The Academy's Evolution Site
The concept of biological evolution is among the most fundamental concepts in biology. The Academies are committed to helping those who are interested in science comprehend the evolution theory and how it can be applied throughout all fields of scientific research.
This site provides students, teachers and general readers with a wide range 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 life. It appears in many spiritual traditions and cultures as a symbol of unity and love. It can be used in many practical ways in addition to providing a framework to understand the evolution of species and how they react to changing environmental conditions.
The earliest attempts to depict the biological world focused on separating species into distinct categories that had been identified by their physical and metabolic characteristics1. These methods, which depend on the sampling of different parts of organisms, or fragments of DNA have significantly increased the diversity of a tree of Life2. However the trees are mostly made up of eukaryotes. Bacterial diversity remains vastly underrepresented3,4.
Genetic techniques have greatly broadened our ability to visualize the Tree of Life by circumventing the need for direct observation and experimentation. Particularly, molecular techniques allow us to construct trees using sequenced markers such as the small subunit ribosomal RNA gene.
Despite the rapid growth of the Tree of Life through genome sequencing, much biodiversity still awaits discovery. This is particularly the case for microorganisms which are difficult to cultivate, and are typically found in a single specimen5. A recent study of all genomes known to date has created a rough draft of the Tree of Life, including many bacteria and archaea that have not been isolated and their diversity is not fully understood6.
This expanded Tree of Life is particularly beneficial in assessing the biodiversity of an area, which can help to determine whether specific habitats require special protection. This information can be used in a range of ways, from identifying new medicines to combating disease to improving crop yields. The information is also useful in conservation efforts. It can aid biologists in identifying those areas that are most likely contain cryptic species with potentially important metabolic functions that may 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 equipped with the knowledge to take action locally to encourage conservation from within.
Phylogeny
A phylogeny, also known as an evolutionary tree, reveals the relationships between various groups of organisms. Using 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 relationships between taxonomic categories. Phylogeny is essential in understanding evolution, biodiversity and genetics.
A basic phylogenetic Tree (see Figure PageIndex 10 Identifies the relationships between organisms with similar traits and evolved from a common ancestor. These shared traits could be analogous, or homologous. Homologous characteristics are identical in terms of their evolutionary journey. Analogous traits may look like they are however they do not have the same origins. Scientists group similar traits together into a grouping referred to as a Clade. All organisms in a group share a trait, such as amniotic egg production. They all evolved from an ancestor that had these eggs. weblink are then connected to form a phylogenetic branch that can identify organisms that have the closest relationship.
Scientists utilize DNA or RNA molecular information to create a phylogenetic chart that is more precise and detailed. This information is more precise and gives evidence of the evolutionary history of an organism. Researchers can use Molecular Data to determine the age of evolution of living organisms and discover the number of organisms that share the same ancestor.
The phylogenetic relationships between species can be influenced by several factors, including phenotypic flexibility, a kind of behavior that alters in response to specific environmental conditions. This can make a trait appear more similar to one species than another and obscure the phylogenetic signals. However, this problem can be reduced by the use of techniques like cladistics, which combine homologous and analogous features into the tree.
Furthermore, phylogenetics may help predict the duration and rate of speciation. This information can aid conservation biologists to make decisions about the species they should safeguard from extinction. In the end, it's the conservation of phylogenetic variety which will create an ecosystem that is complete and balanced.
Evolutionary Theory
The central theme in evolution is that organisms change over time due to their interactions with their environment. Many scientists have developed theories of evolution, such as the Islamic naturalist Nasir al-Din al-Tusi (1201-274) who believed that an organism could evolve according to its individual requirements, the Swedish taxonomist Carolus Linnaeus (1707-1778), who created the modern hierarchical taxonomy, as well as Jean-Baptiste Lamarck (1844-1829), who suggested that the usage or non-use of certain traits can result in changes that are passed on to the next generation.
In the 1930s & 1940s, ideas from different fields, including natural selection, genetics & particulate inheritance, came together to form a contemporary synthesis of evolution theory. This explains how evolution occurs by the variations in genes within the population and how these variations alter over time due to natural selection. This model, which encompasses genetic drift, mutations, gene flow and sexual selection can be mathematically described.
Recent advances in evolutionary developmental biology have demonstrated how variations can be introduced to a species by mutations, genetic drift, reshuffling genes during sexual reproduction and 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 as well as changes in phenotype (the expression of genotypes in individuals).
Incorporating evolutionary thinking into all areas of biology education can increase student understanding of the concepts of phylogeny and evolutionary. A recent study conducted by Grunspan and colleagues, for example, showed that teaching about the evidence supporting evolution increased students' acceptance of evolution in a college-level biology course. For more details on how to teach about evolution, see 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, studying fossils, comparing species, and observing living organisms. However, evolution isn't something that occurred in the past, it's an ongoing process that is taking place today. Bacteria transform and resist antibiotics, viruses evolve and escape new drugs and animals change their behavior in response to the changing climate. The results are often evident.
However, it wasn't until late 1980s that biologists understood that natural selection can be seen in action, as well. The reason is that different traits confer different rates of survival and reproduction (differential fitness) and are transferred from one generation to the next.
In the past when one particular allele, the genetic sequence that defines color in a population of interbreeding organisms, it could quickly become more prevalent than the other alleles. In time, this could mean the number of black moths in a particular population could rise. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
It is easier to see evolution when the species, like bacteria, has a rapid generation turnover. Since 1988 biologist Richard Lenski has been tracking twelve populations of E. bacteria that descend from a single strain. samples of each are taken every day and over 50,000 generations have now passed.
Lenski's research has shown that a mutation can dramatically alter the efficiency with which a population reproduces and, consequently the rate at which it changes. It also demonstrates that evolution takes time, which is difficult for some to accept.
Microevolution can be observed in the fact that mosquito genes that confer resistance to pesticides are more prevalent in areas where insecticides are used. This is due to pesticides causing an enticement that favors those who have resistant genotypes.
The rapidity of evolution has led to an increasing awareness of its significance especially in a planet shaped largely by human activity. This includes the effects of climate change, pollution and habitat loss that hinders many species from adapting. Understanding evolution can assist you in making better choices regarding the future of the planet and its inhabitants.