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🔗 Biology 🔗 Science Fiction 🔗 Chemistry

Hypothetical types of biochemistry are forms of biochemistry speculated to be scientifically viable but not proven to exist at this time. The kinds of living organisms currently known on Earth all use carbon compounds for basic structural and metabolic functions, water as a solvent, and DNA or RNA to define and control their form. If life exists on other planets or moons, it may be chemically similar; it is also possible that there are organisms with quite different chemistries—for instance, involving other classes of carbon compounds, compounds of another element, or another solvent in place of water.

The possibility of life-forms being based on "alternative" biochemistries is the topic of an ongoing scientific discussion, informed by what is known about extraterrestrial environments and about the chemical behaviour of various elements and compounds. It is of interest in synthetic biology and is also a common subject in science fiction.

The element silicon has been much discussed as a hypothetical alternative to carbon. Silicon is in the same group as carbon on the periodic table and, like carbon, it is tetravalent. Hypothetical alternatives to water include ammonia, which, like water, is a polar molecule, and cosmically abundant; and non-polar hydrocarbon solvents such as methane and ethane, which are known to exist in liquid form on the surface of Titan.

🔗 Biology 🔗 Cognitive science 🔗 Neuroscience

The free energy principle tries to explain how (biological) systems maintain their order (non-equilibrium steady-state) by restricting themselves to a limited number of states. It says that biological systems minimise a free energy function of their internal states, which entail beliefs about hidden states in their environment. The implicit minimisation of variational free energy is formally related to variational Bayesian methods and was originally introduced by Karl Friston as an explanation for embodied perception in neuroscience, where it is also known as active inference.

The free energy principle is that systems—those that are defined by their enclosure in a Markov blanket—try to minimize the difference between their model of the world and their sense and associated perception. This difference can be described as "surprise" and is minimized by continuous correction of the world model of the system. As such, the principle is based on the Bayesian idea of the brain as an “inference engine”. Friston added a second route to minimization: action. By actively changing the world into the expected state, systems can also minimize the free energy of the system. Friston assumes this to be the principle of all biological reaction.. Friston also believes his principle applies to mental disorders as well as to artificial intelligence. AI implementations based on the active inference principle have shown advantages over other methods.

The free energy principle has been criticized for being very difficult to understand, even for experts. Discussions of the principle have also been criticized as invoking metaphysical assumptions far removed from a testable scientific prediction, making the principle unfalsifiable. In a 2018 interview, Friston acknowledged that the free energy principle is not properly falsifiable: "the free energy principle is what it is — a principle. Like Hamilton’s Principle of Stationary Action, it cannot be falsified. It cannot be disproven. In fact, there’s not much you can do with it, unless you ask whether measurable systems conform to the principle."

🔗 Biology 🔗 Genetics 🔗 Computational Biology 🔗 Evolutionary biology 🔗 Human Genetic History

The last universal common ancestor (LUCA), also called the last universal ancestor (LUA), or concestor, is the most recent population of organisms from which all organisms now living on Earth have a common descent, the most recent common ancestor of all current life on Earth. (A related concept is that of progenote.) LUCA is not thought to be the first life on Earth but only one of many early organisms, all the others becoming extinct.

While there is no specific fossil evidence of LUCA, it can be studied by comparing the genomes of all modern organisms, its descendants. By this means, a 2016 study identified a set of 355 genes most likely to have been present in LUCA. (However, some of those genes could have developed later, then spread universally by horizontal gene transfer between archaea and bacteria.) The genes describe a complex life form with many co-adapted features, including transcription and translation mechanisms to convert information from DNA to RNA to proteins. The study concluded that the LUCA probably lived in the high-temperature water of deep sea vents near ocean-floor magma flows.

Studies from 2000 to 2018 have suggested an increasingly ancient time for LUCA. In 2000, estimations suggested LUCA existed 3.5 to 3.8 billion years ago in the Paleoarchean era, a few hundred million years after the earliest fossil evidence of life, for which there are several candidates ranging in age from 3.48 to 4.28 billion years ago. A 2018 study from the University of Bristol, applying a molecular clock model, places the LUCA shortly after 4.5 billion years ago, within the Hadean.

