The Academy's Evolution Site
The concept of biological evolution is among the most fundamental concepts in biology. The Academies are committed to helping those who are interested in science to comprehend the evolution theory and how it is incorporated across all areas of scientific research.
This site provides students, teachers and general readers with a wide range of learning resources about evolution. It has important 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 used in many spiritual traditions and cultures as a symbol of unity and love. It can be used in many practical ways as well, including providing a framework for understanding the history of species and how they react to changing environmental conditions.
Early attempts to represent the world of biology were built on categorizing organisms based on their metabolic and physical characteristics. These methods, which relied on the sampling of various parts of living organisms, or small fragments of their DNA significantly expanded the diversity that could be included in a tree of life2. These trees are largely composed by eukaryotes and bacteria are largely underrepresented3,4.
Genetic techniques have significantly expanded our ability to visualize the Tree of Life by circumventing the need for direct observation and experimentation. We can create trees using molecular methods, such as the small-subunit ribosomal gene.
Despite the dramatic growth of the Tree of Life through genome sequencing, a lot of biodiversity awaits discovery. This is particularly true of microorganisms, which can be difficult to cultivate and are often only found in a single specimen5. A recent study of all known genomes has created a rough draft of the Tree of Life, including a large number of archaea and bacteria that have not been isolated and whose diversity is poorly understood6.
The expanded Tree of Life is particularly useful for assessing the biodiversity of an area, which can help to determine if specific habitats require special protection. This information can be used in many ways, including identifying new drugs, combating diseases and enhancing crops. This information is also beneficial in conservation efforts. It helps biologists determine those areas that are most likely contain cryptic species with important metabolic functions that could be at risk from anthropogenic change. Although funds to protect biodiversity are crucial, ultimately the best way to protect the world's biodiversity is for more people living in developing countries to be equipped with the knowledge to act locally to promote conservation from within.
Phylogeny
A phylogeny, also known as an evolutionary tree, shows the connections between groups of organisms. Utilizing molecular data as well as morphological similarities and distinctions or ontogeny (the course of development of an organism) scientists can create a phylogenetic tree which illustrates the evolutionary relationship between taxonomic categories. Phylogeny is crucial in understanding biodiversity, evolution and genetics.
A basic phylogenetic tree (see Figure PageIndex 10 ) determines the relationship between organisms with similar traits that evolved from common ancestors. These shared traits may be analogous or homologous. Homologous traits are the same in terms of their evolutionary path. Analogous traits could appear similar, but they do not have the same origins. Scientists put similar traits into a grouping called a the clade. For instance, all the organisms that make up a clade share the trait of having amniotic eggs and evolved from a common ancestor who had eggs. The clades then join to create a phylogenetic tree to identify organisms that have the closest connection to each other.
Scientists make use of molecular DNA or RNA data to create a phylogenetic chart which is more precise and precise. This data is more precise than morphological data and gives evidence of the evolutionary history of an individual or group. Molecular data allows researchers to determine the number of species that have the same ancestor and estimate their evolutionary age.
The phylogenetic relationships of a species can be affected by a number of factors, including the phenomenon of phenotypicplasticity. This is a kind of behavior that alters as a result of unique environmental conditions. This can cause a trait to appear more like a species another, clouding the phylogenetic signal. However, this issue can be reduced by the use of methods like cladistics, which include a mix of homologous and analogous features into the tree.
Furthermore, phylogenetics may aid in predicting the time and pace of speciation. This information will assist conservation biologists in making decisions about which species to save from extinction. Ultimately, it is the preservation of phylogenetic diversity which will lead to a complete and balanced ecosystem.
Evolutionary Theory
The central theme in evolution is that organisms change over time due to their interactions with their environment. Many theories of evolution have been proposed by a variety of scientists including the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who proposed that a living organism develop gradually according to its requirements, the Swedish botanist Carolus Linnaeus (1707-1778) who designed the modern hierarchical taxonomy Jean-Baptiste Lamarck (1744-1829) who suggested that the use or misuse of traits can cause changes that could be passed on to the offspring.
In the 1930s and 1940s, concepts from various fields, including genetics, natural selection, and particulate inheritance -- came together to create the modern synthesis of evolutionary theory, which defines how evolution is triggered by the variations of genes within a population and how those variations change over time due to natural selection. This model, which encompasses genetic drift, mutations, gene flow and sexual selection, can be mathematically described mathematically.
Recent discoveries in evolutionary developmental biology have shown how variation can be introduced to a species through mutations, genetic drift or reshuffling of genes in sexual reproduction and the movement between populations. These processes, as well as others such as the directional selection process and the erosion of genes (changes to the 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 within individuals).
Incorporating evolutionary thinking into all areas of biology education can improve student understanding of the concepts of phylogeny as well as evolution. A recent study conducted by Grunspan and colleagues, for instance demonstrated that teaching about the evidence for evolution increased students' understanding of evolution in a college biology course. For more information on how to teach about evolution, look up The Evolutionary Potential in 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 studying fossils, comparing species, and observing 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 elude new medications, and animals adapt their behavior to a changing planet. just click the following document that result are often apparent.
It wasn't until the late 1980s that biologists began to realize that natural selection was also in play. The key is that different characteristics result in 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 species, it could quickly become more common than the other alleles. Over time, that would mean that the number of black moths 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 track evolution when a species, such as bacteria, has a high generation turnover. Since 1988 the biologist Richard Lenski has been tracking twelve populations of E. Coli that descended from a single strain; samples of each population are taken regularly, and over 500.000 generations have been observed.
Lenski's work has shown that mutations can alter the rate of change and the rate at which a population reproduces. It also demonstrates that evolution takes time, a fact that is difficult for some to accept.
Microevolution is also evident in the fact that mosquito genes for resistance to pesticides are more common in populations that have used insecticides. This is because pesticides cause a selective pressure which favors those who have resistant genotypes.
The speed at which evolution takes place has led to an increasing appreciation of its importance in a world shaped by human activity--including climate change, pollution, and the loss of habitats which prevent the species from adapting. Understanding evolution will help us make better decisions about the future of our planet as well as the life of its inhabitants.