The Academy's Evolution Site
Biological evolution is a central concept in biology. The Academies have long been involved in helping people who are interested in science comprehend the theory of evolution and how it permeates every area of scientific inquiry.
This site provides a wide range of sources for students, teachers and general readers of evolution. It includes key video clips from NOVA and WGBH's science programs on DVD.
Tree of Life
The Tree of Life is an ancient symbol of the interconnectedness of life. It is an emblem of love and unity across many cultures. It has many practical applications in addition to providing a framework for understanding the evolution of species and how they react to changing environmental conditions.
The first attempts to depict the world of biology were founded on categorizing organisms on their metabolic and physical characteristics. These methods, which relied on sampling of different parts of living organisms, or sequences of small fragments of their DNA greatly increased the variety of organisms that could be represented in a tree of life2. The trees are mostly composed of eukaryotes, while bacteria are largely underrepresented3,4.
Genetic techniques have greatly broadened our ability to visualize the Tree of Life by circumventing the requirement for direct observation and experimentation. Particularly, molecular techniques allow us to build trees using sequenced markers like the small subunit ribosomal RNA gene.
The Tree of Life has been dramatically expanded through genome sequencing. However there is still a lot of diversity to be discovered. This is particularly the case for microorganisms which are difficult to cultivate, and are usually present in a single sample5. A recent analysis of all known genomes has produced a rough draft of the Tree of Life, including many bacteria and archaea that have not been isolated and their diversity is not fully understood6.
The expanded Tree of Life is particularly useful in assessing the diversity of an area, helping to determine if specific habitats require special protection. The information is useful in a variety of ways, including finding new drugs, battling diseases and improving crops. The information is also incredibly valuable for conservation efforts. It helps biologists determine the areas that are most likely to contain cryptic species with important metabolic functions that could be vulnerable to anthropogenic change. While funds to protect biodiversity are essential, the best way to conserve the biodiversity of the world is to equip more people in developing countries with the necessary knowledge to act locally and promote conservation.
Phylogeny
A phylogeny (also called an evolutionary tree) depicts the relationships between different organisms. Using molecular data, morphological similarities and differences or ontogeny (the process of the development of an organism) scientists can construct a phylogenetic tree which illustrates the evolution of taxonomic categories. The concept of phylogeny is fundamental to understanding evolution, biodiversity and genetics.
A basic phylogenetic Tree (see Figure PageIndex 10 ) identifies the relationships between organisms that share similar traits that evolved from common ancestral. These shared traits can be either homologous or analogous. Homologous traits are the same in their evolutionary journey. Analogous traits could appear like they are but they don't share the same origins. Scientists organize similar traits into a grouping referred to as a Clade. For instance, all of the species in a clade have the characteristic of having amniotic egg and evolved from a common ancestor that had these eggs. weblink join to create a phylogenetic tree to identify organisms that have the closest connection to each other.
To create a more thorough and accurate phylogenetic tree, scientists make use of molecular data from DNA or RNA to determine the connections between organisms. This data is more precise than the morphological data and provides evidence of the evolution background of an organism or group. The analysis of molecular data can help researchers identify the number of organisms who share the same ancestor and estimate their evolutionary age.
Phylogenetic relationships can be affected by a number of factors, including the phenotypic plasticity. This is a type of behavior that changes as a result of specific environmental conditions. This can cause a trait to appear more similar to one species than another, obscuring the phylogenetic signals. However, this problem can be reduced by the use of methods like cladistics, which include a mix of similar and homologous traits into the tree.
In addition, phylogenetics can help predict the length and speed of speciation. This information can aid conservation biologists to make decisions about which species to protect from extinction. It is ultimately the preservation of phylogenetic diversity which will lead to a complete and balanced ecosystem.
Evolutionary Theory
The central theme of evolution is that organisms acquire different features over time as a result of their interactions with their environments. A variety of theories about 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 requirements as well as the Swedish botanist Carolus Linnaeus (1707-1778) who developed the modern hierarchical taxonomy, as well as Jean-Baptiste Lamarck (1744-1829) who suggested that the use or non-use of traits cause changes that could be passed onto offspring.
In the 1930s and 1940s, theories from a variety of fields -- including genetics, natural selection, and particulate inheritance -- came together to form the current evolutionary theory synthesis that explains how evolution occurs through the variation of genes within a population, and how these variants change over time as a result of natural selection. This model, which is known as genetic drift mutation, gene flow and sexual selection, is a key element of current evolutionary biology, and can be mathematically explained.
Recent developments in the field of evolutionary developmental biology have shown that variations can be introduced into a species by mutation, genetic drift and reshuffling of genes in sexual reproduction, and also through the movement of populations. These processes, in conjunction with others such as the directional selection process and the erosion of genes (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).
Incorporating 에볼루션 게이밍 into all areas of biology education can improve students' understanding of phylogeny and evolution. A recent study by Grunspan and colleagues, for instance, showed that teaching about the evidence supporting evolution helped students accept the concept of evolution in a college-level biology class. For more information on how to teach about evolution read The Evolutionary Potency in all Areas of Biology or Thinking Evolutionarily as a Framework for Integrating Evolution into Life Sciences Education.
Evolution in Action
Scientists have traditionally looked at evolution through the past--analyzing fossils and comparing species. They also study living organisms. But evolution isn't a thing that happened in the past, it's an ongoing process, taking place today. Bacteria mutate and resist antibiotics, viruses evolve and elude new medications and animals alter their behavior in response to the changing climate. The results are often apparent.
It wasn't until late 1980s that biologists understood that natural selection could be seen in action, as well. The reason is that different characteristics result in different rates of survival and reproduction (differential fitness) and are passed down 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 could quickly become more prevalent than other alleles. As time passes, that 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 see evolutionary change when the species, like bacteria, has a rapid generation turnover. Since 1988, biologist Richard Lenski has been tracking twelve populations of E. coli that descended from a single strain. samples from each population are taken on a regular basis and more than 50,000 generations have now been observed.
Lenski's work has demonstrated that a mutation can profoundly alter the efficiency with which a population reproduces--and so, the rate at which it evolves. It also shows that evolution is slow-moving, a fact that some find difficult to accept.
Microevolution is also evident in the fact that mosquito genes for resistance to pesticides are more prevalent in populations that have used insecticides. This is due to pesticides causing an exclusive pressure that favors individuals who have resistant genotypes.
The rapid pace of evolution taking place has led to a growing appreciation of its importance in a world shaped by human activity, including climate changes, pollution and the loss of habitats that prevent the species from adapting. Understanding the evolution process will assist you in making better choices regarding the future of the planet and its inhabitants.