Twins are two offspring produced by the same pregnancy. Twins can be either monozygotic ('identical'), meaning that they develop from one zygote, which splits and forms two embryos, or dizygotic ('fraternal'), meaning that each twin develops from a separate egg and each egg is fertilized by its own sperm cell.
In contrast, a fetus that develops alone in the womb is called a singleton, and the general term for one offspring of a multiple birth is multiple. Non-related look-alikes whose resemblance parallels that of twins are referred to as doppelgangers.
The human twin birth rate in the United States rose 76% from 1980 through 2009, from 18.8 to 33.3 per 1,000 births.
The Yoruba peoples have the highest rate of twinning in the world, at 45–50 twin sets (or 90–100 twins) per 1,000 live births, possibly because of high consumption of a specific type of yam containing a natural phytoestrogen which may stimulate the ovaries to release an egg from each side.
In Central Africa, there are 18–30 twin sets (or 36–60 twins) per 1,000 live births. In Latin America, India, Pakistan, Bangladesh, Nepal, and Southeast Asia, the lowest rates are found; only 6 to 9 twin sets per 1,000 live births. North America and Europe have intermediate rates of 9 to 16 twin sets per 1,000 live births.
Multiple pregnancies are much less likely to carry to full term than single births, with twin pregnancies lasting on average 37 weeks, three weeks less than full term.
Women who have a family history of fraternal twins have a higher chance of producing fraternal twins themselves, as there is a genetically linked tendency to hyper-ovulate. There is no known genetic link for identical twinning. Other factors that increase the odds of having fraternal twins include maternal age, fertility drugs and other fertility treatments, nutrition, and prior births. Some women intentionally turn to fertility drugs in order to conceive twins.
The vast majority of twins are either dizygotic (fraternal) or monozygotic (identical). Less common variants are discussed further down the article.
Twins can be:
Among non-twin births, male singletons are slightly (about five percent) more common than female singletons. The rates for singletons vary slightly by country. For example, the sex ratio of birth in the US is 1.05 males/female, while it is 1.07 males/female in Italy. However, males are also more susceptible than females to die in utero, and since the death rate in utero is higher for twins, it leads to female twins being more common than male twins.
|Common name||Scientific name||Zygosity||Development||Occurrence||Identification||Health||Other|
|Superfecundation||x||x||Eggs are fertilized during different acts of intercourse||x||x||x||Usage is practically equivalent with heteropaternal superfecundation, which occurs when two different males father fraternal twins, because though superfecundation by the same father is thought to be a common occurrence, it can only be proven to have occurred with multiple fathers.|
|Superfetation||x||x||A woman gets pregnant again while already pregnant, resulting in multiple fetuses at differing developmental stages||x||x||x||x|
|Parasitic twin||x||x||x||x||x||By definition only healthy fully formed fetus||x|
|Vanishing twin||Fetal resorption, twin embolisation syndrome||x||x||Up to 1 of every 8 multifetus pregnancies||x||By definition only healthy fully formed fetus||Chimerism, mosaicism|
|Conjoined twin||x||x||x||x||x||Ranges from normal to compromised||x|
Dizygotic (DZ) or fraternal twins (also referred to as "non-identical twins", "dissimilar twins", "biovular twins", and, informally in the case of females, "sororal twins") usually occur when two fertilized eggs are implanted in the uterus wall at the same time. When two eggs are independently fertilized by two different sperm cells, fraternal twins result. The two eggs, or ova, form two zygotes, hence the terms dizygotic and biovular. Fraternal twins are, essentially, two ordinary siblings who happen to be born at the same time, since they arise from two separate eggs fertilized by two separate sperm, just like ordinary siblings.
This is the most common type of twin.
Dizygotic twins, like any other siblings, have an extremely small chance of having the same chromosome profile. Even if they happen to have the same chromosome profile, they will always have different genetic material on each chromosome, due to chromosomal crossover during meiosis. Like any other siblings, dizygotic twins may look similar, particularly given that they are the same age. However, dizygotic twins may also look very different from each other.
Studies show that there is a genetic proclivity for dizygotic twinning. However, it is only the mother who has any effect on the chances of having such twins; there is no known mechanism for a father to cause the release of more than one ovum. Dizygotic twinning ranges from six per thousand births in Japan (similar to the rate of monozygotic twins) to 14 and more per thousand in some African countries.
Dizygotic twins are also more common for older mothers, with twinning rates doubling in mothers over the age of 35. With the advent of technologies and techniques to assist women in getting pregnant, the rate of fraternals has increased markedly.
Regarding spontaneous or natural monozygotic twinning, a recent theory proposes that monozygotic twins are formed after a blastocyst essentially collapses, splitting the progenitor cells (those that contain the body's fundamental genetic material) in half, leaving the same genetic material divided in two on opposite sides of the embryo. Eventually, two separate fetuses develop. Spontaneous division of the zygote into two embryos is not considered to be a hereditary trait, but rather a spontaneous and random event.
Monozygotic twins may also be created artificially by embryo splitting. It can be used as an expansion of in vitro fertilization (IVF) to increase the number of available embryos for embryo transfer.
Monozygotic twinning occurs in birthing at a rate of about 3 in every 1000 deliveries worldwide. (about 0.3% of the world population).
