The Academy's Evolution Site
Biology is a key concept in biology. The Academies are involved in helping those interested in science comprehend the evolution theory and how it is incorporated in all areas of scientific research.
This site provides students, teachers and general readers with a variety of learning resources about evolution. It includes the most important video clips from NOVA and WGBH's science programs on DVD.
Tree of Life
The Tree of Life, an ancient symbol, symbolizes the interconnectedness of all life. It is seen in a variety of spiritual traditions and cultures as a symbol of unity and love. It also has important practical applications, such as providing a framework for understanding the history of species and how they react to changes in the environment.
The first attempts to depict the world of biology were based on categorizing organisms based on their physical and metabolic characteristics. These methods, which relied on the sampling of various parts of living organisms or on sequences of short DNA fragments, greatly increased the variety of organisms that could be included in a tree of life2. However these trees are mainly composed of eukaryotes; bacterial diversity is still largely unrepresented3,4.
In avoiding the necessity of direct observation and experimentation genetic techniques have allowed us to depict the Tree of Life in a more precise manner. We can create trees by using molecular methods like the small-subunit ribosomal gene.
Despite the dramatic growth of the Tree of Life through genome sequencing, much biodiversity still awaits discovery. This is especially true for microorganisms that are difficult to cultivate and which are usually only found in a single specimen5. A recent analysis of all genomes has produced a rough draft of a Tree of Life. This includes a wide range of archaea, bacteria and other organisms that have not yet been isolated or whose diversity has not been fully understood6.
The expanded Tree of Life can be used to evaluate the biodiversity of a particular area and determine if particular habitats require special protection. The information can be used in a range of ways, from identifying new treatments to fight disease to enhancing the quality of the quality of crops. This information is also valuable for conservation efforts. It can aid biologists in identifying areas that are likely to have species that are cryptic, which could have important metabolic functions and be vulnerable to changes caused by humans. While conservation funds are important, the best method to preserve the world's biodiversity is to equip more people in developing countries with the information they require to act locally and promote conservation.
Phylogeny
A phylogeny (also known as an evolutionary tree) depicts the relationships between different organisms. Utilizing molecular data as well as morphological similarities and distinctions or ontogeny (the course of development of an organism) scientists can create a phylogenetic tree that illustrates the evolution of taxonomic groups. The role of phylogeny is crucial in understanding genetics, biodiversity and evolution.
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 ancestors. These shared traits can be either homologous or analogous. Homologous traits are the same in their evolutionary journey. Analogous traits may look similar, but they do not have the same origins. Scientists put similar traits into a grouping known as a Clade. All members of a clade have a common trait, such as amniotic egg production. They all came from an ancestor that had these eggs. The clades are then connected to form a phylogenetic branch to determine the organisms with the closest relationship to.
Scientists use molecular DNA or RNA data to construct a phylogenetic graph that is more accurate and precise. This data is more precise than morphological information and provides evidence of the evolutionary background of an organism or group. Researchers can utilize Molecular Data to estimate the evolutionary age of organisms and determine how many species have an ancestor common to all.
Phylogenetic relationships can be affected by a number of factors, including the phenotypic plasticity. This is a type of behavior that alters as a result of unique environmental conditions. This can make a trait appear more similar to a species than another and obscure the phylogenetic signals. However, this issue can be reduced by the use of techniques such as cladistics which incorporate a combination of analogous and homologous features into the tree.
Additionally, phylogenetics aids predict the duration and rate at which speciation occurs. 에볼루션 can aid conservation biologists to make decisions about which species to protect from extinction. In the end, it is the conservation of phylogenetic diversity which will create an ecosystem that is balanced and complete.
Evolutionary Theory
The central theme of evolution is that organisms acquire distinct characteristics over time based on their interactions with their surroundings. A variety of theories about evolution have been developed by a wide range of scientists such as the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who envisioned an organism developing slowly according to its needs as well as the Swedish botanist Carolus Linnaeus (1707-1778) who developed the modern hierarchical taxonomy Jean-Baptiste Lamarck (1744-1829) who suggested that the use or non-use of traits causes changes that can be passed onto offspring.
In the 1930s and 1940s, theories from various fields, including natural selection, genetics, and particulate inheritance--came together to form the modern evolutionary theory which explains how evolution occurs through the variations of genes within a population and how these variants change over time due to natural selection. This model, called genetic drift mutation, gene flow, and sexual selection, is a cornerstone of modern evolutionary biology and can be mathematically described.
Recent advances in evolutionary developmental biology have shown how variations can be introduced to a species by genetic drift, mutations and reshuffling of genes during sexual reproduction and migration between populations. These processes, along with others such as directional selection or genetic erosion (changes in the frequency of a genotype over time) can lead to evolution which is defined by changes in the genome of the species over time, and also by changes in phenotype as time passes (the expression of that genotype within the individual).
Students can better understand the concept of phylogeny through incorporating evolutionary thinking throughout all areas of biology. In a recent study by Grunspan and colleagues. It was demonstrated that teaching students about the evidence for evolution increased 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 as a Framework for Integrating Evolution into Life Sciences Education.
Evolution in Action
Scientists have looked at evolution through the past, analyzing fossils and comparing species. They also study living organisms. However, evolution isn't something that happened in the past, it's an ongoing process happening in the present. Bacteria transform and resist antibiotics, viruses evolve and elude new medications, and animals adapt their behavior in response to the changing climate. The results are usually evident.
It wasn't until the late 1980s that biologists began to realize that natural selection was at work. The key is that different traits confer different rates of survival and reproduction (differential fitness) and can be passed down from one generation to the next.
In the past, when one particular allele, the genetic sequence that defines color in a group of interbreeding species, it could rapidly become more common than the other alleles. Over time, this would mean that the number of moths sporting black pigmentation in a 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 track evolution when a species, such as bacteria, has a rapid generation turnover. Since 1988, Richard Lenski, a biologist, has tracked twelve populations of E.coli that are descended from a single strain. The samples of each population have been taken frequently and more than 500.000 generations of E.coli have passed.
Lenski's work has shown that mutations can alter the rate of change and the effectiveness of a population's reproduction. It also shows evolution takes time, which is difficult for some to accept.
Microevolution is also evident in the fact that mosquito genes for resistance to pesticides are more prevalent in populations where insecticides are used. This is due to the fact that the use of pesticides creates a selective pressure that favors those with resistant genotypes.
The rapid pace at which evolution takes place has led to an increasing recognition of its importance in a world that is shaped by human activity, including climate changes, pollution and the loss of habitats that prevent the species from adapting. Understanding evolution can help us make smarter decisions about the future of our planet, and the lives of its inhabitants.