The Academy's Evolution Site
The concept of biological evolution is among the most important concepts in biology. The Academies are committed to helping those interested in science understand evolution theory and how it is permeated in all areas of scientific research.
This site provides a range of resources for students, teachers as well as general readers about 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 symbolizes the interconnectedness of life. It appears in many religions and cultures as a symbol of unity and love. It also has important practical applications, like providing a framework for understanding the history of species and how they respond to changes in environmental conditions.
Early attempts to describe the biological world were founded on categorizing organisms on their physical and metabolic characteristics. These methods, which relied on the sampling of various parts of living organisms, or small fragments of their DNA significantly expanded the diversity that could be included in the tree of life2. However, these trees are largely comprised of eukaryotes, and bacterial diversity is still largely unrepresented3,4.
By avoiding the necessity for direct observation and experimentation genetic techniques have allowed us to depict the Tree of Life in a much more accurate way. Particularly, molecular techniques allow us to construct trees using sequenced markers like the small subunit of ribosomal RNA gene.
The Tree of Life has been dramatically expanded through genome sequencing. However, there is still much biodiversity to be discovered. This is particularly the case for microorganisms which are difficult to cultivate, and which are usually only found in a single specimen5. Recent analysis of all genomes resulted in an unfinished draft of the Tree of Life. This includes a variety of archaea, bacteria, and other organisms that have not yet been identified or their diversity is not thoroughly understood6.
This expanded Tree of Life is particularly useful for assessing the biodiversity of an area, helping to determine whether specific habitats require protection. The information can be used in a variety of ways, from identifying the most effective treatments to fight disease to enhancing the quality of crops. This information is also extremely valuable in conservation efforts. It helps biologists determine the areas that are most likely to contain cryptic species with potentially significant metabolic functions that could be at risk from anthropogenic change. While funds to protect biodiversity are crucial but the most effective way to ensure the preservation of biodiversity around the world is for more people in developing countries to be equipped with the knowledge to act locally in order to promote conservation from within.
Phylogeny
A phylogeny (also known as an evolutionary tree) depicts the relationships between organisms. By using molecular information similarities and differences in morphology or ontogeny (the process of the development of an organism) scientists can construct a phylogenetic tree which illustrates the evolutionary relationship between taxonomic categories. The phylogeny of a tree plays an important role in understanding biodiversity, genetics and evolution.
A basic phylogenetic Tree (see Figure PageIndex 10 Finds the connections between organisms with similar traits and evolved from a common ancestor. These shared traits may be analogous, or homologous. Homologous traits are similar in their evolutionary origins, while analogous traits look similar but do not have the same ancestors. Scientists group similar traits together into a grouping called a clade. All members of a clade have a common trait, such as amniotic egg production. They all evolved from an ancestor with these eggs. A phylogenetic tree is then built by connecting the clades to identify the species which are the closest to one another.
Scientists use molecular DNA or RNA data to construct a phylogenetic graph which is more precise and detailed. This information is more precise than morphological information and provides evidence of the evolution history of an organism or group. see this can utilize Molecular Data to estimate the evolutionary age of organisms and identify how many organisms share the same ancestor.
The phylogenetic relationship can be affected by a number of factors that include the phenomenon of phenotypicplasticity. This is a kind of behaviour that can change as a result of unique environmental conditions. This can cause a trait to appear more like a species another, obscuring the phylogenetic signal. This problem can be addressed by using cladistics. This is a method that incorporates the combination of analogous and homologous features in the tree.
Additionally, phylogenetics can help predict the duration and rate of speciation. This information will assist conservation biologists in making choices about which species to safeguard from extinction. In the end, it's the conservation of phylogenetic variety which will create an ecosystem that is balanced and complete.
Evolutionary Theory
The fundamental concept of evolution is that organisms acquire distinct characteristics over time as a result of their interactions with their environment. Many theories of evolution have been developed by a wide variety of scientists including the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who believed that an organism would evolve slowly according to its requirements, the Swedish botanist Carolus Linnaeus (1707-1778) who developed modern hierarchical taxonomy, and Jean-Baptiste Lamarck (1744-1829) who suggested that the use or non-use of traits causes changes that could be passed on to offspring.
In the 1930s and 1940s, concepts 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 occurs through the variations of genes within a population, and how these variants change over time due to natural selection. This model, known as genetic drift, mutation, gene flow and sexual selection, is a key element of the current evolutionary biology and can be mathematically explained.
Recent discoveries in the field of evolutionary developmental biology have revealed that variation can be introduced into a species through mutation, genetic drift and reshuffling of genes during sexual reproduction, and also through migration between populations. These processes, along with others such as directional selection and gene erosion (changes in the frequency of genotypes over time) can result in evolution. Evolution is defined as changes in the genome over time as well as changes in the phenotype (the expression of genotypes in individuals).
Incorporating evolutionary thinking into all areas of biology education can improve students' understanding of phylogeny as well as evolution. A recent study by Grunspan and colleagues, for example revealed that teaching students about the evidence for evolution helped students accept the concept of evolution in a college biology class. For more details on how to teach evolution read The Evolutionary Potential in All Areas of Biology or Thinking Evolutionarily A Framework for Infusing Evolution into Life Sciences Education.
Evolution in Action
Scientists have traditionally looked at evolution through the past, analyzing fossils and comparing species. They also study living organisms. But evolution isn't just something that occurred in the past, it's an ongoing process happening in the present. Bacteria evolve and resist antibiotics, viruses reinvent themselves and elude new medications and animals alter their behavior in response to a changing planet. The changes that occur are often visible.
It wasn't until late 1980s that biologists realized that natural selection can be observed in action as well. The key is that various traits confer different rates of survival and reproduction (differential fitness), and can be passed 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 common than other alleles. In time, this could mean that the number of moths sporting black pigmentation in a group may increase. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
It is easier to observe evolution when the species, like bacteria, has a rapid generation turnover. 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 on a regular basis and over fifty thousand generations have been observed.
Lenski's work has shown that mutations can alter the rate at which change occurs and the rate at which a population reproduces. It also demonstrates that evolution takes time, a fact that some people are unable to accept.
Microevolution is also evident in the fact that mosquito genes for pesticide resistance are more prevalent in populations that have used insecticides. This is because pesticides cause a selective pressure which favors those who have resistant genotypes.
The rapidity of evolution has led to an increasing recognition of its importance especially in a planet which is largely shaped by human activities. This includes climate change, pollution, and habitat loss, which prevents many species from adapting. Understanding the evolution process can help us make better decisions regarding the future of our planet, as well as the life of its inhabitants.