The likelihood of a single fertilization resulting in monozygotic twins is uniformly distributed in all populations around the world. This is in marked contrast to dizygotic twinning, which ranges from about six per thousand births in Japan (almost similar to the rate of identical twins, which is around 4–5) to 15 and more per thousand in some parts of India and up to over 20 in some Central African countries. The exact cause for the splitting of a zygote or embryo is unknown.
IVF techniques are more likely to create dizygotic twins. For IVF deliveries, there are nearly 21 pairs of twins for every 1,000.
Monozygotic twins are genetically nearly identical and they are always the same sex unless there has been a mutation during development. The children of monozygotic twins test genetically as half-siblings (or full siblings, if a pair of monozygotic twins reproduces with another pair or with the same person), rather than first cousins. Identical twins do not have the same fingerprints however, because even within the confines of the womb, the fetuses touch different parts of their environment, giving rise to small variations in their corresponding prints and thus making them unique.
Monozygotic twins always have the same phenotype. Normally due to an environmental factor or the deactivation of different X chromosomes in female monozygotic twins, and in some extremely rare cases, due to aneuploidy, twins may express different sexual phenotypes, normally from an XXY Klinefelter syndrome zygote splitting unevenly.
Monozygotic twins, although genetically very similar, are not genetically exactly the same. The DNA in white blood cells of 66 pairs of monozygotic twins was analyzed for 506,786 single-nucleotide polymorphisms known to occur in human populations. Polymorphisms appeared in 2 of the 33 million comparisons, leading the researchers to extrapolate that the blood cells of monozygotic twins may have on the order of one DNA-sequence difference for every 1.2 x 107 nucleotides, which would imply hundreds of differences across the entire genome.The mutations producing the differences detected in this study would have occurred during embryonic cell-division (after the point of fertilization). If they occur early in fetal development, they will be present in a very large proportion of body cells.
Another cause of difference between monozygotic twins is epigenetic modification, caused by differing environmental influences throughout their lives. Epigenetics refers to the level of activity of any particular gene. A gene may become switched on, switched off, or could become partially switched on or off in an individual. This epigenetic modification is triggered by environmental events. Monozygotic twins can have markedly different epigenetic profiles. A study of 80 pairs of monozygotic twins ranging in age from three to 74 showed that the youngest twins have relatively few epigenetic differences. The number of epigenetic differences increases with age. Fifty-year-old twins had over three times the epigenetic difference of three-year-old twins. Twins who had spent their lives apart (such as those adopted by two different sets of parents at birth) had the greatest difference. However, certain characteristics become more alike as twins age, such as IQ and personality.
A 1981 study of a deceased triploid XXX twin fetus without a heart showed that although its fetal development suggested that it was an identical twin, as it shared a placenta with its healthy twin, tests revealed that it was probably a polar body twin. The authors were unable to predict whether a healthy fetus could result from a polar body twinning.
In 2003, a study argued that many cases of triploidity arise from semi-identical twinning.
In 2007, a study reported a case of a pair of living twins, one intersex and one a phenotypical male. The twins were both found to be chimeras and to share all of their maternal DNA but only half of their father's DNA. The exact mechanism of fertilization could not be determined but the study stated that it was unlikely to be a case of polar body twinning.
The degree of separation of the twins in utero depends on if and when they split into two zygotes. Dizygotic twins were always two zygotes. Monozygotic twins split into two zygotes at some time very early in the pregnancy. The timing of this separation determines the chorionicity (the number of placentae) and amniocity (the number of sacs) of the pregnancy. Dichorionic twins either never divided (i.e.: were dizygotic) or they divided within the first 4 days. Monoamnionic twins divide after the first week.
In very rare cases, twins become conjoined twins. Non-conjoined monozygotic twins form up to day 14 of embryonic development, but when twinning occurs after 14 days, the twins will likely be conjoined. Furthermore, there can be various degrees of shared environment of twins in the womb, potentially leading to pregnancy complications.
It is a common misconception that two placentas means twins are dizygotic. But if monozygotic twins separate early enough, the arrangement of sacs and placentas in utero is indistinguishable from dizygotic twins.
|Dichorionic-Diamniotic||Normally, twins have two separate (di- being a numerical prefix for two) chorions and amniotic sacs, termed Dichorionic-Diamniotic or "DiDi". It occurs in almost all cases of dizygotic twins (except in very rare cases of fusion between their blastocysts) and in 18–36% (or around 25%) of monozygotic (identical) twins.
DiDi twins have the lowest mortality risk at about 9 percent, although that is still significantly higher than that of singletons.
|Dichorionic-Diamniotic twins form when splitting takes place by the third day after fertilization.|
|Monochorionic-Diamniotic||Monochorionic twins share the same placenta.
Monochorionic twins generally have two amniotic sacs (called Monochorionic-Diamniotic "MoDi"), which occurs in 60–70% of the pregnancies with monozygotic twins, and in 0.3% of all pregnancies. Monochorionic-Diamniotic twins are almost always monozygotic, with a few exceptions where the blastocysts have fused.
|Monochorionic-Monoamniotic||Monochorionic twins share the same amnion in 1–2% of monozygotic twin pregnancies.
Monoamniotic twins, as with diamniotic monochorionic twins, have a risk of twin-to-twin transfusion syndrome. Also, the two umbilical cords have an increased chance of being tangled around the babies. Because of this, there is an increased chance that the newborns may be miscarried or suffer from cerebral palsy due to lack of oxygen.
|Monoamniotic twins occur when the split takes place after the ninth day after fertilization.|
When the division of the developing zygote into 2 embryos occurs, 99% of the time it is within 8 days of fertilization.
