A hunter-gatherer is a human living in a society in which most or all food is obtained by foraging. Hunter-gatherer societies stand in contrast to agricultural societies, which rely on domesticated species. Hunting and gathering was humanity's first and most successful adaptation, occupying at least 90 percent of human history. Following the invention of agriculture, hunter-gatherers who did not change have been displaced or conquered by farming or pastoralist groups in most parts of the world. In West Eurasia, agriculture lead to widespread genetic changes when older hunter-gatherer populations were replaced by Middle Eastern farmers during the Neolithic who in turn were overrun by Indo-Europeans during the Bronze Age. Only a few contemporary societies are classified as hunter-gatherers, many supplement their foraging activity with horticulture or pastoralism. During the 1970s, Lewis Binford suggested that early humans were obtaining food via scavenging, not hunting. Early humans in the Lower Paleolithic lived in forests and woodlands, which allowed them to collect seafood, eggs and fruits besides scavenging.
Rather than killing large animals for meat, according to this view, they used carcasses of such animals that had either been killed by predators or that had died of natural causes. Archaeological and genetic data suggest that the source populations of Paleolithic hunter-gatherers survived in sparsely wooded areas and dispersed through areas of high primary productivity while avoiding dense forest cover. According to the endurance running hypothesis, long-distance running as in persistence hunting, a method still practiced by some hunter-gatherer groups in modern times, was the driving evolutionary force leading to the evolution of certain human characteristics; this hypothesis does not contradict the scavenging hypothesis: both subsistence strategies could have been in use – sequentially, alternating or simultaneously. Hunting and gathering was the subsistence strategy employed by human societies beginning some 1.8 million years ago, by Homo erectus, from its appearance some 0.2 million years ago by Homo sapiens.
Prehistoric hunter-gatherers lived in groups that consisted of several families resulting in a size of a few dozen people. It remained the only mode of subsistence until the end of the Mesolithic period some 10,000 years ago, after this was replaced only with the spread of the Neolithic Revolution. Starting at the transition between the Middle to Upper Paleolithic period, some 80,000 to 70,000 years ago, some hunter-gatherers bands began to specialize, concentrating on hunting a smaller selection of game and gathering a smaller selection of food; this specialization of work involved creating specialized tools such as fishing nets and bone harpoons. The transition into the subsequent Neolithic period is chiefly defined by the unprecedented development of nascent agricultural practices. Agriculture originated as early as 12,000 years ago in the Middle East, independently originated in many other areas including Southeast Asia, parts of Africa and the Andes. Forest gardening was being used as a food production system in various parts of the world over this period.
Forest gardens originated in prehistoric times along jungle-clad river banks and in the wet foothills of monsoon regions. In the gradual process of families improving their immediate environment, useful tree and vine species were identified and improved, whilst undesirable species were eliminated. Superior introduced species were selected and incorporated into the gardens. Many groups continued their hunter-gatherer ways of life, although their numbers have continually declined as a result of pressure from growing agricultural and pastoral communities. Many of them reside in arid regions or tropical forests. Areas that were available to hunter-gatherers were—and continue to be—encroached upon by the settlements of agriculturalists. In the resulting competition for land use, hunter-gatherer societies either adopted these practices or moved to other areas. In addition, Jared Diamond has blamed a decline in the availability of wild foods animal resources. In North and South America, for example, most large mammal species had gone extinct by the end of the Pleistocene—according to Diamond, because of overexploitation by humans, one of several explanations offered for the Quaternary extinction event there.
As the number and size of agricultural societies increased, they expanded into lands traditionally used by hunter-gatherers. This process of agriculture-driven expansion led to the development of the first forms of government in agricultural centers, such as the Fertile Crescent, Ancient India, Ancient China, Sub-Saharan Africa and Norte Chico; as a result of the now near-universal human reliance upon agriculture, the few contemporary hunter-gatherer cultures live in areas unsuitable for agricultural use. Archaeologists can use evidence such as stone tool use to track hunter-gatherer activities, including mobility. Most hunter-gatherers are semi-nomadic and live in temporary settlements. Mobile communities construct shelters using impermanent building materials, or they may use natural rock shelters, where they are available; some hunter-gatherer cultures, such as the indigenous peoples of the Pacific Northwest Coast and the Yakuts, lived in rich environments that allowed them to be sedentary or semi-sedentary.
