The Academy's Evolution Site
Biological evolution is one of the most fundamental concepts in biology. The Academies have long been involved in helping those interested in science understand the theory of evolution and how it affects all areas of scientific research.
This site provides teachers, students and general readers with a wide range of learning resources on evolution. It contains key video clips from NOVA and WGBH produced science programs on DVD.
Tree of Life
The Tree of Life is an ancient symbol that symbolizes the interconnectedness of all life. It is a symbol of love and unity across many cultures. It can be used in many practical ways as well, such as providing a framework for understanding the history of species, and how they react to changes in environmental conditions.
Early attempts to describe the biological world were based on categorizing organisms based on their metabolic and physical characteristics. These methods, which rely on the sampling of various parts of living organisms or on small fragments of their DNA significantly expanded the diversity that could be represented in the tree of life2. However, these trees are largely made up of eukaryotes. Bacterial diversity remains vastly underrepresented3,4.
Genetic techniques have greatly broadened our ability to depict the Tree of Life by circumventing the requirement for direct observation and experimentation. Particularly, molecular techniques allow us to build trees by using sequenced markers such as the small subunit ribosomal gene.
The Tree of Life has been dramatically expanded through genome sequencing. However there is a lot of biodiversity to be discovered. This is particularly relevant to microorganisms that are difficult to cultivate, and are usually present in a single sample5. Recent analysis of all genomes has produced an initial draft of the Tree of Life. This includes a wide range 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 area and determine if specific habitats need special protection. This information can be utilized in a variety of ways, including identifying new drugs, combating diseases and improving the quality of crops. It is also useful in conservation efforts. It helps biologists determine the areas most likely to contain cryptic species with potentially important metabolic functions that could be at risk from anthropogenic change. Although funding to safeguard biodiversity are vital, ultimately the best way to protect the world's biodiversity is for more people living in developing countries to be empowered with the knowledge to act locally to promote conservation from within.
Phylogeny
A phylogeny is also known as an evolutionary tree, shows the relationships between different groups of organisms. By using molecular information as well as morphological similarities and distinctions, or ontogeny (the course of development of an organism) scientists can construct a phylogenetic tree that illustrates the evolutionary relationships between 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 with similar traits and have evolved from an ancestor with common traits. These shared traits could be either analogous or homologous. Homologous traits are similar in their evolutionary origins and analogous traits appear like they do, but don't have the same ancestors. Scientists organize similar traits into a grouping referred to as a clade. For instance, all the species in a clade have the characteristic of having amniotic eggs. They evolved from a common ancestor that had eggs. A phylogenetic tree is constructed by connecting clades to determine the organisms which are the closest to each other.
To create a more thorough and accurate phylogenetic tree scientists make use of molecular data from DNA or RNA to identify the relationships among organisms. This data is more precise than morphological data and provides evidence of the evolution background of an organism or group. Researchers can use Molecular Data to estimate the age of evolution of organisms and identify the number of organisms that share an ancestor common to all.
The phylogenetic relationships between organisms can be influenced by several factors including phenotypic plasticity, an aspect of behavior that changes in response to unique environmental conditions. This can cause a characteristic to appear more similar to a species than to another and obscure the phylogenetic signals. This problem can be addressed by using cladistics, which incorporates the combination of homologous and analogous traits in the tree.
Additionally, phylogenetics aids determine the duration and speed at which speciation occurs. This information can assist conservation biologists make decisions about which species they should protect from the threat of extinction. In the end, it's the conservation of phylogenetic diversity which will create an ecosystem that is balanced and complete.
Evolutionary Theory
The main idea behind evolution is that organisms develop different features over time as a result of their interactions with their environments. Many scientists have proposed theories of evolution, such as the Islamic naturalist Nasir al-Din al-Tusi (1201-274), who believed that a living thing would evolve according to its individual requirements as well as the Swedish taxonomist Carolus Linnaeus (1707-1778) who developed the modern hierarchical taxonomy and 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
In the 1930s and 1940s, concepts from various areas, including genetics, natural selection and particulate inheritance, came together to form a modern theorizing of evolution. 에볼루션 슬롯 explains how evolution occurs by the variation in genes within the population and how these variations alter over time due to natural selection. This model, which includes genetic drift, mutations, gene flow and sexual selection is mathematically described.
Recent discoveries in the field of evolutionary developmental biology have demonstrated that variation can be introduced into a species via mutation, genetic drift and reshuffling genes during sexual reproduction, and also by migration between populations. These processes, along with other ones like directional selection and genetic erosion (changes in the frequency of a genotype over time) can result in evolution that is defined as change in the genome of the species over time and the change in phenotype over time (the expression of the genotype in the individual).
Students can gain a better understanding of phylogeny by incorporating evolutionary thinking in all areas of biology. A recent study conducted by Grunspan and colleagues, for example, showed that teaching about the evidence for evolution increased students' acceptance of evolution in a college biology course. For more details on how to teach about evolution read The Evolutionary Potency in All Areas of Biology or Thinking Evolutionarily: a Framework for Integrating Evolution into Life Sciences Education.
Evolution in Action
Traditionally scientists have studied evolution by looking back, studying fossils, comparing species, and observing living organisms. However, evolution isn't something that happened in the past; it's an ongoing process, that is taking place in the present. Bacteria transform and resist antibiotics, viruses reinvent themselves and escape new drugs and animals alter their behavior to the changing environment. The resulting changes are often evident.
It wasn't until late 1980s that biologists understood that natural selection could be seen in action, as well. The reason is that different traits have different rates of survival and reproduction (differential fitness) and can be passed down from one generation to the next.
In the past, if an allele - the genetic sequence that determines color - was present in a population of organisms that interbred, it might become more prevalent than any other allele. Over time, this would mean that the number of moths sporting 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 evolution when a species, such as bacteria, has a rapid generation turnover. Since 1988, Richard Lenski, a biologist, has tracked twelve populations of E.coli that descend from one strain. Samples from each population were taken 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, consequently, the rate at which it evolves. It also shows that evolution takes time, which is hard for some to accept.
Another example of microevolution is how mosquito genes that confer resistance to pesticides show up more often in populations where insecticides are used. This is due to the fact that the use of pesticides creates a pressure that favors people with resistant genotypes.
The rapid pace of evolution taking place has led to a growing awareness of its significance in a world shaped by human activity, including climate change, pollution and the loss of habitats which prevent many species from adjusting. Understanding the evolution process can aid you in making better decisions about the future of the planet and its inhabitants.