Mortality is highest for conjoined twins due to the many complications resulting from shared organs.
|If the division of the zygote occurs later than the 12 days then conjoined twins are usually the result.|
A 2006 study has found that insulin-like growth factor present in dairy products may increase the chance of dizygotic twinning. Specifically, the study found that vegan mothers (who exclude dairy from their diets) are one-fifth as likely to have twins as vegetarian or omnivore mothers, and concluded that "Genotypes favoring elevated IGF and diets including dairy products, especially in areas where growth hormone is given to cattle, appear to enhance the chances of multiple pregnancies due to ovarian stimulation."
From 1980 to 1997, the number of twin births in the United States rose 52%. This rise can at least partly be attributed to the increasing popularity of fertility drugs and procedures such as IVF, which result in multiple births more frequently than unassisted fertilizations do. It may also be linked to the increase of growth hormones in food.
About 1 in 90 human births (1.1%) results from a twin pregnancy. The rate of dizygotic twinning varies greatly among ethnic groups, ranging as high as about 45 per 1000 births (4.5%) for the Yoruba to 10% for Linha São Pedro, a tiny Brazilian settlement which belongs to the city of Cândido Godói. In Cândido Godói, one in five pregnancies has resulted in twins. The Argentine historian Jorge Camarasa has put forward the theory that experiments of the Nazi doctor Josef Mengele could be responsible for the high ratio of twins in the area. His theory was rejected by Brazilian scientists who had studied twins living in Linha São Pedro; they suggested genetic factors within that community as a more likely explanation. A high twinning rate has also been observed in other places of the world, including:
The widespread use of fertility drugs causing hyperovulation (stimulated release of multiple eggs by the mother) has caused what some call an "epidemic of multiple births". In 2001, for the first time ever in the US, the twinning rate exceeded 3% of all births. Nevertheless, the rate of monozygotic twins remains at about 1 in 333 across the globe.
In a study on the maternity records of 5750 Hausa women living in the Savannah zone of Nigeria, there were 40 twins and 2 triplets per 1000 births. Twenty-six percent of twins were monozygotic. The incidence of multiple births, which was about five times higher than that observed in any western population, was significantly lower than that of other ethnic groups, who live in the hot and humid climate of the southern part of the country. The incidence of multiple births was related to maternal age but did not bear any association to the climate or prevalence of malaria.
The predisposing factors of monozygotic twinning are unknown.
Dizygotic twin pregnancies are slightly more likely when the following factors are present in the woman:
Women undergoing certain fertility treatments may have a greater chance of dizygotic multiple births. In the United States it has been estimated that by 2011 36% of twin births resulted from conception by assisted reproductive technology.
The risk of twin birth can vary depending on what types of fertility treatments are used. With in vitro fertilisation (IVF), this is primarily due to the insertion of multiple embryos into the uterus. Ovarian hyperstimulation without IVF has a very high risk of multiple birth. Reversal of anovulation with clomifene (trade names including Clomid) has a relatively less but yet significant risk of multiple pregnancy.
A 15-year German study of 8,220 vaginally delivered twins (that is, 4,110 pregnancies) in Hesse yielded a mean delivery time interval of 13.5 minutes. The delivery interval between the twins was measured as follows:
The study stated that the occurrence of complications "was found to be more likely with increasing twin-to-twin delivery time interval" and suggested that the interval be kept short, though it noted that the study did not examine causes of complications and did not control for factors such as the level of experience of the obstetrician, the wish of the women giving birth, or the "management strategies" of the procedure of delivering the second twin.
Researchers suspect that as many as 1 in 8 pregnancies start out as multiples, but only a single fetus is brought to full term, because the other fetus has died very early in the pregnancy and has not been detected or recorded. Early obstetric ultrasonography exams sometimes reveal an "extra" fetus, which fails to develop and instead disintegrates and vanishes in the uterus. There are several reasons for the "vanishing" fetus, including it being embodied or absorbed by the other fetus, placenta or the mother. This is known as vanishing twin syndrome. Also, in an unknown proportion of cases, two zygotes may fuse soon after fertilization, resulting in a single chimeric embryo, and, later, fetus.
Conjoined twins (or the once-commonly used term "siamese") are monozygotic twins whose bodies are joined together during pregnancy. This occurs when the zygote starts to split after day 12 following fertilization and fails to separate completely. This condition occurs in about 1 in 50,000 human pregnancies. Most conjoined twins are now evaluated for surgery to attempt to separate them into separate functional bodies. The degree of difficulty rises if a vital organ or structure is shared between twins, such as the brain, heart or liver.
A chimera is an ordinary person or animal except that some of their parts actually came from their twin or from the mother. A chimera may arise either from monozygotic twin fetuses (where it would be impossible to detect), or from dizygotic fetuses, which can be identified by chromosomal comparisons from various parts of the body. The number of cells derived from each fetus can vary from one part of the body to another, and often leads to characteristic mosaicism skin coloration in human chimeras. A chimera may be intersex, composed of cells from a male twin and a female twin. In one case DNA tests determined that a woman, mystifyingly, was not the mother of two of her three children; she was found to be a chimera, and the two children were conceived from eggs derived from cells of their mother's twin.
Sometimes one twin fetus will fail to develop completely and continue to cause problems for its surviving twin. One fetus acts as a parasite towards the other. Sometimes the parasitic twin becomes an almost indistinguishable part of the other, and sometimes this needs to be treated medically.
