160-509: The breasts are two prominences located on the upper ventral region of the torso among humans and other primates . Both sexes develop breasts from the same embryological tissues. The relative size and development of the breasts is a major secondary sex distinction between females and males. There is also considerable variation in size between individuals. Female humans are the only mammals which permanently develop breasts at puberty ; all other mammals develop their mammary tissue during
320-617: A chronospecies , H. ergaster may have persisted to as late as 600,000 years ago, when new lineages of Homo arose in Africa. Those who believe H. ergaster should be subsumed into H. erectus consider there to be too little difference between the two to separate them into distinct species. Proponents of keeping the two species as distinct cite morphological differences between the African fossils and H. erectus fossils from Asia, as well as early Homo evolution being more complex than what
480-502: A 1952 article in Parents' Magazine , Frank H. Crowell erroneously reported that it was important for teen girls to begin wearing bras early. According to Crowell, this would prevent sagging breasts, stretched blood vessels, and poor circulation later on. This belief was based on the false idea that breasts cannot anatomically support themselves. Sports bras are sometimes used for cardiovascular exercise, sports bras are designed to secure
640-421: A C shape (see image). The location of anatomical structures can also be described in relation to different anatomical landmarks . They are used in anatomy, surface anatomy, surgery, and radiology. Structures may be described as being at the level of a specific spinal vertebra , depending on the section of the vertebral column the structure is at. The position is often abbreviated. For example, structures at
800-448: A definition of what is at the front ("anterior"), behind ("posterior") and so on. As part of defining and describing terms, the body is described through the use of anatomical planes and anatomical axes . The meaning of terms that are used can change depending on whether an organism is bipedal or quadrupedal . Additionally, for some animals such as invertebrates , some terms may not have any meaning at all; for example, an animal that
960-604: A family history of breast cancer. About five to ten percent of cases are the result of an inherited genetic predisposition, including BRCA mutations among others. Breast cancer most commonly develops in cells from the lining of milk ducts and the lobules that supply these ducts with milk. Cancers developing from the ducts are known as ductal carcinomas , while those developing from lobules are known as lobular carcinomas . There are more than 18 other sub-types of breast cancer. Some, such as ductal carcinoma in situ , develop from pre-invasive lesions . The diagnosis of breast cancer
1120-440: A famous Australopithecus fossil, would only have been about 1 m (3 ft 3 in) tall at her death, Turkana Boy was about 1.62 m (5 ft 4 in) tall and would probably have reached 1.82 m (6 ft) or more if he had survived to adulthood. Adult H. ergaster are believed to have ranged in size from about 1.45 to 1.85 m (4 ft 9 in to 6 ft 1 in) tall. Because of being adapted to
1280-578: A forward-bending, self-protecting posture". A popular legend at the time was of the Amazons , a tribe of fierce female warriors who socialized with men only for procreation and even removed one breast to become better warriors (the idea being that the right breast would interfere with the operation of a bow and arrow). The legend was a popular motif in art during Greek and Roman antiquity and served as an antithetical cautionary tale. Many women regard their breasts as important to their sexual attractiveness , as
1440-630: A fragmentary skull from Olorgesailie in Kenya (dated to between 970,000 and 900,000 years ago). The Olduvai skull is similar to Asian H. erectus in its massive brow ridge, but the others only show minor differences to earlier H. ergaster skulls. The H. erectus in Asia, as well as later hominins in Europe (i. e. H. heidelbergensis and H. neanderthalensis ) and Africa ( H. sapiens ) are all probably lineages descended from H. ergaster. Because H. ergaster
1600-440: A hot and arid climate, H. ergaster might also have been the earliest human species to have nearly hairless and naked skin. If instead H. ergaster had an ape-like covering of body hair, sweating (the primary means through which modern humans prevent their brains and bodies from overheating) would not have been as efficient. Though sweating is the generally accepted explanation for hairlessness, other proposed explanations include
1760-576: A long history of female breasts being used by comedians as a subject for comedy fodder (e.g., British comic Benny Hill's burlesque/slapstick routines). In European pre-historic societies, sculptures of female figures with pronounced or highly exaggerated breasts were common. A typical example is the so-called Venus of Willendorf , one of many Paleolithic Venus figurines with ample hips and bosom. Artifacts such as bowls, rock carvings and sacred statues with breasts have been recorded from 15,000 BC up to late antiquity all across Europe, North Africa and
