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 comprehend the evolution theory and how it is incorporated across all areas of scientific research.
This site provides a wide range of tools for teachers, students and general readers of evolution. It contains the most 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 all life. It is an emblem of love and unity in many cultures. It has many practical applications as well, including providing a framework to understand the history of species, and how they respond to changes in environmental conditions.
The earliest attempts to depict the world of biology focused on separating organisms into distinct categories that were identified by their physical and metabolic characteristics1. These methods, based on the sampling of different parts of living organisms, or short fragments of their DNA, significantly expanded the diversity that could be represented in the tree of life2. These trees are largely composed by eukaryotes, and bacteria are largely underrepresented3,4.
Genetic techniques have greatly expanded our ability to represent the Tree of Life by circumventing the need for direct observation and experimentation. Particularly, molecular methods allow us to construct trees using sequenced markers, such as the small subunit ribosomal RNA gene.
The Tree of Life has been greatly expanded thanks to genome sequencing. However there is a lot of biodiversity to be discovered. This is particularly true for microorganisms that are difficult to cultivate, and which are usually only found in a single specimen5. Recent analysis of all genomes resulted in an unfinished draft of a Tree of Life. This includes a variety of archaea, bacteria, and other organisms that have not yet been isolated, or whose diversity has not been fully understood6.
The expanded Tree of Life is particularly useful for assessing the biodiversity of an area, helping to determine if specific habitats require protection. This information can be used in a variety of ways, such as finding new drugs, battling diseases and improving the quality of crops. The information is also valuable in conservation efforts. It helps biologists discover areas that are likely to have cryptic species, which may have important metabolic functions and be vulnerable to the effects of human activity. While funds to protect biodiversity are important, the best method to protect the world's biodiversity is to empower more people in developing nations with the necessary knowledge to act locally and promote conservation.
Phylogeny
A phylogeny (also known as an evolutionary tree) illustrates the relationship between species. Utilizing molecular data similarities and differences in morphology, or ontogeny (the course of development of an organism) scientists can create a phylogenetic tree that illustrates the evolution of taxonomic groups. Phylogeny is essential in understanding evolution, biodiversity and genetics.
A basic phylogenetic tree (see Figure PageIndex 10 ) determines the relationship between organisms that share similar traits that evolved from common ancestors. These shared traits could be either homologous or analogous. Homologous traits are identical in their evolutionary roots, while analogous traits look like they do, but don't have the same ancestors. Scientists organize similar traits into a grouping called a clade. All organisms in a group have a common characteristic, like amniotic egg production. They all came from an ancestor with these eggs. The clades are then linked to form a phylogenetic branch to identify organisms that have the closest connection to each other.
To create a more thorough and accurate phylogenetic tree, scientists rely on molecular information from DNA or RNA to determine the connections between organisms. This information is more precise and gives evidence of the evolution history of an organism. The analysis of molecular data can help researchers determine the number of organisms that share 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 type of behaviour that can change as a result of specific environmental conditions. This can cause a trait to appear more similar to one species than another, clouding the phylogenetic signal. This issue can be cured by using cladistics. This is a method that incorporates an amalgamation of homologous and analogous traits in the tree.
In addition, phylogenetics helps determine the duration and speed at which speciation takes place. This information can aid conservation biologists to make decisions about which species to protect from extinction. In the end, it's the preservation of phylogenetic diversity which will result in an ecosystem that is complete and balanced.
Evolutionary Theory
The central theme of evolution is that organisms acquire different features over time as a result of their interactions with their surroundings. Many scientists have developed theories of evolution, such as the Islamic naturalist Nasir al-Din al-Tusi (1201-274) who believed that an organism would develop according to its own needs as well as the Swedish taxonomist Carolus Linnaeus (1707-1778) who developed the modern hierarchical taxonomy, as well as Jean-Baptiste Lamarck (1844-1829), who suggested that the use or non-use of traits can lead to changes that are passed on to the next generation.
In the 1930s and 1940s, ideas from a variety of fields--including natural selection, genetics, and particulate inheritance -- came together to form the modern synthesis of evolutionary theory that explains how evolution occurs through the variations of genes within a population, and how those variants change in time as a result of natural selection. This model, which includes mutations, genetic drift, gene flow and sexual selection, can be mathematically described.
Recent discoveries in evolutionary developmental biology have revealed how variation can be introduced to a species by mutations, genetic drift, reshuffling genes during sexual reproduction, and even migration between populations. These processes, as well as other ones like directional selection and gene erosion (changes in the frequency of genotypes over time), can lead towards evolution. Evolution is defined as changes in the genome over time as well as changes in phenotype (the expression of genotypes within individuals).
Incorporating evolutionary thinking into all areas of biology education could increase student understanding of the concepts of phylogeny as well as evolution. A recent study by Grunspan and colleagues, for instance, showed that teaching about the evidence supporting evolution helped students accept the concept of evolution in a college-level biology class. For more information on how to teach about evolution, please look up The Evolutionary Potential of all Areas of Biology and Thinking Evolutionarily A Framework for Infusing Evolution in 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 occurred in the past. It's an ongoing process that is happening right now. Bacteria mutate and resist antibiotics, viruses reinvent themselves and escape new drugs and animals alter their behavior to the changing environment. The changes that occur are often evident.
It wasn't until the late 1980s that biologists began realize that natural selection was also at work. 에볼루션 카지노 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 allele - the genetic sequence that determines colour - appeared in a population of organisms that interbred, it could become more common than any other allele. As time passes, that could 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.
Observing evolutionary change in action is easier when a particular species has a fast generation turnover, as with bacteria. Since 1988, biologist Richard Lenski has been tracking twelve populations of E. bacteria that descend from a single strain. samples of each are taken on a regular basis and more than 50,000 generations have now been observed.
Lenski's work has shown that mutations can alter the rate at which change occurs and the effectiveness of a population's reproduction. It also demonstrates that evolution takes time, a fact that some find difficult to accept.
Another example of microevolution is how mosquito genes that are resistant to pesticides appear more frequently in areas where insecticides are employed. This is because the use of pesticides creates a selective pressure that favors people who have resistant genotypes.
The speed at which evolution takes place has led to an increasing recognition of its importance in a world shaped by human activity, including climate changes, pollution and the loss of habitats that hinder many species from adapting. Understanding the evolution process can help us make better choices about the future of our planet and the life of its inhabitants.