The Academy's Evolution Site
Biology is one of the most central concepts in biology. The Academies are committed to helping those interested in science comprehend the evolution theory and how it can be applied throughout all fields of scientific research.
This site provides a range of sources for students, teachers and general readers of evolution. It also includes 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 harmony in a variety of cultures. It has many practical applications as well, including providing a framework for understanding the history of species and how they respond to changing environmental conditions.
The first attempts at depicting the biological world focused on categorizing organisms into distinct categories which had been distinguished by physical and metabolic characteristics1. These methods, which relied on sampling of different parts of living organisms or on sequences of small fragments of their DNA, significantly expanded the diversity that could be included in a tree of life2. However these trees are mainly composed of eukaryotes; bacterial diversity is not represented in a large way3,4.
By avoiding the need for direct experimentation and observation genetic techniques have enabled us to depict the Tree of Life in a much more accurate way. Particularly, 에볼루션 allow us to construct trees using sequenced markers like the small subunit of ribosomal RNA gene.
The Tree of Life has been greatly expanded thanks to genome sequencing. However there is a lot of diversity to be discovered. This is particularly the case for microorganisms which are difficult to cultivate and are typically present in a single sample5. Recent analysis of all genomes produced an initial draft of a Tree of Life. This includes a large number of archaea, bacteria and other organisms that haven't yet been isolated or the diversity of which is not fully understood6.
The expanded Tree of Life can be used to determine the diversity of a specific region and determine if particular habitats require special protection. This information can be used in a variety of ways, including identifying new drugs, combating diseases and improving crops. The information is also valuable for conservation efforts. It helps biologists discover areas that are likely to have cryptic species, which may have vital metabolic functions and be vulnerable to changes caused by humans. While conservation funds are important, the most effective method to preserve the world's biodiversity is to empower more people in developing nations with the knowledge they need to act locally and promote conservation.
Phylogeny
A phylogeny is also known as an evolutionary tree, reveals the connections between various groups of organisms. By using molecular information, morphological similarities and differences, or ontogeny (the process of the development of an organism) scientists can construct a phylogenetic tree that illustrates the evolutionary relationships between taxonomic groups. Phylogeny is essential in understanding biodiversity, evolution and genetics.
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 share their underlying evolutionary path, while analogous traits look similar, but do not share the same origins. Scientists arrange similar traits into a grouping referred to as a clade. Every organism in a group share a trait, such as amniotic egg production. They all came from an ancestor with these eggs. The clades then join to form a phylogenetic branch that can determine which organisms have the closest relationship to.
For a more detailed and accurate phylogenetic tree, scientists make use of molecular data from DNA or RNA to determine the relationships between organisms. This information is more precise and gives evidence of the evolutionary history of an organism. The use of molecular data lets researchers determine the number of species that have an ancestor common to them and estimate their evolutionary age.
The phylogenetic relationship can be affected by a number of factors that include phenotypicplasticity. This is a type of behavior that changes due to particular environmental conditions. This can cause a trait to appear more similar in one species than another, clouding the phylogenetic signal. However, this problem can be solved through the use of methods like cladistics, which incorporate a combination of homologous and analogous features into the tree.
Furthermore, phylogenetics may help predict the time and pace of speciation. This information can assist conservation biologists in deciding which species to safeguard from disappearance. Ultimately, it is the preservation of phylogenetic diversity which will result in an ecosystem that is complete and balanced.
Evolutionary Theory
The fundamental concept of evolution is that organisms develop distinct characteristics over time due to their interactions with their environment. Several theories of evolutionary change have been developed by a wide variety of scientists such as the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who believed that an organism would evolve slowly in accordance with its requirements as well as the Swedish botanist Carolus Linnaeus (1707-1778) who designed modern hierarchical taxonomy, and Jean-Baptiste Lamarck (1744-1829) who suggested that use or disuse of traits causes changes that can be passed onto offspring.
In the 1930s and 1940s, concepts from a variety of fields--including natural selection, genetics, and particulate inheritance--came together to form the modern evolutionary theory synthesis, which defines how evolution occurs through the variation of genes within a population, and how these variants change in time as a result of natural selection. This model, which encompasses mutations, genetic drift, gene flow and sexual selection can be mathematically described.
Recent discoveries in the field of evolutionary developmental biology have demonstrated that genetic variation can be introduced into a species by genetic drift, mutation, and reshuffling of genes during sexual reproduction, and also through the movement of populations. These processes, in conjunction with others, such as directionally-selected selection and erosion of genes (changes to the frequency of genotypes over time), can lead towards evolution. Evolution is defined by changes in the genome over time and changes in the phenotype (the expression of genotypes in individuals).
Students can better understand the concept of phylogeny by using evolutionary thinking in all areas of biology. In a recent study conducted by Grunspan and colleagues. It was demonstrated that teaching students about the evidence for evolution increased their understanding of evolution in the course of a college biology. To find out more about how to teach about evolution, see The Evolutionary Potential in All Areas of Biology and Thinking Evolutionarily A Framework for Infusing the Concept of Evolution into Life Sciences Education.
Evolution in Action
Scientists have looked at evolution through the past, studying fossils, and comparing species. They also observe living organisms. Evolution is not a past event; it is an ongoing process. Viruses reinvent themselves to avoid new drugs and bacteria evolve to resist antibiotics. Animals adapt their behavior in the wake of the changing environment. The changes that result are often visible.
It wasn't until the late 1980s that biologists began to realize that natural selection was also in action. The key to this is that different traits result in a different rate of survival and reproduction, and they can be passed down from generation to generation.
In the past, if a certain allele - the genetic sequence that determines colour - was found in a group of organisms that interbred, it could be more common than other allele. In time, this could mean that the number of moths that have black pigmentation in a group may increase. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
It is easier to observe evolutionary change when an organism, like bacteria, has a high generation turnover. Since 1988 biologist Richard Lenski has been tracking twelve populations of E. Coli that descended from a single strain. samples of each population are taken on a regular basis and over fifty thousand generations have passed.
Lenski's research has shown that mutations can drastically alter the speed at the rate at which a population reproduces, and consequently the rate at which it alters. It also demonstrates that evolution takes time, a fact that some people are unable to accept.
Another example of microevolution is how mosquito genes for resistance to pesticides are more prevalent in populations where insecticides are used. That's because the use of pesticides causes a selective pressure that favors individuals with resistant genotypes.
The rapid pace of evolution taking place has led to a growing recognition of its importance in a world shaped by human activities, including climate change, pollution, and the loss of habitats that prevent the species from adapting. Understanding evolution will help us make better decisions about the future of our planet, and the lives of its inhabitants.