The Academy's Evolution Site
The concept of biological evolution is a fundamental concept in biology. The Academies are committed to helping those interested in science understand evolution theory and how it is incorporated in all areas of scientific research.
This site offers a variety of tools for teachers, students, and general readers on 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 an emblem of love and unity across many cultures. It can be used in many practical ways as well, such as providing a framework for understanding the history of species, and how they respond to changes in environmental conditions.
Early approaches to depicting the world of biology focused on the classification of organisms into distinct categories which had been identified by their physical and metabolic characteristics1. These methods, which relied on the sampling of various parts of living organisms or sequences of short fragments of their DNA greatly increased the variety of organisms that could be represented in the tree of life2. However, these trees are largely comprised of eukaryotes, and bacterial diversity is not represented in a large way3,4.
Genetic techniques have significantly expanded our ability to depict the Tree of Life by circumventing the requirement for direct observation and experimentation. Particularly, molecular techniques enable us to create trees by using sequenced markers, such as the small subunit ribosomal RNA gene.
Despite the massive expansion of the Tree of Life through genome sequencing, much biodiversity still awaits discovery. This is particularly relevant to microorganisms that are difficult to cultivate, and are typically present 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 bacteria and archaea that have not been isolated, and whose diversity is poorly understood6.
The expanded Tree of Life can be used to determine the diversity of a particular area and determine if particular habitats require special protection. This information can be used in a range of ways, from identifying the most effective treatments to fight disease to enhancing the quality of crops. This information is also extremely valuable for conservation efforts. It can aid biologists in identifying the areas most likely to contain cryptic species with potentially significant metabolic functions that could be vulnerable to anthropogenic change. While conservation funds are essential, the best method to protect the world's biodiversity is to empower the people of developing nations with the knowledge they need to act locally and promote conservation.
Phylogeny
A phylogeny is also known as an evolutionary tree, reveals the relationships between various groups of organisms. Scientists can build a phylogenetic chart that shows the evolutionary relationships between taxonomic groups based on molecular data and morphological differences or similarities. The role of phylogeny is crucial in understanding biodiversity, genetics and evolution.
A basic phylogenetic Tree (see Figure PageIndex 10 Identifies the relationships between organisms with similar characteristics and have evolved from an ancestor that shared traits. These shared traits are either homologous or analogous. Homologous traits are similar in their evolutionary roots while analogous traits appear similar, but do not share the same origins. 에볼루션바카라 organize similar traits into a grouping called a Clade. For example, all of the species in a clade have the characteristic of having amniotic eggs and evolved from a common ancestor which had eggs. The clades are then linked to form a phylogenetic branch that can determine which organisms have the closest connection to each other.
To create a more thorough and accurate phylogenetic tree, scientists make use of molecular data from DNA or RNA to identify the relationships among organisms. This information is more precise than morphological data and provides evidence of the evolutionary history of an organism or group. The analysis of molecular data can help researchers determine the number of organisms that have the same ancestor and estimate their evolutionary age.
The phylogenetic relationships between species can be influenced by several factors, including phenotypic plasticity a kind of behavior that changes in response to unique environmental conditions. This can cause a characteristic to appear more like a species another, clouding the phylogenetic signal. This problem can be addressed by using cladistics. This is a method that incorporates the combination of homologous and analogous features in the tree.
In addition, phylogenetics helps determine the duration and speed at which speciation occurs. This information can assist conservation biologists in making decisions about which species to safeguard from the threat of 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 of evolution is that organisms develop various characteristics over time based on their interactions with their surroundings. Many theories of 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 developed modern hierarchical taxonomy, and Jean-Baptiste Lamarck (1744-1829) who suggested that the use or non-use of traits cause changes that can be passed on to offspring.
In the 1930s and 1940s, concepts from various fields, including genetics, natural selection and particulate inheritance, came together to form a modern evolutionary theory. This defines how evolution occurs by the variation of genes in the population, and how these variants change with time due to natural selection. This model, called genetic drift mutation, gene flow and sexual selection, is a key element of the current evolutionary biology and can be mathematically described.
Recent developments in the field of evolutionary developmental biology have revealed that variation can be introduced into a species by mutation, genetic drift and reshuffling of genes during sexual reproduction, and also through migration between populations. These processes, as well as other ones like the directional selection process and the erosion of genes (changes to the frequency of genotypes over time) can result in evolution. Evolution is defined as changes in the genome over time and changes in phenotype (the expression of genotypes in an individual).
Incorporating evolutionary thinking into all aspects of biology education can improve student understanding of the concepts of phylogeny and evolutionary. A recent study conducted by Grunspan and colleagues, for example revealed that teaching students about the evidence that supports evolution helped students accept the concept of evolution in a college-level biology class. For more details about how to teach evolution read The Evolutionary Power of Biology in All Areas of Biology or Thinking Evolutionarily: a Framework for Integrating Evolution into Life Sciences Education.
Evolution in Action
Traditionally scientists have studied evolution through looking back--analyzing fossils, comparing species and observing living organisms. Evolution is not a distant event; it is a process that continues today. Bacteria transform and resist antibiotics, viruses evolve and elude new medications, and animals adapt their behavior in response to a changing planet. The changes that occur are often evident.
It wasn't until late 1980s when biologists began to realize that natural selection was in play. The key is the fact that different traits result in the ability to survive at different rates as well as reproduction, and may be passed down from one generation to another.
In the past, if one allele - the genetic sequence that determines colour was present in a population of organisms that interbred, it could become more prevalent than any other allele. In time, this 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 see evolution when an organism, like bacteria, has a rapid generation turnover. Since 1988, biologist Richard Lenski has been tracking twelve populations of E. Coli that descended from a single strain; samples of each are taken every day and over 500.000 generations have passed.
Lenski's work has demonstrated that a mutation can profoundly alter the efficiency with which a population reproduces and, consequently, the rate at which it changes. It also shows evolution takes time, which is hard for some to accept.
Another example of microevolution is that mosquito genes for resistance to pesticides appear more frequently in populations where insecticides are used. This is due to the fact that the use of pesticides creates a selective pressure that favors individuals who have resistant genotypes.
The speed at which evolution can take place has led to a growing recognition of its importance in a world that is 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 decisions about the future of our planet as well as the lives of its inhabitants.