The Academy's Evolution Site
The concept of biological evolution is a fundamental concept in biology. The Academies are committed to helping those who are interested in the sciences comprehend the evolution theory and how it is permeated across all areas of scientific research.
This site provides teachers, students and general readers with a wide range of learning resources on evolution. It has important video clips from NOVA and the WGBH-produced science programs on DVD.
Tree of Life
The Tree of Life is an ancient symbol of the interconnectedness of life. It is a symbol of love and harmony in a variety of cultures. It has many practical applications in addition to 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 based on categorizing organisms based on their metabolic and physical characteristics. These methods, which relied on sampling of different parts of living organisms or on short fragments of their DNA significantly increased the variety that could be included in the tree of life2. However the trees are mostly composed of eukaryotes; bacterial diversity is still largely unrepresented3,4.
By avoiding the need for direct experimentation and observation genetic techniques have allowed us to depict the Tree of Life in a much more accurate way. Particularly, molecular methods allow us to construct trees by using sequenced markers such as the small subunit of ribosomal RNA gene.
Despite the rapid growth of the Tree of Life through genome sequencing, a large amount of biodiversity is waiting to be discovered. This is particularly true of microorganisms, which can be difficult to cultivate and are typically only represented in a single sample5. A recent analysis of all known genomes has created a rough draft of the Tree of Life, including a large number of bacteria and archaea that have not been isolated, and which are not well understood.
This expanded Tree of Life is particularly beneficial in assessing the biodiversity of an area, which can help to determine whether specific habitats require special protection. This information can be utilized in a range of ways, from identifying new remedies to fight diseases to enhancing the quality of the quality of crops. The information is also incredibly useful in conservation efforts. It helps biologists determine the areas that are most likely to contain cryptic species that could have significant metabolic functions that could be at risk of anthropogenic changes. Although funding to safeguard biodiversity are vital but the most effective way to preserve the world's biodiversity is for more people in developing countries to be equipped with the knowledge to act locally in order to promote conservation from within.
Phylogeny
A phylogeny (also called an evolutionary tree) illustrates the relationship between organisms. Scientists can construct a phylogenetic diagram that illustrates the evolution of taxonomic groups based on molecular data and morphological differences or similarities. 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 with similar traits and have evolved from an ancestor that shared traits. These shared traits are either homologous or analogous. Homologous traits share their evolutionary roots and analogous traits appear similar, but do not share the identical origins. Scientists group similar traits together into a grouping known as a the clade. All organisms in a group share a characteristic, like amniotic egg production. They all came from an ancestor that had these eggs. A phylogenetic tree is constructed by connecting clades to identify the species that are most closely related to each other.
For a more detailed and precise phylogenetic tree scientists use molecular data from DNA or RNA to identify the relationships among organisms. This information is more precise than morphological information and provides evidence of the evolution history of an organism or group. The use of molecular data lets researchers identify the number of organisms that have an ancestor common to them and estimate their evolutionary age.
The phylogenetic relationships of organisms can be affected by a variety of factors, including phenotypic plasticity an aspect of behavior that changes in response to specific environmental conditions. This can cause a particular trait to appear more like a species another, clouding the phylogenetic signal. However, this problem can be cured by the use of methods such as cladistics which include a mix of analogous and homologous features into the tree.
In addition, phylogenetics helps determine the duration and speed at which speciation takes place. This information can assist conservation biologists make decisions about the species they should safeguard from the threat of extinction. In the end, it's the preservation of phylogenetic diversity that will result in an ecosystem that is complete and balanced.
Evolutionary Theory
The central theme in evolution is that organisms alter over time because of their interactions with their environment. Many scientists have proposed theories of evolution, including the Islamic naturalist Nasir al-Din al-Tusi (1201-274) who believed that an organism would develop according to its own requirements as well as the Swedish taxonomist Carolus Linnaeus (1707-1778) who developed the modern hierarchical taxonomy as well as Jean-Baptiste Lamarck (1844-1829), who suggested that the use or non-use of certain traits can result in changes that are passed on to the next generation.
In the 1930s and 1940s, theories from a variety of fields--including genetics, natural selection and particulate inheritance--came together to form the modern evolutionary theory synthesis, which defines how evolution happens through the variation of genes within a population, and how those variants change over time due to natural selection. This model, called genetic drift, mutation, gene flow, and sexual selection, is the foundation of the current evolutionary biology and is mathematically described.
Recent advances in the field of evolutionary developmental biology have demonstrated how variation can be introduced to a species through genetic drift, mutations and reshuffling of genes during sexual reproduction and migration between populations. These processes, along with others such as directionally-selected selection and erosion of genes (changes to the frequency of genotypes over time) can lead to evolution. Evolution is defined as changes in the genome over time as well as changes in the phenotype (the expression of genotypes in individuals).
Incorporating evolutionary thinking into all areas of biology education could increase students' understanding of phylogeny as well as evolution. In a recent study conducted by Grunspan and co., it was shown that teaching students about the evidence for evolution boosted their understanding of evolution during a college-level course in biology. To find out more about how to teach about evolution, read The Evolutionary Potential of All Areas of Biology and Thinking Evolutionarily A Framework for Infusing Evolution into Life Sciences Education.
Evolution in Action
Traditionally, scientists have studied evolution through looking back--analyzing fossils, comparing species and studying living organisms. But mouse click the next page isn't just something that happened in the past. It's an ongoing process that is taking place right now. The virus reinvents itself to avoid new drugs and bacteria evolve to resist antibiotics. Animals alter their behavior as a result of a changing world. The results are usually evident.
It wasn't until the late 1980s when biologists began to realize that natural selection was in action. The key is the fact that different traits can confer an individual rate of survival as well as reproduction, and may be passed down from one generation to the next.
In the past, if one allele - the genetic sequence that determines colour was present in a population of organisms that interbred, it could become more common than other allele. In time, this could mean that the number of moths that have 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.
It is easier to observe evolutionary change when an organism, like bacteria, has a high generation turnover. Since 1988, Richard Lenski, a biologist, has studied twelve populations of E.coli that descend from a single strain. Samples from each population were taken regularly and more than 50,000 generations of E.coli have passed.
Lenski's research has revealed that a mutation can profoundly alter the speed at which a population reproduces and, consequently the rate at which it changes. It also demonstrates that evolution takes time, something that is difficult for some to accept.
Microevolution can also be seen in the fact that mosquito genes that confer resistance to pesticides are more common in populations where insecticides are used. That's because the use of pesticides creates a selective pressure that favors individuals 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 climate change, pollution, and habitat loss that prevents many species from adapting. Understanding the evolution process can help us make smarter choices about the future of our planet and the lives of its inhabitants.
