The Academy's Evolution Site
Biology is a key concept in biology. The Academies are involved in helping those interested in the sciences understand evolution theory and how it can be applied throughout all fields of scientific research.
This site provides a wide range of resources for students, teachers and general readers of evolution. It contains key video clips 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 appears in many cultures and spiritual beliefs as a symbol of unity and love. It also has important practical uses, like providing a framework for understanding the evolution of species and how they react to changes in the environment.
The first attempts at depicting the biological world focused on categorizing organisms into distinct categories which had been distinguished by their physical and metabolic characteristics1. These methods, which rely on the sampling of different parts of organisms or short DNA fragments, have greatly increased the diversity of a Tree of Life2. The trees are mostly composed by eukaryotes, and bacteria are largely underrepresented3,4.
Genetic techniques have significantly expanded our ability to visualize the Tree of Life by circumventing the requirement for direct observation and experimentation. We can create trees using molecular methods like the small-subunit ribosomal gene.
The Tree of Life has been significantly expanded by genome sequencing. However there is still a lot of biodiversity to be discovered. This is particularly true for microorganisms, which are difficult to cultivate and are typically only represented in a single sample5. A recent analysis of all known genomes has produced a rough draft version of the Tree of Life, including many archaea and bacteria that have not been isolated, and their diversity is not fully understood6.
The expanded Tree of Life can be used to assess the biodiversity of a specific area and determine if particular habitats require special protection. This information can be utilized in a variety of ways, such as identifying new drugs, combating diseases and improving the quality of crops. This information is also valuable for conservation efforts. It can help biologists identify areas most likely to be home to cryptic species, which may have important metabolic functions, and could be susceptible to the effects of human activity. Although funding to protect biodiversity are essential but the most effective way to protect the world's biodiversity is for more people living in developing countries to be empowered with the knowledge to take action locally to encourage conservation from within.
Phylogeny
A phylogeny (also known as an evolutionary tree) illustrates the relationship between species. Scientists can construct an phylogenetic chart which shows the evolution of taxonomic groups based on molecular data and morphological differences or similarities. Phylogeny is crucial in understanding biodiversity, evolution and genetics.
A basic phylogenetic Tree (see Figure PageIndex 10 Determines the relationship between organisms with similar traits and have evolved from a common ancestor. These shared traits may be analogous or homologous. Homologous traits share their evolutionary roots while analogous traits appear similar, but do not share the identical origins. Scientists put similar traits into a grouping called a the clade. Every organism in a group have a common characteristic, like amniotic egg production. They all derived from an ancestor with these eggs. A phylogenetic tree is constructed by connecting the clades to identify the species which are the closest to each other.
For a more detailed and precise phylogenetic tree scientists make use of molecular data from DNA or RNA to identify the connections between organisms. This information is more precise and provides evidence of the evolution of an organism. The analysis of molecular data can help researchers determine the number of organisms that have an ancestor common to them and estimate their evolutionary age.
The phylogenetic relationships of a species can be affected by a variety of factors that include the phenotypic plasticity. This is a type behaviour that can change in response to specific environmental conditions. This can cause a characteristic to appear more similar to a species than to another which can obscure the phylogenetic signal. However, this problem can be solved through the use of techniques like cladistics, which combine homologous and analogous features into the tree.
Furthermore, phylogenetics may aid in predicting the length and speed of speciation. This information can assist conservation biologists decide the species they should safeguard from the threat of extinction. In the end, it is the preservation of phylogenetic diversity that will result in an ecosystem that is complete and balanced.
Evolutionary Theory
The central theme of evolution is that organisms develop different features over time due to their interactions with their surroundings. Many scientists have come up with theories of evolution, including the Islamic naturalist Nasir al-Din al-Tusi (1201-274) who believed that an organism could evolve according to its individual requirements and needs, the Swedish taxonomist Carolus Linnaeus (1707-1778) who conceived the modern hierarchical taxonomy as well as Jean-Baptiste Lamarck (1844-1829), who believed that the use or absence of traits can cause changes that are passed on to the
In the 1930s and 1940s, ideas from a variety of fields--including genetics, natural selection, and particulate inheritance - came together to create the modern evolutionary theory synthesis that explains how evolution happens through the variation of genes within a population, and how those variants change in time due to natural selection. This model, which is known as genetic drift mutation, gene flow and sexual selection, is a key element of modern evolutionary biology and can be mathematically explained.
Recent advances in the field of evolutionary developmental biology have revealed how variation can be introduced to a species by mutations, genetic drift, reshuffling genes during sexual reproduction, and even migration between populations. These processes, along with other ones like the directional selection process and the erosion of genes (changes in the frequency of genotypes over time), can lead towards evolution. Evolution is defined by changes in the genome over time, as well as changes in phenotype (the expression of genotypes within individuals).
Incorporating evolutionary thinking into all aspects of biology education could increase student understanding of the concepts of phylogeny and evolution. In a recent study conducted by Grunspan and co., it was shown that teaching students about the evidence for evolution increased their acceptance of evolution during an undergraduate biology course. To find out more about how to teach about evolution, look up The Evolutionary Potential in all Areas of Biology and Thinking Evolutionarily A Framework for Infusing the Concept of Evolution into Life Sciences Education.
Evolution in Action
Traditionally scientists have studied evolution through looking back, studying fossils, comparing species and studying living organisms. Evolution is not a distant event, but an ongoing process. Bacteria mutate and resist antibiotics, viruses evolve and are able to evade new medications and animals change their behavior to the changing environment. The changes that occur are often apparent.
But it wasn't until the late 1980s that biologists realized that natural selection can be seen in action, as well. The key is that different characteristics result in different rates of survival and reproduction (differential fitness) and can be passed down from one generation to the next.
In the past, if one particular allele - the genetic sequence that controls coloration - was present in a population of interbreeding organisms, it could rapidly become more common than other alleles. In time, Evolutionkr.Kr this could mean that the number of moths that have black pigmentation may increase. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
The ability to observe evolutionary change is easier when a particular species has a fast generation turnover such as bacteria. Since 1988, Richard Lenski, a biologist, has studied twelve populations of E.coli that are descended from a single strain. Samples of each population have been taken regularly, and more than 500.000 generations of E.coli have been observed to have passed.
Lenski's research has shown that a mutation can profoundly alter the efficiency with which a population reproduces--and so the rate at which it changes. It also proves that evolution takes time--a fact that some find difficult to accept.
Microevolution can also be seen in the fact that mosquito genes that confer resistance to pesticides are more common in populations where insecticides have been used. This is because the use of pesticides creates a selective pressure that favors people with resistant genotypes.
The rapidity of evolution has led to an increasing appreciation of its importance particularly in a world that is largely shaped by human activity. This includes the effects of climate change, pollution and habitat loss that prevents many species from adapting. Understanding evolution can help us make better decisions regarding the future of our planet as well as the life of its inhabitants.