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#17327879069711920-539: A major change in diet) as well as body proportions and inferred lifestyles more similar to modern humans than to earlier and contemporary hominins. With these features in mind, some researchers view H. ergaster as being the earliest true representative of the genus Homo . H. ergaster lived on the savannah in Africa, a unique environment with challenges that would have resulted in the need for many new and distinct behaviours. Earlier Homo probably used counter-attack tactics, like modern primates, to keep predators away. By
2080-408: A mammary gland. They are distributed throughout the body of the breast. Approximately two-thirds of the lactiferous tissue is within 30 mm of the base of the nipple. The terminal lactiferous ducts drain the milk from TDLUs into 4–18 lactiferous ducts, which drain to the nipple. The milk-glands-to-fat ratio is 2:1 in a lactating woman, and 1:1 in a non-lactating woman. In addition to the milk glands,
2240-599: A more barrel-shaped chest over narrow hips, another similarity to modern humans. The tibia (shin bone) of Turkana Boy is relatively longer than the same bone in modern humans, potentially meaning that there was more bend in the knee when walking. The slim and long build of Turkana Boy may be explained by H. ergaster living in hot and arid, seasonal environments. Through thinning of the body, body volume decreases faster than skin area and greater skin area means more effective heat dissipation. H. ergaster individuals were significantly taller than their ancestors. Whereas Lucy ,
2400-414: A more easily digested diet composed of food of higher quality. It is likely that H. ergaster consumed meat in higher proportions than the earlier australopithecines. Meat was probably acquired through a combination of ambushes, active hunting and confrontational scavenging. H. ergaster must not only have possessed the ability of endurance running , but must also have been able to defend themselves and
2560-479: A nearly complete skeleton, as representing H. erectus . Turkana Boy was the first discovered comprehensively preserved specimen of H. ergaster / erectus found and constitutes an important fossil in establishing the differences and similarities between early Homo and modern humans. Turkana Boy was placed in H. ergaster by paleoanthropologist Bernard Wood in 1992, and is today, alongside other fossils in Africa previously designated as H. erectus , commonly seen as
2720-442: A number of features as well, notably in that the margins of KNM ER 3883's brow ridges are very thickened and protrude outwards but slightly downwards rather than upwards. Both skulls can be distinguished from the skull of Turkana Boy, which possesses only slightly substantial thickenings of the superior orbital margins, lacking the more vertical thickening of KNM ER 3883 and the aggressive protrusion of KNM ER 3733. In addition to this,
2880-468: A part in increasing brain size. Breast enlargement may for this purpose have occurred as early as Homo ergaster (1.7–1.4 MYA ). Other breast formation hypotheses may have then taken over as principal drivers. It has been suggested by zoologists Avishag and Amotz Zahavi that the size of the human breasts can be explained by the handicap theory of sexual dimorphism . This would see the explanation for larger breasts as them being an honest display of
3040-399: A platter, signifying that they died as a martyr by having their breasts severed; one example of this is Saint Agatha of Sicily . Femen is a feminist activist group which uses topless protests as part of their campaigns against sex tourism religious institutions, sexism , and homophobia . Femen activists have been regularly detained by police in response to their protests. There is
3200-538: A receding forehead. Many of the features of H. ergaster are clearly more primitive versions of features later expressed in H. erectus , which somewhat obscures the differences between the two. There are subtle, potentially significant, differences between the East African and East Asian fossils. Among these are the somewhat higher-domed and thinner-walled skulls of H. ergaster , and the even more massive brow ridges and faces of Asian H. erectus . The question
3360-602: A reduction of parasite load and sexual selection . It is doubtful if australopithecines and earlier Homo were sufficiently mobile to make hair loss an advantageous trait, whereas H. ergaster was clearly adapted for long-distance travel and noted for inhabiting lower altitudes (and open, hot savannah environments) than their ancestors. Australopithecines typically inhabited colder and higher altitudes 1,000–1,600 m (3,300–5,200 ft), where nighttime temperatures would have gotten significantly colder and insulating body hair may have been required. Alternatively and despite this,