A very rare type of parasitic twinning is one where a single viable twin is endangered when the other zygote becomes cancerous, or molar. This means that the molar zygote's cellular division continues unchecked, resulting in a cancerous growth that overtakes the viable fetus. Typically, this results when one twin has either triploidy or complete paternal uniparental disomy, resulting in little or no fetus and a cancerous, overgrown placenta, resembling a bunch of grapes.
Occasionally, a woman will suffer a miscarriage early in pregnancy, yet the pregnancy will continue; one twin was miscarried but the other was able to be carried to term. This occurrence is similar to the vanishing twin syndrome, but typically occurs later, as the twin is not reabsorbed.
It is very common for twins to be born at a low birth weight. More than half of twins are born weighing less than 5.5 pounds (2.5 kg), while the average birth weight of a healthy baby should be around 6–8 pounds (3–4 kg). This is largely due to the fact that twins are typically born premature. Premature birth and low birth weights, especially when under 3.5 pounds (1.6 kg), can increase the risk of several health-related issues, such as vision and hearing loss, mental disabilities, and cerebral palsy. There is an increased possibility of potential complications as the birth weight of the baby decreases.
Monozygotic twins who share a placenta can develop twin-to-twin transfusion syndrome. This condition means that blood from one twin is being diverted into the other twin. One twin, the 'donor' twin, is small and anemic, the other, the 'recipient' twin, is large and polycythemic. The lives of both twins are endangered by this condition.
Stillbirths occurs when a fetus dies after 20 weeks of gestation. There are two types of stillbirth, including intrauterine death and intrapartum death. Intrauterine death occurs when a baby dies during late pregnancy. Intrapartum death, which is more common, occurs when a baby dies while the mother is giving birth. The cause of stillbirth is often unknown, but the rate of babies who are stillborn is higher in twins and multiple births. Caesareans or inductions are advised after 38 weeks of pregnancy for twins, because the risk of stillbirth increases after this time.
For otherwise healthy twin pregnancies where both twins are head down a trial of vaginal delivery is recommended at between 37 and 38 weeks. Vaginal delivery in this case does not worsen the outcome for the infant as compared with Caesarean section. There is controversy on the best method of delivery where the first twin is head first and the second is not. When the first twin is not head down a caesarean section is often recommended. It is estimated that 75% of twin pregnancies in the United States were delivered by caesarean section in 2008. In comparison, the rate of caesarean section for all pregnancies in the general population varies between 14% and 40%. In twins that share the same placenta, delivery may be considered at 36 weeks.
Twin studies are utilized in an attempt to determine how much of a particular trait is attributable to either genetics or environmental influence. These studies compare monozygotic and dizygotic twins for medical, genetic, or psychological characteristics to try to isolate genetic influence from epigenetic and environmental influence. Twins that have been separated early in life and raised in separate households are especially sought-after for these studies, which have been used widely in the exploration of human nature. Classical twin studies are now being supplemented with molecular genetic studies which identify individual genes.
Among dizygotic twins, in rare cases, the eggs are fertilized at different times with two or more acts of sexual intercourse, either within one menstrual cycle (superfecundation) or, even more rarely, later on in the pregnancy (superfetation). This can lead to the possibility of a woman carrying fraternal twins with different fathers (that is, half-siblings). This phenomenon is known as heteropaternal superfecundation. One 1992 study estimates that the frequency of heteropaternal superfecundation among dizygotic twins, whose parents were involved in paternity suits, was approximately 2.4%; see the references section, below, for more details.
Dizygotic twins from biracial couples can sometimes be mixed twins, which exhibit differing ethnic and racial features. One such pairing was born in Germany in 2008 to a white father from Germany and a black mother from Ghana.
Heterotopic pregnancy is an exceedingly rare type of dizygotic twinning in which one twin implants in the uterus as normal and the other remains in the fallopian tube as an ectopic pregnancy. Ectopic pregnancies must be resolved because they can be life-threatening to the mother. However, in most cases, the intrauterine pregnancy can be salvaged.
Among monozygotic twins, in extremely rare cases, twins have been born with different sexes (one male, one female). When monozygotic twins are born with different sexes it is because of chromosomal defects. The probability of this is so small that multiples having different sexes is universally accepted as a sound basis for in utero clinical determination that the multiples are not monozygotic.
Another abnormality that can result in monozygotic twins of different sexes is if the egg is fertilized by a male sperm but during cell division only the X chromosome is duplicated. This results in one normal male (XY) and one female with Turner syndrome (45,X). In these cases, although the twins did form from the same fertilized egg, it is incorrect to refer to them as genetically identical, since they have different karyotypes.
Monozygotic twins can develop differently, due to different genes being activated. More unusual are "semi-identical twins". These "half-identical twins" are hypothesized to occur when an unfertilized egg cleaves into two identical attached ova, both of which are viable for fertilization. Both cloned ova are then fertilized, by different sperm, and the coalesced eggs undergo further cell duplications developing as a chimeric blastomere. If this blastomere then undergoes a twinning event, two embryos will be formed, with different paternal genes and identical maternal genes.
This results in a set of twins with identical genes from the mother's side, but different genes from the father's side. Cells in each fetus carry genes from either sperm, resulting in chimeras. This form had been speculated until only recently being recorded in western medicine.
