The Academy's Evolution Site
Biological evolution is a central concept in biology. The Academies are committed to helping those who are interested in the sciences learn about the theory of evolution and how it is permeated throughout all fields of scientific research.
This site offers a variety of sources for students, teachers as well as general readers about evolution. It contains key video clips from NOVA and WGBH produced science programs on DVD.
Tree of Life
The Tree of Life, an ancient symbol, symbolizes the interconnectedness of all life. It is seen in a variety of cultures and spiritual beliefs as symbolizing unity and love. It has numerous practical applications in addition to providing a framework for understanding the history of species and how they react to changing environmental conditions.
The first attempts at depicting the biological world focused on the classification of species into distinct categories that were distinguished by their physical and metabolic characteristics1. These methods, which relied on sampling of different parts of living organisms or on short fragments of their DNA significantly expanded the diversity that could be represented in a tree of life2. These trees are mostly populated by eukaryotes, and the diversity of bacterial species is greatly underrepresented3,4.
In avoiding the necessity of direct experimentation and observation, genetic techniques have made it possible to depict the Tree of Life in a more precise manner. Particularly, molecular methods allow us to construct trees by using sequenced markers, such as the small subunit of ribosomal RNA gene.
The Tree of Life has been greatly expanded thanks to genome sequencing. However, there is still much biodiversity to be discovered. This is especially true for microorganisms that are difficult to cultivate and which are usually only found in one sample5. A recent analysis of all genomes has produced an initial draft of the Tree of Life. This includes a variety of bacteria, archaea and other organisms that have not yet been isolated or their diversity is not thoroughly understood6.
This expanded Tree of Life is particularly useful in assessing the diversity of an area, assisting to determine whether specific habitats require protection. The information can be used in a range of ways, from identifying the most effective remedies to fight diseases to enhancing the quality of the quality of crops. This information is also useful to conservation efforts. It helps biologists determine the areas that are most likely to contain cryptic species with important metabolic functions that could be at risk of anthropogenic changes. Although funding to protect biodiversity are essential but the most effective way to ensure the preservation of biodiversity around the world is for more people in developing countries to be empowered with the necessary knowledge to act locally in order to promote conservation from within.
Phylogeny
A phylogeny, also called an evolutionary tree, reveals the connections between various groups of organisms. Scientists can build a phylogenetic chart that shows the evolution of taxonomic groups based on molecular data and morphological differences or similarities. The concept of phylogeny is fundamental to understanding evolution, biodiversity and genetics.
A basic phylogenetic tree (see Figure PageIndex 10 Identifies the relationships between organisms with similar traits and evolved from a common ancestor. These shared traits may be analogous or homologous. Homologous traits are similar in their evolutionary paths. Analogous traits might appear like they are but they don't share the same origins. Scientists arrange similar traits into a grouping known as a the clade. Every organism in a group have a common characteristic, like amniotic egg production. They all came from an ancestor that had these eggs. A phylogenetic tree is built by connecting the clades to determine the organisms that are most closely related to one another.
Scientists make use of DNA or RNA molecular information to build a phylogenetic chart that is more accurate and precise. This data is more precise than morphological data and provides evidence of the evolutionary history of an organism or group. Researchers can utilize Molecular Data to calculate the age of evolution of living organisms and discover the number of organisms that have an ancestor common to all.
The phylogenetic relationships between organisms are influenced by many factors including phenotypic plasticity, an aspect of behavior that alters in response to specific environmental conditions. This can cause a trait to appear more resembling to one species than to another and obscure the phylogenetic signals. This problem can be addressed by using cladistics, which incorporates a combination of homologous and analogous features in the tree.
Additionally, phylogenetics aids determine the duration and rate of speciation. This information can assist conservation biologists in deciding which species to save from the threat of extinction. Ultimately, it is the preservation of phylogenetic diversity which will create an ecosystem that is complete and balanced.
Evolutionary Theory
The fundamental concept of evolution is that organisms develop different features over time as a result of their interactions with their environments. A variety of theories about evolution have been proposed by a wide variety of scientists such as the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who believed that an organism would evolve slowly according to its requirements and needs, the Swedish botanist Carolus Linnaeus (1707-1778) who conceived the modern hierarchical taxonomy Jean-Baptiste Lamarck (1744-1829) who suggested that the use or non-use of traits causes changes that could be passed on to the offspring.
In the 1930s and 1940s, concepts from a variety of fields--including natural selection, genetics, and particulate inheritance--came together to form the current evolutionary theory synthesis that explains how evolution occurs through the variation of genes within a population and how those variations change over time due to natural selection. This model, which encompasses genetic drift, mutations as well as gene flow and sexual selection can be mathematically described.
Recent advances in evolutionary developmental biology have revealed how variations can be introduced to a species via mutations, genetic drift or reshuffling of genes in sexual reproduction, and even migration between populations. These processes, as well as other ones like directional selection and genetic erosion (changes in the frequency of the genotype over time) can lead to evolution that is defined as change in the genome of the species over time and the change in phenotype as time passes (the expression of that genotype in the individual).
Students can better understand phylogeny by incorporating evolutionary thinking into all aspects of biology. A recent study by Grunspan and colleagues, for example, showed that teaching about the evidence for evolution helped students accept the concept of evolution in a college biology course. To find out more about how to teach about evolution, read 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 through looking back--analyzing fossils, comparing species and studying living organisms. But evolution isn't a thing that happened in the past; it's an ongoing process taking place in the present. Bacteria transform and resist antibiotics, viruses evolve and are able to evade new medications and animals change their behavior to the changing climate. The resulting changes are often visible.
It wasn't until late 1980s that biologists realized that natural selection can be seen in action, as well. The reason is that different traits confer different rates of survival and reproduction (differential fitness), and can be transferred from one generation to the next.
In the past, if a certain allele - the genetic sequence that determines colour appeared in a population of organisms that interbred, it could become more common than any other allele. In 바카라 에볼루션 , this could mean that the number of black moths within a particular population could rise. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
It is easier to observe evolutionary change when the species, like bacteria, has a rapid generation turnover. Since 1988, Richard Lenski, a biologist, has been tracking twelve populations of E.coli that are descended from a single strain. The samples of each population have been collected regularly, and more than 50,000 generations of E.coli have passed.
Lenski's research has demonstrated that mutations can alter the rate of change and the effectiveness of a population's reproduction. It also demonstrates that evolution takes time, a fact that many find hard to accept.
Another example of microevolution is how mosquito genes that are resistant to pesticides show up more often in populations where insecticides are used. This is because pesticides cause a selective pressure which favors those with resistant genotypes.
The speed at which evolution can take place has led to an increasing awareness of its significance in a world shaped by human activities, including climate change, pollution and the loss of habitats that prevent many species from adjusting. Understanding evolution will help us make better decisions about the future of our planet, and the life of its inhabitants.