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41-435: It is also a portmanteau term that describes all biological aspects of the human body, typically using the human body as a type organism for Mammalia , and in that context it is the basis for many undergraduate University degrees and modules. Most aspects of human biology are identical or very similar to general mammalian biology. In particular, and as examples, humans : The study of integrated human biology started in

82-454: A triglyceride (ester of glycerin ) rather than as a free fatty acid . It is one of two essential fatty acids for humans, who must obtain it through their diet, and the most essential, because the body uses it as a base to make the others. The word "linoleic" derives from Latin linum  ' flax ' and oleum  'oil', reflecting the fact that it was first isolated from linseed oil . In 1844, F. Sacc , working at

123-581: A human can synthesize Vitamin D3 using natural UV light from the sun on the skin. This capability may be widespread in the mammalian world but few other mammals share the almost naked skin of humans. The darker the human's skin, the less it can manufacture Vitamin D3. Human biology also encompasses all those organisms that live on or in the human body. Such organisms range from parasitic insects such as fleas and ticks , parasitic helminths such as liver flukes through to bacterial and viral pathogens . Many of

164-440: Is a surfactant with a critical micelle concentration of 1.5 x 10 M @ pH 7.5. Linoleic acid has become increasingly popular in the beauty products industry because of its beneficial properties on the skin. Research points to linoleic acid's anti-inflammatory, acne reductive, skin-lightening and moisture retentive properties when applied topically on the skin . Linoleic acid is also used in some bar of soap products. It

205-415: Is a component of quick- drying oils , which are useful in oil paints and varnishes . These applications exploit the lability of the doubly allylic C−H groups ( −CH=CH−C H 2 −CH=CH− ) toward oxygen in air ( autoxidation ). Addition of oxygen leads to crosslinking and formation of a stable film. Reduction of the carboxylic acid group of linoleic acid yields linoleyl alcohol . Linoleic acid

246-454: Is abundant in safflower , and corn oil, and comprises over half their composition by weight. It is present in medium quantities in soybean oils , sesame , and almonds . Cockroaches release oleic and linoleic acid upon death, which discourages other roaches from entering the area. This is similar to the mechanism found in ants and bees, which release oleic acid upon death. Consumption of linoleic acid has been associated with lowering

287-472: Is an organic compound with the formula HOOC(CH 2 ) 7 CH=CHCH 2 CH=CH(CH 2 ) 4 CH 3 . Both alkene groups ( −CH=CH− ) are cis . It is a fatty acid sometimes denoted 18:2 (n−6) or 18:2 cis -9,12. A linoleate is a salt or ester of this acid. Linoleic acid is a polyunsaturated , omega−6 fatty acid . It is a colorless liquid that is virtually insoluble in water but soluble in many organic solvents . It typically occurs in nature as

328-486: Is not sustainable in the medium to long term. All other fatty acids can be synthesized from dietary fats. Similarly, human life requires a range of vitamins to be present in food and if these are missing or are supplied at unacceptably low levels, metabolic disorders result which can end in death. The human metabolism is similar to most other mammals except for the need to have an intake of Vitamin C to prevent scurvy and other deficiency diseases. Unusually amongst mammals,

369-572: Is primarily driven by human poaching and habitat destruction , primarily deforestation . Over 70% of mammal species are in the orders Rodentia , Chiroptera , and Eulipotyphla . Mammal classification has been through several revisions since Carl Linnaeus initially defined the class, and at present , no classification system is universally accepted. McKenna & Bell (1997) and Wilson & Reeder (2005) provide useful recent compendiums. Simpson (1945) provides systematics of mammal origins and relationships that had been taught universally until

410-426: Is the viviparous placental mammals , so named for the temporary organ ( placenta ) used by offspring to draw nutrition from the mother during gestation . Most mammals are intelligent , with some possessing large brains, self-awareness , and tool use . Mammals can communicate and vocalize in several ways, including the production of ultrasound , scent marking , alarm signals , singing , echolocation ; and, in

451-658: Is vital to proper health, as it is an essential fatty acid. [REDACTED] Linoleic acid (LA: C 18 H 32 O 2 ; 18: 2 , n−6 ) is a precursor to arachidonic acid (AA: C 20 H 32 O 2 ; 20: 4 ,n−6) with elongation and unsaturation. AA is the precursor to some prostaglandins , leukotrienes (LTA, LTB, LTC), thromboxane (TXA) and the N-acylethanolamine (NAE) arachidonoylethanolamine (AEA: C 22 H 37 NO 2 ; 20:4,n−6), and other endocannabinoids and eicosanoids . The metabolism of LA to AA begins with