Charles Darwin first proposed the theory of universal common descent through an evolutionary process in his book On the Origin of Species in 1859: "Therefore I should infer from analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed." Later biologists have separated the problem of the origin of life from that of the LUCA.

🔗 Human rights 🔗 Military history 🔗 Military history/North American military history 🔗 Military history/United States military history 🔗 Military history/Military science, technology, and theory 🔗 Military history/Weaponry 🔗 Medicine 🔗 Biology 🔗 Military history/World War II 🔗 Military history/Cold War 🔗 United States History 🔗 Medicine/Society and Medicine

Unethical human experimentation in the United States describes numerous experiments performed on human test subjects in the United States that have been considered unethical, and were often performed illegally, without the knowledge, consent, or informed consent of the test subjects. Such tests have occurred throughout American history, but particularly in the 20th century. The experiments include: the exposure of humans to many chemical and biological weapons (including infection with deadly or debilitating diseases), human radiation experiments, injection of toxic and radioactive chemicals, surgical experiments, interrogation and torture experiments, tests involving mind-altering substances, and a wide variety of others. Many of these tests were performed on children, the sick, and mentally disabled individuals, often under the guise of "medical treatment". In many of the studies, a large portion of the subjects were poor, racial minorities, or prisoners.

Funding for many of the experiments was provided by the United States government, especially the United States military, the Central Intelligence Agency, or private corporations involved with military activities. The human research programs were usually highly secretive, and in many cases information about them was not released until many years after the studies had been performed.

The ethical, professional, and legal implications of this in the United States medical and scientific community were quite significant, and led to many institutions and policies that attempted to ensure that future human subject research in the United States would be ethical and legal. Public outrage in the late 20th century over the discovery of government experiments on human subjects led to numerous congressional investigations and hearings, including the Church Committee and Rockefeller Commission, both of 1975, and the 1994 Advisory Committee on Human Radiation Experiments, among others.

🔗 Biology 🔗 Evolutionary biology 🔗 Tree of Life

The three-domain system is a biological classification introduced by Carl Woese et al. in 1990 that divides cellular life forms into archaea, bacteria, and eukaryote domains. In particular, it emphasizes the separation of prokaryotes into two groups, originally called Eubacteria (now Bacteria) and Archaebacteria (now Archaea). Woese argued that, on the basis of differences in 16S rRNA genes, these two groups and the eukaryotes each arose separately from an ancestor with poorly developed genetic machinery, often called a progenote. To reflect these primary lines of descent, he treated each as a domain, divided into several different kingdoms. Woese initially used the term "kingdom" to refer to the three primary phylogenic groupings, and this nomenclature was widely used until the term "domain" was adopted in 1990.

Parts of the three-domain theory have been fiercly challenged by scientists such as Radhey S. Gupta, who argues that the primary division within prokaryotes should be between those surrounded by a single membrane, and those with two membranes.

🔗 Biology 🔗 Insects 🔗 Ecology

A hyperparasite, also known as a metaparasite is a parasite whose host, often an insect, is also a parasite, often specifically a parasitoid. Hyperparasites are found mainly among the wasp-waisted Apocrita within the Hymenoptera, and in two other insect orders, the Diptera (true flies) and Coleoptera (beetles). Seventeen families in Hymenoptera and a few species of Diptera and Coleoptera are hyperparasitic. Hyperparasitism developed from primary parasitism, which evolved in the Jurassic period in the Hymenoptera. Hyperparasitism intrigues entomologists because of its multidisciplinary relationship to evolution, ecology, behavior, biological control, taxonomy, and mathematical models.