Mirror image twins result when a fertilized egg splits later in the embryonic stage than normal timing, around day 9–12. This type of twinning could exhibit characteristics with reversed asymmetry, such as opposite dominant handedness, dental structure, or even organs (situs inversus). If the split occurs later than this time period, the twins risk being conjoined. There is no DNA-based zygosity test that can determine if twins are indeed mirror image. The term "mirror image" is used because the twins, when facing each other, appear as matching reflections.
There have been many studies highlighting the development of language in twins compared to single-born children. These studies have converged on the notion that there is a greater rate of delay in language development in twins compared to their single-born counterparts. The reasons for this phenomenon are still in question; however, cryptophasia was thought to be the major cause. Idioglossia is defined as a private language that is usually invented by young children, specifically twins. Another term to describe what some people call "twin talk" is cryptophasia where a language is developed by twins that only they can understand. The increased focused communication between two twins may isolate them from the social environment surrounding them. Idioglossia has been found to be a rare occurrence and the attention of scientists has shifted away from this idea. However, there are researchers and scientists that say cryptophasia or idioglossia is not a rare phenomenon. Current research is looking into the impacts of a richer social environment for these twins to stimulate their development of language.
Twins are common in many mammal species, including cats, sheep, ferrets, giant pandas, dolphins, dogs, deer, marmosets, tamarins, and elephants. The incidence of twinning among cattle is about 1–4%, and research is under way to improve the odds of twinning, which can be more profitable for the breeder if complications can be sidestepped or managed. A female calf that is the twin of a bull becomes partially masculinized and is known as a freemartin.
Unlike singleton gestation where identification of patients at risk for PTL is often difficult, every multiple gestation is at risk for PTL, so all patients can be managed as being at risk.
The 3″/50 caliber gun (spoken "three-inch fifty-caliber") in United States naval gun terminology indicates the gun fired a projectile 3 inches (76 mm) in diameter, and the barrel was 50 calibers long (barrel length is 3 in × 50 = 150 in or 3.8 m). Different guns (identified by Mark numbers) of this caliber were used by the U.S. Navy and U.S. Coast Guard from 1890 through the 1990s on a variety of combatant and transport ship classes.
The gun is still in use with the Spanish Navy on Serviola-class patrol boats.Aphex Twin
Richard David James (born 18 August 1971), best known by the alias Aphex Twin, is an Irish-born British musician. He is best known for his influential and idiosyncratic work in styles such as ambient techno and intelligent dance music during the 1990s, and is among the most acclaimed figures in contemporary electronic music.Raised in Cornwall, James began releasing acid techno records in the early 1990s under aliases such as AFX and Polygon Window. He first received widespread acclaim for his 1992 debut album Selected Ambient Works 85–92. During this period, he became associated with UK record label Warp and co-founded the independent label Rephlex Records. He rose to mainstream popularity with the charting singles "Come to Daddy" (1997) and "Windowlicker" (1999), as well as for their music videos, both directed by Chris Cunningham.
After releasing the studio album Drukqs in 2001, James went into a period of inactivity as Aphex Twin, but he continued to issue music under other aliases, including the Analord EPs in 2005 as AFX and a pair of EPs in 2007 as The Tuss. James returned as Aphex Twin in 2014 with the album Syro, which won a Grammy Award for Best Dance/Electronic Album.Benji Madden
Benjamin Levi Madden (né Combs; born March 11, 1979) is an American guitarist, vocalist, songwriter, and producer. He is the lead guitarist and backing vocalist for the band Good Charlotte, as well as pop rock collaboration The Madden Brothers. He formed both of these acts with his identical twin brother, Joel Madden. Benji was a coach on The Voice Australia from 2015-16 with his brother Joel.Conjoined twins
Conjoined twins are identical twins joined in utero. An extremely rare phenomenon, the occurrence is estimated to range from 1 in 49,000 births to 1 in 189,000 births, with a somewhat higher incidence in Southwest Asia and Africa. Approximately half are stillborn, and an additional one-third die within 24 hours. Most live births are female, with a ratio of 3:1.Two contradicting theories exist to explain the origins of conjoined twins. The more generally accepted theory is fission, in which the fertilized egg splits partially. The other theory, no longer believed to be the basis of conjoined twinning, is fusion, in which a fertilized egg completely separates, but stem cells (which search for similar cells) find similar stem cells on the other twin and fuse the twins together. Conjoined twins share a single common chorion, placenta, and amniotic sac, although these characteristics are not exclusive to conjoined twins, as there are some monozygotic but non-conjoined twins who also share these structures in utero.The most famous pair of conjoined twins was Chang and Eng Bunker (1811–1874), Thai brothers born in Siam, now Thailand. They traveled widely for many years and were labeled as the Siamese twins. Chang and Eng were joined at the torso by a band of flesh, cartilage, and their fused livers. In modern times, they could have been easily separated. Due to the brothers' fame and the rarity of the condition, the term "Siamese twins" came to be used as a synonym for conjoined twins.David Lynch
David Keith Lynch (born January 20, 1946) is an American filmmaker, painter, musician, actor, and photographer. He has been described by The Guardian as "the most important director of this era", while AllMovie called him "the Renaissance man of modern American filmmaking". His films Blue Velvet (1986) and Mulholland Drive (2001) are widely regarded by critics to be among the greatest films of their respective decades, while the success of his 1990–91 television series Twin Peaks led to him being labeled "the first popular Surrealist" by film critic Pauline Kael. He has received three Academy Award nominations for Best Director, and has won France's César Award for Best Foreign Film twice, as well as the Palme d'Or at the Cannes Film Festival and a Golden Lion award for lifetime achievement at the Venice Film Festival. In 2016, Mulholland Drive, was named the top film of the 21st century by the BBC following a poll of 177 film critics from 36 countries.Born to a middle-class family in Missoula, Montana, Lynch spent his childhood traveling around the United States before he studied painting at the Pennsylvania Academy of Fine Arts in Philadelphia, where he first made the transition to producing short films. He moved to Los Angeles, where he produced his first motion picture, the surrealist horror film Eraserhead (1977). After Eraserhead became a cult classic on the midnight movie circuit, Lynch was employed to direct the biographical film The Elephant Man (1980), from which he gained mainstream success. He was then employed by the De Laurentiis Entertainment Group and proceeded to make two films: the science-fiction epic Dune (1984), which proved to be a critical and commercial failure, and then a neo-noir mystery film Blue Velvet (1986), which stirred controversy over its violence but later grew in critical reputation.