Hunter-gatherers tend to have an egalitarian social ethos, although settled hunter-gatherers are an exception to this rule. Nearly
A wrinkle known as a rhytide, is a fold, ridge or crease in the skin or on fabric. Skin wrinkles appear as a result of aging processes such as glycation, habitual sleeping positions, loss of body mass, or temporarily, as the result of prolonged immersion in water. Age wrinkling in the skin is promoted by habitual facial expressions, sun damage, poor hydration, various other factors. Development of facial wrinkles is a kind of fibrosis of the skin. Misrepair-accumulation aging theory suggests that wrinkles develop from incorrect repairs of injured elastic fibers and collagen fibers. Repeated extensions and compressions of the skin cause repeated injuries of extracellular fibers in derma. During the repairing process, some of the broken elastic fibers and collagen fibers are not regenerated and restored but replaced by altered fibers; when an elastic fiber is broken in an extended state, it may be replaced by a “long” collagen fiber. Accumulation of “long” collagen fibers makes part of the skin looser and stiffer, as a consequence, a big fold of skin appears.
When a “long” collagen is broken in a compressed state, it may be replaced by a “short” collagen fiber. The “shorter” collagen fibers will restrict the extension of "longer" fibers, make the “long” fibers in a folding state permanently. A small fold, namely a permanent wrinkle appears. Sleep wrinkles are created and reinforced when the face is compressed against a pillow or bed surface in side or stomach sleeping positions during sleep, they appear in predictable locations due to the underlying superficial musculoaponeurotic system, are distinct from wrinkles of facial expression. As with wrinkles of facial expression, sleep wrinkles can deepen and become permanent over time, unless the habitual sleeping positions which cause the wrinkles are altered; the wrinkles that occur in skin after prolonged exposure to water are sometimes referred to as pruney fingers or water aging. This is a temporary skin condition where the skin on the palms of feet becomes wrinkly; this wrinkling response may have imparted an evolutionary benefit by providing improved traction in wet conditions, a better grasp of wet objects.
However, a 2014 study attempting to reproduce these results was unable to demonstrate any improvement of handling wet objects with wrinkled fingertips. Furthermore, the same study found no connection between fingertip touch sensation. Prior to a 1935 study, the common explanation was based on water absorption in the keratin-laden epithelial skin when immersed in water, causing the skin to expand and resulting in a larger surface area, forcing it to wrinkle; the tips of the fingers and toes are the first to wrinkle because of a thicker layer of keratin and an absence of hairs which secrete the protective oil called sebum. In the 1935 study, however and Pickering were studying patients with palsy of the median nerve when they discovered that skin wrinkling did not occur in the areas of the patients' skin innervated by the damaged nerve; this suggested that the nervous system plays an essential role in wrinkling, so the phenomenon could not be explained by water absorption. Recent research shows.
Water initiates the wrinkling process by altering the balance of electrolytes in the skin as it diffuses into the hands and soles via their many sweat ducts. This could alter the stability of the membranes of the many neurons that synapse on the many blood vessels underneath skin, causing them to fire more rapidly. Increased neuronal firing causes blood vessels to constrict, decreasing the amount of fluid underneath the skin; this decrease in fluid would cause a decrease in tension. This insight resulted in bedside tests for nerve vasoconstriction. Wrinkling is scored with immersion of the hands for 30 minutes in water or EMLA cream with measurements steps of 5 minutes, counting the number of visible wrinkles in time. Not all healthy persons have finger wrinkling after immersion, so it would be safe to say that sympathetic function is preserved if finger wrinkling after immersion in water is observed, but if the fingers emerge smooth it cannot be assumed that there is a lesion to the autonomic supply or to the peripheral nerves of the hand.
Examples of wrinkles can be found in various animal species that grow loose, excess skin when they are young. Several breeds of dog, such as the Pug and the Shar Pei, have been bred to exaggerate this trait. In dogs bred for fighting, this is the result of selection for loose skin, which confers a protective advantage. Wrinkles are associated with neoteny, as they are a trait associated with juvenile animals. Current evidence suggests that tretinoin decreases cohesiveness of follicular epithelial cells, although the exact mode of action is unknown. Additionally, tretinoin stimulates mitotic activity and increased turnover of follicular epithelial cells. Tretinoin is better known by the brand name Retin-A. Topical glycosaminoglycans supplements can help to provide temporary restoration of enzyme balance to slow or prevent matrix breakdown and consequent onset of wrinkle formation. Glycosaminoglycans are produced by the body to maintain structural integrity in tissues and to maintain fluid balance.
