The Academy's Evolution Site
The concept of biological evolution is a fundamental concept in biology. The Academies have been for a long time involved in helping those interested in science understand the theory of evolution and how it affects all areas of scientific research.
This site offers a variety of sources for students, teachers and general readers of evolution. It includes key video clip from NOVA and WGBH produced science programs on DVD.
Tree of Life
The Tree of Life, an ancient symbol, symbolizes the interconnectedness of all life. It is an emblem of love and unity in many cultures. It has numerous practical applications as well, such as providing a framework for understanding the history of species and how they react to changing environmental conditions.
에볼루션 at depicting the world of biology focused on separating species into distinct categories that had been identified by their physical and metabolic characteristics1. These methods, based on the sampling of various parts of living organisms or sequences of short fragments of their DNA, significantly expanded the diversity that could be represented in the tree of life2. These trees are largely composed by eukaryotes, and 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. Particularly, molecular methods allow us to construct trees using sequenced markers, such as the small subunit ribosomal RNA gene.
Despite the rapid expansion of the Tree of Life through genome sequencing, a large amount of biodiversity remains to be discovered. This is particularly relevant to microorganisms that are difficult to cultivate, and are typically present in a single sample5. A recent study of all genomes that are known has created a rough draft of the Tree of Life, including many archaea and bacteria that have not been isolated and their diversity is not fully understood6.
The expanded Tree of Life is particularly useful for assessing the biodiversity of an area, assisting to determine if certain habitats require special protection. The information is useful in a variety of ways, such as finding new drugs, fighting diseases and improving the quality of crops. It is also beneficial to conservation efforts. It helps biologists determine the areas that are most likely to contain cryptic species with potentially significant metabolic functions that could be vulnerable to anthropogenic change. While funding to protect biodiversity are essential, the best method to preserve the world's biodiversity is to empower more people in developing countries with the knowledge they need to act locally and promote conservation.
Phylogeny
A phylogeny, also known as an evolutionary tree, reveals the connections between groups of organisms. Scientists can construct a phylogenetic diagram that illustrates the evolutionary relationships between taxonomic groups using molecular data and morphological differences or similarities. Phylogeny plays a crucial role in understanding the relationship between genetics, biodiversity and evolution.
A basic phylogenetic tree (see Figure PageIndex 10 ) determines the relationship between organisms that share similar traits that evolved from common ancestors. These shared traits are either homologous or analogous. Homologous characteristics are identical in their evolutionary paths. Analogous traits could appear like they are however they do not have the same origins. Scientists group similar traits into a grouping referred to as a the clade. All organisms in a group share a characteristic, like amniotic egg production. They all came from an ancestor that had these eggs. A phylogenetic tree can be constructed by connecting clades to identify the species who are the closest to each other.
To create a more thorough and accurate phylogenetic tree, scientists rely on molecular information from DNA or RNA to determine the connections between organisms. This information is more precise than the morphological data and provides evidence of the evolution history of an organism or group. The analysis of molecular data can help researchers determine the number of species who share a common ancestor and to estimate their evolutionary age.
The phylogenetic relationships of organisms can be affected by a variety of factors, including phenotypic flexibility, an aspect of behavior that alters in response to unique environmental conditions. This can make a trait appear more similar to one species than to another which can obscure the phylogenetic signal. However, this issue can be cured by the use of methods like cladistics, which incorporate a combination of homologous and analogous features into the tree.
In addition, phylogenetics can help predict the duration and rate of speciation. This information can aid conservation biologists to decide which species to protect from the threat of extinction. In the end, it's the preservation of phylogenetic diversity that will lead to an ecologically balanced and complete ecosystem.
Evolutionary Theory
The fundamental concept of evolution is that organisms develop different features over time based on their interactions with their environments. Many scientists have come up with theories of evolution, such as the Islamic naturalist Nasir al-Din al-Tusi (1201-274) who believed that an organism would evolve according to its own requirements and needs, the Swedish taxonomist Carolus Linnaeus (1707-1778), who created the modern hierarchical system of taxonomy as well as Jean-Baptiste Lamarck (1844-1829), who suggested that the use or non-use of certain traits can result in changes that can be passed on to future generations.
In the 1930s and 1940s, concepts from a variety of fields--including genetics, natural selection and particulate inheritance -- came together to form the modern evolutionary theory synthesis that explains how evolution happens through the variation of genes within a population and how those variations change in time as a result of natural selection. This model, called genetic drift or mutation, gene flow, and sexual selection, is a key element of modern evolutionary biology and is mathematically described.
Recent discoveries in the field of evolutionary developmental biology have revealed that variation can be introduced into a species by genetic drift, mutation, and reshuffling genes during sexual reproduction, and also through migration between populations. These processes, along with others such as directionally-selected selection and erosion of genes (changes to the frequency of genotypes over time) can result in evolution. Evolution is defined as changes in the genome over time and changes in phenotype (the expression of genotypes in an individual).
Students can better understand the concept of phylogeny by using evolutionary thinking in all aspects of biology. A recent study conducted by Grunspan and colleagues, for example demonstrated that teaching about the evidence supporting evolution helped students accept the concept of evolution in a college biology course. To find out more about how to teach about evolution, please look up The Evolutionary Potential in all Areas of Biology and Thinking Evolutionarily A Framework for Infusing the Concept of Evolution into Life Sciences Education.
Evolution in Action
Scientists have traditionally studied evolution by looking in the past--analyzing fossils and comparing species. They also observe living organisms. But evolution isn't just something that happened in the past. It's an ongoing process, that is taking place in the present. The virus reinvents itself to avoid new medications and bacteria mutate to resist antibiotics. Animals alter their behavior as a result of a changing environment. The results are usually easy to see.
It wasn't until late 1980s when biologists began to realize that natural selection was also in action. The reason is that different traits have 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 controls coloration - was present in a population of interbreeding species, it could quickly become more prevalent than the other alleles. 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.
Monitoring evolutionary changes in action is easier when a particular species has a rapid turnover of its generation, as with bacteria. 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 regularly, and over 50,000 generations have now been observed.
Lenski's research has demonstrated that mutations can alter the rate at which change occurs and the efficiency of a population's reproduction. It also shows that evolution is slow-moving, a fact that some are unable to accept.
Microevolution can also be seen in the fact that mosquito genes for resistance to pesticides are more prevalent in populations where insecticides are used. Pesticides create a selective pressure which favors those who have resistant genotypes.
The speed at which evolution can take place has led to an increasing awareness of its significance in a world that is shaped by human activity, including climate change, pollution and the loss of habitats which 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.