Next, Lynch created his own television series with Mark Frost, the popular murder mystery Twin Peaks (1990–1991). He also created a cinematic prequel, Twin Peaks: Fire Walk with Me (1992), a road film Wild at Heart (1990) and a family film The Straight Story (1999) in the same period. Turning further towards surrealist filmmaking, three of his subsequent films operated on dream logic non-linear narrative structures: Lost Highway (1997), Mulholland Drive (2001), and Inland Empire (2006). Meanwhile, Lynch embraced the Internet as a medium, producing several web-based shows, such as the animated DumbLand (2002) and the surreal sitcom Rabbits (2002). Lynch and Frost reunited for the Showtime limited series Twin Peaks: The Return (2017), with Lynch co-writing and directing every episode.
Lynch's other artistic endeavours include: his work as a musician, encompassing two solo albums—Crazy Clown Time (2011) and The Big Dream (2013)—as well as music and sound design for a variety of his films; painting and photography; writing three books—Images (1994), Catching the Big Fish (2006), and Room to Dream (2018); and directing several music videos and advertisements, including the Dior promotional film Lady Blue Shanghai (2006). An avid practitioner of Transcendental Meditation (TM), Lynch founded the David Lynch Foundation in 2005, which sought to fund the teaching of TM in schools and has since widened its scope to other at-risk populations, including the homeless, veterans and refugees.De Havilland Canada DHC-6 Twin Otter
The de Havilland Canada DHC-6 Twin Otter, currently marketed as the Viking Air DHC-6 Twin Otter, is a Canadian 19-passenger STOL (Short Takeoff and Landing) utility aircraft developed by de Havilland Canada and currently produced by Viking Air. The aircraft's fixed tricycle undercarriage, STOL capabilities, twin turboprop engines and high rate of climb have made it a successful commuter passenger airliner as well as a cargo and medical evacuation aircraft. In addition, the Twin Otter has been popular with commercial skydiving operations, and is used by the United States Army Parachute Team and the United States Air Force's 98th Flying Training Squadron.Doppelgänger
A doppelgänger (; German: [ˈdɔpl̩ˌɡɛŋɐ] (listen), literally "double-goer") is a non-biologically related look-alike or double of a living person, sometimes portrayed as a ghostly or paranormal phenomenon and usually seen as a harbinger of bad luck. Other traditions and stories equate a doppelgänger with an evil twin. In modern times, the term twin stranger is occasionally used. The word "doppelgänger" is often used in a more general and neutral sense, and in slang, to describe any person who physically or behaviorally resembles another person.Mary-Kate Olsen
Mary-Kate Olsen (born June 13, 1986) is an American fashion designer, businesswoman, author, and former actress and producer. She began her acting career one year after her birth, sharing the role of Michelle Tanner with her twin sister Ashley Olsen in the television sitcom Full House (1987–1995). They also starred in numerous films together.
In 1993, the production company Dualstar Entertainment Group was founded, which produced a long string of TV movies and direct-to-video releases featuring the girls; they starred in Passport to Paris (1999), Our Lips Are Sealed (2000), Winning London (2001), Holiday in the Sun (2001) and in the television series, So Little Time (2001–2002), for which she was nominated for a Daytime Emmy Award for Outstanding Performer in Children's Programming.
They starred in Getting There (2002), When in Rome (2002), The Challenge (2003) and made cameos in Charlie's Angels: Full Throttle (2003). The last film she starred in with her twin sister was New York Minute (2004). She continued with her acting career independently, appearing with a few guest-star roles in films and television shows, and with her last film being Beastly (2011).
In March 2012, both Mary-Kate and Ashley officially indicated their interest to retire as actresses in order to focus on their careers in the fashion industry.
She and her twin sister co-founded luxury fashion brands The Row, Elizabeth and James, and more affordable fashion lines Olsenboye and StyleMint. They co-authored the book Influence, featuring interviews with fashion designers that have inspired their fashion lines. They are members of the Council of Fashion Designers of America.Minneapolis–Saint Paul
Minneapolis–Saint Paul is a major metropolitan area built around the Mississippi, Minnesota and St. Croix rivers in east central Minnesota. The area is commonly known as the Twin Cities after its two largest cities, Minneapolis, the most populous city in the state, and Saint Paul, the state capital. It is an example of twin cities in the sense of geographical proximity. Minnesotans living outside of Minneapolis and Saint Paul often refer to the two together (or the seven-county metro area collectively) as "The Cities".
