The Academy's Evolution Site
Biological evolution is a central concept in biology. The Academies are committed to helping those interested in the sciences learn about the theory of evolution and how it is incorporated across all areas of scientific research.
This site provides a wide range of sources for teachers, students and general readers of 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 represents the interconnectedness of all life. It is a symbol of love and unity across many cultures. It also has practical uses, like 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 founded on categorizing organisms on their metabolic and physical characteristics. These methods, which rely on the collection of various parts of organisms, or DNA fragments have greatly increased the diversity of a tree of Life2. However these trees are mainly made up of eukaryotes. Bacterial diversity is still largely unrepresented3,4.
Genetic techniques have greatly broadened our ability to represent the Tree of Life by circumventing the need for direct observation and experimentation. We can create trees using molecular techniques, such as the small-subunit ribosomal gene.
Despite the rapid expansion of the Tree of Life through genome sequencing, a lot of biodiversity remains to be discovered. This is especially true of microorganisms, which are difficult to cultivate and are usually only found in a single sample5. A recent analysis of all genomes known to date has produced a rough draft of the Tree of Life, including many archaea and bacteria that have not been isolated and their diversity is not fully understood6.
The expanded Tree of Life is particularly useful in assessing the diversity of an area, assisting to determine whether specific habitats require special protection. The information is useful in many ways, including finding new drugs, battling diseases and improving the quality of crops. This information is also extremely beneficial for conservation efforts. It can aid biologists in identifying areas that are most likely to have cryptic species, which could perform important metabolic functions, and could be susceptible to changes caused by humans. While conservation funds are important, the best method to preserve the biodiversity of the world is to equip the people of developing nations with the information they require to act locally and support conservation.
Phylogeny
A phylogeny (also called an evolutionary tree) depicts the relationships between species. Scientists can build a phylogenetic diagram that illustrates the evolution of taxonomic categories using molecular information and morphological differences or similarities. 에볼루션 블랙잭 of phylogeny is crucial in understanding biodiversity, genetics and evolution.
A basic phylogenetic Tree (see Figure PageIndex 10 Finds the connections between organisms with similar traits and evolved from a common ancestor. These shared traits can be either homologous or analogous. Homologous traits share their evolutionary origins and analogous traits appear similar, but do not share the same origins. Scientists put similar traits into a grouping known as a Clade. For instance, all the organisms that make up a clade share the trait of having amniotic eggs. They evolved from a common ancestor who had eggs. The clades are then linked to form a phylogenetic branch to determine the organisms with the closest connection to each other.
For a more detailed and accurate phylogenetic tree scientists rely on molecular information from DNA or RNA to determine the relationships between organisms. This data is more precise than morphological data and gives evidence of the evolutionary history of an organism or group. Researchers can use Molecular Data to estimate the evolutionary age of living organisms and discover how many species have the same ancestor.
The phylogenetic relationship can be affected by a variety of factors, including the phenomenon of phenotypicplasticity. This is a type of behaviour that can change due to unique environmental conditions. This can cause a characteristic to appear more resembling to one species than to the other, obscuring the phylogenetic signals. This problem can be mitigated by using cladistics. This is a method that incorporates a combination of analogous and homologous features in the tree.
Additionally, phylogenetics aids determine the duration and speed at which speciation occurs. This information can assist conservation biologists in making choices about which species to protect from disappearance. In the end, it's the preservation of phylogenetic diversity which will create an ecosystem that is balanced and complete.
Evolutionary Theory
The main idea behind evolution is that organisms acquire distinct characteristics over time due to their interactions with their surroundings. Many scientists have come up with theories of evolution, including the Islamic naturalist Nasir al-Din al-Tusi (1201-274) who believed that an organism would evolve according to its individual requirements, the Swedish taxonomist Carolus Linnaeus (1707-1778) who developed the modern taxonomy system that is hierarchical as well as Jean-Baptiste Lamarck (1844-1829), who believed that the use or absence of certain traits can result in changes that can be passed on to future generations.
In the 1930s and 1940s, theories from a variety of fields--including genetics, natural selection, and particulate inheritance--came together to form the modern evolutionary theory synthesis, which defines how evolution happens through the variation of genes within a population and how these variants change over time due to natural selection. This model, which includes mutations, genetic drift in gene flow, and sexual selection can be mathematically described.
Recent developments in evolutionary developmental biology have revealed how variations 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 other ones like directional selection and genetic erosion (changes in the frequency of an individual's genotype over time) can lead to evolution, which is defined by change in the genome of the species over time, and also by changes in phenotype over time (the expression of that genotype within the individual).
Students can better understand the concept of phylogeny by using evolutionary thinking into all aspects of biology. A recent study by Grunspan and colleagues, for example, showed that teaching about the evidence supporting evolution helped students accept the concept of evolution in a college biology course. For more details on how to teach evolution read The Evolutionary Potential in All Areas of Biology or Thinking Evolutionarily as a Framework for Infusing Evolution into Life Sciences Education.
Evolution in Action
Traditionally, scientists have studied evolution by looking back, studying fossils, comparing species, and observing living organisms. But evolution isn't just something that happened in the past. It's an ongoing process, that is taking place right now. The virus reinvents itself to avoid new medications and bacteria mutate to resist antibiotics. Animals alter their behavior as a result of a changing world. The resulting changes are often visible.
However, it wasn't until late 1980s that biologists realized that natural selection could be seen in action, as well. The main reason is that different traits can confer a different rate of survival and reproduction, and they can be passed down from one generation to another.
In the past, if a certain allele - the genetic sequence that determines colour was present in a population of organisms that interbred, it could become more common than any other allele. Over time, that would mean that the number of black moths in the population could 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 rapid generation turnover like bacteria. Since 1988, Richard Lenski, a biologist, has studied twelve populations of E.coli that are descended from one strain. Samples from each population were taken regularly, and more than 50,000 generations of E.coli have passed.
Lenski's research has shown that mutations can drastically alter the rate at the rate at which a population reproduces, and consequently the rate at which it changes. It also demonstrates that evolution takes time, which is hard for some to accept.
Microevolution can be observed in the fact that mosquito genes that confer resistance to pesticides are more prevalent in populations where insecticides are used. This is due to pesticides causing an exclusive pressure that favors those with resistant genotypes.
The rapid pace of evolution taking 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 many species from adapting. Understanding evolution can assist you in making better choices about the future of our planet and its inhabitants.