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#17327879069713520-470: A representative of H. ergaster by those who support H. ergaster as a distinct species. H. ergaster is easily distinguished from earlier and more basal species of Homo , notably H. habilis and H. rudolfensis , by a number of features that align them, and their inferred lifestyle, more closely to modern humans than to earlier and contemporary hominins. As compared to their relatives, H. ergaster had body proportions more similar to later members of
3680-410: A sex signal of ovulation. He notes how humans have, relatively speaking, large penises as well as large breasts. Furthermore, early humans adopted bipedalism and face-to-face coitus. He therefore suggested enlarged sexual signals helped maintain the bond between a mated male and female even though they performed different duties and therefore were separated for lengths of time. A 2001 study proposed that
3840-422: A sign of femininity that is important to their sense of self . A woman with smaller breasts may regard her breasts as less attractive. Ventral Standard anatomical terms of location are used to describe unambiguously the anatomy of animals , including humans . The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position . This position provides
4000-469: A species of its own or should be subsumed into H. erectus is an ongoing and unresolved dispute within palaeoanthropology . Proponents of synonymisation typically designate H. ergaster as " African Homo erectus " or " Homo erectus ergaster ". The name Homo ergaster roughly translates to " working man", a reference to the more advanced tools used by the species in comparison to those of their ancestors. The fossil range of H. ergaster mainly covers
4160-414: A standard set of terms to communicate clearly the position of a structure. Standard anatomical and zoological terms of location have been developed, usually based on Latin and Greek words, to enable all biological and medical scientists, veterinarians , doctors and anatomists to precisely delineate and communicate information about animal bodies and their organs, even though the meaning of some of
4320-403: A state in which a part further away is abnormally placed towards (varus) or away from (valgus) the midline. The terms proximal (from Latin proximus 'nearest') and distal (from Latin distare 'to stand away from') are used to describe parts of a feature that are close to or distant from the main mass of the body, respectively. Thus the upper arm in humans
4480-435: A well-fitted sports bra during activity. The breast is susceptible to numerous benign and malignant conditions. The most frequent benign conditions are puerperal mastitis , fibrocystic breast changes and mastalgia . Lactation unrelated to pregnancy is known as galactorrhea . It can be caused by certain drugs (such as antipsychotic medications), extreme physical stress, or endocrine disorders. Lactation in newborns
4640-573: A woman's breasts are severely asymmetrical, surgery can be performed to either enlarge the smaller breast, reduce the size of the larger breast, or both. Breast augmentation surgery generally does not interfere with future ability to breastfeed. Breast reduction surgery more frequently leads to decreased sensation in the nipple-areola complex, and to low milk supply in women who choose to breastfeed. Implants can interfere with mammography (breast x-rays images). In Christian iconography , some works of art depict women with their breasts in their hands or on
4800-452: A wound on the upper arm, but proximal to a wound on the lower arm. The terms are also applied to internal anatomy, such as to the reproductive tract of snails . Unfortunately, different authors use the terms in opposite senses. Some consider "distal" as further from a point of origin near the centre of the body and others as further from where the organ reaches the body's surface; or other points of origin may be envisaged. This terminology
4960-413: Is also employed in molecular biology and therefore by extension is also used in chemistry, specifically referring to the atomic loci of molecules from the overall moiety of a given compound. Central and peripheral refer to the distance towards and away from the centre of something. That might be an organ, a region in the body, or an anatomical structure. For example, the central nervous system and
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5120-455: Is also possible that the loss of body hair occurred at a significantly later date. Genetic analysis suggests that high activity in the melanocortin 1 receptor , which produces dark skin, dates back to about 1.2 million years ago. This could indicate the evolution of hairlessness around this time, as a lack of body hair would have left the skin exposed to harmful UV radiation . Differences to modern humans would have been readily apparent in
5280-411: Is also the oldest known H. erectus s.l. specimen overall, showing clear similarities to KNM ER 3733, and demonstrates that early H. ergaster coexisted with other hominins such as Paranthropus robustus and Australopithecus sediba . There are also younger specimens of H. ergaster ; notably, Turkana Boy is dated to about 1.56 million years ago. A handful of even younger African skulls make