There are several different definitions of the region. Many refer to the Twin Cities as the seven-county region which is governed under the Metropolitan Council regional governmental agency and planning organization. The Office of Management and Budget officially designates 16 counties as the "Minneapolis–St. Paul–Bloomington MN–WI Metropolitan Statistical Area", the 16th largest in the United States. The entire region known as the "Minneapolis–St. Paul MN–WI Combined Statistical Area", has a population of 3,946,533, the 14th largest, according to 2017 Census estimates.
Despite the Twin moniker, both cities are independent municipalities with defined borders. Minneapolis is somewhat younger with more modern skyscrapers downtown, while Saint Paul has been likened to an East Coast city, with quaint neighborhoods and a vast collection of well-preserved late-Victorian architecture.Minneapolis was influenced by its early Scandinavian and Lutheran heritage. St. Paul was influenced by its early French, Irish and German Catholic roots.North American F-82 Twin Mustang
The North American F-82 Twin Mustang is the last American piston-engine fighter ordered into production by the United States Air Force. Based on the P-51 Mustang, the F-82 was originally designed as a long-range escort fighter in World War II. The war ended well before the first production units were operational.
In the postwar era, Strategic Air Command used the planes as a long-range escort fighter. Radar-equipped F-82s were used extensively by the Air Defense Command as replacements for the Northrop P-61 Black Widow as all-weather day/night interceptors. During the Korean War, Japan-based F-82s were among the first USAF aircraft to operate over Korea. The first three North Korean aircraft destroyed by U.S. forces were shot down by F-82s, the first being a North-Korean Yak-11 downed over Gimpo Airfield by the USAF 68th Fighter Squadron.Overhead camshaft
Overhead camshaft, commonly abbreviated to OHC, is a valvetrain configuration which places the camshaft of an internal combustion engine of the reciprocating type within the cylinder heads ("above" the pistons and combustion chambers) and drives the valves or lifters in a more direct manner compared with overhead valves (OHV) and pushrods.Petronas Towers
The Petronas Towers, also known as the Petronas Twin Towers (Malay: Menara Petronas, or Menara Berkembar Petronas), are twin skyscrapers. According to the Council on Tall Buildings and Urban Habitat (CTBUH)'s official definition and ranking, they were the tallest buildings in the world from 1998 to 2004 and remain the tallest twin towers in the world. The buildings are a landmark of Kuala Lumpur, along with nearby Kuala Lumpur Tower.Shoot 'em up
Shoot 'em up (also known as shmup or STG) is a subgenre of the shooter genre of video games. There is no consensus as to which design elements compose a shoot 'em up. Some restrict the definition to games featuring spacecraft and certain types of character movement; others allow a broader definition including characters on foot and a variety of perspectives.
The genre's origins can be traced back to Spacewar!, one of the earliest computer games, developed in 1962. In the late 1970s, games such as Space Invaders and Asteroids popularized the genre. Shoot 'em ups were popular throughout the 1980s and early 1990s. In the mid-1990s, shoot 'em ups became a niche genre based on design conventions established in the 1980s, and increasingly catered to specialist enthusiasts, particularly in Japan. "Bullet hell" games are a subgenre that features overwhelming numbers of enemy projectiles, often in visually impressive formations.Sister city
Sister cities or twin towns are a form of legal or social agreement between towns, cities, counties, oblasts, prefectures, provinces, regions, states, and even countries in geographically and politically distinct areas to promote cultural and commercial ties. The modern concept of town twinning, conceived after the Second World War in 1947, was intended to foster friendship and understanding among different cultures and between former foes as an act of peace and reconciliation, and to encourage trade and tourism. By the 2000s, town twinning became increasingly used to form strategic international business links among member cities.Turbocharger
A turbocharger, colloquially known as a turbo, is a turbine-driven forced induction device that increases an internal combustion engine's efficiency and power output by forcing extra compressed air into the combustion chamber. This improvement over a naturally aspirated engine's power output is due to the fact that the compressor can force more air—and proportionately more fuel—into the combustion chamber than atmospheric pressure (and for that matter, ram air intakes) alone.
Turbochargers were originally known as turbosuperchargers when all forced induction devices were classified as superchargers. Today the term "supercharger" is typically applied only to mechanically driven forced induction devices. The key difference between a turbocharger and a conventional supercharger is that a supercharger is mechanically driven by the engine, often through a belt connected to the crankshaft, whereas a turbocharger is powered by a turbine driven by the engine's exhaust gas. Compared with a mechanically driven supercharger, turbochargers tend to be more efficient, but less responsive. Twincharger refers to an engine with both a supercharger and a turbocharger.
