and the movement between populations. These processes, as well as others, such as directionally-selected selection and erosion of genes (changes in the frequency of genotypes over time), can lead towards evolution. Evolution is defined by changes in the genome over time and changes in phenotype (the expression of genotypes within individuals).
Incorporating evolutionary thinking into all areas of biology education could increase student understanding of the concepts of phylogeny as well as evolution. A recent study conducted by Grunspan and colleagues, for example revealed that teaching students about the evidence supporting evolution increased students' acceptance of evolution in a college-level biology class. For more details about how to teach evolution, see 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, studying fossils, comparing species, and studying living organisms. Evolution is not a distant event, but a process that continues today. Bacteria evolve and resist antibiotics, viruses re-invent themselves and are able to evade new medications, and animals adapt their behavior in response to the changing environment. The changes that result are often apparent.
However, it wasn't until late 1980s that biologists realized that natural selection could be observed in action as well. The reason is that different traits confer different rates of survival and reproduction (differential fitness), and can be passed down from one generation to the next.
In the past when 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. Over time, that would mean that the number of black moths within a particular population could rise. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
Monitoring evolutionary changes in action is easier when a particular species has a fast generation turnover, as with bacteria. Since 1988, Richard Lenski, a biologist, has studied twelve populations of E.coli that are descended from one strain. The samples of each population were taken frequently and more than 500.000 generations of E.coli have passed.
Lenski's research has revealed that mutations can drastically alter the rate at the rate at which a population reproduces, and consequently, the rate at which it evolves. It also shows that evolution takes time, a fact that is hard for some to accept.
Microevolution can be observed in the fact that mosquito genes for pesticide resistance are more prevalent in areas that have used insecticides. This is because pesticides cause an exclusive pressure that favors individuals who have resistant genotypes.
The rapidity of evolution has led to a greater recognition of its importance especially in a planet shaped largely by human activity. This includes climate change, pollution, and habitat loss that hinders many species from adapting. Understanding evolution will help us make better decisions regarding the future of our planet as well as the lives of its inhabitants.