The Academy's Evolution Site
Biological evolution is one of the most central concepts in biology. The Academies have been for a long time involved in helping those interested in science understand the concept of evolution and how it affects all areas of scientific exploration.
This site provides students, teachers and general readers with a range of educational resources on evolution. It contains key video clips from NOVA and the WGBH-produced science programs on DVD.
Tree of Life
The Tree of Life is an ancient symbol that represents the interconnectedness of life. It is a symbol of love and harmony in a variety of cultures. It has numerous practical applications as well, including providing a framework for understanding the history of species, and how they respond to changing environmental conditions.
The earliest attempts to depict the world of biology focused on separating species into distinct categories that were distinguished by their physical and metabolic characteristics1. These methods, which rely on the sampling of different parts of living organisms, or sequences of short fragments of their DNA, significantly increased the variety that could be included in a tree of life2. The trees are mostly composed by eukaryotes, and bacterial diversity is vastly underrepresented3,4.
In avoiding the necessity of direct experimentation and observation genetic techniques have enabled us to depict the Tree of Life in a more precise manner. In particular, molecular methods allow us to build trees by using sequenced markers such as the small subunit ribosomal RNA gene.
Despite the dramatic growth of the Tree of Life through genome sequencing, a large amount of biodiversity is waiting to be discovered. This is especially true of microorganisms, which can be difficult to cultivate and are often only represented in a single sample5. A recent analysis of all genomes has 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 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, from identifying the most effective treatments to fight disease to enhancing the quality of crops. The information is also incredibly useful for conservation efforts. It can help biologists identify the areas most likely to contain cryptic species with important metabolic functions that could be at risk of anthropogenic changes. While funds to protect biodiversity are important, the best method to protect the world's biodiversity is to empower more people in developing countries with the necessary knowledge to take action locally and encourage conservation.
Phylogeny
A phylogeny, also known as an evolutionary tree, shows the connections between different groups of organisms. Utilizing molecular data, morphological similarities and differences or ontogeny (the process of the development of an organism) scientists can construct a phylogenetic tree that illustrates the evolution of taxonomic groups. Phylogeny plays a crucial role in understanding genetics, biodiversity and evolution.
A basic phylogenetic tree (see Figure PageIndex 10 ) determines the relationship between organisms that share similar traits that have evolved from common ancestral. These shared traits could be analogous, or homologous. Homologous characteristics are identical in terms of their evolutionary path. Analogous traits may look similar, but they do not have the same ancestry. Scientists arrange similar traits into a grouping referred to as a the clade. For example, all of the organisms in a clade share the trait of having amniotic eggs and evolved from a common ancestor that had these eggs. The clades are then connected to create a phylogenetic tree to determine which organisms have the closest relationship to.
For a more detailed and precise phylogenetic tree scientists make use of molecular data from DNA or RNA to establish the relationships among organisms. This information is more precise and provides evidence of the evolution of an organism. Researchers can utilize Molecular Data to estimate the age of evolution of organisms and determine how many species share the same ancestor.
Going In this article of organisms can be influenced by several factors, including phenotypic flexibility, a type of behavior that changes in response to unique environmental conditions. This can make a trait appear more resembling to one species than to the other which can obscure the phylogenetic signal. However, this issue can be solved through the use of techniques such as cladistics which incorporate a combination of similar and homologous traits into the tree.
Additionally, phylogenetics can help determine the duration and speed at which speciation occurs. This information can aid conservation biologists to decide which species to protect from the threat of extinction. Ultimately, it is the preservation of phylogenetic diversity that will lead to 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 developed theories of evolution, including the Islamic naturalist Nasir al-Din al-Tusi (1201-274), who believed that an organism would evolve according to its own needs and needs, the Swedish taxonomist Carolus Linnaeus (1707-1778) who developed the modern hierarchical system of taxonomy and Jean-Baptiste Lamarck (1844-1829), who believed that the use or absence of traits can cause changes that can be passed on to future generations.
In the 1930s & 1940s, ideas from different fields, including natural selection, genetics & particulate inheritance, merged to form a contemporary evolutionary theory. This defines how evolution is triggered by the variation of genes in the population and how these variations change with time due to natural selection. This model, which includes genetic drift, mutations, gene flow and sexual selection, can be mathematically described mathematically.
Recent developments in evolutionary developmental biology have demonstrated the ways in which variation can be introduced to a species by mutations, genetic drift, reshuffling genes during sexual reproduction and the movement between populations. These processes, as well as others such as directional selection or genetic erosion (changes in the frequency of the genotype over time) can result in evolution, which is defined by changes in the genome of the species over time, and also the change in phenotype as time passes (the expression of that genotype in an individual).
Students can better understand the concept of phylogeny by using evolutionary thinking throughout all aspects of biology. In a recent study by Grunspan and colleagues. It was found that teaching students about the evidence for evolution boosted their acceptance of evolution during a college-level course in biology. To find out more about how to teach about evolution, please 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
Traditionally, scientists have studied evolution by studying fossils, comparing species and studying living organisms. Evolution is not a past event, but an ongoing process. The virus reinvents itself to avoid new medications and bacteria mutate to resist antibiotics. Animals alter their behavior because of the changing environment. The changes that result are often visible.
However, 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 confer different rates of survival and reproduction (differential fitness) and can be passed down from one generation to the next.
In the past, when one particular allele--the genetic sequence that determines coloration--appeared in a population of interbreeding organisms, it might rapidly become more common than all other alleles. Over time, this would mean that the number of moths that have black pigmentation in a population may increase. The same 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, Richard Lenski, a biologist, has tracked twelve populations of E.coli that are descended from one strain. Samples of each population have been collected regularly and more than 500.000 generations of E.coli have been observed to have passed.
Lenski's work has shown that mutations can alter the rate of change and the effectiveness at which a population reproduces. It also demonstrates that evolution takes time--a fact that some people find hard to accept.
Another example of microevolution is how mosquito genes that are resistant to pesticides are more prevalent in areas in which insecticides are utilized. This is due to the fact that the use of pesticides creates a selective pressure that favors those with resistant genotypes.
The speed at which evolution can take 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 hinder many species from adapting. Understanding evolution can help you make better decisions about the future of our planet and its inhabitants.