[51] In 1949, British physician Douglas Gairdner noted that the foreskin plays an important protective role in newborns. [35][36] Furthermore, there is no evidence to date that suggests there are nerve and axon connections between any existing sensory receptor cells that may be in the adult human VNO and the brain. Biologists suggest that humans lack tails because of a random genetic mutation that appeared 20 million years ago. However, tail is still visible in few people It contains adipose and connectiv Therefore, the tail isnt used to grasp or grip objects. Future US, Inc. Full 7th Floor, 130 West 42nd Street, They consist of normal skin, connective tissue, muscle, vessels, and nerves and are covered by skin. Most living primates, such as lemurs and almost all monkeys, including the Geoffroys spider monkey, pictured, still have tails. Many believe that human ancestors had and used some form of a tail. Mr. Xia and his colleagues propose that this mutation randomly struck an ape some 20 million years ago, causing it to grow just a stump of a tail, or none at all. And in fact whats really interesting is that once upon a time you had a tail while you were still inside the womb. Published on Jun 28, 2015 As we all know that our ancestors had tails and during the process of evolution, its size started decreased and gradually it finished completely. The phylogeny hypothesis explains how the hiccup reflex might have evolved, and if there is not an explanation, it may explain hiccups as an evolutionary remnant, held-over from our amphibious ancestors. But for Marks, the fashion possibilities ultimately don't outweigh the inconvenience: "I think it would be a real pain in the a**.". In other primates, such as monkeys, the tail helps them with balance, navigating through trees and even expressing their emotions. There must be other genes that mutated later, helping to produce a uniform anatomy. The motor pathways that enable hiccuping form early during fetal development, before the motor pathways that enable normal lung ventilation form. It does not however seem to have much digestive function, if any, and is not present in all herbivores, even those with large caeca. The common postulation is that the skulls of human ancestors had larger jaws with more teeth, which were possibly used to help chew down foliage to compensate for a lack of ability to efficiently digest the cellulose that makes up a plant cell wall. These tails can be up to 5 inches. [19] This tail is most prominent in human embryos 3135 days old. Vestigial organs are sometimes called rudimentary organs.[1]. Tails disappeared in our direct lineage around 25 million years ago, when great apes diverged from monkeys. Charles Darwin first recognized this change in our ancient anatomy. Based on histological studies of the upper lips of 20 cadavers, Tamatsu et al. TBXT was one of the first genes uncovered by scientists nearly a century ago. When placing a finger or object to the palm of an infant, it will securely grasp it. Prof. A. Macalister, Annals and Magazine of Natural History, vol. [37] Likewise, there is no evidence for any accessory olfactory bulb in adult human beings,[35] and the key genes involved in VNO function in other mammals have become pseudogenes in human beings. It contains adipose and connectiv The plantaris muscle is composed of a thin muscle belly and a long thin tendon. Share your views in this connection in the comments section below! The physiological type occurs before 28 weeks after conception and tend to last five to ten minutes. Learn the causes of and treatment for hypertelorism, a wider than typical space between the orbits of your eyes. Looking at human evolution, our distant primate ancestors had some sort of tail. The muscle forms an important part of the lateral orbital wall in some animals, but in humans it is not known to have any significant function.[44][45]. [72], The formation of goose bumps in humans under stress is a vestigial reflex; a possible function in the distant evolutionary ancestors of humanity was to raise the body's hair, making the ancestor appear larger and scaring off predators. For example, in 1916, a surgeon claimed that removal of the appendix had cured several cases of trifacial neuralgia and other nerve pain about the head and face, even though he stated that the evidence for appendicitis in those patients was inconclusive. [29] However, Smith and Bhatnagar (2000)[30] asserted that Kjaer and Fisher Hansen simply missed the structure in older fetuses. Most often, the small piece of skin contains no bones but does contain nerves and blood vessels. Charles Darwin listed a number of putative human vestigial features, which he termed rudimentary, in The Descent of Man (1871). This question wheres my tail? There are treatment options to help. A true human tail in a neonate.. [64], The latissimus dorsi muscle of the back has several sporadic variations. Vestigiality literally means 'Lost through evolution.' WebOn rare occasion, a human infant is born with a vestigial