The Academy's Evolution Site
Biology is one of the most central concepts in biology. The Academies are committed to helping those interested in science learn about the theory of evolution and how it can be applied in all areas of scientific research.
This site provides teachers, students and general readers with a variety of learning resources on evolution. It also includes important video clips from NOVA and 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 spiritual traditions and cultures as a symbol of unity and love. It has numerous practical applications in addition to providing a framework for understanding the evolution of species and how they respond to changing environmental conditions.
The first attempts to depict the biological world were founded on categorizing organisms on their physical and metabolic characteristics. These methods depend on the sampling of different parts of organisms or DNA fragments, have significantly increased the diversity of a tree of Life2. The trees are mostly composed of eukaryotes, while bacteria are largely underrepresented3,4.
Genetic techniques have significantly expanded our ability to represent the Tree of Life by circumventing the need for direct observation and experimentation. Particularly, molecular techniques enable us to create trees using sequenced markers like the small subunit of ribosomal RNA gene.
Despite the massive growth of the Tree of Life through genome sequencing, a lot of biodiversity remains to be discovered. This is particularly true of microorganisms that are difficult to cultivate and are usually only present in a single specimen5. A recent study of all genomes that are known has created a rough draft of the Tree of Life, including numerous bacteria and archaea that have not been isolated and which are not well understood.
This expanded Tree of Life is particularly useful in assessing the diversity of an area, which can help to determine if certain habitats require protection. The information is useful in a variety of ways, such as finding new drugs, fighting diseases and enhancing crops. It is also useful in conservation efforts. It helps biologists determine the areas that are most likely to contain cryptic species that could have important metabolic functions that may be at risk of anthropogenic changes. While funds to protect biodiversity are essential, the best way to conserve the world's biodiversity is to empower the people of developing nations with the necessary knowledge to take action locally and encourage conservation.
Phylogeny
A phylogeny, also called an evolutionary tree, illustrates the relationships between groups of organisms. Utilizing molecular data similarities and differences in morphology, or ontogeny (the process of the development of an organism) scientists can create a phylogenetic tree that illustrates the evolutionary relationships between taxonomic groups. Phylogeny is crucial in understanding the evolution of biodiversity, evolution and genetics.
A basic phylogenetic tree (see Figure PageIndex 10 ) is a method of identifying the relationships between organisms that share similar traits that have evolved from common ancestral. These shared traits could be homologous, or analogous. Homologous traits share their underlying evolutionary path and analogous traits appear like they do, but don't have the same ancestors. Scientists arrange similar traits into a grouping called a the clade. All organisms in a group have a common trait, such as amniotic egg production. They all came from an ancestor that had these eggs. The clades then join to form a phylogenetic branch to determine the organisms with the closest relationship to.
For a more precise 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 the morphological data and gives evidence of the evolutionary history of an individual or group. The use of molecular data lets researchers identify the number of organisms that have the same ancestor and estimate their evolutionary age.
The phylogenetic relationships between species can be affected by a variety of factors, including phenotypic plasticity an aspect of behavior that alters in response to unique environmental conditions. This can cause a trait to appear more similar to one species than to another and obscure the phylogenetic signals. However, this problem can be solved through the use of methods such as cladistics which incorporate a combination of similar and homologous traits into the tree.
Additionally, phylogenetics can help predict the duration and rate of speciation. This information can assist conservation biologists in making 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 ecologically balanced and complete ecosystem.
Evolutionary Theory
The fundamental concept in evolution is that organisms alter over time because of their interactions with their environment. Many scientists have come up with theories of evolution, such as the Islamic naturalist Nasir al-Din al-Tusi (1201-274), who believed that a living thing would develop according to its own needs, the Swedish taxonomist Carolus Linnaeus (1707-1778) who conceived the modern hierarchical taxonomy, as well as Jean-Baptiste Lamarck (1844-1829), who suggested that the usage or non-use of traits can cause changes that are passed on to the next generation.
In the 1930s & 1940s, theories from various fields, such as genetics, natural selection, and particulate inheritance, came together to create a modern evolutionary theory. This explains how evolution happens through the variations in genes within the population, and how these variants change with time due to natural selection. This model, known as genetic drift mutation, gene flow and sexual selection, is the foundation of the current evolutionary biology and is mathematically described.
Recent developments in the field of evolutionary developmental biology have shown that genetic variation can be introduced into a species by genetic drift, mutation, and reshuffling of genes in sexual reproduction, as well as by migration between populations. These processes, along with others, such as directional selection and gene erosion (changes to 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 the phenotype (the expression of genotypes within individuals).
Students can gain a better understanding of the concept of phylogeny through incorporating evolutionary thinking in all aspects of biology. In a study by Grunspan et al., it was shown that teaching students about the evidence for evolution boosted their understanding of evolution in a college-level course in biology. For more information about how to teach evolution look up The Evolutionary Power of Biology in All Areas of Biology or Thinking Evolutionarily A Framework for Infusing Evolution into Life Sciences Education.
Evolution in Action
Traditionally, scientists have studied evolution through studying fossils, comparing species and studying living organisms. However, evolution isn't something that occurred in the past; it's an ongoing process that is that is taking place right now. Viruses reinvent themselves to avoid new drugs and bacteria evolve to resist antibiotics. Animals alter their behavior because of a changing environment. evolutionkr that occur are often evident.
It wasn't until late 1980s that biologists understood that natural selection can be observed in action as well. The reason is that different characteristics result in 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 controls coloration - was present in a population of interbreeding species, it could quickly become more prevalent than the other alleles. In time, this could mean that the number of black moths in a particular population could rise. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
It is easier to observe evolutionary change when an organism, like bacteria, has a high generation turnover. Since 1988, Richard Lenski, a biologist, has studied twelve populations of E.coli that descend from a single strain. Samples from each population were taken frequently and more than 50,000 generations of E.coli have been observed to have passed.
Lenski's work has demonstrated that a mutation can dramatically alter the rate at the rate at which a population reproduces, and consequently, the rate at which it alters. It also shows evolution takes time, a fact that is hard for some to accept.
Another example of microevolution is the way mosquito genes that confer resistance to pesticides are more prevalent in populations where insecticides are employed. This is because the use of pesticides creates a selective pressure that favors individuals with resistant genotypes.
The rapidity of evolution has led to a growing recognition of its importance especially in a planet which is largely shaped by human activities. This includes the effects of climate change, pollution and habitat loss that prevents many species from adapting. Understanding evolution can help us make smarter choices about the future of our planet, and the life of its inhabitants.