The Academy's Evolution Site
Biological evolution is one of the most important concepts in biology. The Academies are involved in helping those interested in science comprehend the evolution theory and how it is permeated throughout all fields of scientific research.
This site provides students, teachers and general readers with a variety of educational resources on 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 of the interconnectedness of all life. It is a symbol of love and unity across many cultures. It also has practical applications, such as providing a framework for understanding the history of species and how they respond to changes in the environment.
Early attempts to describe the biological world were founded on categorizing organisms on their metabolic and physical characteristics. These methods, which rely on the sampling of various parts of living organisms, or small DNA fragments, significantly increased the variety that could be included in the tree of life2. These trees are largely composed of eukaryotes, while bacterial diversity is vastly underrepresented3,4.
Genetic techniques have greatly expanded our ability to represent the Tree of Life by circumventing the need for direct observation and experimentation. In particular, molecular methods allow us to build trees using sequenced markers like the small subunit ribosomal gene.
The Tree of Life has been significantly expanded by genome sequencing. However, there is still much biodiversity to be discovered. This is especially true of microorganisms, which are difficult to cultivate and are typically only represented in a single specimen5. A recent study of all genomes known to date has created a rough draft of the Tree of Life, including numerous bacteria and archaea that have not been isolated and their diversity is not fully understood6.
The expanded Tree of Life can be used to evaluate the biodiversity of a particular area and determine if particular habitats need special protection. The information is useful in a variety of ways, such as finding new drugs, fighting diseases and improving crops. This information is also extremely beneficial in 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 funds to protect biodiversity are important, the best method to protect the biodiversity of the world is to equip more people in developing countries with the necessary knowledge to act locally and promote conservation.
Phylogeny
A phylogeny (also known as an evolutionary tree) illustrates the relationship between organisms. Using molecular data as well as morphological similarities and distinctions, or ontogeny (the process of the development of an organism) scientists can construct an phylogenetic tree that demonstrates the evolutionary relationships between taxonomic categories. 에볼루션사이트 is crucial in understanding biodiversity, evolution and genetics.
A basic phylogenetic tree (see Figure PageIndex 10 Finds the connections between organisms with similar traits and have evolved from a common ancestor. These shared traits could be homologous, or analogous. Homologous traits share their evolutionary roots and analogous traits appear like they do, but don't have the identical origins. Scientists organize similar traits into a grouping known as a the clade. Every organism in a group share a characteristic, for example, amniotic egg production. They all evolved from an ancestor that had these eggs. The clades then join to create a phylogenetic tree to identify organisms that have the closest relationship.
For a more precise and accurate phylogenetic tree scientists use molecular data from DNA or RNA to determine the connections between organisms. This data is more precise than morphological data and gives evidence of the evolutionary history of an individual or group. Researchers can utilize Molecular Data to estimate the evolutionary age of organisms and identify how many organisms have an ancestor common to all.
The phylogenetic relationships of organisms can be affected by a variety of factors, including phenotypic plasticity a type of behavior that changes in response to unique environmental conditions. This can make a trait appear more similar to one species than another and obscure the phylogenetic signals. This issue can be cured by using cladistics, which is a an amalgamation of homologous and analogous features in the tree.
In addition, phylogenetics can aid in predicting the length and speed of speciation. This information can aid conservation biologists to make decisions about which species to protect from the threat of extinction. It is ultimately the preservation of phylogenetic diversity which will result in an ecologically balanced and complete ecosystem.
Evolutionary Theory
The central theme in evolution is that organisms change over time as a result of their interactions with their environment. Several theories of evolutionary change have been proposed by a variety of scientists such as the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who envisioned an organism developing slowly according to its requirements, the Swedish botanist Carolus Linnaeus (1707-1778) who designed the modern hierarchical taxonomy, as well as Jean-Baptiste Lamarck (1744-1829) who suggested that use or disuse of traits causes changes that can be passed on to the offspring.
In the 1930s and 1940s, theories from a variety of fields -- including genetics, natural selection, and particulate inheritance - came together to form the modern evolutionary theory that explains how evolution occurs through the variation of genes within a population and how these variants change in time due to natural selection. This model, which encompasses mutations, genetic drift in gene flow, and sexual selection is mathematically described.
Recent developments in the field of evolutionary developmental biology have shown how variations can be introduced to a species through genetic drift, mutations and reshuffling of genes during sexual reproduction and the movement between populations. These processes, as well as others like directional selection and 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 also by changes in phenotype as time passes (the expression of the genotype in the individual).
Students can better understand the concept of phylogeny through incorporating evolutionary thinking into all areas of biology. In a recent study conducted by Grunspan et al. It was found that teaching students about the evidence for evolution boosted their understanding of evolution during a college-level course in biology. To find out more about how to teach about evolution, see 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 studied evolution by looking in the past, analyzing fossils and comparing species. They also observe living organisms. Evolution isn't a flims event, but an ongoing process that continues to be observed today. Bacteria mutate and resist antibiotics, viruses evolve and escape new drugs and animals alter their behavior in response to the changing environment. The resulting changes are often evident.
It wasn't until the 1980s that biologists began to realize that natural selection was at work. 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 the next.
In the past when one particular allele, the genetic sequence that determines coloration--appeared in a group of interbreeding species, it could rapidly become more common than the other alleles. As time passes, this could mean that the number of moths that have black pigmentation in a population may increase. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
Monitoring evolutionary changes in action is easier when a particular species has a fast generation turnover, as with bacteria. Since 1988 the biologist Richard Lenski has been tracking twelve populations of E. bacteria that descend from a single strain; samples from each population are taken every day and over fifty thousand generations 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 evolves. It also demonstrates that evolution takes time, something that is difficult for some to accept.
Another example of microevolution is that mosquito genes for resistance to pesticides appear more frequently in populations where insecticides are employed. Pesticides create a selective pressure which favors those who have resistant genotypes.
The rapid pace at which evolution takes place has led to an increasing recognition of its importance in a world that is shaped by human activities, including climate change, pollution, and the loss of habitats that prevent many species from adapting. Understanding evolution will help us make better decisions regarding the future of our planet, as well as the lives of its inhabitants.