Turbochargers are commonly used on truck, car, train, aircraft, and construction equipment engines. They are most often used with Otto cycle and Diesel cycle internal combustion engines.Twin Peaks
Twin Peaks is an American mystery horror drama television series created by Mark Frost and David Lynch that premiered on April 8, 1990, on ABC. It was one of the top-rated series of 1990, but declining ratings led to its cancellation after its second season in 1991. It nonetheless gained a cult following and has been referenced in a wide variety of media. In subsequent years, Twin Peaks has often been listed among the greatest television series of all time.The series follows an investigation headed by FBI Special Agent Dale Cooper (Kyle MacLachlan) into the murder of homecoming queen Laura Palmer (Sheryl Lee) in the fictional suburban town of Twin Peaks, Washington. The show's narrative draws on elements of detective fiction, but its uncanny tone, supernatural elements, and campy, melodramatic portrayal of eccentric characters also draw on American soap opera and horror tropes. Like much of Lynch's work, it is distinguished by surrealism, offbeat humor, and distinctive cinematography. The acclaimed score was composed by Angelo Badalamenti in collaboration with Lynch.The series was followed by a 1992 feature film, Twin Peaks: Fire Walk with Me, that serves as a prequel to the series. Following a hiatus of over 25 years, the show returned in May 2017 with a third season on Showtime, marketed as Twin Peaks: The Return. The season comprised 18 episodes written by Lynch and Frost, and was entirely directed by Lynch. Many original cast members, including MacLachlan, returned.Twin Peaks (season 3)
The third season of Twin Peaks, also known as Twin Peaks: The Return, consists of 18 episodes and premiered on Showtime on May 21, 2017. Developed and written by David Lynch and Mark Frost over several years, the season is a continuation of the 1990–91 ABC series. An ensemble of returning and new cast members appear, led by original star Kyle MacLachlan.Set 25 years after the events of the original Twin Peaks, the season follows multiple storylines, many of which are associated with FBI Special Agent Dale Cooper (MacLachlan) and his investigation into the murder of Twin Peaks homecoming queen Laura Palmer (Sheryl Lee) decades earlier. It takes place in a variety of settings beyond the fictional Washington State town of Twin Peaks, including Las Vegas, South Dakota, Philadelphia, and New Mexico. Showtime president David Nevins said that "the core of [the plot] is Agent Cooper's odyssey back to Twin Peaks".The season garnered critical acclaim, with praise centering on its unconventional narrative and structure, visual invention, and performances. Many publications, including Rolling Stone, The Washington Post, and Esquire, named it the best television show of 2017. The film journals Sight & Sound and Cahiers du cinéma named The Return the second-best and best "film" of the year respectively, sparking discussion about the artistic difference, if any, between theatrical film and TV series in the era of streaming.University of Minnesota
The University of Minnesota, Twin Cities (often referred to as the University of Minnesota, Minnesota, the U of M, UMN, or simply the U) is a public research university in Minneapolis and Saint Paul, Minnesota. The Minneapolis and St. Paul campuses are approximately 3 miles (4.8 km) apart, and the Saint Paul campus is actually in neighboring Falcon Heights. It is the oldest and largest campus within the University of Minnesota system and has the sixth-largest main campus student body in the United States, with 50,943 students in 2018-19. The university is the flagship institution of the University of Minnesota system, and is organized into 19 colleges and schools, with sister campuses in Crookston, Duluth, Morris, and Rochester.
The University of Minnesota is one of America's Public Ivy universities, which refers to top public universities in the United States capable of providing a collegiate experience comparable with the Ivy League. Founded in 1851, The University of Minnesota is categorized as a Doctoral University – Highest Research Activity (R1) in the Carnegie Classification of Institutions of Higher Education. Minnesota is a member of the Association of American Universities and is ranked 14th in research activity with $881 million in research and development expenditures in the fiscal year ending June 30, 2015.The University of Minnesota faculty, alumni, and researchers have won 29 Nobel Prizes and three Pulitzer Prizes.
Notable University of Minnesota alumni include two Vice Presidents of the United States, Hubert Humphrey and Walter Mondale, and Bob Dylan, who received the 2016 Nobel Prize in Literature.World Trade Center (1973–2001)
The original World Trade Center was a large complex of seven buildings in Lower Manhattan, New York City, United States. It featured the landmark Twin Towers, which opened on April 4, 1973 and were destroyed in 2001 during the September 11 attacks. At the time of their completion, the Twin Towers — the original 1 World Trade Center, at 1,368 feet (417 m); and 2 World Trade Center, at 1,362 feet (415.1 m) — were the tallest buildings in the world. Other buildings in the complex included the Marriott World Trade Center (3 WTC), 4 WTC, 5 WTC, 6 WTC, and 7 WTC. The complex was located in New York City's Financial District and contained 13,400,000 square feet (1,240,000 m2) of office space.The core of the complex was built between 1975 and 1985, with a cost of $400 million (equivalent to $2.27 billion in 2018). The World Trade Center experienced a fire on February 13, 1975, a bombing on February 26, 1993, and a bank robbery on January 14, 1998. In 1998, the Port Authority decided to privatize the World Trade Center, leasing the buildings to a private company to manage, and awarded the lease to Silverstein Properties in July 2001.On the morning of September 11, 2001, Al-Qaeda-affiliated hijackers flew two Boeing 767 jets into the North and South Towers within minutes of each other; two hours later, both towers collapsed. The attacks killed 2,606 people in and within the vicinity of the towers, as well as all 157 on board the two aircraft. Falling debris from the towers, combined with fires that the debris initiated in several surrounding buildings, led to the partial or complete collapse of all the buildings in the complex and caused catastrophic damage to ten other large structures in the surrounding area.
The cleanup and recovery process at the World Trade Center site took eight months, during which the remains of the other buildings were demolished. The World Trade Center complex was rebuilt over more than a decade. The site is being rebuilt with six new skyscrapers, while a memorial to those killed in the attacks, a new rapid transit hub, and an elevated park were all opened. One World Trade Center, the tallest building in the Western Hemisphere at 1,776 feet (541 m), is the lead building for the new complex, having been completed in November 2014.