The Academy's Evolution Site
Biological evolution is one of the most fundamental concepts in biology. The Academies are committed to helping those interested in science to comprehend the evolution theory and how it can be applied throughout all fields of scientific research.
This site provides a wide range of tools for teachers, students and general readers of 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 of the interconnectedness of all life. It appears in many cultures and spiritual beliefs as an emblem of unity and love. It has many practical applications as well, such as providing a framework for understanding the evolution of species and how they react to changes in environmental conditions.
The earliest attempts to depict the biological world focused on separating species into distinct categories that had been distinguished by their physical and metabolic characteristics1. These methods, which rely on the sampling of different parts of living organisms or on short fragments of their DNA, greatly increased the variety of organisms that could be included in a tree of life2. The trees are mostly composed by eukaryotes, and the diversity of bacterial species is greatly underrepresented3,4.
By avoiding the necessity for direct experimentation and observation, genetic techniques have made it possible to depict the Tree of Life in a more precise manner. We can create trees using molecular techniques such as the small subunit ribosomal gene.
Despite the dramatic expansion of the Tree of Life through genome sequencing, much biodiversity still is waiting to be discovered. This is especially true of microorganisms, which can be difficult to cultivate and are typically only represented in a single specimen5. A recent study of all genomes known to date 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 determine the diversity of a specific region and determine if specific habitats require special protection. This information can be utilized in a variety of ways, such as finding new drugs, battling diseases and improving the quality of crops. The information is also incredibly beneficial to conservation efforts. It can aid biologists in identifying areas that are most likely to be home to cryptic species, which could perform important metabolic functions and be vulnerable to human-induced change. Although funding to protect biodiversity are crucial, ultimately the best way to ensure the preservation of biodiversity around the world is for more people living 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) shows the relationships between species. Using molecular data, morphological similarities and differences, or ontogeny (the course of development of an organism) scientists can create a phylogenetic tree which illustrates the evolution of taxonomic categories. Phylogeny is crucial in understanding evolution, biodiversity and genetics.
A basic phylogenetic tree (see Figure PageIndex 10 ) determines the relationship between organisms with similar traits that evolved from common ancestors. These shared traits are either homologous or analogous. Homologous traits are identical in their evolutionary origins, while analogous traits look similar, but do not share the same origins. Scientists combine similar traits into a grouping called a Clade. Every organism in a group share a characteristic, for example, amniotic egg production. They all derived from an ancestor with these eggs. A phylogenetic tree is then constructed by connecting the clades to determine the organisms that are most closely related to one another.
For a more precise and precise phylogenetic tree scientists make use of molecular data from DNA or RNA to identify the relationships between organisms. This data is more precise than morphological data and provides evidence of the evolutionary background of an organism or group. Molecular data allows researchers to identify the number of species that share an ancestor common to them and estimate their evolutionary age.
The phylogenetic relationships of organisms can be influenced by several factors, including phenotypic plasticity a kind of behavior that alters in response to specific environmental conditions. This can cause a characteristic to appear more similar in one species than other species, which can obscure the phylogenetic signal. However, this issue can be reduced by the use of techniques such as cladistics which incorporate a combination of similar and homologous traits into the tree.
Additionally, phylogenetics can aid in predicting the length and speed of speciation. This information can aid conservation biologists in making decisions about which species to save from extinction. It is ultimately the preservation of phylogenetic diversity that will create a complete and balanced ecosystem.
Evolutionary Theory
The central theme of evolution is that organisms develop different features over time based on their interactions with their surroundings. A variety of theories about evolution have been developed by a wide variety of scientists such as the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who proposed that a living organism develop slowly according to its requirements as well as the Swedish botanist Carolus Linnaeus (1707-1778) who conceived modern hierarchical taxonomy, and Jean-Baptiste Lamarck (1744-1829) who suggested that the use or non-use of traits cause changes that could be passed on to the offspring.
In the 1930s and 1940s, theories from a variety of fields -- including natural selection, genetics, and particulate inheritance - came together to create the modern synthesis of evolutionary theory, which defines how evolution is triggered by the variation of genes within a population and how these variants change in time due to natural selection. This model, known as genetic drift or mutation, gene flow, and sexual selection, is a cornerstone of the current evolutionary biology and is mathematically described.
Recent developments in the field of evolutionary developmental biology have revealed the ways in which variation can be introduced to a species by mutations, genetic drift, reshuffling genes during sexual reproduction, and even migration between populations. These processes, as well as others such as directional selection and gene erosion (changes to the frequency of genotypes over time) can lead to evolution. similar site is defined by changes in the genome over time and changes in the phenotype (the expression of genotypes in an individual).
Incorporating evolutionary thinking into all aspects of biology education could increase student understanding of the concepts of phylogeny as well as evolution. A recent study conducted by Grunspan and colleagues, for instance, showed that teaching about the evidence that supports evolution helped students accept the concept of evolution in a college-level biology class. For more information on how to teach evolution look up The Evolutionary Potency in all Areas of Biology or Thinking Evolutionarily A Framework for Integrating Evolution into Life Sciences Education.
Evolution in Action
Traditionally scientists have studied evolution through studying fossils, comparing species and observing living organisms. However, evolution isn't something that happened in the past; it's an ongoing process happening today. Viruses reinvent themselves to avoid new medications and bacteria mutate to resist antibiotics. Animals alter their behavior in the wake of the changing environment. The changes that result are often evident.
It wasn't until the 1980s when biologists began to realize that natural selection was in action. The main reason is that different traits result in a different rate of survival and reproduction, and they can be passed on from one generation to the next.
In the past, if one allele - the genetic sequence that determines colour - was present in a population of organisms that interbred, it could be more common than other allele. Over time, that would mean the number of black moths within the population could increase. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
It is easier to see evolutionary change when a species, such as bacteria, has a high generation turnover. Since 1988, biologist Richard Lenski has been tracking twelve populations of E. bacteria that descend from a single strain. samples of each population are taken every day and more than 50,000 generations have now passed.
Lenski's work has shown that mutations can alter the rate at which change occurs and the efficiency of a population's reproduction. It also shows evolution takes time, a fact that is hard for some to accept.
Another example of microevolution is how mosquito genes that are resistant to pesticides are more prevalent in populations where insecticides are employed. This is because pesticides cause an enticement that favors those who have resistant genotypes.
The rapidity of evolution has led to a greater recognition of its importance particularly in a world shaped largely by human activity. This includes the effects of climate change, pollution and habitat loss, which prevents many species from adapting. Understanding the evolution process will assist you in making better choices regarding the future of the planet and its inhabitants.