Topic: Evolutionary biology
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Endurance Running Hypothesis
The endurance running hypothesis is the hypothesis that the evolution of certain human characteristics can be explained as adaptations to long-distance running. The hypothesis suggests that endurance running played an important role for early hominins in obtaining food. Researchers have proposed that endurance running began as an adaptation for scavenging and later for persistence hunting.
- "Endurance Running Hypothesis" | 2019-09-17 | 97 Upvotes 52 Comments
Evolution of metal ions in biological systems
Evolution of metal ions in biological systems refers to the incorporation of metallic ions into living organisms and how it has changed over time. Metal ions have been associated with biological systems for billions of years, but only in the last century have scientists began to truly appreciate the scale of their influence. Major (iron, manganese, magnesium and zinc) and minor (copper, cobalt, nickel, molybdenum, tungsten) metal ions have become aligned with living organisms through the interplay of biogeochemical weathering and metabolic pathways involving the products of that weathering. The associated complexes have evolved over time.
Natural development of chemicals and elements challenged organisms to adapt or die. Current organisms require redox reactions to induce metabolism and other life processes. Metals have a tendency to lose electrons and are important for redox reactions.
Metals have become so central to cellular function that the collection of metal-binding proteins (referred to as the metallomes) accounts for over 30% of all proteins in the cell. Metals are known to be involved in over 40% of enzymatic reactions, and metal-binding proteins carry out at least one step in almost all biological pathways.
Metals are also toxic so a balance must be acquired to regulate where the metals are in an organism as well as in what quantities. Many organisms have flexible systems in which they can exchange one metal for another if one is scarce. Metals in this discussion are naturally occurring elements that have a tendency to undergo oxidation. Vanadium, molybdenum, cobalt, copper, chromium, iron, manganese, nickel, and zinc are deemed essential because without them biological function is impaired.
Great Oxidation Event
The Great Oxidation Event (GOE), sometimes also called the Great Oxygenation Event, Oxygen Catastrophe, Oxygen Crisis, Oxygen Holocaust, or Oxygen Revolution, was a time period when the Earth's atmosphere and the shallow ocean experienced a rise in oxygen, approximately 2.4 billion years ago (2.4 Ga) to 2.1–2.0 Ga during the Paleoproterozoic era. Geological, isotopic, and chemical evidence suggests that biologically induced molecular oxygen (dioxygen, O2) started to accumulate in Earth's atmosphere and changed Earth's atmosphere from a weakly reducing atmosphere to an oxidizing atmosphere, causing almost all life on Earth to go extinct. The cyanobacteria producing the oxygen caused the event which enabled the subsequent development of multicellular forms.
- "Great Oxidation Event" | 2019-07-21 | 64 Upvotes 24 Comments
HeLa, the oldest and most commonly used human cell line
HeLa (; also Hela or hela) is an immortal cell line used in scientific research. It is the oldest and most commonly used human cell line. The line was derived from cervical cancer cells taken on February 8, 1951 from Henrietta Lacks, a patient who died of cancer on October 4, 1951. The cell line was found to be remarkably durable and prolific, which gives rise to its extensive use in scientific research.
The cells from Lacks's cancerous cervical tumor were taken without her knowledge or consent, which was common practice at the time. Cell biologist George Otto Gey found that they could be kept alive, and developed a cell line. Previously, cells cultured from other human cells would only survive for a few days. Scientists would spend more time trying to keep the cells alive than performing actual research on them. Cells from Lacks' tumor behaved differently. As was custom for Gey's lab assistant, she labeled the culture 'HeLa', the first two letters of the patient's first and last name; this became the name of the cell line.
These were the first human cells grown in a lab that were naturally "immortal", meaning that they do not die after a set number of cell divisions (i.e. cellular senescence). These cells could be used for conducting a multitude of medical experiments—if the cells died, they could simply be discarded and the experiment attempted again on fresh cells from the culture. This represented an enormous boon to medical and biological research, as previously stocks of living cells were limited and took significant effort to culture.
The stable growth of HeLa enabled a researcher at the University of Minnesota hospital to successfully grow polio virus, enabling the development of a vaccine, and by 1952, Jonas Salk developed a vaccine for polio using these cells. To test Salk's new vaccine, the cells were put into mass production in the first-ever cell production factory.
In 1953, HeLa cells were the first human cells successfully cloned and demand for the HeLa cells quickly grew in the nascent biomedical industry. Since the cells' first mass replications, they have been used by scientists in various types of investigations including disease research, gene mapping, effects of toxic substances on organisms, and radiation on humans. Additionally, HeLa cells have been used to test human sensitivity to tape, glue, cosmetics, and many other products.
Scientists have grown an estimated 50 million metric tons of HeLa cells, and there are almost 11,000 patents involving these cells.