5440-410: Is an apocrine gland that produces the milk used to feed an infant. The nipple of the breast is surrounded by the areola (nipple-areola complex). The areola has many sebaceous glands, and the skin color varies from pink to dark brown. The basic units of the breast are the terminal duct lobular units (TDLUs), which produce the fatty breast milk. They give the breast its offspring-feeding functions as
5600-534: Is caused by hormones from the mother that crossed into the baby's bloodstream during pregnancy. Breast cancer is the most common cause of cancer death among women and it is one of the leading causes of death among women. Factors that appear to be implicated in decreasing the risk of breast cancer are regular breast examinations by health care professionals, regular mammograms , self-examination of breasts , healthy diet, exercise to decrease excess body fat, and breastfeeding . Both females and males develop breasts from
5760-520: Is common, especially during the first trimester. By mid-pregnancy, the breast is physiologically capable of lactation and some women can express colostrum , a form of breast milk. Pregnancy causes elevated levels of the hormone prolactin , which has a key role in the production of milk. However, milk production is blocked by the hormones progesterone and estrogen until after delivery, when progesterone and estrogen levels plummet. At menopause, breast atrophy occurs. The breasts can decrease in size when
5920-428: Is confirmed by taking a biopsy of the concerning tissue. Once the diagnosis is made, further tests are carried out to determine if the cancer has spread beyond the breast and which treatments are most likely to be effective. The primary function of the breasts, as mammary glands, is the nourishing of an infant with breast milk . Milk is produced in milk-secreting cells in the alveoli. When the breasts are stimulated by
6080-399: Is considered a symptom of a disorder of the pituitary gland . Plastic surgery can be performed to augment or reduce the size of breasts, or reconstruct the breast in cases of deformative disease, such as breast cancer. Breast augmentation and breast lift ( mastopexy ) procedures are done only for cosmetic reasons, whereas breast reduction is sometimes medically indicated. In cases where
6240-411: Is considered. With all H. ergaster skulls considered, the brain volume of the species mostly varied between 600 and 910 cc, with some small examples only having a volume of 508–580 cc. Since their brain was smaller than that of modern humans, the skull of H. ergaster immediately narrowed behind the eye sockets ( post-orbital constriction ). The brain case was long and low, and Turkana Boy's forehead
6400-409: Is implied by subsuming species such as H. ergaster into H. erectus . Additionally, morphological differences between the specimens commonly seen as constituting H. ergaster might suggest that H. ergaster itself does not represent a cohesive species. Regardless of their most correct classification, H. ergaster exhibit primitive versions of traits later expressed in H. erectus and are thus likely
6560-697: Is instead whether these fossils represent a radiation of different species or the radiation of a single, highly variable and diverse, species over the course of almost two million years. This long-running debate remains unresolved, with researchers typically using the terms H. erectus s.s. ( sensu stricto ) to refer to H. erectus fossils in Asia and the term H. erectus s.l. ( sensu lato ) to refer to fossils of other species that may or may not be included in H. erectus , such as H. ergaster , H. antecessor and H. heidelbergensis . For obvious reasons, H. ergaster shares many features with H. erectus , such as large forward-projecting jaws, large brow ridges and
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6720-506: Is known on when and which Homo first appeared in Europe and Asia, since Early Pleistocene fossil hominins are scarce on both continents, and that it would have been H. ergaster (or "early H. erectus ") that expanded, as well as the particular manner in which they did, remains conjecture. The presence of H. erectus fossils in East Asia means that a human species, most likely H. ergaster , had left Africa before 1 million years ago,
6880-427: Is made more difficult since it regards how much intraspecific variation can be exhibited in a single species before it needs to be split into more, a question that in and of itself does not have a clear-cut answer. A 2008 analysis by anthropologist Karen L. Baab, examining fossils of various H. erectus subspecies, and including fossils attributed to H. ergaster , found that the intraspecific variation within H. erectus
