The Academy's Evolution Site
Biology is one of the most fundamental concepts in biology. The Academies are committed to helping those who are interested in the sciences learn about the theory of evolution and how it can be applied in all areas of scientific research.
This site offers a variety of tools for students, teachers and general readers of evolution. It includes key video clip from NOVA and WGBH produced science programs on DVD.
Tree of Life
The Tree of Life is an ancient symbol that symbolizes the interconnectedness of all life. It is a symbol of love and unity across many cultures. It has many practical applications as well, such as providing a framework for understanding the history of species and how they react to changes in environmental conditions.
The first attempts at depicting the biological world focused on categorizing species into distinct categories that were identified 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, greatly increased the variety of organisms that could be represented in the tree of life2. The trees are mostly composed by eukaryotes and bacterial diversity is vastly underrepresented3,4.
By avoiding the need for direct experimentation and observation, genetic techniques have allowed us to depict the Tree of Life in a more precise way. We can create trees using molecular methods like the small-subunit ribosomal gene.
The Tree of Life has been greatly expanded thanks to genome sequencing. However there is still a lot of diversity to be discovered. This is especially the case for microorganisms which are difficult to cultivate, and are typically found in a single specimen5. A recent analysis of all genomes known to date has produced a rough draft version of the Tree of Life, including a large number of bacteria and archaea that have not been isolated and which are not well understood.
This expanded Tree of Life can be used to assess the biodiversity of a specific area and determine if certain habitats require special protection. The information is useful in a variety of ways, such as finding new drugs, battling diseases and enhancing crops. This information is also extremely beneficial in conservation efforts. It helps biologists discover areas that are most likely to be home to cryptic species, which could have vital metabolic functions and be vulnerable to human-induced change. While conservation funds are essential, the best way to conserve the world's biodiversity is to equip more people in developing countries with the necessary knowledge to act locally and support conservation.
Phylogeny
A phylogeny, also called an evolutionary tree, shows the relationships between groups of organisms. Utilizing molecular data similarities and differences in morphology, or ontogeny (the process of the development of an organism) scientists can create a phylogenetic tree that illustrates the evolutionary relationship between taxonomic categories. Phylogeny plays a crucial role in understanding genetics, biodiversity and evolution.
A basic phylogenetic tree (see Figure PageIndex 10 ) identifies the relationships between organisms that share similar traits that have evolved from common ancestral. These shared traits could be homologous, or analogous. Homologous traits are similar in terms of their evolutionary paths. Analogous traits might appear similar however they do not share the same origins. Scientists group similar traits into a grouping referred to as a clade. All members of a clade share a characteristic, for example, amniotic egg production. They all derived from an ancestor that had these eggs. A phylogenetic tree can be constructed by connecting the clades to identify the species which are the closest to one another.
To create a more thorough and accurate phylogenetic tree, scientists rely on molecular information from DNA or RNA to establish the relationships among organisms. This information is more precise and gives evidence of the evolution of an organism. The analysis of molecular data can help researchers identify the number of species that share the same ancestor and estimate their evolutionary age.
The phylogenetic relationships of organisms are influenced by many factors, including phenotypic flexibility, a type of behavior that changes in response to unique environmental conditions. This can cause a characteristic to appear more similar in one species than another, obscuring the phylogenetic signal. However, this issue can be reduced by the use of methods such as cladistics which incorporate a combination of homologous and analogous features into the tree.
Additionally, phylogenetics can help determine the duration and rate at which speciation takes place. This information can help conservation biologists decide which species to protect from the threat of extinction. It is ultimately the preservation of phylogenetic diversity that will result in an ecosystem that is complete and balanced.
Evolutionary Theory
The fundamental concept in evolution is that organisms alter over time because of their interactions with their environment. Many scientists have developed theories of evolution, including the Islamic naturalist Nasir al-Din al-Tusi (1201-274) who believed that a living thing would evolve according to its individual needs as well as the Swedish taxonomist Carolus Linnaeus (1707-1778) who developed the modern hierarchical taxonomy and Jean-Baptiste Lamarck (1844-1829), who believed that the use or non-use of certain traits can result in changes that can be passed on to future generations.
In the 1930s and 1940s, ideas from various fields, including genetics, natural selection, and particulate inheritance--came together to create the modern evolutionary theory, which defines how evolution occurs through the variation of genes within a population, and how those variations change in time due to natural selection. This model, which includes mutations, genetic drift, gene flow and sexual selection can be mathematically described.
Recent developments in the field of evolutionary developmental biology have demonstrated that genetic variation can be introduced into a species by genetic drift, mutation, and reshuffling of genes in sexual reproduction, as well as by migration between populations. These processes, along with others such as directional selection or genetic erosion (changes in the frequency of an individual's genotype over time), can lead to evolution that is defined as changes 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 the concept of phylogeny through incorporating evolutionary thinking into all aspects of biology. A recent study by Grunspan and colleagues, for instance, showed that teaching about the evidence supporting evolution increased students' understanding of evolution in a college biology class. For more information on how to teach about evolution, 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
Scientists have traditionally studied evolution through looking back in the past, studying fossils, and comparing species. They also observe living organisms. Evolution is not a past event; it is a process that continues today. Bacteria mutate and resist antibiotics, viruses reinvent themselves and are able to evade new medications, and animals adapt their behavior to the changing environment. 무료 에볼루션 are often evident.
But it wasn't until the late 1980s that biologists realized that natural selection can be observed in action as well. The key is the fact that different traits can confer a different rate of survival and reproduction, and can be passed on from one generation to the next.
In the past, if an allele - the genetic sequence that determines colour was present in a population of organisms that interbred, it might become more prevalent than any other allele. Over time, this would mean that the number of moths sporting black pigmentation 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 evolutionary change when the species, like bacteria, has a high generation turnover. Since 1988, Richard Lenski, a biologist, has tracked twelve populations of E.coli that are descended from a single strain. Samples of each population were taken regularly, and more than 500.000 generations of E.coli have passed.
Lenski's work has demonstrated that a mutation can dramatically alter the efficiency with which a population reproduces and, consequently, the rate at which it evolves. It also shows 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 areas where insecticides are employed. Pesticides create an enticement that favors those who have resistant genotypes.
The rapid pace of evolution taking place has led to a growing appreciation of its importance in a world that is shaped by human activity, including climate change, pollution and the loss of habitats which prevent many species from adapting. Understanding evolution can help us make better decisions regarding the future of our planet, and the life of its inhabitants.