The Academy's Evolution Site
Biological evolution is a central concept in biology. The Academies are committed to helping those who are interested in science to learn about the theory of evolution and how it is permeated in all areas of scientific research.
This site provides a wide range of resources for teachers, students as well as general readers about evolution. It includes important video clips from NOVA and WGBH's 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 numerous practical applications as well, including providing a framework for understanding the evolution of species and how they react to changes in environmental conditions.
Early attempts to describe the world of biology 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 small fragments of their DNA, greatly increased the variety of organisms that could be represented in a tree of life2. These trees are mostly populated by eukaryotes, and bacterial diversity is vastly underrepresented3,4.
By avoiding the need for direct experimentation and observation, genetic techniques have allowed us to depict the Tree of Life in a more precise way. Trees can be constructed using molecular techniques like the small-subunit ribosomal gene.
Despite the dramatic expansion of the Tree of Life through genome sequencing, a lot of biodiversity awaits discovery. This is especially true of microorganisms that are difficult to cultivate and are typically only represented in a single sample5. A recent analysis of all genomes known to date has produced a rough draft of the Tree of Life, including numerous archaea and bacteria that are not isolated and which are not well understood.
The expanded Tree of Life is particularly beneficial in assessing the biodiversity of an area, assisting to determine if specific habitats require special protection. This information can be used in a variety of ways, such as identifying new drugs, combating diseases and enhancing crops. This information is also extremely beneficial in conservation efforts. It can aid biologists in identifying areas that are most likely to be home to cryptic species, which may have important metabolic functions and be vulnerable to changes caused by humans. While funds to protect biodiversity are crucial however, the most effective method to protect the world's biodiversity is for more people living in developing countries to be empowered with the necessary knowledge to take action locally to encourage conservation from within.
Phylogeny
A phylogeny, also called an evolutionary tree, shows the connections between various groups of organisms. Scientists can construct an phylogenetic chart which shows the evolution of taxonomic categories using molecular information and morphological differences or similarities. The phylogeny of a tree plays an important role in understanding biodiversity, genetics and evolution.
A basic phylogenetic tree (see Figure PageIndex 10 Determines the relationship between organisms with similar traits and have evolved from a common ancestor. These shared traits are either homologous or analogous. Homologous traits are similar in their underlying evolutionary path while analogous traits appear 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 linked to create a phylogenetic tree to determine which organisms have the closest relationship to.
For a more detailed and precise phylogenetic tree scientists use molecular data from DNA or RNA to determine the relationships among organisms. This information is more precise than morphological information and provides evidence of the evolution history of an individual or group. Researchers can use Molecular Data to determine the age of evolution of organisms and identify the number of organisms that share a common ancestor.
The phylogenetic relationships 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 cause a characteristic to appear more like a species another, obscuring the phylogenetic signal. This problem can be addressed by using cladistics, which incorporates the combination of analogous and homologous features in the tree.
In addition, phylogenetics can help predict the length and speed of speciation. This information will assist conservation biologists in deciding which species to safeguard from extinction. In the end, it's the preservation of phylogenetic diversity that will create an ecosystem that is complete and balanced.
Evolutionary Theory
The central theme in evolution is that organisms change over time as a result of their interactions with their environment. Many theories of evolution have been proposed by a wide variety of scientists including the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who envisioned an organism developing gradually according to its needs and needs, the Swedish botanist Carolus Linnaeus (1707-1778) who designed the modern hierarchical taxonomy, as well as Jean-Baptiste Lamarck (1744-1829) who suggested that use or disuse of traits cause changes that could be passed on to offspring.
In the 1930s and 1940s, concepts from a variety of fields--including genetics, natural selection, and particulate inheritance -- came together to form the modern evolutionary theory which explains how evolution happens through the variation of genes within a population and how these variants change in time as a result of natural selection. This model, which incorporates mutations, genetic drift, gene flow and sexual selection, can be mathematically described mathematically.
Recent developments in the field of evolutionary developmental biology have shown how variation can be introduced to a species by genetic drift, mutations and reshuffling of genes during sexual reproduction, and even migration between populations. These processes, in conjunction with other ones like directional selection and gene erosion (changes in frequency of genotypes over time) can lead to evolution. Evolution is defined by changes in the genome over time as well as changes in the phenotype (the expression of genotypes in an individual).
Students can gain a better understanding of the concept of phylogeny through incorporating evolutionary thinking throughout all areas of biology. A recent study by Grunspan and colleagues, for instance revealed that teaching students about the evidence for evolution increased students' acceptance of evolution in a college-level biology course. For more information on how to teach evolution look up The Evolutionary Potency in All Areas of Biology or Thinking Evolutionarily A Framework for Infusing Evolution into Life Sciences Education.
evolutionkr in Action
Scientists have traditionally studied evolution through looking back in the past, analyzing fossils and comparing species. They also observe living organisms. Evolution isn't a flims moment; it is an ongoing process. Viruses evolve to stay away from new medications and bacteria mutate to resist antibiotics. Animals alter their behavior as a result of a changing world. The changes that result are often visible.
It wasn't until the late 1980s that biologists began realize that natural selection was also in action. The key 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, when one particular allele--the genetic sequence that determines coloration--appeared in a population of interbreeding organisms, it might quickly become more common than other alleles. As time passes, that could mean that the number of black moths within 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 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 been observed to have passed.
Lenski's work has demonstrated that a mutation can dramatically alter the speed at the rate at which a population reproduces, and consequently, the rate at which it evolves. It also proves that evolution takes time, a fact that some people are unable to accept.
Microevolution can also be seen in the fact that mosquito genes for pesticide resistance 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 with resistant genotypes.
The rapidity of evolution has led to a greater awareness of its significance particularly in a world shaped largely by human activity. This includes pollution, climate change, and habitat loss that hinders many species from adapting. Understanding evolution can help us make better decisions regarding the future of our planet and the life of its inhabitants.