Hyaluronic acid is a type of GAG that promotes collagen synthesis and hydration. GAGs serve as a natural moisturizer and lubricant between epidermal cells to inhibit the production of matrix metalloproteinases. Dermal fillers are injectable products used to correct wrinkles, other depressions in the skin, they are a kind of soft tissue designed to enable injection into the skin for purposes of improving t
The occipital bone is a cranial dermal bone and the main bone of the occiput. It is trapezoidal in shape and curved on itself like a shallow dish; the occipital bone overlies the occipital lobes of the cerebrum. At the base of skull in the occipital bone, there is a large oval opening called the foramen magnum, which allows the passage of the spinal cord. Like the other cranial bones, it is classed as a flat bone. Due to its many attachments and features, the occipital bone is described in terms of separate parts. From its front to the back is the basilar part called the basioccipital, at the sides of the foramen magnum are the lateral parts called the exoccipitals, the back is named as the squamous part; the basilar part is a thick, somewhat quadrilateral piece in front of the foramen magnum and directed towards the pharynx. The squamous part is the curved, expanded plate behind the foramen magnum and is the largest part of the occipital bone; the occipital bone, like the other seven cranial bones, has outer and inner layers of cortical bone tissue between, the cancellous bone tissue known in the cranial bones as diploë.
The bone is thick at the ridges, protuberances and anterior part of the basilar part. Near the middle of the outer surface of the squamous part of the occipital there is a prominence – the external occipital protuberance; the highest point of this is called the inion. From the inion, along the midline of the squamous part until the foramen magnum, runs a ridge – the external occipital crest and this gives attachment to the nuchal ligament. Running across the outside of the occipital bone are three curved lines and one line that runs down to the foramen magnum; these are known as the nuchal lines which give attachment to various muscles. They are named as the highest and inferior nuchal lines; the inferior nuchal line runs across the midpoint of the medial nuchal line. The area above the highest nuchal line is termed the occipital plane and the area below this line is termed the nuchal plane; the inner surface of the occipital bone forms the base of the posterior cranial fossa. The foramen magnum is a large hole situated in the middle, with the clivus, a smooth part of the occipital bone travelling upwards in front of it.
The median internal occipital crest travels behind it to the internal occipital protuberance, serves as a point of attachment to the falx cerebri. To the sides of the foramen sitting at the junction between the lateral and base of the occipital bone are the hypoglossal canals. Further out, at each junction between the occipital and petrous portion of the temporal bone lies a jugular foramen; the inner surface of the occipital bone is marked by dividing lines as shallow ridges, that form four fossae or depressions. The lines are called the cruciform eminence. At the midpoint where the lines intersect a raised part is formed called the internal occipital protuberance. From each side of this eminence runs a groove for the transverse sinuses. There are two midline skull landmarks at the foramen magnum; the basion is the most anterior point of the opening and the opisthion is the point on the opposite posterior part. The basion lines up with the dens; the foramen magnum is a large oval foramen longest front to back.
The clivus, a smooth bony section, travels upwards on the front surface of the foramen, the median internal occipital crest travels behind it. Through the foramen passes the medulla oblongata and its membranes, the accessory nerves, the vertebral arteries, the anterior and posterior spinal arteries, the tectorial membrane and alar ligaments; the superior angle of the occipital bone articulates with the occipital angles of the parietal bones and, in the fetal skull, corresponds in position with the posterior fontanelle. The lateral angles are situated at the extremities of the groove for the transverse sinuses: each is received into the interval between the mastoid angle of the parietal bone, the mastoid portion of the temporal bone; the inferior angle is fused with the body of the sphenoid bone. The superior borders extend from the superior to the lateral angles: they are serrated for articulation with the occipital borders of the parietals, form by this union the lambdoidal suture; the inferior borders extend from the lateral angles to the inferior angle.