7040-617: Is more similar to that of a modern 15-year-old and the brain is comparable to that of a modern 1-year-old. By modern standards, H. ergaster would thus have been cognitively limited, though the invention of new tools prove that they were more intelligent than their predecessors. H. ergaster possessed a significantly larger body mass in comparison to earlier hominins such as early Homo , Australopithecus and Paranthropus . Whereas australopithecines typically ranged in weight from 29–48 kg (64–106 lbs), H. ergaster typically ranged in weight from 52–63 kg (115–139 lbs). It
7200-462: Is possible that the increased body size was the result of life in an open savannah environment, where increased size gives the ability to exploit broader diets in larger foraging areas, increases mobility and also gives the ability to hunt larger prey. The increased body mass also means that parents would have been able to carry their children to an older age and larger mass. Though reduced sexual dimorphism has often been cited historically as one of
7360-402: Is proximal and the hand is distal. "Proximal and distal" are frequently used when describing appendages , such as fins , tentacles , and limbs . Although the direction indicated by "proximal" and "distal" is always respectively towards or away from the point of attachment, a given structure can be either proximal or distal in relation to another point of reference. Thus the elbow is distal to
7520-515: Is radially symmetrical will have no anterior surface, but can still have a description that a part is close to the middle ("proximal") or further from the middle ("distal"). International organisations have determined vocabularies that are often used as standards for subdisciplines of anatomy. For example, Terminologia Anatomica for humans and Nomina Anatomica Veterinaria for animals. These allow parties that use anatomical terms, such as anatomists , veterinarians , and medical doctors , to have
7680-402: Is rarely used in human anatomy, apart from embryology, and refers more to the front of the face than the superior aspect of the organism. Similarly, the term "caudal" is used more in embryology and only occasionally used in human anatomy. This is because the brain is situated at the superior part of the head whereas the nose is situated in the anterior part. Thus, the "rostrocaudal axis" refers to
7840-481: Is roughly symmetrical. To do this, distinct ends of an organism are chosen, and the axis is named according to those directions. An organism that is symmetrical on both sides has three main axes that intersect at right angles . An organism that is round or not symmetrical may have different axes. Example axes are: Examples of axes in specific animals are shown below. Several terms are commonly seen and used as prefixes : Other terms are used as suffixes , added to
8000-428: Is thought to have been ancestral to these later Homo , it might have persisted in Africa until around 600,000 years ago, when brain size increased rapidly and H. heidelbergensis emerged. Traditionally, H. erectus was seen as the hominin that first left Africa to colonise Europe and Asia. If H. ergaster is distinct from H. erectus , this role would apply to H. ergaster instead. Very little concrete information
8160-458: Is to the head or tail of an animal. To describe how close to the head of an animal something is, three distinct terms are used: For example, in horses , the eyes are caudal to the nose and rostral to the back of the head. These terms are generally preferred in veterinary medicine and not used as often in human medicine. In humans, "cranial" and "cephalic" are used to refer to the skull, with "cranial" being used more commonly. The term "rostral"
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#17327879069718320-434: Is to the midline, or the medial plane. Lateral (from Latin lateralis 'to the side') describes something to the sides of an animal, as in "left lateral" and "right lateral". Medial (from Latin medius 'middle') describes structures close to the midline, or closer to the midline than another structure. For example, in a human, the arms are lateral to the torso . The genitals are medial to
8480-407: Is unclear if H. ergaster was truly uniquely capable of expanding outside Africa; australopithecines had likely colonised savannah grasslands throughout Africa by 3 million years ago and there are no clear reasons as to why they would not have been able to expand into the grasslands of Asia before H. ergaster . The general assumption is that hominins migrated out of the continent either across
8640-615: The Ancient Greek ἐργαστήρ, ergastḗr , 'workman') roughly translates to "working man" or "workman". Groves and Mazák also included many of the Koobi Fora fossils, such as KNM ER 803 (a partial skeleton and some isolated teeth) in their designation of the species, but did not provide any comparison with the Asian fossil record of H. erectus in their diagnosis, inadvertently causing some of the later taxonomic confusion in regards to
8800-438: The anterior superior iliac spine , the medial malleolus or the medial epicondyle . Anatomical lines are used to describe anatomical location. For example, the mid-clavicular line is used as part of the cardiac exam in medicine to feel the apex beat of the heart . Special terms are used to describe the mouth and teeth. Fields such as osteology , palaeontology and dentistry apply special terms of location to describe