🔗 Medicine 🔗 Biology

Closed-eye hallucinations and closed-eye visualizations (CEV) are a distinct class of hallucination. These types of hallucinations generally only occur when one's eyes are closed or when one is in a darkened room. They can be a form of phosphene. Some people report closed-eye hallucinations under the influence of psychedelics. These are reportedly of a different nature than the "open-eye" hallucinations of the same compounds. Similar hallucinations that occur due to loss of vision are called visual release hallucinations.

🔗 History 🔗 Biology 🔗 Politics 🔗 Anthropology 🔗 Sociology 🔗 Conservatism 🔗 Folklore

Invented traditions are cultural practices that are presented or perceived as traditional, arising from the people starting in the distant past, but which in fact are relatively recent and often even consciously invented by identifiable historical actors. The concept was highlighted in the 1983 book The Invention of Tradition, edited by Eric Hobsbawm and Terence Ranger. Hobsbawm's introduction argues that many "traditions" which "appear or claim to be old are often quite recent in origin and sometimes invented." This "invention" is distinguished from "starting" or "initiating" a tradition that does not then claim to be old. The phenomenon is particularly clear in the modern development of the nation and of nationalism, creating a national identity promoting national unity, and legitimising certain institutions or cultural practices.

🔗 United States 🔗 Medicine 🔗 Oregon 🔗 Crime 🔗 Religion 🔗 Biology 🔗 Terrorism

The 1984 Rajneeshee bioterror attack was the food poisoning of 751 individuals in The Dalles, Oregon, through the deliberate contamination of salad bars at ten local restaurants with Salmonella. A group of prominent followers of Bhagwan Shree Rajneesh (later known as Osho) led by Ma Anand Sheela had hoped to incapacitate the voting population of the city so that their own candidates would win the 1984 Wasco County elections. The incident was the first and is the single largest bioterrorist attack in United States history.

Having previously gained political control of Antelope, Oregon, Rajneesh's followers, who were based in nearby Rajneeshpuram, sought election to two of the three seats on the Wasco County Circuit Court that were up for election in November 1984. Fearing they would not gain enough votes, some Rajneeshpuram officials decided to incapacitate voters in The Dalles, the largest population center in Wasco County. The chosen biological agent was Salmonella enterica Typhimurium, which was first delivered through glasses of water to two County Commissioners and then, on a larger scale, at salad bars and in salad dressing.

As a result of the attack, 751 people contracted salmonellosis, 45 of whom were hospitalized, but none died. Although an initial investigation by the Oregon Public Health Division and the Centers for Disease Control did not rule out deliberate contamination, the agents and contamination were only confirmed a year later. On February 28, 1985, Congressman James H. Weaver gave a speech in the United States House of Representatives in which he "accused the Rajneeshees of sprinkling Salmonella culture on salad bar ingredients in eight restaurants".

At a press conference in September 1985, Rajneesh accused several of his followers of participation in this and other crimes, including an aborted plan in 1985 to assassinate a United States Attorney, and he asked state and federal authorities to investigate. Oregon Attorney General David B. Frohnmayer set up an interagency task force, composed of Oregon State Police and the Federal Bureau of Investigation, and executed search warrants in Rajneeshpuram. A sample of bacteria matching the contaminant that had sickened the town residents was found in a Rajneeshpuram medical laboratory. Two leading Rajneeshpuram officials were convicted on charges of attempted murder and served 29 months of 20-year sentences in a minimum-security federal prison.

🔗 Biology 🔗 Molecular and Cell Biology 🔗 Genetics

DNA origami is the nanoscale folding of DNA to create non-arbitrary two- and three-dimensional shapes at the nanoscale. The specificity of the interactions between complementary base pairs make DNA a useful construction material, through design of its base sequences. DNA is a well-understood material that is suitable for creating scaffolds that hold other molecules in place or to create structures all on its own.

DNA origami was the cover story of Nature on March 16, 2006. Since then, DNA origami has progressed past an art form and has found a number of applications from drug delivery systems to uses as circuitry in plasmonic devices; however, most applications remain in a concept or testing phase.