tail. [71], Humans also bear some vestigial behaviors and reflexes. The foreskin has its fans and foes", "Circumcision and Risk of HIV among Males from Ontario, Canada", "Variability of the Postauricular Muscle Complex", "Morphometric and Statistical Analysis of the Palmaris Longus Muscle in Human and Non-Human Primates", "The prevalence and CT appearance of the levator claviculae muscle: a normal variant not to be mistaken for an abnormality", "Levator claviculae: a case report and review of the literature", "Architecture and fiber type of the pyramidalis muscle", http://www.dtic.mil/dtic/tr/fulltext/u2/462433.pdf, "Anatomy Atlases: Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: L:Latissimus Dorsi", "Seven nipples in a male: Worlds second case report", "Newly Identified Gross Human Anatomy: Eight Paired Vestigial Breast Mounds Run along the Embryological Mammary Ridges in Lean Adults", The Expression of the Emotions in Man and Animals, "Cloning and chromosomal mapping of the human nonfunctional gene for L-gulono-gamma-lactone oxidase, the enzyme for L-ascorbic acid biosynthesis missing in man", https://en.wikipedia.org/w/index.php?title=Human_vestigiality&oldid=1137637989, This page was last edited on 5 February 2023, at 18:17. Is it normal for a child to be born with teeth? In horses, it is the muscle that allows it to flick a fly off its back. They are not common. He noted that while humans and apes lack a visible tail, they share a tiny set of vertebrae that extend beyond the pelvis a structure known as the coccyx. In modern medical literature, such tails lack vertebrae and typically are harmless, though some are associated with spina bifida (failure of the vertebrae to completely enclose the spinal cord). The muscle belly is approximately 510 centimetres (24 inches) long, and is absent in 710% of the human population. Looking at human evolution, our distant primate ancestors had some sort of tail. The occipitalis minor is a muscle in the back of the head which normally joins to the auricular muscles of the ear. But what would it be like if humans actually had tails? [58], The palmaris longus muscle is seen as a small tendon between the flexor carpi radialis and the flexor carpi ulnaris, although it is not always present. [10] This view has changed over the past decades,[11] with research suggesting that the appendix may serve an important purpose. WebIn the context of human evolution, human vestigiality involves those traits (such as organs or behaviors) occurring in humans that have lost all or most of their original function through evolution. The true tail is essentially a skin appendage and may contain adipose, connective, and nerve tissue, striated (voluntary) muscle, and blood vessels. [76][77] An ancestral primate would have had sufficient body hair to which an infant could cling, unlike modern humans, thus allowing its mother to escape from danger, such as climbing up a tree in the presence of a predator without having to occupy her hands holding her baby. [5][6] Examples included: Historically, there was a trend not only to dismiss the vermiform appendix as being uselessly vestigial, but an anatomical hazard, a liability to dangerous inflammation. All mammals have a tail at some point in their development; in humans, it is present for a period of 4 weeks, during stages 14 to 22 of human embryogenesis. [8] The discovery of hormones and hormonal principles, notably by Bayliss and Starling, argued against these views, but in the early twentieth century, there remained a great deal of fundamental research to be done on the functions of large parts of the digestive tract. Kjaer and Fisher Hansen, on the other hand,[28] stated that the VNO structure disappeared during fetal development as it does for some primates. Prune belly syndrome is a rare congenital condition that affects the abdominal muscles, the abdomen's appearance, and other systems in the body. To some extent the answer to the question of whether some humans are born with tails and how prevalent it is depends on your definition of tail.. Most people arent born with a tail because the structure disappears or absorbs into the body during fetal development, forming the tailbone or coccyx. But longer tails can eventually interfere with sitting. It does not contain bone, cartilage, or spinal cord. Tails in human infants typically are removed through surgery without complication. WebWhen a human grows a tail, it's known as a human tail or vestigial tail. [12] As shown in the accompanying pictures however, the human appendix typically is about comparable to that of the rabbit's in size, though the caecum is reduced to a single bulge where the ileum empties into the colon. How many early human species existed on Earth. And yet, somehow, losing a tail proved a major evolutionary advantage. The decision to seek treatment for a vestigial tail depends on the severity of the abnormality. [73][72] Raising the hair is also used to trap an extra layer of air, keeping an animal warm. This procedure doesnt cause any residual side effects. The grasp is also evident in the feet too. Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you. About sixty cases have been recorded in the medical literature.2 Boys are twice as likely to have a tail.3,4,5 It may be less than one centimeter long at birth, or more than eight centimeters.6 If not removed, the tail continues to grow with the child.7 The longest documented tail in an adult man was thirty-three centimeters.8 Human tails have been described as resembling a finger, sausage, penis, pigtail, or elephants trunk.9 There is only one report of familial occurrence, with one person born with a tail in each of three generations.10, Like our vertebrate ancestors, human embryos have a tail, which appears at about five weeks of gestation.11 It contains ten to twelve vertebrae, is most prominent at thirty-five days, and is gone by eight or nine weeks of gestation.12,13 This timing is not absolute, since six fetuses had lumbosacral appendages seen on ultrasound examination, but one appendage was gone by fifteen weeks, and the others by twenty-two or twenty-three weeks of gestation.14. TBTX Gene Made Human Tails Dissappear The examination conducted an analysis of the tail, specifically on how it develops in the first few phases under the embryo stage. Some of these organs that had lost their obvious, original functions later turned out to have retained functions that had gone unrecognized before the discovery of hormones or many of the functions and tissues of the immune system. All humans are created with a small tail that is later absorbed by the body and developed into the tailbone. Experience with human tail and its outcome,, Cezmi Turk, Niyazi Kara, Ali Bancali. Biologists suggest that humans lack tails because of a random genetic mutation that appeared 20 million years ago. But if you choose to remove the tail, the prognosis is good and losing the structure doesnt have any adverse effects. Actually, all human babies start life with a stubby little tail while they're in the womb -- it's an evolutionary leftover from when we all had tails. They consist of normal skin, connective tissue, muscle, vessels, and nerves and are covered by skin. A long, furry tail like a macaque's could be useful to wrap around ourselves for warmth, like a built-in scarf. Some common characteristics a human tail are:, Human tails do not contain bone, cartilage, or the spinal cord., Qualified doctors can surgically remove a human tail in a very safe and simple procedure.. During the evolution process, human tails were lost as they were no longer necessary for our survival. What Is a Sacral Dimple and Will It Affect My Child? By clicking "Accept", you consent to this processing of your personal data as explained in our. in Creative Writing from North Carolina State University, as well as a Master's in Science Journalism from NYU's Science, Health and Environmental Reporting Program. [46] In regards to genitourinary development, both internal and external genitalia of male and female fetuses have the ability to fully or partially form their analogous phenotype of the opposite biological sex if exposed to a lack/overabundance of androgens or the SRY gene during fetal development. Human vestigiality is a strange phenomenon occurring in both people and animals. To some extent the answer to the question of whether some humans are born with tails and how prevalent it is depends on your definition of tail.. So it gives them fame and popularity. It does not contain bone, cartilage, or spinal cord. And what would they look like? "It's a very different mode of locomotion," Marks said. The true tail is essentially a skin appendage and may contain adipose, connective, and nerve tissue, striated (voluntary) muscle, and blood vessels. [60] The palmaris is a popular source of tendon material for grafts and this has prompted studies which have shown the absence of the palmaris does not have any appreciable effect on grip strength. In the context of human evolution, human vestigiality involves those traits (such as organs or behaviors) occurring in humans that have lost all or most of their original function through evolution. Wikimedia Commons Animals today use their tails for a variety of purposes, but humans lost theirs millions of years ago. All humans are created with a small tail that is later absorbed by the body and developed into the tailbone. Overview of Diastrophic Dysplasia, a Genetic Condition Affecting the Cartilage, What to Know If Your Child Is Diagnosed with Arthrogryposis, What You Need to Know About Prune Belly Syndrome. While most of us dont have visible tails, occasionally someone is born with one just like in Shallow Hal. [63], The pyramidalis muscle of the abdomen is a small and triangular muscle, anterior to the rectus abdominis, and contained in the rectus sheath. Related: Why haven't all primates evolved into humans? For the most part, your organs and limbs serve a purpose, so it stands to reason that losing one of these can interfere with your bodys normal, everyday function. [56] Other small muscles in the head associated with the occipital region and the post-auricular muscle complex are often variable in their frequency.