8960-405: The axilla (armpit), and can reach as far to the back as the latissimus dorsi muscle , extending from the lower back to the humerus bone (the bone of the upper arm). As a mammary gland , the breast is composed of differing layers of tissue , predominantly two types: adipose tissue ; and glandular tissue , which affects the lactation functions of the breasts. The natural resonant frequency of
9120-449: The head . Anterior (from Latin ante 'before') describes what is in front, and posterior (from Latin post 'after') describes what is to the back of something. For example, for a dog the nose is anterior to the eyes and the tail is considered the most posterior part; for many fish the gill openings are posterior to the eyes but anterior to the tail. These terms describe how close something
9280-648: The neuraxis is different between the two groups, and so is what is considered the standard anatomical position , such as how humans tend to be standing upright and with their arms reaching forward. Thus, the "top" of a human is the head, whereas the "top" of a dog would be the back, and the "top" of a flounder may be on either the left or right side. Unique terms are also used to describe invertebrates as well, because of their wider variety of shapes and symmetry. Because animals can change orientation with respect to their environment, and because appendages like limbs and tentacles can change position with respect to
9440-467: The pectoralis major muscle). In radiology , an X-ray image may be said to be "anteroposterior", indicating that the beam of X-rays, known as its projection, passes from their source to patient's anterior body wall first, then through the body to exit through posterior body wall and into the detector/film to produce a radiograph. The opposite is true for the term "posteroanterior," while side-to-side projections are known as either "lateromedial" (from
9600-415: The peripheral nervous systems . Central (from Latin centralis ) describes something close to the centre. For example, the great vessels run centrally through the body; many smaller vessels branch from these. Peripheral (from Latin peripheria , originally from Ancient Greek ) describes something further away from the centre of something. For example, the arm is peripheral to
9760-604: The Dmanisi fossils, stone tools manufactured by hominins have been discovered on the Loess Plateau in China and dated to 2.12 million years old, meaning that hominins must have left Africa before that time. An alternative hypothesis historically has been that Homo evolved in Asia from earlier ancestors that had migrated there from Africa, and then expanded back into Europe, where it gave rise to H. sapiens . This view
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#17327879069719920-641: The Middle East. Many female deities representing love and fertility were associated with breasts and breast milk. Figures of the Phoenician goddess Astarte were represented as pillars studded with breasts. Isis , an Egyptian goddess who represented, among many other things, ideal motherhood, was often portrayed as suckling pharaohs , thereby confirming their divine status as rulers. Even certain male deities representing regeneration and fertility were occasionally depicted with breast-like appendices, such as
10080-639: The aforementioned Dmanisi skulls, which share many traits with H. ergaster in Africa, suggesting that H. ergaster might have expanded out of Africa as early as 1.7–1.9 million years ago. In addition to H. ergaster -like traits, the Dmanisi skulls possess a wide assortment of other traits, some of which are similar to traits in earlier hominins such as H. habilis , and the site notably lacks preserved hand axes (otherwise characteristic of H. ergaster ), which means that hominins might have spread out of Africa even earlier than H. ergaster . The skull D2700 (Dmanisi skull 3) in particular resembles H. habilis in
10240-569: The anatomic breast. Normal breast tissue typically has a texture that feels nodular or granular, to an extent that varies considerably from woman to woman. The breasts are principally composed of adipose, glandular , and connective tissues. Because these tissues have hormone receptors, their sizes and volumes fluctuate according to the hormonal changes particular to thelarche (sprouting of breasts), menstruation (egg production), pregnancy (reproduction), lactation (feeding of offspring), and menopause (end of menstruation). The morphological structure of
10400-769: The assumption historically having been that they first migrated out of Africa around 1.9 to 1.7 million years ago. Discoveries in Georgia and China push the latest possible date further back, before 2 million years ago, also casting doubt on the idea that H. ergaster was the first hominin to leave Africa. The main reason for leaving Africa is likely to have been an increasing population periodically outgrowing their resource base, with splintering groups moving to establishing themselves in neighboring, empty territories over time. The physiology and improved technology of H. ergaster might have allowed them to travel to and colonise territories that no one had ever occupied before. It