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492-428: Is well developed especially in the hands where dextrous tasks are performed but the sensitivity is still significantly less than in other animals, particularly those equipped with sensory bristles such as cats . Human biology tries to understand and promotes research on humans as living beings as a scientific discipline. It makes use of various scientific methods , such as experiments and observations , to detail

533-473: The Cretaceous . The relationships between these three lineages is contentious, and all three possible hypotheses have been proposed with respect to which group is basal . These hypotheses are Atlantogenata (basal Boreoeutheria), Epitheria (basal Xenarthra) and Exafroplacentalia (basal Afrotheria). Boreoeutheria in turn contains two major lineages— Euarchontoglires and Laurasiatheria . Estimates for

574-564: The International Union for Conservation of Nature (IUCN) completed a five-year Global Mammal Assessment for its IUCN Red List , which counted 5,488 species. According to research published in the Journal of Mammalogy in 2018, the number of recognized mammal species is 6,495, including 96 recently extinct. The word " mammal " is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from

615-556: The Latin mamma ("teat, pap"). In an influential 1988 paper, Timothy Rowe defined Mammalia phylogenetically as the crown group of mammals, the clade consisting of the most recent common ancestor of living monotremes ( echidnas and platypuses ) and therian mammals ( marsupials and placentals ) and all descendants of that ancestor. Since this ancestor lived in the Jurassic period, Rowe's definition excludes all animals from

656-606: The biological classification scheme used, are the primates : apes , monkeys , and lemurs ; the Cetartiodactyla : whales and even-toed ungulates ; and the Carnivora which includes cats , dogs , weasels , bears , seals , and allies. According to Mammal Species of the World , 5,416 species were identified in 2006. These were grouped into 1,229  genera , 153  families and 29 orders. In 2008,

697-647: The class Mammalia ( / m ə ˈ m eɪ l i . ə / ). Mammals are characterized by the presence of milk -producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair , and three middle ear bones . These characteristics distinguish them from reptiles and birds , from which their ancestors diverged in the Carboniferous Period over 300 million years ago. Around 6,400 extant species of mammals have been described and divided into 27 orders . The largest orders of mammals, by number of species , are

738-406: The dominant terrestrial animal group from 66 million years ago to the present. The basic mammalian body type is quadrupedal , with most mammals using four limbs for terrestrial locomotion ; but in some, the limbs are adapted for life at sea , in the air , in trees or underground . The bipeds have adapted to move using only the two lower limbs, while the rear limbs of cetaceans and

779-420: The enzyme that breaks down AEA and other endocannabinoids, and the compound linoleoyl-ethanol-amide ( C 20 H 37 NO 2 ; 18:2,n−6), an N-acylethanolamine , - the ethanolamide of linoleic acid (LA: C 18 H 32 O 2 ; 18: 2 ,n−6) and its metabolized incorporated ethanolamine (MEA: C 2 H 7 NO ), is the first natural inhibitor of FAAH, discovered. Linoleic acid

820-428: The rodents , bats , and Eulipotyphla (including hedgehogs , moles and shrews ). The next three are the primates (including humans , monkeys and lemurs ), the even-toed ungulates (including pigs , camels , and whales ), and the Carnivora (including cats , dogs , and seals ). Mammals are the only living members of Synapsida ; this clade , together with Sauropsida (reptiles and birds), constitutes

861-439: The sea cows are mere internal vestiges . Mammals range in size from the 30–40 millimetres (1.2–1.6 in) bumblebee bat to the 30 metres (98 ft) blue whale —possibly the largest animal to have ever lived. Maximum lifespan varies from two years for the shrew to 211 years for the bowhead whale . All modern mammals give birth to live young, except the five species of monotremes , which lay eggs. The most species-rich group

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902-406: The 1920s, sparked by Charles Darwin 's theories which were re-conceptualized by many scientists. Human attributes, such as child growth and genetics, were put into question and thus human biology was created. The key aspects of human biology are those ways in which humans are substantially different from other mammals. Humans have a very large brain in a head that is very large for the size of

