Biology is one of the most important concepts in biology. The Academies have long been involved in helping those interested in science understand the theory of evolution and how it influences all areas of scientific research.
This site provides students, teachers and general readers with a wide range of learning resources about evolution. It contains key video clips from NOVA and WGBH's science programs on DVD.
Tree of Life
The Tree of Life, an ancient symbol, symbolizes the interconnectedness of all life. It is used in many religions and cultures as an emblem of unity and love. It has many practical applications as well, including providing a framework to understand the history of species and how they react 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 rely on the sampling of different parts of organisms or short DNA fragments, have greatly increased the diversity of a tree of Life2. However, these trees are largely comprised of eukaryotes, and bacterial diversity is not represented in a large way3,4.
By avoiding the necessity for direct observation and experimentation genetic techniques have enabled us to represent the Tree of Life in a much more accurate way. Particularly, molecular methods allow us to build trees by using sequenced markers like the small subunit of ribosomal RNA gene.
The Tree of Life has been greatly expanded thanks to genome sequencing. However, there is still much biodiversity to be discovered. This is particularly true of microorganisms, which can be difficult to cultivate and are usually only represented in a single specimen5. A recent analysis of all known genomes has created a rough draft of the Tree of Life, including numerous bacteria and archaea that have not been isolated and whose diversity is poorly understood6.This expanded Tree of Life can be used to assess the biodiversity of a specific area and determine if certain habitats need special protection. This information can be utilized in a range of ways, from identifying the most effective treatments to fight disease to enhancing the quality of crops. The information is also valuable to conservation efforts. It helps biologists discover areas most likely to have cryptic species, which may have vital metabolic functions and are susceptible to human-induced change. Although funding to protect biodiversity are essential but the most effective way to protect the world's biodiversity is for more people in developing countries to be equipped with the knowledge to act locally to promote conservation from within.
Phylogeny
A phylogeny is also known as an evolutionary tree, shows 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 biodiversity, evolution and genetics.
A basic phylogenetic Tree (see Figure PageIndex 10 ) determines the relationship between organisms that share similar traits that evolved from common ancestral. These shared traits can be either analogous or homologous. Homologous traits are similar in their underlying evolutionary path, while analogous traits look like they do, but don't have the same ancestors. Scientists organize similar traits into a grouping referred to as a the clade. Every organism in a group have a common trait, such as amniotic egg production. They all evolved from an ancestor that had these eggs. The clades are then connected to create a phylogenetic tree to determine the organisms with the closest relationship.
For a more detailed and accurate phylogenetic tree scientists rely on molecular information from DNA or RNA to identify the relationships between organisms. This data is more precise than morphological data and provides evidence of the evolution background of an organism or group. The analysis of molecular data can help researchers determine the number of species who share the same ancestor and estimate their evolutionary age.
The phylogenetic relationship can be affected by a variety of factors that include the phenotypic plasticity. This is a type of behavior that changes 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 mitigated by using cladistics. This is a method that incorporates the combination of homologous and analogous features in the tree.
Additionally, phylogenetics can aid in predicting the length and speed of speciation. This information can aid conservation biologists to make decisions about which species to protect from the threat of extinction. In the end, it's the preservation of phylogenetic diversity that will result in an ecosystem that is balanced and complete.
Evolutionary Theory
The main idea behind evolution is that organisms acquire different features over time due to their interactions with their environment. Many theories of evolution have been developed by a variety of scientists including the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who proposed that a living organism develop gradually according to its needs and needs, 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 non-use of traits can cause changes that can be passed on to the offspring.
In the 1930s and 1940s, concepts from a variety of fields -- including genetics, natural selection and particulate inheritance - came together to form the modern synthesis of evolutionary theory that explains how evolution happens through the variations of genes within a population and how these variants change in time due to natural selection. This model, known as genetic drift mutation, gene flow, and sexual selection, is the foundation of current evolutionary biology, and is mathematically described.
Recent discoveries in evolutionary developmental biology have revealed how variation can be introduced to a species through mutations, genetic drift or reshuffling of genes in sexual reproduction and the movement between populations. These processes, along with others like directional selection and genetic erosion (changes in the frequency of an individual's genotype over time) can result in evolution that is defined as changes in the genome of the species over time, and also the change in phenotype over time (the expression of the genotype within the individual).
Students can gain a better understanding of the concept of phylogeny through incorporating evolutionary thinking throughout all aspects of biology. A recent study conducted by Grunspan and colleagues, for instance revealed that teaching students about the evidence for evolution helped students accept the concept of evolution in a college-level biology course. To learn more about how to teach about evolution, please read The Evolutionary Potential of All Areas of Biology and Thinking Evolutionarily: A Framework for Infusing Evolution into Life Sciences Education.
Evolution in Action
Scientists have studied evolution by looking in the past, analyzing fossils and comparing species. They also study living organisms. Evolution is not a past event, but an ongoing process that continues to be observed today. Bacteria evolve and resist antibiotics, viruses evolve and elude new medications and animals alter their behavior to a changing planet. The resulting changes are often easy to see.
It wasn't until late 1980s when biologists began to realize that natural selection was also in action. The key to this is that different traits confer an individual rate of survival and reproduction, and they can be passed on from one generation to the next.
In the past, if one particular allele--the genetic sequence that determines coloration--appeared in a population of interbreeding organisms, it might 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 track evolution when an organism, like bacteria, has a high generation turnover. Since 1988, Richard Lenski, a biologist, has been tracking twelve populations of E.coli that descend from a single strain. Samples of each population have been collected frequently and more than 500.000 generations of E.coli have been observed to have passed.
Lenski's work has demonstrated that a mutation can dramatically alter the speed at which a population reproduces and, consequently the rate at which it changes. It also proves that evolution is slow-moving, a fact that many find difficult to accept.
Another example of microevolution is that mosquito genes for resistance to pesticides are more prevalent in areas where insecticides are used. This is because pesticides cause a selective pressure which favors those who have resistant genotypes.
The speed of evolution taking place has led to an increasing appreciation of its importance in a world shaped by human activities, including climate change, pollution, and the loss of habitats which prevent the species from adapting. Understanding the evolution process can help us make better choices about the future of our planet, as well as the lives of its inhabitants.
