The Academy's Evolution Site
The concept of biological evolution is a fundamental concept in biology. The Academies have been for a long time involved in helping those interested in science understand the theory of evolution and how it permeates all areas of scientific exploration.
This site offers a variety of sources for students, teachers and general readers of evolution. It contains important video clips from NOVA and the WGBH-produced science programs on DVD.
Tree of Life
The Tree of Life is an ancient symbol that represents the interconnectedness of life. It is seen in a variety of cultures and spiritual beliefs as symbolizing unity and love. It has numerous practical applications as well, such as providing a framework to understand the history of species and how they react to changing environmental conditions.
Early approaches to depicting the biological world focused on separating organisms into distinct categories which were distinguished by physical and metabolic characteristics1. These methods, which rely on sampling of different parts of living organisms or sequences of small fragments of their DNA significantly increased the variety that could be included in a tree of life2. However the trees are mostly 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 need for direct observation and experimentation. We can create trees using molecular techniques, such as the small-subunit ribosomal gene.
The Tree of Life has been greatly expanded thanks to genome sequencing. However, there is still much diversity to be discovered. This is especially relevant to microorganisms that are difficult to cultivate, and which are usually only found in a single specimen5. A recent analysis of all genomes has produced an unfinished draft of a Tree of Life. This includes a variety of bacteria, archaea and other organisms that have not yet been isolated, or their diversity is not well 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. The information is useful in a variety of ways, including identifying new drugs, combating diseases and improving the quality of crops. The information is also incredibly beneficial to conservation efforts. It helps biologists determine the areas most likely to contain cryptic species that could have significant metabolic functions that could be at risk of anthropogenic changes. Although funds to protect biodiversity are crucial however, the most effective method to preserve the world's biodiversity is for more people in developing countries to be empowered with the necessary knowledge to act locally in order to promote conservation from within.
Phylogeny
A phylogeny (also called an evolutionary tree) shows the relationships between different organisms. Scientists can create a phylogenetic diagram that illustrates the evolutionary relationships between taxonomic groups based on molecular data and morphological differences or similarities. The concept of phylogeny is fundamental to understanding biodiversity, evolution and genetics.
A basic phylogenetic tree (see Figure PageIndex 10 ) identifies the relationships between organisms with similar traits that have evolved from common ancestral. These shared traits can be either analogous or homologous. Homologous characteristics are identical in their evolutionary path. Analogous traits might appear similar but they don't have the same ancestry. 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. The clades are then linked to form a phylogenetic branch that can determine the organisms with the closest relationship.
To create a more thorough and accurate phylogenetic tree scientists use molecular data from DNA or RNA to establish the relationships among organisms. This information is more precise and gives evidence of the evolution history of an organism. The analysis of molecular data can help researchers identify the number of organisms who share the same ancestor and estimate their evolutionary age.
The phylogenetic relationships between species can be influenced by several factors, including phenotypic flexibility, an aspect of behavior that alters in response to unique environmental conditions. This can cause a trait to appear more similar to one species than to another which can obscure the phylogenetic signal. However, this problem can be solved through the use of methods such as cladistics which combine analogous and homologous features into the tree.
Additionally, phylogenetics can help predict the duration and rate of speciation. This information can assist conservation biologists make decisions about which species to protect from the threat of extinction. It is ultimately the preservation of phylogenetic diversity which will create an ecosystem that is complete and balanced.
Evolutionary Theory
The main idea behind evolution is that organisms develop distinct characteristics over time based on their interactions with their surroundings. Many scientists have come up with theories of evolution, such as the Islamic naturalist Nasir al-Din al-Tusi (1201-274) who believed that an organism would evolve according to its own needs, the Swedish taxonomist Carolus Linnaeus (1707-1778) who developed the modern hierarchical system of taxonomy as well as Jean-Baptiste Lamarck (1844-1829), who believed that the use or non-use of certain traits can result in changes that are passed on to the
In the 1930s and 1940s, ideas from various fields, including natural selection, genetics, and particulate inheritance--came together to form the current evolutionary theory, which defines how evolution occurs through the variations of genes within a population and how those variants change in time as a result of natural selection. This model, known as genetic drift, mutation, gene flow and sexual selection, is the foundation of the current evolutionary biology and can be mathematically explained.
Recent discoveries in the field of evolutionary developmental biology have shown that variation can be introduced into a species by mutation, genetic drift, and reshuffling genes during sexual reproduction, as well as by migration between populations. These processes, along with others, such as the directional selection process and the erosion of genes (changes in frequency of genotypes over time) can lead to evolution. Evolution is defined as changes in the genome over time and changes in the phenotype (the expression of genotypes in individuals).
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 instance revealed that teaching students about the evidence for evolution helped students accept the concept of evolution in a college-level biology course. To learn more about how to teach about evolution, please look up The Evolutionary Potential of all Areas of Biology and Thinking Evolutionarily: A Framework for Infusing Evolution in Life Sciences Education.
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Scientists have traditionally looked at evolution through the past--analyzing fossils and comparing species. They also observe living organisms. However, evolution isn't something that occurred in the past, it's an ongoing process that is that is taking place today. The virus reinvents itself to avoid new medications and bacteria mutate to resist antibiotics. Animals alter their behavior because of the changing environment. The results are usually visible.
It wasn't until late 1980s that biologists began to realize that natural selection was at work. The key is that various characteristics result in different rates of survival and reproduction (differential fitness), and can be transferred from one generation to the next.
In the past, if an allele - the genetic sequence that determines colour was found in a group of organisms that interbred, it might become more common than other allele. As time passes, that could mean that the number of black moths within a particular population could rise. 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 rapid generation turnover, as with bacteria. Since 1988 the biologist Richard Lenski has been tracking twelve populations of E. Coli that descended from a single strain. samples from each population are taken every day and more than 50,000 generations have now been observed.
Lenski's research has revealed that mutations can drastically alter the efficiency with which a population reproduces--and so the rate at which it alters. It also demonstrates that evolution is slow-moving, a fact that some people find difficult to accept.
Another example of microevolution is the way mosquito genes that are resistant to pesticides are more prevalent in populations where insecticides are used. This is due to pesticides causing a selective pressure which favors those with resistant genotypes.
The rapidity of evolution has led to a growing recognition of its importance particularly in a world shaped largely by human activity. This includes pollution, climate change, and habitat loss, which prevents many species from adapting. Understanding evolution can help us make smarter choices about the future of our planet as well as the life of its inhabitants.