10560-576: The body by means of the lymphatic system. The morphologic variations in the size, shape, volume, tissue density, pectoral locale, and spacing of the breasts determine their natural shape, appearance, and position on a woman's chest. Breast size and other characteristics do not predict the fat-to-milk-gland ratio or the potential for the woman to nurse an infant. The size and the shape of the breasts are influenced by normal-life hormonal changes (thelarche, menstruation, pregnancy, menopause) and medical conditions (e.g. virginal breast hypertrophy ). The shape of
10720-400: The body in a standing position with arms at the side and palms facing forward, with thumbs out and to the sides. Many anatomical terms can be combined, either to indicate a position in two axes simultaneously or to indicate the direction of a movement relative to the body. For example, "anterolateral" indicates a position that is both anterior and lateral to the body axis (such as the bulk of
10880-570: The body. These terms refer to the distance of a structure from the surface. Deep (from Old English ) describes something further away from the surface of the organism. For example, the external oblique muscle of the abdomen is deep to the skin. "Deep" is one of the few anatomical terms of location derived from Old English rather than Latin – the anglicised Latin term would have been "profound" (from Latin profundus 'due to depth'). Superficial (from Latin superficies 'surface') describes something near
11040-439: The breast is also composed of connective tissues ( collagen , elastin ), white fat, and the suspensory Cooper's ligaments. Sensation in the breast is provided by the peripheral nervous system innervation by means of the front (anterior) and side (lateral) cutaneous branches of the fourth-, fifth-, and sixth intercostal nerves . The T-4 nerve ( Thoracic spinal nerve 4 ), which innervates the dermatomic area , supplies sensation to
11200-457: The breast. The chest ( thoracic cavity ) progressively slopes outwards from the thoracic inlet (atop the breastbone ) and above to the lowest ribs that support the breasts. The inframammary fold, where the lower portion of the breast meets the chest, is an anatomic feature created by the adherence of the breast skin and the underlying connective tissues of the chest; the IMF is the lower-most extent of
11360-403: The breasts closely to the body to prevent movement during high-motion activity such as running. Studies have indicated sports bras which are overly tight may restrict respiratory function. The base of each breast is attached to the chest by the deep fascia over the pectoralis major muscles. The space between the breast and the pectoralis major muscle, called retromammary space , gives mobility to
11520-420: The breasts is naturally determined by the support of the suspensory Cooper's ligaments, the underlying muscle and bone structures of the chest, and by the skin envelope. The suspensory ligaments sustain the breast from the clavicle (collarbone) and the clavico-pectoral fascia (collarbone and chest) by traversing and encompassing the fat and milk-gland tissues. The breast is positioned, affixed to, and supported upon
11680-432: The breasts overlie the pectoralis major muscles and extend on average from the level of the second rib to the level of the sixth rib in the front of the rib cage ; thus, the breasts cover much of the chest area and the chest walls. At the front of the chest, the breast tissue can extend from the clavicle (collarbone) to the middle of the sternum (breastbone). At the sides of the chest, the breast tissue can extend into
11840-535: The carcasses of their prey from the variety of contemporary African predators. It is possible that a drop in African carnivoran species variety around 1.5 million years ago can be ascribed to competition with opportunistic and carnivorous hominins. On its own, meat might not have been able to fully sustain H. ergaster . Modern humans can not sufficiently metabolize protein to meet more than 50% of their energy needs and modern humans who heavily rely on animal-based products in their diet mostly rely on fat to sustain
12000-553: The case for long-term anatomical continuity, though it is unclear if they can appropriately be formally regarded as H. ergaster specimens; the " Olduvai Hominid 9 " skull from Olduvai Gorge is dated to about 1.2 to 1.1 million years ago and there are also skulls from Buia (near the coast of Eritrea, dated to ~1 million years old), the Bouri Formation in Ethiopia (dated to between 1 million and 780,000 years old) and
