The Academy's Evolution Site
Biological evolution is a central concept in biology. The Academies have long been involved in helping those interested in science comprehend the theory of evolution and how it influences all areas of scientific research.
This site provides students, teachers and general readers with a variety of educational resources on evolution. It includes important video clips from NOVA and WGBH-produced science programs on DVD.
Tree of Life
The Tree of Life, an ancient symbol, represents the interconnectedness of all life. It appears in many cultures and spiritual beliefs as an emblem of unity and love. It also has many practical applications, like providing a framework for understanding the history of species and how they react to changes in environmental conditions.
Early attempts to describe the biological world were based on categorizing organisms based on their metabolic and physical characteristics. These methods, which relied on the sampling of various parts of living organisms or sequences of small DNA fragments, greatly increased the variety of organisms that could be represented in the tree of life2. The trees are mostly composed by eukaryotes and bacterial diversity is vastly underrepresented3,4.
Genetic techniques have significantly expanded our ability to visualize the Tree of Life by circumventing the requirement for direct observation and experimentation. Particularly, molecular methods allow us to build trees by using sequenced markers such as the small subunit ribosomal gene.
Despite the dramatic growth of the Tree of Life through genome sequencing, a large amount of biodiversity is waiting to be discovered. This is especially relevant to microorganisms that are difficult to cultivate and are usually found in one sample5. A recent analysis of all genomes that are known has produced a rough draft version of the Tree of Life, including numerous bacteria and archaea that have not been isolated and whose diversity is poorly understood6.
The expanded Tree of Life can be used to evaluate the biodiversity of a specific area and determine if specific habitats require special protection. This information can be used in a variety of ways, including finding new drugs, fighting diseases and enhancing crops. The information is also valuable to conservation efforts. It can aid biologists in identifying those areas that are most likely contain cryptic species with potentially important metabolic functions that could be at risk of anthropogenic changes. While funds to protect biodiversity are crucial, ultimately the best way to protect the world's biodiversity is for more people 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, reveals the connections between groups of organisms. Using molecular data, morphological similarities and differences or ontogeny (the process of the development of an organism) scientists can create a phylogenetic tree that illustrates the evolution of taxonomic categories. Phylogeny is crucial in understanding biodiversity, evolution and genetics.
A basic phylogenetic tree (see Figure PageIndex 10 Determines the relationship between organisms that have similar traits and have evolved from an ancestor that shared traits. These shared traits can be either homologous or analogous. Homologous traits are similar in their evolutionary roots and analogous traits appear similar but do not have the identical origins. Scientists put similar traits into a grouping called a Clade. For instance, all the organisms that make up a clade have the characteristic of having amniotic egg and evolved from a common ancestor who had eggs. A phylogenetic tree is then built by connecting the clades to identify the organisms who are the closest to one another.
Scientists utilize DNA or RNA molecular data to create a phylogenetic chart that is more precise and detailed. This information is more precise and provides evidence of the evolution of an organism. The use of molecular data lets researchers determine the number of species that share a common ancestor and to estimate their evolutionary age.
The phylogenetic relationships between organisms can be affected by a variety of factors, including phenotypic plasticity a kind of behavior that changes in response to specific environmental conditions. This can cause a trait to appear more resembling to one species than to another which can obscure the phylogenetic signal. However, this problem can be solved through the use of methods such as cladistics which include a mix of homologous and analogous features into the tree.
Additionally, phylogenetics aids predict the duration and rate of speciation. This information will assist conservation biologists in making choices about which species to protect from the threat of extinction. It is ultimately the preservation of phylogenetic diversity which will create an ecologically balanced and complete ecosystem.
Evolutionary Theory
The fundamental concept of evolution is that organisms acquire distinct characteristics over time as a result of their interactions with their surroundings. Several theories of evolutionary change have been developed by a variety of scientists such as the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who believed that an organism would evolve slowly according to its requirements 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 use or disuse of traits causes changes that can be passed on to offspring.
In the 1930s and 1940s, concepts from various areas, including natural selection, genetics & particulate inheritance, came together to create a modern synthesis of evolution theory. This defines 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, mutation, gene flow and sexual selection, is a cornerstone of the current evolutionary biology and can be mathematically explained.
Recent discoveries in the field of evolutionary developmental biology have shown that genetic variation can be introduced into a species through genetic drift, mutation, and reshuffling of genes in sexual reproduction, as well as through the movement of populations. These processes, along with others like directional selection and genetic erosion (changes in the frequency of an individual's genotype over time) can lead to evolution which is defined by change in the genome of the species over time and the change in phenotype as time passes (the expression of that genotype within the individual).
Students can gain a better understanding of the concept of phylogeny by using evolutionary thinking into all aspects of biology. A recent study by Grunspan and colleagues, for example demonstrated that teaching about the evidence for evolution helped students accept the concept of evolution in a college-level biology course. To find out more about how to teach about evolution, please read The Evolutionary Potential in All Areas of Biology and Thinking Evolutionarily: A Framework for Infusing Evolution in Life Sciences Education.
Evolution in Action
Traditionally, scientists have studied evolution through studying fossils, comparing species, and observing living organisms. Evolution is not a past event, but a process that continues today. Bacteria transform and resist antibiotics, viruses evolve and are able to evade new medications and animals change their behavior in response to the changing environment. The results are usually visible.
But it wasn't until the late 1980s that biologists realized that natural selection could be seen in action, as well. The key is the fact that different traits confer a different rate of survival and reproduction, and they can be passed on from one generation to the next.
In the past when one particular allele--the genetic sequence that controls coloration - was present in a population of interbreeding organisms, it might quickly become more prevalent than all other alleles. As time passes, that could mean the number of black moths in the population could increase. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
Observing 에볼루션 룰렛 in action is easier when a particular species has a rapid generation turnover, as with bacteria. Since 1988 the biologist Richard Lenski has been tracking twelve populations of E. coli that descended from a single strain. samples of each are taken on a regular basis, and over 500.000 generations have been observed.
Lenski's research has demonstrated that mutations can alter the rate of change and the effectiveness of a population's reproduction. It also shows that evolution takes time, which is hard for some to accept.
Another example of microevolution is how mosquito genes for resistance to pesticides show up more often in areas in which insecticides are utilized. Pesticides create an exclusive pressure that favors individuals who have resistant genotypes.
The rapidity of evolution has led to a greater recognition of its importance especially in a planet shaped largely by human activity. This includes climate change, pollution, and habitat loss, which prevents many species from adapting. Understanding the evolution process can help us make smarter decisions regarding the future of our planet and the lives of its inhabitants.