The HeLa cell lines are also notorious for invading other cell cultures in laboratory settings. Some have estimated that HeLa cells have contaminated 10–20% of all cell lines currently in use.
- "HeLa, the oldest and most commonly used human cell line" | 2015-10-30 | 54 Upvotes 12 Comments
- "Immortal cells of Henrietta Lacks" | 2010-02-01 | 36 Upvotes 7 Comments
Homo floresiensis ("Flores Man"; nicknamed "hobbit") is a pygmy archaic human which inhabited the island of Flores, Indonesia, until the arrival of modern humans about 50,000 years ago.
The remains of an individual who would have stood about 1.1 m (3 ft 7 in) in height were discovered in 2003 at Liang Bua on the island of Flores in Indonesia. Partial skeletons of nine individuals have been recovered, including one complete skull, referred to as "LB1". These remains have been the subject of intense research to determine whether they represent a species distinct from modern humans; the dominant consensus is that these remains do represent a distinct species due to genetic and anatomical differences.
This hominin had originally been considered remarkable for its survival until relatively recent times, only 12,000 years ago. However, more extensive stratigraphic and chronological work has pushed the dating of the most recent evidence of its existence back to 50,000 years ago. The Homo floresiensis skeletal material is now dated from 60,000 to 100,000 years ago; stone tools recovered alongside the skeletal remains were from archaeological horizons ranging from 50,000 to 190,000 years ago.
- "Homo floresiensis" | 2013-10-14 | 12 Upvotes 3 Comments
Horizontal Gene Transfer
Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between unicellular and/or multicellular organisms other than by the ("vertical") transmission of DNA from parent to offspring (reproduction). HGT is an important factor in the evolution of many organisms.
Horizontal gene transfer is the primary mechanism for the spread of antibiotic resistance in bacteria, and plays an important role in the evolution of bacteria that can degrade novel compounds such as human-created pesticides and in the evolution, maintenance, and transmission of virulence. It often involves temperate bacteriophages and plasmids. Genes responsible for antibiotic resistance in one species of bacteria can be transferred to another species of bacteria through various mechanisms of HGT such as transformation, transduction and conjugation, subsequently arming the antibiotic resistant genes' recipient against antibiotics. The rapid spread of antibiotic resistance genes in this manner is becoming medically challenging to deal with. Ecological factors may also play a role in the LGT of antibiotic resistant genes. It is also postulated that HGT promotes the maintenance of a universal life biochemistry and, subsequently, the universality of the genetic code.
Most thinking in genetics has focused upon vertical transfer, but the importance of horizontal gene transfer among single-cell organisms is beginning to be acknowledged.
Gene delivery can be seen as an artificial horizontal gene transfer, and is a form of genetic engineering.
- "Horizontal gene transfer" | 2014-04-29 | 14 Upvotes 1 Comments
Last universal ancestor
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.
- "Last universal ancestor" | 2015-04-05 | 63 Upvotes 24 Comments
List of common misconceptions
This is a list of common misconceptions. Each entry is formatted as a correction; the misconceptions themselves are implied rather than stated. These entries are meant to be concise, but more detail can be found in the main subject articles.
- "List of Common Misconceptions" | 2022-07-13 | 21 Upvotes 8 Comments
- "List of Common Misconceptions" | 2020-05-22 | 52 Upvotes 15 Comments
- "List of common misconceptions" | 2018-06-14 | 94 Upvotes 26 Comments
- "List of Common Misconceptions" | 2010-06-27 | 169 Upvotes 53 Comments
R/K selection theory
In ecology, r/K selection theory relates to the selection of combinations of traits in an organism that trade off between quantity and quality of offspring. The focus on either an increased quantity of offspring at the expense of individual parental investment of r-strategists, or on a reduced quantity of offspring with a corresponding increased parental investment of K-strategists, varies widely, seemingly to promote success in particular environments.
The terminology of r/K-selection was coined by the ecologists Robert MacArthur and E. O. Wilson in 1967 based on their work on island biogeography; although the concept of the evolution of life history strategies has a longer history (see e.g. plant strategies).
The theory was popular in the 1970s and 1980s, when it was used as a heuristic device, but lost importance in the early 1990s, when it was criticized by several empirical studies. A life-history paradigm has replaced the r/K selection paradigm but continues to incorporate many of its important themes.
- "R/K selection theory" | 2014-03-31 | 17 Upvotes 3 Comments
Spiegelman's Monster is the name given to an RNA chain of only 218 nucleotides that is able to be reproduced by the RNA replication enzyme RNA-dependent RNA polymerase, also called RNA replicase. It is named after its creator, Sol Spiegelman, of the University of Illinois at Urbana-Champaign who first described it in 1965.
- "Spiegelman's Monster" | 2016-06-06 | 125 Upvotes 34 Comments