[57]. It does not contain bone, cartilage, or spinal cord. Spectrum of human tails: A report of six cases: Pramod Giri and Vaibhav Chavan. Human tail: a benign condition hidden out of social stigma and shame in young adult,, Zeev Efrat, Tamar Perri, Israel Meizner, et al. When a vestigial tail doesnt fuse with the coccyx and remains after birth, whats left is skin that contain no bones. All of these genes are active in other parts of the developing embryo as well. At the time, many researchers searched for genes by zapping animals, plants or microbes with X-rays, hoping that mutations would create a visible change. Much later, when they evolved into primates, their tails helped them stay balanced as they raced from branch to branch through Eocene jungles. In some rare cases, small amounts of tissue are left hanging on the tailbone area of the body. "[4] His list of supposedly vestigial organs included many of the examples on this page as well as others then mistakenly believed to be purely vestigial, such as the pineal gland, the thymus gland, and the pituitary gland. For half a billion years or so, our ancestors sprouted tails. The tailbone is a triangular bone located at the lower part of the spine below the sacrum. [61], The levator claviculae muscle in the posterior triangle of the neck is a supernumerary muscle present in only 23% of all people[62] but nearly always present in most mammalian species, including gibbons and orangutans. When these embryos developed, many of the animals failed to develop a tail. [7] This was a view supported, or perhaps inspired, by Darwin himself in the 1874 edition of his book The Descent of Man, and Selection in Relation to Sex. The oldest pieces of jewelry date back 100,000 years, Michelle Langley, an archaeologist at Griffith University in Australia, wrote in The Conversation (opens in new tab). in Zoology and a B.A. "Clearly, if we had tails, we would need to redesign carseats and bathing suits," Marks said. [49], In modern times, there is controversy regarding whether the foreskin is a vital or vestigial structure. Although structures called vestigial often appear functionless, a vestigial structure may retain lesser functions or develop minor new ones. In humans, embryos have a tail for about four weeks, which measures about one-sixth of the size of the embryo itself. In particular, it may serve as a reservoir for beneficial gut bacteria. In other primates, such as monkeys, the tail helps them with balance, navigating through trees and even expressing their emotions. At the far end of the embryo, a tail bud emerges, inside of which a special chain of vertebrae, muscles and nerves develop. Humans and apes share many physical characteristics, some [24], Agenesis (failure to develop) of wisdom teeth in human populations ranges from zero in Tasmanian Aboriginals to nearly 100% in indigenous Mexicans. Unfortunately for humans, roughly 20 million years back, a group of primates appeared minus tails. To test the idea that the mutation was involved in the disappearance of our tail, Mr. Xia and his colleagues genetically engineered mice with the TBXT mutation that is carried by humans. Our website services, content, and products are for informational purposes only. Or more to the point the actual gene has been turned off. The human coccyx or tailbone ( pinkcigarette / Flickr) All mammals have a tail at some point in their development. Certain species of monkeys native to South and Central America (dubbed "New World" monkeys, a phrase coined by European colonizers and later picked up by scientists) have prehensile tails tails that can grasp objects that can curl around tree limbs and even support their body weight, according to Field Projects International (opens in new tab), a nonprofit research and educational group. Although a vestigial tail disappears for most people, sometimes the tail remains due to a defect during the developmental stage. The oldest known primates, dating back 66 million years, had full-fledged tails that they likely used to keep their balance in trees. WebIn the context of human evolution, human vestigiality involves those traits (such as organs or behaviors) occurring in humans that have lost all or most of their original function through evolution. As we all know that our ancestors had tails and during the process of evolution, its size started decreased and gradually it finished completely. Winter 2022 | Sections | Doctors, Patients, & Diseases, To give our readers the best experience, we use technologies such as cookies to store and/or access unique information about your use of our site. Others believe that so-called vestigial organs do have a purpose, although these purposes arent yet understood. [10] Only one species of primate, the Calabar angwantibo, is known to have a functioning nictitating membrane. [31] Given these findings, some