The Academy's Evolution Site
Biological evolution is a central concept in biology. The Academies are committed to helping those interested in science understand evolution theory and how it can be applied throughout all fields of scientific research.
This site provides a range of sources for teachers, students and general readers of evolution. It includes key video clips from NOVA and WGBH-produced science programs on DVD.
Tree of Life
The Tree of Life, an ancient symbol, represents the interconnectedness of all life. It is a symbol of love and unity in many cultures. It can be used in many practical ways in addition to providing a framework to understand the evolution of species and how they respond to changing environmental conditions.
Early attempts to represent the world of biology were founded on categorizing organisms on their physical and metabolic characteristics. These methods rely on the sampling of different parts of organisms or short DNA fragments have greatly increased the diversity of a Tree of Life2. However these trees are mainly composed of eukaryotes; bacterial diversity is not represented in a large way3,4.
Genetic techniques have greatly expanded our ability to depict the Tree of Life by circumventing the need for direct observation and experimentation. We can construct trees using molecular methods, such as the small-subunit ribosomal gene.
Despite the rapid growth of the Tree of Life through genome sequencing, much biodiversity still is waiting to be discovered. This is particularly true of microorganisms that are difficult to cultivate and are typically only found in a single sample5. Recent analysis of all genomes resulted in a rough 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 well understood6.
The expanded Tree of Life is particularly useful in assessing the diversity of an area, assisting to determine if certain habitats require special protection. This information can be used in a variety of ways, including finding new drugs, battling diseases and enhancing crops. The information is also incredibly beneficial for conservation efforts. It can help biologists identify the areas most likely to contain cryptic species that could have important metabolic functions that may be at risk from anthropogenic change. While funding to protect biodiversity are important, the most effective way to conserve the biodiversity of the world is to equip the people of developing nations with the knowledge they need to take action locally and encourage conservation.
Phylogeny
A phylogeny (also called an evolutionary tree) shows the relationships between different organisms. Using mouse click the up coming post , morphological similarities and differences or ontogeny (the process of the development of an organism) scientists can construct a phylogenetic tree which illustrates the evolution of taxonomic categories. The concept of phylogeny is fundamental to understanding the evolution of biodiversity, evolution and genetics.
A basic phylogenetic tree (see Figure PageIndex 10 Finds the connections between organisms with similar traits and evolved from an ancestor with common traits. These shared traits may be homologous, or analogous. Homologous traits are similar in their evolutionary roots, while analogous traits look similar but do not have the identical origins. Scientists group similar traits together into a grouping referred to as a the clade. Every organism in a group share a trait, such as amniotic egg production. They all evolved from an ancestor that had these eggs. The clades are then linked to create a phylogenetic tree to identify organisms that have the closest relationship to.
For a more precise and accurate phylogenetic tree scientists use molecular data from DNA or RNA to determine the relationships among organisms. This information is more precise and provides evidence of the evolution history of an organism. The use of molecular data lets researchers determine the number of organisms that share the same ancestor and estimate their evolutionary age.
The phylogenetic relationships between species are influenced by many factors, including phenotypic plasticity an aspect of behavior that alters in response to unique environmental conditions. This can cause a characteristic to appear more similar to one species than other species, which can obscure the phylogenetic signal. This issue can be cured by using cladistics, which is a a combination of homologous and analogous traits in the tree.
Furthermore, phylogenetics may aid in predicting the length and speed of speciation. This information can aid conservation biologists to decide which species they should protect from the threat of extinction. In the end, it is the conservation of phylogenetic diversity that will result in an ecosystem that is complete and balanced.
Evolutionary Theory
The main idea behind evolution is that organisms acquire distinct characteristics over time due to their interactions with their environments. Many scientists have come up with theories of evolution, such as the Islamic naturalist Nasir al-Din al-Tusi (1201-274), who believed that a living thing would evolve according to its individual requirements, the Swedish taxonomist Carolus Linnaeus (1707-1778), who created the modern hierarchical system of taxonomy, as well as Jean-Baptiste Lamarck (1844-1829), who believed that the usage or non-use of traits can cause changes that are passed on to the next generation.
In the 1930s and 1940s, ideas from different fields, including genetics, natural selection and particulate inheritance, were brought together to form a modern synthesis of evolution theory. This describes how evolution is triggered by the variations in genes within a population and how these variations change with time due to natural selection. This model, which encompasses mutations, genetic drift in gene flow, and sexual selection is mathematically described mathematically.
Recent advances in evolutionary developmental biology have demonstrated the ways in which variation can be introduced to a species via mutations, genetic drift and reshuffling of genes during sexual reproduction and migration between populations. These processes, along with others like directional selection and genetic erosion (changes in the frequency of the genotype over time) can result in evolution that is defined as change in the genome of the species over time, and the change in phenotype over time (the expression of the genotype within the individual).
Incorporating evolutionary thinking into all aspects of biology education can improve students' understanding of phylogeny and evolution. In a study by Grunspan et al. It was demonstrated that teaching students about the evidence for evolution boosted their understanding of evolution in an undergraduate biology course. To learn more about how to teach about evolution, please read The Evolutionary Potential in all Areas of Biology and Thinking Evolutionarily A Framework for Infusing the Concept of Evolution into Life Sciences Education.
Evolution in Action
Scientists have looked at evolution through the past, analyzing fossils and comparing species. They also observe living organisms. But evolution isn't a thing that occurred in the past; it's an ongoing process that is taking place today. Viruses reinvent themselves to avoid new drugs and bacteria evolve to resist antibiotics. Animals alter their behavior as a result of a changing world. The changes that occur are often apparent.
However, it wasn't until late-1980s that biologists realized that natural selection can be seen in action, as well. The main reason is that different traits confer a different rate of survival and reproduction, and can be passed down from one generation to another.
In the past, if one allele - the genetic sequence that determines color - appeared in a population of organisms that interbred, it might become more common than any other allele. Over time, that would mean the number of black moths in a particular population could rise. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
Observing evolutionary change in action is much easier when a species has a rapid turnover of its generation like bacteria. Since 1988, Richard Lenski, a biologist, has studied twelve populations of E.coli that are descended from one strain. Samples of each population have been taken regularly, and more than 50,000 generations of E.coli have passed.
Lenski's work has shown that mutations can alter the rate at which change occurs and the efficiency of a population's reproduction. It also shows evolution takes time, a fact that is hard for some to accept.
Microevolution can be observed in the fact that mosquito genes for pesticide resistance are more common in populations where insecticides have been used. This is because pesticides cause an enticement that favors individuals who have resistant genotypes.
The rapidity of evolution has led to a growing recognition of its importance especially in a planet that is largely shaped by human activity. This includes the effects of climate change, pollution and habitat loss that hinders many species from adapting. Understanding the evolution process can assist you in making better choices regarding the future of the planet and its inhabitants.
