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 science to understand evolution theory and how it can be applied throughout all fields of scientific research.
This site provides students, teachers and general readers with a variety of learning resources about 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 an emblem of love and unity across many cultures. It also has many practical applications, like providing a framework for understanding the history of species and how they respond to changes in the environment.
Early attempts to represent the world of biology were founded on categorizing organisms on their metabolic and physical characteristics. These methods, which rely on sampling of different parts of living organisms or on small fragments of their DNA, greatly increased the variety of organisms that could be represented in the tree of life2. These trees are mostly populated of eukaryotes, while the diversity of bacterial species is greatly underrepresented3,4.
By avoiding the need for direct observation and experimentation genetic techniques have enabled us to depict the Tree of Life in a more precise way. In particular, molecular methods allow us to construct trees by using sequenced markers such as the small subunit ribosomal RNA gene.
Despite the rapid growth of the Tree of Life through genome sequencing, much biodiversity still is waiting to be discovered. This is particularly relevant to microorganisms that are difficult to cultivate and which are usually only present in a single sample5. Recent analysis of all genomes resulted in an initial draft of the Tree of Life. This includes a large number of archaea, bacteria and other organisms that haven't yet been identified or their diversity is not thoroughly understood6.
This expanded Tree of Life is particularly useful in assessing the diversity of an area, assisting to determine if certain habitats require protection. This information can be utilized in a variety of ways, such as finding new drugs, battling diseases and improving crops. It is also useful for conservation efforts. It can aid biologists in identifying those areas that are most likely contain cryptic species with important metabolic functions that could be at risk from anthropogenic change. Although funding to protect biodiversity are crucial however, the most effective method to ensure the preservation of biodiversity around the world is for more people living in developing countries to be empowered with the knowledge to act locally in order to promote conservation from within.
Phylogeny
A phylogeny, also called an evolutionary tree, illustrates the relationships between groups of organisms. Scientists can create a phylogenetic chart that shows the evolution of taxonomic groups based on molecular data and morphological similarities or differences. The role of phylogeny is crucial in understanding genetics, biodiversity and evolution.
A basic phylogenetic Tree (see Figure PageIndex 10 ) identifies the relationships between organisms that share similar traits that evolved from common ancestral. These shared traits can be homologous, or analogous. Homologous traits are similar in their underlying evolutionary path, while analogous traits look like they do, but don't have the same ancestors. Scientists combine similar traits into a grouping called a Clade. For instance, all of the organisms that make up a clade have the characteristic of having amniotic egg and evolved from a common ancestor that had eggs. The clades are then connected to form a phylogenetic branch to determine the organisms with the closest relationship.
For a more precise and accurate phylogenetic tree scientists make use of molecular data from DNA or RNA to determine the connections between organisms. This information is more precise than morphological information and gives evidence of the evolutionary history of an organism or group. Researchers can utilize Molecular Data to determine the evolutionary age of organisms and determine how many species share a common ancestor.
The phylogenetic relationships between organisms are influenced by many factors including phenotypic plasticity, a kind of behavior that alters in response to unique environmental conditions. This can cause a trait to appear more like a species other species, which can obscure the phylogenetic signal. This issue can be cured by using cladistics. This is a method that incorporates the combination of analogous and homologous features in the tree.
Additionally, phylogenetics can aid in predicting the time and pace of speciation. This information can aid conservation biologists in making decisions about which species to save from extinction. In the end, it is the conservation of phylogenetic diversity which will create an ecosystem that is balanced and complete.
Evolutionary Theory
The central theme in evolution is that organisms change over time due to their interactions with their environment. A variety of theories about evolution have been proposed by a wide variety of scientists such as the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who envisioned an organism developing slowly according to its requirements, the Swedish botanist Carolus Linnaeus (1707-1778) who conceived modern hierarchical taxonomy, and Jean-Baptiste Lamarck (1744-1829) who suggested that the use or misuse of traits causes changes that could be passed on to offspring.
In the 1930s and 1940s, concepts from various areas, including genetics, natural selection, and particulate inheritance, were brought together to form a contemporary evolutionary theory. This defines how evolution is triggered by the variations in genes within the population and how these variations alter over time due to natural selection. This model, which is known as genetic drift, mutation, gene flow and sexual selection, is a key element of modern evolutionary biology and can be mathematically explained.
Recent developments in the field of evolutionary developmental biology have demonstrated that variation can be introduced into a species by mutation, genetic drift, and reshuffling genes during sexual reproduction, and also through the movement of populations. These processes, in conjunction with others, such as the directional selection process and the erosion of genes (changes in frequency of genotypes over time) can result in evolution. Evolution is defined as changes in the genome over time, as well as changes in the phenotype (the expression of genotypes in individuals).
Students can gain a better understanding of the concept of phylogeny by using evolutionary thinking in all areas of biology. In a recent study conducted by Grunspan and co., it was shown that teaching students about the evidence for evolution increased their understanding of evolution in a college-level course in biology. For more details about how to teach evolution, see The Evolutionary Potential in all Areas of Biology or Thinking Evolutionarily as a Framework for Integrating Evolution into Life Sciences Education.
Evolution in Action
Scientists have looked at evolution through the past--analyzing fossils and comparing species. They also study living organisms. Evolution isn't a flims event, but an ongoing process that continues to be observed today. Bacteria transform and resist antibiotics, viruses evolve and escape new drugs, and animals adapt their behavior to the changing climate. The results are usually visible.
But it wasn't until the late-1980s that biologists realized that natural selection can be seen in action, as well. The key is that various characteristics result in different rates of survival and reproduction (differential fitness) and are passed from one generation to the next.
In the past, if one particular allele--the genetic sequence that determines coloration--appeared in a population of interbreeding organisms, it might rapidly become more common than the other alleles. In time, this could mean that the number of black moths in a population could increase. simply click the next document is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
The ability to observe evolutionary change is much easier when a species has a fast generation turnover like bacteria. Since 1988 the biologist Richard Lenski has been tracking twelve populations of E. coli that descended from a single strain. samples of each are taken on a regular basis and more than 50,000 generations have now passed.
Lenski's research has demonstrated that mutations can alter the rate of change and the effectiveness at which a population reproduces. It also shows evolution takes time, a fact that is difficult for some to accept.
Microevolution can be observed in the fact that mosquito genes for resistance to pesticides are more prevalent in populations where insecticides are used. This is due to the fact that the use of pesticides creates a pressure that favors individuals who have resistant genotypes.
The rapid pace at which evolution can take place has led to a growing recognition of its importance in a world that is shaped by human activity--including climate change, pollution and the loss of habitats that prevent the species from adapting. Understanding evolution will help us make better choices about the future of our planet and the lives of its inhabitants.