The Academy's Evolution Site
Biological evolution is one of the most fundamental concepts in biology. The Academies are committed to helping those who are interested in science understand evolution theory and how it is incorporated throughout all fields of scientific research.
This site provides students, teachers and general readers with a range of learning resources about evolution. It includes key video clip from NOVA and WGBH produced science programs on DVD.
Tree of Life
The Tree of Life is an ancient symbol that represents the interconnectedness of life. It is a symbol of love and unity in many cultures. It also has important practical uses, like providing a framework for understanding the evolution of species and how they respond to changes in environmental conditions.
The first attempts to depict the world of biology were built on categorizing organisms based on their physical and metabolic characteristics. These methods, which rely on sampling of different parts of living organisms, or sequences of short fragments of their DNA, significantly increased the variety that could be included in a tree of life2. The trees are mostly composed of eukaryotes, while bacterial diversity is vastly underrepresented3,4.
Genetic techniques have greatly expanded our ability to depict the Tree of Life by circumventing the need for direct observation and experimentation. We can create trees using molecular techniques like the small-subunit ribosomal gene.
The Tree of Life has been significantly expanded by genome sequencing. However there is still a lot of diversity 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 resulted in a rough draft of the Tree of Life. This includes a variety of bacteria, archaea and other organisms that have not yet been identified or their diversity 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 specific habitats require protection. This information can be used in many ways, including identifying new drugs, combating diseases and improving the quality of crops. The information is also incredibly beneficial in conservation efforts. It can aid biologists in identifying the areas most likely to contain cryptic species that could have significant metabolic functions that could be at risk from anthropogenic change. While funds to protect biodiversity are essential, the best way to conserve the world's biodiversity is to equip more people in developing nations with the necessary knowledge to take action locally and encourage conservation.
Phylogeny
A phylogeny, also called an evolutionary tree, reveals the relationships between various groups of organisms. By using molecular information similarities and differences in morphology or ontogeny (the process of the development of an organism) scientists can create a phylogenetic tree which illustrates the evolution of taxonomic groups. Phylogeny is essential in understanding biodiversity, evolution and genetics.
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 can be either homologous or analogous. Homologous traits are identical in their evolutionary origins and analogous traits appear similar, but do not share the same origins. Scientists arrange similar traits into a grouping referred to as a clade. All organisms in a group share a characteristic, like amniotic egg production. They all evolved from an ancestor that had these eggs. A phylogenetic tree is then constructed by connecting the clades to identify the organisms that are most closely related to one another.
For a more precise and accurate phylogenetic tree scientists rely on molecular information from DNA or RNA to determine the connections between organisms. This information is more precise and provides evidence of the evolutionary history of an organism. The analysis of molecular data can help researchers determine the number of species that share the same ancestor and estimate their evolutionary age.
The phylogenetic relationships of organisms can be affected by a variety of factors, including phenotypic flexibility, a type of behavior that changes in response to specific environmental conditions. This can cause a trait to appear more similar to one species than another, clouding the phylogenetic signal. This issue can be cured by using cladistics, which incorporates an amalgamation of homologous and analogous traits in the tree.
Additionally, phylogenetics can aid in predicting the time and pace of speciation. This information can help conservation biologists decide which species to protect from the threat of extinction. In the end, it's the conservation of phylogenetic variety that will result in an ecosystem that is complete and balanced.
Evolutionary Theory
The fundamental concept in evolution is that organisms alter over time because of their interactions with their environment. Many theories of evolution have been developed by a wide variety of scientists such as the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who believed that an organism would evolve slowly in accordance with its needs, the Swedish botanist Carolus Linnaeus (1707-1778) who conceived the modern hierarchical taxonomy Jean-Baptiste Lamarck (1744-1829) who suggested that the use or misuse of traits causes changes that can be passed onto offspring.
In the 1930s and 1940s, concepts from various fields, including genetics, natural selection, and particulate inheritance--came together to create the modern synthesis of evolutionary theory, which defines how evolution occurs through the variation of genes within a population, and how these variants change over time due to natural selection. This model, which encompasses genetic drift, mutations, gene flow and sexual selection can be mathematically described mathematically.
Recent discoveries in the field of evolutionary developmental biology have revealed how variations can be introduced to a species by mutations, genetic drift or reshuffling of genes in sexual reproduction, and even migration between populations. These processes, in conjunction with others, such as directionally-selected selection and erosion of genes (changes in frequency of genotypes over time) can lead to evolution. Evolution is defined by changes in the genome over time, as well as changes in phenotype (the expression of genotypes in individuals).
Students can gain a better understanding of the concept of phylogeny through incorporating evolutionary thinking into all aspects of biology. In a recent study conducted by Grunspan et al. It was demonstrated that teaching students about the evidence for evolution boosted their acceptance of evolution during a college-level course in biology. To find out more about how to teach about evolution, please see The Evolutionary Potential in All Areas of Biology and Thinking Evolutionarily: A Framework for Infusing Evolution in Life Sciences Education.
Evolution in Action
Traditionally, scientists have studied evolution by studying fossils, comparing species, and observing living organisms. Evolution is not a distant event, but an ongoing process. The virus reinvents itself to avoid new antibiotics and bacteria transform to resist antibiotics. Animals adapt their behavior in the wake of a changing world. The results are often evident.
However, it wasn't until late-1980s that biologists realized that natural selection can be observed in action as well. The main reason is that different traits result in the ability to survive at different rates and reproduction, and can be passed down from one generation to the next.
In the past, if one particular allele - the genetic sequence that defines color in a group of interbreeding organisms, it might quickly become more common than other alleles. In time, this could mean that the number of moths that have black pigmentation may increase. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms.
It is easier to see evolution when the species, like bacteria, has a high generation turnover. Since 1988 the biologist Richard Lenski has been tracking twelve populations of E. bacteria that descend from a single strain; samples of each population are taken regularly, and over 500.000 generations have been observed.
Lenski's work has demonstrated that a mutation can profoundly alter the rate at the rate at which a population reproduces, and consequently, the rate at which it evolves. It also demonstrates that evolution is slow-moving, a fact that many find difficult to accept.
Microevolution can be observed in the fact that mosquito genes for resistance to pesticides are more common in populations where insecticides are used. This is due to the fact that the use of pesticides causes a selective pressure that favors those with resistant genotypes.
에볼루션 게이밍 of evolution taking place has led to a growing appreciation of its importance in a world shaped by human activity--including climate change, pollution and the loss of habitats that hinder the species from adapting. Understanding evolution will aid you in making better decisions regarding the future of the planet and its inhabitants.