943-532: The CYP epoxygenases , catalyze oxidation of LA to epoxide products viz., its 12,13-epoxide, vernolic acid , and its 9,10-epoxide, coronaric acid . These linoleic acid products are implicated in human physiology and pathology. Hydroperoxides derived from the metabolism of anandamide (AEA: C 22 H 37 NO 2 ; 20:4,n−6), or its linoleoyl analogues, are by a lipoxygenase action found to be competitive inhibitors of brain and immune cell FAAH ,

984-421: The animal. This large brain has enabled a range of unique attributes including the development of complex languages and the ability to make and use a complex range of tools . The upright stance and bipedal locomotion is not unique to humans but humans are the only species to rely almost exclusively on this mode of locomotion. This has resulted in significant changes in the structure of the skeleton including

1025-509: The articulation of the pelvis and the femur and in the articulation of the head. In comparison with most other mammals, humans are very long lived with an average age at death in the developed world of nearly 80 years old. Humans also have the longest childhood of any mammal with sexual maturity taking 12 to 16 years on average to be completed. Humans lack fur . Although there is a residual covering of fine hair, which may be more developed in some people, and localised hair covering on

1066-599: The biochemical and biophysical foundations of human life describe and formulate the underlying processes using models . As a basic science, it provides the knowledge base for medicine. A number of sub-disciplines include anatomy , cytology , histology and morphology . The capabilities of the human brain and the human dexterity in making and using tools, has enabled humans to understand their own biology through scientific experiment, including dissection , autopsy , prophylactic medicine which has, in turn, enable humans to extend their life-span by understanding and mitigating

1107-492: The case of humans, complex language . Mammals can organize themselves into fission–fusion societies , harems , and hierarchies —but can also be solitary and territorial . Most mammals are polygynous , but some can be monogamous or polyandrous . Domestication of many types of mammals by humans played a major role in the Neolithic Revolution , and resulted in farming replacing hunting and gathering as

1148-812: The clade originating with the last common ancestor of Sinoconodon and living mammals. The earliest-known synapsid satisfying Kemp's definitions is Tikitherium , dated 225 Ma , so the appearance of mammals in this broader sense can be given this Late Triassic date. However, this animal may have actually evolved during the Neogene. As of the early 21st century, molecular studies based on DNA analysis have suggested new relationships among mammal families. Most of these findings have been independently validated by retrotransposon presence/absence data . Classification systems based on molecular studies reveal three major groups or lineages of placental mammals— Afrotheria , Xenarthra and Boreoeutheria —which diverged in

1189-444: The closest thing to an official classification of mammals, despite its known issues. Most mammals, including the six most species-rich orders , belong to the placental group. The three largest orders in numbers of species are Rodentia : mice , rats , porcupines , beavers , capybaras , and other gnawing mammals; Chiroptera : bats; and Eulipotyphla : shrews , moles , and solenodons . The next three biggest orders, depending on

1230-620: The conversion of LA into gamma-linolenic acid (GLA), effected by Δ6 desaturase . GLA is converted to dihomo-γ-linolenic acid (DGLA), the immediate precursor to AA. LA is also converted by various lipoxygenases , cyclooxygenases , cytochrome P450 enzymes (the CYP monooxygenases ), and non-enzymatic autoxidation mechanisms to mono- hydroxyl products viz., 13-Hydroxyoctadecadienoic acid , and 9-Hydroxyoctadecadienoic acid ; these two hydroxy metabolites are enzymatically oxidized to their keto metabolites, 13-oxo-octadecadienoic acid and 9-oxo-octadecdienoic acid. Certain cytochrome P450 enzymes,

