The Academy's Evolution Site
The concept of biological evolution is among the most central concepts in biology. The Academies are committed to helping those interested in science to understand evolution theory and how it is permeated across all areas of scientific research.
This site provides teachers, students and general readers with a range of learning resources about evolution. It includes the most important video clips from NOVA and the WGBH-produced science programs on DVD.
Tree of Life
The Tree of Life, an ancient symbol, represents the interconnectedness of all life. It appears in many religions and cultures as symbolizing unity and love. It also has important practical applications, such as providing a framework for understanding the evolution of species and how they respond to changes in environmental conditions.
Early attempts to represent the biological world were founded on categorizing organisms on their physical and metabolic characteristics. These methods, which relied on the sampling of different parts of living organisms or on sequences of small fragments of their DNA, significantly expanded the diversity that could be included in the tree of life2. However the trees are mostly comprised of eukaryotes, and bacterial diversity is still largely unrepresented3,4.
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 by using molecular methods, such as the small-subunit ribosomal gene.
The Tree of Life has been significantly expanded by genome sequencing. However, there is still much diversity to be discovered. This is especially true of microorganisms, which can be difficult to cultivate and are usually only present in a single specimen5. A recent analysis of all genomes produced a rough draft of the Tree of Life. This includes a wide range of bacteria, archaea and other organisms that haven't yet been identified or the diversity of which is not fully understood6.
The expanded Tree of Life is particularly useful in assessing the diversity of an area, assisting to determine if specific habitats require special protection. This information can be used in a range of ways, from identifying the most effective medicines to combating disease to improving crops. This information is also beneficial to conservation efforts. It can aid biologists in identifying areas that are likely to be home to species that are cryptic, which could perform important metabolic functions and be vulnerable to changes caused by humans. Although funds to safeguard biodiversity are vital, ultimately the best way to protect 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 known as an evolutionary tree, illustrates the relationships between different groups of organisms. Scientists can create a phylogenetic chart that shows the evolutionary relationship of taxonomic categories using molecular information and morphological similarities or differences. Phylogeny is crucial in understanding the evolution of biodiversity, evolution and genetics.
A basic phylogenetic tree (see Figure PageIndex 10 ) is a method of identifying the relationships between organisms with similar traits that have evolved from common ancestral. These shared traits can be either homologous or analogous. Homologous characteristics are identical in their evolutionary journey. Analogous traits may look similar however they do not share the same origins. Scientists combine similar traits into a grouping called a Clade. For example, all of the organisms that make up a clade share the trait of having amniotic eggs and evolved from a common ancestor that had eggs. A phylogenetic tree is built by connecting the clades to determine the organisms that are most closely related to one another.
For a more detailed and accurate phylogenetic tree scientists use molecular data from DNA or RNA to establish the relationships between organisms. This information is more precise and provides evidence of the evolution history of an organism. The use of molecular data lets researchers identify the number of organisms who share a common ancestor and to estimate their evolutionary age.
Phylogenetic relationships can be affected by a number of factors that include phenotypicplasticity. page is a kind of behavior that alters as a result of particular environmental conditions. This can cause a trait to appear more similar to one species than to the other and obscure the phylogenetic signals. This issue can be cured by using cladistics, which is a the combination of homologous and analogous traits in the tree.
In addition, phylogenetics helps determine the duration and rate of speciation. This information can aid conservation biologists to decide which species they should protect from extinction. It is ultimately the preservation of phylogenetic diversity that will lead to an ecologically balanced and complete ecosystem.
Evolutionary Theory
The main idea behind evolution is that organisms alter over time because of their interactions with their environment. Many theories of evolution have been proposed by a variety of scientists such as the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who proposed that a living organism develop slowly in accordance with its requirements as well as the Swedish botanist Carolus Linnaeus (1707-1778) who designed the modern hierarchical taxonomy, as well as Jean-Baptiste Lamarck (1744-1829) who suggested that the use or misuse of traits cause changes that could be passed on to offspring.
In the 1930s & 1940s, concepts from various fields, such as genetics, natural selection and particulate inheritance, were brought together to create a modern synthesis of evolution theory. This describes how evolution occurs by the variation of genes in a population and how these variations change over time as a result of natural selection. This model, which includes genetic drift, mutations in gene flow, and sexual selection can be mathematically described mathematically.
Recent discoveries in the field of evolutionary developmental biology have revealed that variation can be introduced into a species by mutation, genetic drift and reshuffling genes during sexual reproduction, as well as through the movement of 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 towards evolution. Evolution is defined as changes in the genome over time as well as changes in the phenotype (the expression of genotypes in an individual).
Students can gain a better understanding of phylogeny by incorporating evolutionary thinking throughout all aspects of biology. A recent study conducted by Grunspan and colleagues, for example, showed that teaching about the evidence supporting evolution helped students accept the concept of evolution in a college biology course. To find out 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 the Concept of Evolution into Life Sciences Education.
Evolution in Action
Scientists have traditionally studied evolution by looking in the past, analyzing fossils and comparing species. They also observe living organisms. Evolution is not a distant moment; it is an ongoing process. The virus reinvents itself to avoid new drugs and bacteria evolve to resist antibiotics. Animals alter their behavior as a result of a changing world. The results are often visible.
But it wasn't until the late 1980s that biologists realized that natural selection could be seen in action, as well. The key is that various traits confer different rates of survival and reproduction (differential fitness) and are passed down from one generation to the next.
In the past, if an allele - the genetic sequence that determines colour appeared in a population of organisms that interbred, it could become more common than other allele. In time, this could mean that the number of moths with 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 see evolutionary change when a species, such as bacteria, has a rapid generation turnover. Since 1988, Richard Lenski, a biologist, has studied twelve populations of E.coli that descend from one strain. Samples of each population have been collected regularly, and more than 50,000 generations of E.coli have passed.
Lenski's research has shown that a mutation can dramatically alter the speed at the rate at which a population reproduces, and consequently the rate at which it changes. It also demonstrates that evolution takes time, a fact that some find difficult to accept.
Another example of microevolution is that mosquito genes for resistance to pesticides appear more frequently in populations in which insecticides are utilized. Pesticides create an exclusive pressure that favors those who have resistant genotypes.
The speed at which evolution takes 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 hinder the species from adapting. Understanding evolution can aid you in making better decisions about the future of the planet and its inhabitants.