The Academy's Evolution Site
The concept of biological evolution is a fundamental concept in biology. The Academies are involved in helping those who are interested in science understand evolution theory and how it is permeated throughout all fields of scientific research.
This site provides teachers, students 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.
에볼루션 바카라 체험 of Life
The Tree of Life is an ancient symbol of the interconnectedness of life. It appears in many cultures and spiritual beliefs as an emblem of unity and love. It has many practical applications as well, including providing a framework for understanding the evolution of species and how they respond to changing environmental conditions.
Early attempts to describe the world of biology were based on categorizing organisms based on their physical and metabolic characteristics. These methods, based on sampling of different parts of living organisms or small DNA fragments, greatly increased the variety of organisms that could be represented in the tree of life2. However these trees are mainly comprised of eukaryotes, and bacterial diversity remains vastly underrepresented3,4.
Genetic techniques have significantly expanded our ability to represent the Tree of Life by circumventing the need for direct observation and experimentation. Particularly, molecular techniques allow us to construct trees by using sequenced markers such as the small subunit ribosomal gene.
The Tree of Life has been greatly expanded thanks to genome sequencing. However there is still a lot of diversity to be discovered. This is especially true for microorganisms that are difficult to cultivate, and are typically found in one sample5. Recent analysis of all genomes produced a rough draft of a Tree of Life. This includes a wide range of archaea, bacteria, and other organisms that haven't yet been isolated or whose diversity has not been thoroughly understood6.
This expanded Tree of Life can be used to determine the diversity of a particular area and determine if particular habitats require special protection. This information can be utilized in many ways, including finding new drugs, battling diseases and improving crops. This information is also extremely valuable to conservation efforts. It can aid biologists in identifying areas most likely to have species that are cryptic, which could perform important metabolic functions and are susceptible to changes caused by humans. 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 knowledge they need to act locally and promote conservation.
Phylogeny
A phylogeny, also called an evolutionary tree, shows the relationships between different groups of organisms. Using molecular data as well as morphological similarities and distinctions or ontogeny (the process of the development of an organism), scientists can build a phylogenetic tree that illustrates the evolution of taxonomic categories. Phylogeny plays a crucial role in understanding the relationship between genetics, biodiversity and evolution.
A basic phylogenetic tree (see Figure PageIndex 10 ) determines the relationship between organisms that share similar traits that evolved from common ancestral. These shared traits may be homologous, or analogous. Homologous traits are similar in their evolutionary origins while analogous traits appear similar, but do not share the same origins. Scientists group similar traits into a grouping known as a the clade. For instance, all the organisms that make up a clade share the trait of having amniotic eggs. They evolved from a common ancestor which had eggs. The clades are then connected to form a phylogenetic branch to determine the organisms with the closest relationship.
To create a more thorough and accurate phylogenetic tree, scientists use molecular data from DNA or RNA to establish the relationships between organisms. This data is more precise than morphological information and provides evidence of the evolutionary background of an organism or group. Molecular data allows researchers to determine the number of species who share the same ancestor and estimate their evolutionary age.
The phylogenetic relationships of a species can be affected by a number of factors, including phenotypicplasticity. This is a type of behavior that alters due to particular environmental conditions. This can make a trait appear more similar to one species than another and obscure the phylogenetic signals. This problem can be addressed by using cladistics, which is a an amalgamation of homologous and analogous traits in the tree.
Additionally, phylogenetics aids determine the duration and speed of speciation. This information can assist conservation biologists make decisions about which species to protect from extinction. It is ultimately the preservation of phylogenetic diversity that will create an ecologically balanced and complete ecosystem.
Evolutionary Theory
The fundamental concept in evolution is that organisms change over time due to their interactions with their environment. Many theories of evolution have been proposed by a wide variety 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 designed modern hierarchical taxonomy, and Jean-Baptiste Lamarck (1744-1829) who suggested that the use or non-use of traits causes changes that can be passed on to offspring.
In the 1930s and 1940s, concepts from various fields, such as genetics, natural selection, and particulate inheritance, merged to create a modern synthesis of evolution theory. This explains how evolution happens through the variations in genes within a population and how these variations change with time due to natural selection. This model, known as genetic drift mutation, gene flow, and sexual selection, is a cornerstone of modern evolutionary biology and can be mathematically explained.
Recent developments in the field of evolutionary developmental biology have demonstrated the ways in which variation can be introduced to a species by genetic drift, mutations or reshuffling of genes in sexual reproduction and the movement between populations. These processes, along with others such as directional selection and gene erosion (changes in 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 in individuals).
Students can gain a better understanding of phylogeny by incorporating evolutionary thinking in all areas of biology. A recent study by Grunspan and colleagues, for instance demonstrated that teaching about the evidence supporting evolution helped students accept the concept of evolution in a college-level biology course. For more information about how to teach evolution look up The Evolutionary Potency in all Areas of Biology or Thinking Evolutionarily: a Framework for Integrating Evolution into Life Sciences Education.
Evolution in Action
Scientists have traditionally studied evolution by looking in the past--analyzing fossils and comparing species. They also study living organisms. Evolution is not a distant event, but an ongoing process. Bacteria transform and resist antibiotics, viruses reinvent themselves and elude new medications and animals change their behavior in response to the changing environment. The results are usually evident.
It wasn't until late-1980s that biologists realized that natural selection could be seen in action, as well. The key to this is that different traits result in a different rate of survival and reproduction, and can be passed on from generation to generation.
In the past when one particular allele--the genetic sequence that determines coloration--appeared in a population of interbreeding organisms, it could quickly become more common than other alleles. In time, this could mean the number of black moths within a population could increase. 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 rapid generation turnover such as bacteria. Since 1988, Richard Lenski, a biologist, has studied twelve populations of E.coli that are descended from one strain. Samples from each population were taken regularly, and more than 500.000 generations of E.coli have been observed to have passed.
Lenski's research has revealed that mutations can alter the rate of change and the efficiency at which a population reproduces. It also shows that evolution is slow-moving, a fact that many find hard to accept.
Another example of microevolution is the way mosquito genes for resistance to pesticides appear more frequently in populations where insecticides are used. This is because the use of pesticides causes a selective pressure that favors individuals with resistant genotypes.
The rapid pace at which evolution can take place has led to an increasing appreciation of its importance in a world shaped by human activity, including climate change, pollution, and the loss of habitats which prevent the species from adapting. Understanding the evolution process will help us make better decisions about the future of our planet, and the life of its inhabitants.