These two portions of the inferior border are separated from one another by the jugular process, the notch on the anterior surface of which forms the posterior part of the jugular foramen. The lambdoid suture joins the occipital bone to the parietal bones; the occipitomastoid suture joins the occipital mastoid portion of the temporal bone. The sphenobasilar suture joins the basilar part of the occipital bone and the back of the sphenoid bone body; the petrous-basilar suture joins the side edge of the basilar part of the occipital bone to the petrous-part of the temporal bone. The occipital plane of the squamous part of the occipital bone is developed in membrane, may remain separate throughout life when it constitutes the interparietal bone; the number of nuclei for the occipital plane is given as four, two appearing near the middle line about the second month, two some little distance from the middle line about the third month of
Medical Subject Headings
Medical Subject Headings is a comprehensive controlled vocabulary for the purpose of indexing journal articles and books in the life sciences. It serves as a thesaurus. Created and updated by the United States National Library of Medicine, it is used by the MEDLINE/PubMed article database and by NLM's catalog of book holdings. MeSH is used by ClinicalTrials.gov registry to classify which diseases are studied by trials registered in ClinicalTrials. MeSH was introduced in the 1960s, with the NLM's own index catalogue and the subject headings of the Quarterly Cumulative Index Medicus as precursors; the yearly printed version of MeSH was discontinued in 2007 and MeSH is now available online only. It can be downloaded free of charge through PubMed. In English, MeSH has been translated into numerous other languages and allows retrieval of documents from different origins; the 2009 version of MeSH contains a total of 25,186 subject headings known as descriptors. Most of these are accompanied by a short description or definition, links to related descriptors, a list of synonyms or similar terms.
This additional information and the hierarchical structure make the MeSH a thesaurus, rather than a plain subject headings list. The descriptors or subject headings are arranged in a hierarchy. A given descriptor may appear at several locations in the hierarchical tree; the tree locations carry systematic labels known as tree numbers, one descriptor can carry several tree numbers. For example, the descriptor "Digestive System Neoplasms" has the tree numbers C06.301 and C04.588.274. The tree numbers of a given descriptor are subject to change; every descriptor carries a unique alphanumerical ID that will not change. Most subject headings come with definition. See the MeSH description for diabetes type 2 as an example; the explanatory text is written by the MeSH team based on their standard sources if not otherwise stated. References are encyclopaedias and standard textbooks of the subject areas. References for specific statements in the descriptions are not given, instead readers are referred to the bibliography.
In addition to the descriptor hierarchy, MeSH contains a small number of standard qualifiers, which can be added to descriptors to narrow down the topic. For example, "Measles" is; the "epidemiology" qualifier can be added to all other disease descriptors. Not all descriptor/qualifier combinations are allowed. In all there are 83 different qualifiers. In addition to the descriptors, MeSH contains some 139,000 supplementary concept records; these do not belong to the controlled vocabulary as such. Many of these records describe chemical substances. In MEDLINE/PubMed, every journal article is indexed with about 10–15 subject headings and supplementary concept records, with some of them designated as major and marked with an asterisk, indicating the article's major topics; when performing a MEDLINE search via PubMed, entry terms are automatically translated into the corresponding descriptors with a good degree of reliability. By default, a search for a descriptor will include all the descriptors in the hierarchy below the given one.
In ClinicalTrials.gov, each trial has keywords. The ClinicalTrials.gov team assigns each trial two sets of MeSH terms. One set for the conditions studied by the trial and another for the set of interventions used in the trial; the XML file that can be downloaded for each trial contains these MeSH keywords. The XML file has a comment that says: "the assignment of MeSH keywords is done by imperfect algorithm"; the top-level categories in the MeSH descriptor hierarchy are: Anatomy Organisms Diseases Chemicals and Drugs Analytical and Therapeutic Techniques and Equipment Psychiatry and Psychology Biological Sciences Physical Sciences Anthropology, Education and Social Phenomena Technology and Food and Beverages Humanities Information Science Persons Health Care Publication Characteristics Geographic Locations Medical classification Medical literature retrieval Medical Subject Heading Home provided by National Library of Medicine, National Institutes of Health MeSH database tutorials Automatic Term Mapping Browsing MeSH: Entrez MeSH Browser Visual MeSH Browser mapping drug-disease relationships in research Reference.
MD List of qualifiers – 2009