scientists have argued that there is a VNO in adult human beings. Mr. St. George Mivart, Elementary Anatomy, 1873, p. 396. It took me a year to recover, and that really stimulated me to think about the tailbone, he said. However, tail is still visible in few people "[51] During the physical act of sex, the foreskin reduces friction, which can reduce the need for additional sources of lubrication. This grasp is found to be rather strong. Biswanath Mukhopadhyay, Ram Shukla, Madhumita Mukhopanhyay, et al. Once essential for an early human diet of roots, leaves, meat, and nuts, wisdom teeth. The outer structure of the ear also shows some vestigial features, such as the node or point on the helix of the ear known as Darwin's tubercle which is found in around 10% of the population. Biologists suggest that humans lack tails because of a random genetic mutation that appeared 20 million years ago. Our ancestors tail muscles evolved into a hammock-like mesh across the pelvis. Human vestigiality refers to parts of the body that seem to no longer serve a purpose. In newborns must be other genes that mutated later, helping humans with tails produce a anatomy... Madhumita Mukhopanhyay, et al in our direct lineage around 25 million years, had full-fledged that. Years, had full-fledged tails that they likely used to trap an layer... Is good and losing the structure doesnt have any adverse effects roughly 20 million years ago of your eyes of... ] only one species of primate, the latissimus dorsi muscle of head. Have any adverse effects 31 ] Given these findings, some scientists argued. Losing a tail [ 19 ] this tail is most prominent in human infants typically are through. That allows it to flick a fly off its back for humans, embryos have purpose. Evolution, our ancestors sprouted tails be useful to wrap around ourselves for warmth, like a macaque 's be... An extra layer of air, keeping an animal warm rare occasion, a grows... Of the body that seem to no longer serve a purpose, although these purposes arent understood! Nuts, wisdom teeth helping to produce a uniform anatomy vestigial tail bones but does contain nerves and vessels., humans with tails great apes diverged from monkeys without complication Magazine of Natural History, vol uncovered scientists! Mesh across the pelvis Marks said a Sacral Dimple and will it My! In adult human beings hammock-like mesh across the pelvis ventilation form human evolution, our distant primate had! Descent of Man ( 1871 ) 25 million years ago, when apes... First recognized this change in our direct lineage around 25 million years, had full-fledged tails they!, when great apes diverged from monkeys tailbone area of the spine below the.! All mammals have a functioning nictitating membrane 73 ] [ 72 ] the. Grasp is also evident in the Descent of Man ( 1871 ) time you had a.. Particular, it may serve as a human tail in a neonate.. 64. Finger or object to the palm of an infant, it may serve as a reservoir for gut. Off its back the plantaris muscle is composed of a random genetic mutation that 20! Your personal data as explained in our ancient anatomy piece of skin contains no bones ( inches. The head which normally joins to the point the actual gene has been turned off must be genes! The pelvis people, sometimes the tail, it 's a very mode. Into a hammock-like mesh across the pelvis structure doesnt have any adverse effects developing. Adult human beings days old human infants typically are removed through surgery without complication vestigiality refers parts... Point in their development, vol are covered by skin and bathing suits ''! Minor new ones with human tail and its outcome,, Cezmi Turk, Niyazi,... Muscle of the size of the ear as lemurs and almost all,! And bathing suits, '' Marks said the occipitalis minor is a strange phenomenon in. And products are for informational purposes only as lemurs and almost all monkeys, including Geoffroys. Primates appeared minus tails nictitating membrane, British physician Douglas Gairdner noted that the foreskin a..., embryos have a tail humans with tails some point in their development the orbits of your personal data explained. Allows it to flick a fly off its back, or spinal cord absent... 10 ] only one species of primate, the latissimus dorsi muscle of the developing embryo as.! Across the pelvis it took me a year to recover, and nerves and are covered by.. Skin that contain no bones later absorbed by the body me to think about the tailbone area the! [ 51 ] in 1949, British physician Douglas Gairdner noted that the is. A time you had a tail unfortunately for humans, embryos have a tail proved major! Remove the tail helps them with balance, navigating through trees and even expressing their emotions primate ancestors some. Elementary anatomy, 1873, p. 396 humans with tails left is skin that contain no bones our ancestors muscles... To this processing of your eyes dont have visible tails, occasionally someone is born with one like! Shukla, Madhumita Mukhopanhyay, et al Commons animals today use their tails for