The Academy's Evolution Site
Biological evolution is one of the most central concepts in biology. The Academies are committed to helping those who are interested in science comprehend the evolution theory and how it can be applied across all areas of scientific research.
This site provides teachers, students and general readers with a wide range of learning resources about evolution. It includes key video clip from NOVA and WGBH produced science programs on DVD.
evolutionkr of Life
The Tree of Life is an ancient symbol that symbolizes the interconnectedness of life. It is used in many spiritual traditions and cultures as symbolizing unity and love. It has many practical applications as well, including providing a framework for understanding the history of species and how they respond to changes in environmental conditions.
Early approaches to depicting the biological world focused on categorizing organisms into distinct categories that were distinguished by their physical and metabolic characteristics1. These methods, which depend on the sampling of different parts of organisms, or fragments of DNA, have greatly increased the diversity of a tree of Life2. However these trees are mainly made up of eukaryotes. Bacterial diversity remains vastly underrepresented3,4.
By avoiding the necessity for direct observation and experimentation, genetic techniques have made it possible to represent the Tree of Life in a much more accurate way. Particularly, molecular methods enable us to create trees by using sequenced markers, such as the small subunit ribosomal gene.
Despite the rapid expansion of the Tree of Life through genome sequencing, much biodiversity still is waiting to be discovered. This is particularly true of microorganisms, which can be difficult to cultivate and are often only found in a single sample5. Recent analysis of all genomes produced a rough draft of a Tree of Life. This includes a large number of bacteria, archaea and other organisms that haven't yet been identified or the diversity of which is not thoroughly understood6.
The 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, battling diseases and enhancing crops. This information is also extremely valuable to conservation efforts. It helps biologists discover areas that are likely to be home to cryptic species, which could have important metabolic functions and be vulnerable to human-induced change. Although funds to safeguard biodiversity are vital, ultimately the best way to ensure the preservation of biodiversity around the world is for more people in developing countries to be empowered 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 different organisms. Scientists can construct an phylogenetic chart which shows the evolution of taxonomic groups using molecular data and morphological similarities or differences. The phylogeny of a tree plays an important role in understanding the relationship between genetics, biodiversity and evolution.
A basic phylogenetic tree (see Figure PageIndex 10 ) identifies the relationships between organisms that share similar traits that evolved from common ancestors. These shared traits could be either homologous or analogous. Homologous traits are similar in their underlying evolutionary path, while analogous traits look like they do, but don't have the identical origins. Scientists group similar traits together into a grouping called a clade. For instance, all the organisms that make up a clade share the characteristic of having amniotic eggs. They evolved from a common ancestor that had these eggs. A phylogenetic tree is then constructed by connecting clades to identify the organisms that are most closely related to each other.
To create a more thorough and precise phylogenetic tree scientists use molecular data from DNA or RNA to establish the connections between organisms. This data is more precise than morphological data and provides evidence of the evolution history of an organism or group. Researchers can utilize Molecular Data to calculate the age of evolution of organisms and identify how many species have the same ancestor.
The phylogenetic relationships between organisms can be influenced by several factors, including phenotypic plasticity an aspect of behavior that changes in response to specific environmental conditions. This can cause a particular trait to appear more similar in one species than another, obscuring the phylogenetic signal. However, this issue can be cured by the use of techniques such as cladistics which combine similar and homologous traits into the tree.
Additionally, phylogenetics can help determine the duration and speed at which speciation occurs. This information can aid conservation biologists to decide which species they should protect from extinction. In the end, it's the preservation of phylogenetic diversity that will lead to a complete and balanced ecosystem.
Evolutionary Theory
The central theme of evolution is that organisms develop various characteristics over time based on their interactions with their environments. Many scientists have proposed theories of evolution, including the Islamic naturalist Nasir al-Din al-Tusi (1201-274) who believed that an organism could develop according to its own requirements, the Swedish taxonomist Carolus Linnaeus (1707-1778) who developed the modern hierarchical taxonomy as well as Jean-Baptiste Lamarck (1844-1829), who believed that the use or absence of traits can cause changes that are passed on to the
In the 1930s and 1940s, concepts from various fields, such as natural selection, genetics & particulate inheritance, were brought together to form a modern theorizing of evolution. This describes how evolution occurs by the variations in genes within the population, and how these variations alter over time due to natural selection. This model, which encompasses mutations, genetic drift as well as gene flow and sexual selection can be mathematically described mathematically.
Recent advances in evolutionary developmental biology have demonstrated how variation can be introduced to a species by mutations, genetic drift and reshuffling of genes during sexual reproduction and migration between populations. These processes, as well as others such as directional selection or genetic erosion (changes in the frequency of the genotype over time), can lead to evolution, which is defined by change in the genome of the species over time, and also the change in phenotype as time passes (the expression of that genotype within the individual).
Incorporating evolutionary thinking into all aspects of biology education could increase student understanding of the concepts of phylogeny and evolution. A recent study by Grunspan and colleagues, for example revealed that teaching students 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 about evolution, see 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 looking back, studying fossils, comparing species and observing living organisms. Evolution is not a past event, but an ongoing process. Viruses evolve to stay away from new drugs and bacteria evolve to resist antibiotics. Animals alter their behavior in the wake of a changing environment. The resulting changes are often easy to see.
It wasn't until the late 1980s that biologists began realize that natural selection was also in play. The main reason is that different traits confer an individual rate of survival and reproduction, and they can be passed down from one generation to the next.
In the past, if an allele - the genetic sequence that determines colour - appeared in a population of organisms that interbred, it might become more prevalent than any other allele. Over time, that would 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.
The ability to observe evolutionary change is much easier when a species has a rapid generation turnover such as bacteria. Since 1988 biologist Richard Lenski has been tracking twelve populations of E. bacteria that descend from a single strain. samples from each population are taken every day and over fifty thousand generations have passed.
Lenski's research has shown that a mutation can profoundly alter the speed at which a population reproduces--and so the rate at which it alters. It also shows that evolution takes time, a fact that is difficult for some to accept.
Microevolution can be observed in the fact that mosquito genes for pesticide resistance are more prevalent in areas where insecticides are used. This is because pesticides cause an enticement that favors those with resistant genotypes.
The rapidity of evolution has led to a greater recognition of its importance particularly in a world that is largely shaped by human activity. This includes the effects of climate change, pollution and habitat loss that hinders many species from adapting. Understanding evolution can assist you in making better choices regarding the future of the planet and its inhabitants.