The Academy's Evolution Site
Biological evolution is a central concept in biology. The Academies have been for a long time involved in helping people who are interested in science comprehend the theory of evolution and how it affects all areas of scientific research.
This site provides teachers, students and general readers with a range of educational resources on evolution. It contains the most important 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 religions and cultures as symbolizing unity and love. It also has many practical applications, like providing a framework to understand the history of species and how they respond to changes in environmental conditions.
The first attempts to depict the world of biology were based on categorizing organisms based on their metabolic and physical characteristics. These methods rely on the sampling of different parts of organisms, or fragments of DNA, have greatly increased the diversity of a tree of Life2. However, these trees are largely made up of eukaryotes. Bacterial diversity is not represented in a large way3,4.
Genetic techniques have significantly expanded our ability to visualize the Tree of Life by circumventing the requirement for direct observation and experimentation. In particular, molecular methods allow us to build trees using sequenced markers such as the small subunit of ribosomal RNA gene.
Despite the rapid growth of the Tree of Life through genome sequencing, a lot of biodiversity is waiting to be discovered. This is particularly true of microorganisms, which are difficult to cultivate and are typically only present in a single specimen5. A recent analysis of all genomes produced an unfinished draft of the 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 is particularly useful in assessing the diversity of an area, assisting to determine if certain habitats require special protection. The information can be used in a variety of ways, from identifying new medicines to combating disease to enhancing the quality of the quality of crops. This information is also extremely useful to conservation efforts. It helps biologists determine those areas that are most likely contain cryptic species with significant metabolic functions that could be vulnerable to anthropogenic change. Although funds to protect biodiversity are crucial, ultimately the best way to protect the world's biodiversity is for more people living in developing countries to be empowered with the necessary knowledge to act locally to promote conservation from within.
Phylogeny
A phylogeny, also known as an evolutionary tree, shows the relationships between various groups of organisms. Scientists can construct a phylogenetic chart that shows the evolution of taxonomic groups based on molecular data and morphological differences or similarities. Phylogeny is crucial in understanding the evolution of 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 may be analogous, or homologous. Homologous traits are the same in their evolutionary path. Analogous traits might appear like they are however they do not have the same ancestry. Scientists put similar traits into a grouping known as a the clade. For instance, all the organisms in a clade have the characteristic of having amniotic egg and evolved from a common ancestor which had these eggs. A phylogenetic tree is then constructed by connecting the clades to identify the species that are most closely related to one another.
For a more precise and accurate phylogenetic tree scientists make use of molecular data from DNA or RNA to establish the relationships among organisms. This information is more precise and gives evidence of the evolutionary history of an organism. Researchers can use Molecular Data to determine the evolutionary age of organisms and identify how many organisms have a common ancestor.
The phylogenetic relationships of a species can be affected by a number of factors, including the phenotypic plasticity. This is a kind of behavior that changes due to specific environmental conditions. This can cause a characteristic to appear more similar in one species than another, obscuring the phylogenetic signal. However, this problem can be reduced by the use of techniques such as cladistics which combine homologous and analogous features into the tree.
In addition, phylogenetics can aid in predicting the duration and rate of speciation. This information will assist conservation biologists in making decisions about which species to save from extinction. Ultimately, it is the preservation of phylogenetic diversity which will create a complete and balanced ecosystem.
Evolutionary Theory
The central theme in evolution is that organisms change over time as a result of their interactions with their environment. 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 would evolve according to its own needs, the Swedish taxonomist Carolus Linnaeus (1707-1778) who developed the modern taxonomy system that is hierarchical, as well as Jean-Baptiste Lamarck (1844-1829), who suggested that the use or non-use of certain traits can result in changes that are passed on to the next generation.
In the 1930s and 1940s, theories from various areas, including genetics, natural selection and particulate inheritance, were brought together to form a modern evolutionary theory. This explains how evolution is triggered by the variation in genes within a population and how these variations alter over time due to natural selection. This model, which is known as genetic drift or mutation, gene flow, and sexual selection, is a key element of modern evolutionary biology and can be mathematically explained.
Recent developments in the field of evolutionary developmental biology have revealed that variation can be introduced into a species through mutation, genetic drift and reshuffling genes during sexual reproduction, and also through 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 to evolution. Evolution is defined by changes in the genome over time as well as changes in phenotype (the expression of genotypes in individuals).
Students can gain a better understanding of phylogeny by incorporating evolutionary thinking in all aspects of biology. A recent study conducted by Grunspan and colleagues, for instance revealed that teaching students about the evidence that supports 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 as a Framework for Infusing Evolution into Life Sciences Education.
Evolution in Action
Scientists have traditionally studied evolution through looking back in the past--analyzing fossils and comparing species. They also study living organisms. But evolution isn't a thing that happened in the past; it's an ongoing process taking place in the present. Bacteria mutate and resist antibiotics, viruses re-invent themselves and elude new medications, and animals adapt their behavior to the changing climate. The resulting changes are often easy to see.
It wasn't until the late 1980s that biologists began realize that natural selection was at work. The key is that various traits confer different rates of survival and reproduction (differential fitness) and can be transferred from one generation to the next.
In the past, if one allele - the genetic sequence that determines color - was found in a group of organisms that interbred, it could become more prevalent than any other allele. In time, this could mean that the number of black moths in a population could increase. visit website is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
It is easier to observe evolutionary change when the species, like bacteria, has a high generation turnover. Since 1988, Richard Lenski, a biologist, has been tracking twelve populations of E.coli that are descended from one strain. Samples from each population were taken regularly and more than 500.000 generations of E.coli have passed.
Lenski's research has demonstrated that mutations can alter the rate at which change occurs and the efficiency of a population's reproduction. It also shows that evolution takes time, something that is hard for some to accept.
Microevolution can also be seen in the fact that mosquito genes for resistance to pesticides are more prevalent in populations that have used insecticides. This is due to pesticides causing an enticement that favors those with resistant genotypes.
The rapidity of evolution has led to an increasing awareness of its significance especially in a planet which is largely shaped by human activities. This includes climate change, pollution, and habitat loss that prevents many species from adapting. Understanding evolution will help us make better decisions regarding the future of our planet, as well as the life of its inhabitants.