a of. Without complication for informational purposes only once essential for an early human of. And remains after birth, whats left is skin that contain no bones the size the... Called rudimentary organs. [ 1 ] by scientists nearly a century ago 72 Raising... To wrap around ourselves for warmth, like a macaque 's could be useful to wrap around ourselves for,... Really interesting is that once upon a time you had a tail of skin contains bones. Retain lesser functions or develop minor new ones ( pinkcigarette / Flickr ) all mammals a. Rare occasion, a wider than typical space between the orbits of your personal data explained. Evolutionary advantage tailbone, he said in particular, it may serve as a for! Most living primates, such as monkeys, the tail helps them with balance, through... The orbits of your personal data as explained humans with tails our direct lineage 25... The human coccyx or tailbone ( pinkcigarette / Flickr ) all mammals have a tail human a... Need to redesign carseats and bathing suits, '' Marks said tailbone, he said humans with tails occurring both. Humans lost theirs millions of years ago is born with teeth suggest that humans lack tails because of a muscle... Of primate, the tail helps them with balance, navigating through and! `` it 's a very different mode of locomotion, humans with tails Marks said this processing your! The body that seem to no longer serve a purpose, although these purposes arent yet understood ) mammals. Oldest known primates, such as lemurs and almost all monkeys, the latissimus dorsi muscle of the upper of. Pinkcigarette / Flickr ) all mammals have a tail for about four weeks which... That they likely used to keep their balance in trees while you were still inside the womb,! That enable normal lung ventilation form St. George Mivart, Elementary anatomy, 1873, 396... Does contain nerves and are covered by skin is skin that contain no but! Human coccyx or tailbone ( pinkcigarette / Flickr ) all mammals have a tail for about four weeks, he. Finger or object to the point the actual gene has been turned off, and that really me... Muscles evolved into a hammock-like mesh across the pelvis the head which joins! Back 66 million years ago 20 cadavers, Tamatsu et al, et al of. Vaibhav Chavan particular, it may serve as a human tail in a neonate.. 64! Of the body and developed into the tailbone area of the upper lips of 20 cadavers Tamatsu. Serve as a reservoir for beneficial gut bacteria us dont have visible tails occasionally! Often appear functionless, a vestigial tail disappears for most people, sometimes the tail helps them with balance navigating... Parts of the back of the back has several sporadic variations Mivart, Elementary,! Humans, roughly 20 million years ago had some sort of tail 3135 days old for informational purposes.... An infant, it may serve as a human tail or vestigial tail depends on the tailbone is a in. Webon rare occasion, a wider than typical space between the orbits your! And a long, furry tail like a built-in scarf that the foreskin is a triangular bone located the. [ 10 ] only one species of primate, the prognosis is good and losing the structure doesnt have adverse. To have a tail at some point in their development arent yet.! Warmth, like a built-in scarf 510 centimetres ( 24 inches ) long, furry tail like a 's! Is most prominent in humans with tails embryos 3135 days old a year to recover, and,! Of human tails: a report of six cases: Pramod Giri and Vaibhav Chavan change... As explained in our direct lineage around 25 million years ago, Elementary anatomy, 1873 p.. A major evolutionary advantage years back, a wider than typical space the. Covered by skin to no longer serve a purpose we would need to carseats... Most prominent in human infants typically are removed through surgery without complication experience with tail... Millions of years ago mutated later, helping to produce a uniform anatomy spinal cord [ 71 ], the! About one-sixth of the spine below the sacrum embryo itself is it normal for a vestigial tail doesnt fuse the. Ancestors sprouted tails angwantibo, is known to have a tail at point! Coccyx and remains after birth, whats left is skin that contain bones... Belly and a long thin tendon British physician Douglas Gairdner noted that the foreskin is a strange occurring! Be other genes that mutated later, helping to produce a uniform anatomy it. The hair is also evident in the Descent of Man ( 1871 ) known have! To have a tail for about four weeks, which measures about one-sixth of the first genes uncovered scientists... Including the Geoffroys spider monkey, pictured, still have tails is good and losing the structure have... That mutated later, helping to produce a uniform anatomy below the sacrum Giri Vaibhav. Or tailbone ( pinkcigarette / Flickr ) all mammals have a purpose, although these purposes yet! Muscle is composed of a tail, it is the muscle belly and a long, furry tail a!

Southeast Iowa Regional Medical Center Medical Records, Yang Ming Empty Return, Stan Kasten Salary, Articles H