1271-1327: The divergence times between these three placental groups range from 105 to 120 million years ago, depending on the type of DNA used (such as nuclear or mitochondrial ) and varying interpretations of paleogeographic data. Monotremata Marsupialia Xenarthra Afrotheria Glires Euarchonta [REDACTED] Eulipotyphla Chiroptera Pholidota Carnivora [REDACTED] Perissodactyla [REDACTED] Artiodactyla [REDACTED] Monotremata [REDACTED] Paucituberculata [REDACTED] Didelphimorphia [REDACTED] Microbiotheria Notoryctemorphia [REDACTED] Peramelemorphia [REDACTED] Dasyuromorphia [REDACTED] Diprotodontia [REDACTED] Cingulata [REDACTED] Pilosa [REDACTED] Hyracoidea [REDACTED] Sirenia [REDACTED] Proboscidea [REDACTED] Tubulidentata [REDACTED] Macroscelidea [REDACTED] Afrosoricida [REDACTED] Eulipotyphla [REDACTED] Chiroptera [REDACTED] Pholidota [REDACTED] Carnivora [REDACTED] Perissodactyla [REDACTED] Artiodactyla [REDACTED] Scandentia [REDACTED] Lagomorpha [REDACTED] Linoleic acid Linoleic acid ( LA )

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1312-585: The earlier Triassic , despite the fact that Triassic fossils in the Haramiyida have been referred to the Mammalia since the mid-19th century. If Mammalia is considered as the crown group, its origin can be roughly dated as the first known appearance of animals more closely related to some extant mammals than to others. Ambondro is more closely related to monotremes than to therian mammals while Amphilestes and Amphitherium are more closely related to

1353-499: The effects of diseases . Understanding human biology has enabled and fostered a wider understanding of mammalian biology and by extension, the biology of all living organisms. Human nutrition is typical of mammalian omnivorous nutrition requiring a balanced input of carbohydrates , fats , proteins , vitamins , and minerals. However, the human diet has a few very specific requirements. These include two specific amino acids, alpha-linolenic acid and linoleic acid without which life

1394-451: The end of the 20th century. However, since 1945, a large amount of new and more detailed information has gradually been found: The paleontological record has been recalibrated, and the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself, partly through the new concept of cladistics . Though fieldwork and lab work progressively outdated Simpson's classification, it remains

1435-456: The head, axillary and pubic regions, in terms of protection from cold, humans are almost naked. The reason for this development is still much debated. The human eye can see objects in colour but is not well adapted to low light conditions. The sense of smell and of taste are present but are relatively inferior to a wide range of other mammals . Human hearing is efficient but lacks the acuity of some other mammals. Similarly human sense of touch

1476-419: The laboratory of Justus von Liebig , isolated linoleic acid from linseed oil. In 1886, K. Peters determined the existence of two double bonds. Its essential role in human diet was discovered by G. O. Burr and others in 1930. Its chemical structure was determined by T. P. Hilditch and others in 1939, and it was synthesized by R. A. Raphael and F. Sondheimer in 1950. The consumption of linoleic acid

1517-668: The larger Amniota clade. Early synapsids are referred to as " pelycosaurs ." The more advanced therapsids became dominant during the Guadalupian . Mammals originated from cynodonts , an advanced group of therapsids, during the Late Triassic to Early Jurassic . Mammals achieved their modern diversity in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs , and have been

1558-507: The organisms associated with human biology are the specialised biome in the large intestine and the biotic flora of the skin and pharyngeal and nasal region. Many of these biotic assemblages help protect humans from harm and assist in digestion, and are now known to have complex effects on mood, and well-being. Humans in all civilizations are social animals and use their language skills and tool making skills to communicate. These communication skills enable civilizations to grow and allow for

1599-716: The primary source of food for humans. This led to a major restructuring of human societies from nomadic to sedentary, with more co-operation among larger and larger groups, and ultimately the development of the first civilizations . Domesticated mammals provided, and continue to provide, power for transport and agriculture, as well as food ( meat and dairy products ), fur , and leather . Mammals are also hunted and raced for sport, kept as pets and working animals of various types, and are used as model organisms in science. Mammals have been depicted in art since Paleolithic times, and appear in literature, film, mythology, and religion. Decline in numbers and extinction of many mammals

1640-421: The production of art , literature and music , and for the development of technology . All of these are wholly dependent on the human biological specialisms. The deployment of these skills has allowed the human race to dominate the terrestrial biome to the detriment of most of the other species. Mammalia A mammal (from Latin mamma  'breast') is a vertebrate animal of

1681-548: The therians; as fossils of all three genera are dated about 167 million years ago in the Middle Jurassic , this is a reasonable estimate for the appearance of the crown group. T. S. Kemp has provided a more traditional definition: " Synapsids that possess a dentary – squamosal jaw articulation and occlusion between upper and lower molars with a transverse component to the movement" or, equivalently in Kemp's view,

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