The Academy's Evolution Site
Biological evolution is a central concept in biology. The Academies have been active for a long time in helping people who are interested in science understand the concept of evolution and how it permeates all areas of scientific exploration.
This site provides a range of sources for teachers, students as well as general readers about evolution. It includes 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 that represents the interconnectedness of all life. It appears in many cultures and spiritual beliefs as an emblem of unity and love. It has numerous practical applications in addition to providing a framework to understand the evolution of species and how they react to changes in environmental conditions.
Early approaches to depicting the world of biology focused on categorizing organisms into distinct categories which had been distinguished by physical and metabolic characteristics1. These methods are based on the sampling of different parts of organisms or short fragments of DNA have greatly increased the diversity of a Tree of Life2. The trees are mostly composed of eukaryotes, while the diversity of bacterial species is greatly underrepresented3,4.
Genetic techniques have significantly expanded our ability to visualize the Tree of Life by circumventing the need for direct observation and experimentation. Particularly, molecular techniques enable us to create trees 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 remains to be discovered. This is particularly the case for microorganisms which are difficult to cultivate and are usually found in one sample5. A recent analysis of all genomes that are known has produced a rough draft of the Tree of Life, including a large number of archaea and bacteria that have not been isolated and which are not well understood.
This expanded Tree of Life is particularly beneficial in assessing the biodiversity of an area, helping to determine if specific habitats require special protection. This information can be used in a variety of ways, including finding new drugs, battling diseases and enhancing crops. It is also beneficial 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 from anthropogenic change. Although funding to safeguard biodiversity are vital however, the most effective method to ensure the preservation of biodiversity around the world is for more people living in developing countries to be equipped with the knowledge to act locally to promote conservation from within.
Phylogeny
A phylogeny, also called an evolutionary tree, illustrates the relationships between groups of organisms. Using molecular data as well as morphological similarities and distinctions, or ontogeny (the process of the development of an organism) scientists can create a phylogenetic tree which illustrates the evolutionary relationships between taxonomic categories. The role of phylogeny is crucial in understanding genetics, biodiversity and evolution.
에볼루션 바카라 무료체험 (see Figure PageIndex 10 ) identifies the relationships between organisms that share similar traits that evolved from common ancestors. These shared traits may be homologous, or analogous. Homologous traits share their evolutionary origins while analogous traits appear similar, but do not share the same origins. Scientists organize similar traits into a grouping known as a the clade. Every organism in a group share a characteristic, like amniotic egg production. They all derived from an ancestor who had these eggs. A phylogenetic tree can be constructed by connecting clades to identify the organisms that are most closely related to one another.
Scientists use molecular DNA or RNA data to build a phylogenetic chart which is more precise and detailed. This information is more precise and provides evidence of the evolution of an organism. The use of molecular data lets researchers determine the number of organisms that have an ancestor common to them and estimate their evolutionary age.
The phylogenetic relationship can be affected by a number of factors that include phenotypicplasticity. This is a type of behavior that alters due to specific environmental conditions. This can cause a particular trait to appear more like a species another, obscuring the phylogenetic signal. This problem can be addressed by using cladistics, which incorporates a combination of analogous and homologous features in the tree.
Furthermore, phylogenetics may help predict the duration and rate of speciation. This information can assist conservation biologists decide which species to protect from extinction. In the end, it is the preservation of phylogenetic diversity that will result in an ecosystem that is complete and balanced.
Evolutionary Theory
The central theme of evolution is that organisms develop distinct characteristics over time as a result of their interactions with their surroundings. Many scientists have developed theories of evolution, including the Islamic naturalist Nasir al-Din al-Tusi (1201-274), who believed that an organism would evolve according to its own requirements as well as the Swedish taxonomist Carolus Linnaeus (1707-1778) who developed the modern hierarchical system of taxonomy as well as Jean-Baptiste Lamarck (1844-1829), who suggested that the use or absence of certain traits can result in changes that are passed on to the next generation.
In the 1930s and 1940s, theories from various fields, including genetics, natural selection and particulate inheritance--came together to form the current synthesis of evolutionary theory that explains how evolution is triggered by the variation of genes within a population and how these variants change in time due to natural selection. extra resources , which is known as genetic drift, mutation, gene flow and sexual selection, is a cornerstone of the current evolutionary biology and is mathematically described.
Recent developments in evolutionary developmental biology have revealed the ways in which variation 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 others such as directionally-selected selection and erosion of genes (changes to the frequency of genotypes over time) can lead to evolution. Evolution is defined by changes in the genome over time as well as changes in the phenotype (the expression of genotypes within individuals).
Students can better understand the concept of phylogeny by using evolutionary thinking into all aspects of biology. A recent study conducted by Grunspan and colleagues, for instance, showed that teaching about the evidence that supports evolution helped students accept the concept of evolution in a college-level biology course. For more information about how to teach evolution look up The Evolutionary Power of Biology in All Areas of Biology or Thinking Evolutionarily A Framework for Infusing 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 isn't a flims event; it is an ongoing process that continues to be observed today. Viruses reinvent themselves to avoid new drugs and bacteria evolve to resist antibiotics. Animals alter their behavior because of a changing world. The resulting changes are often easy to see.
It wasn't until late 1980s that biologists began to realize that natural selection was also in play. The key is that different characteristics result in different rates of survival and reproduction (differential fitness) and are passed from one generation to the next.
In the past, when one particular allele - the genetic sequence that defines color in a group of interbreeding organisms, it could rapidly become more common than the other alleles. Over time, this would mean that the number of moths that have black pigmentation in a group could increase. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
It is easier to track evolution when the species, like bacteria, has a high generation turnover. Since 1988, Richard Lenski, a biologist, has studied twelve populations of E.coli that are descended from one strain. The samples of each population have been collected regularly, and more than 500.000 generations of E.coli have passed.
Lenski's research has revealed that a mutation can profoundly alter the rate at which a population reproduces--and so the rate at which it changes. It also demonstrates that evolution takes time, which is hard for some to accept.
Another example of microevolution is the way mosquito genes that confer resistance to pesticides are more prevalent in populations in which insecticides are utilized. That's because the use of pesticides causes a selective pressure that favors individuals who have resistant genotypes.
The speed of evolution taking place has led to an increasing appreciation of its importance in a world shaped by human activity, including climate change, pollution, and the loss of habitats that prevent many species from adapting. Understanding evolution will help us make better decisions about the future of our planet, and the lives of its inhabitants.