12160-699: The chest wall, while its shape is established and maintained by the skin envelope. In most women, one breast is slightly larger than the other. More obvious and persistent asymmetry in breast size occurs in up to 25% of women. While it is a common belief that breastfeeding causes breasts to sag , researchers have found that a woman's breasts sag due to four key factors: cigarette smoking, number of pregnancies , gravity , and weight loss or gain. Women sometimes wear bras because they mistakenly believe they prevent breasts from sagging as they get older. Physicians, lingerie retailers, teenagers, and adult women used to believe that bras were medically required to support breasts. In
12320-417: The closeness to the midline of the dental arch. Terms used to describe structures include "buccal" (from Latin bucca 'cheek') and "palatal" (from Latin palatum 'palate') referring to structures close to the cheek and hard palate respectively. Several anatomical terms are particular to the hands and feet. Additional terms may be used to avoid confusion when describing
12480-459: The differences. The differences between Turkana Boy's skull and KNM ER 3733 and KNM ER 3883, as well as the differences in dentition between Turkana Boy and KNM ER 992 have been interpreted by some, such as paleoanthropologist Jeffrey H. Schwartz, as suggesting that Turkana Boy and the rest of the H. ergaster material does not represent the same taxon. Schwartz also noted none of the fossils seemed to represent H. erectus either, which he believed
12640-483: The direct ancestors of later H. erectus populations in Asia. Additionally, H. ergaster is likely ancestral to later hominins in Europe and Africa, such as modern humans and Neanderthals . Several features distinguish H. ergaster from australopithecines as well as earlier and more basal species of Homo , such as H. habilis . Among these features are their larger body mass, relatively long legs, obligate bipedalism , relatively small jaws and teeth (indicating
12800-430: The disease , there may be bone pain , swollen lymph nodes , shortness of breath , or yellow skin . Risk factors for developing breast cancer include obesity , a lack of physical exercise , alcohol consumption, hormone replacement therapy during menopause , ionizing radiation , an early age at first menstruation , having children late in life (or not at all), older age, having a prior history of breast cancer, and
12960-457: The earliest known hand axes . Though undisputed evidence is missing, H. ergaster might also have been the earliest hominin to master control of fire . The systematics and taxonomy of Homo in the Early to Middle Pleistocene is one of the most disputed areas of palaeoanthropology . In early palaeoanthropology and well into the twentieth century, it was generally assumed that Homo sapiens
13120-422: The effects of estrogens in developing excessive breast tissue. In boys and men, abnormal breast development is manifested as gynecomastia , the consequence of a biochemical imbalance between the normal levels of estrogen and testosterone in the male body. Around 70% of boys temporarily develop breast tissue during adolescence. The condition usually resolves by itself within two years. When male lactation occurs, it
13280-421: The end of words: Superior (from Latin super 'above') describes what is above something and inferior (from Latin inferus 'below') describes what is below it. For example, in the anatomical position , the most superior part of the human body is the head and the most inferior is the feet. As a second example, in humans, the neck is superior to the chest but inferior to
13440-795: The ends of the ducts are lobules , or clusters of alveoli , where milk is produced and stored in response to hormonal signals . During pregnancy, the breast responds to a complex interaction of hormones, including estrogens , progesterone , and prolactin , that mediate the completion of its development, namely lobuloalveolar maturation, in preparation of lactation and breastfeeding . Along with their major function in providing nutrition for infants, several cultures ascribe social and sexual characteristics to female breasts, and may regard bare breasts in public as immodest or indecent . Breasts have been featured in ancient and modern sculpture, art, and photography. Breasts can represent fertility , femininity , or abundance . They can figure prominently in
13600-411: The energy requirements of earlier species. If they had increased energy requirements, H. ergaster would have needed to eat either vastly more food than australopithecines, or would have needed to eat food of superior quality. If they ate the same type of foods as the australopithecines, feeding time would then have had to be dramatically increased in proportion to the extra calories required, reducing
13760-551: The expected lifespan of H. ergaster and H. erectus was lower than that of later and modern humans. It is frequently assumed that the larger body and brain size of H. ergaster , compared to its ancestors, would have brought with it increased dietary and energy needs. In 2002, palaeoanthropologists Leslie C. Aiello and Jonathan C. K. Wells stated that the average resting metabolic requirements of H. ergaster would have been 39% higher than those of Australopithecus afarensis , 30% higher in males and 54% higher in females. However,
13920-405: The face and skull of H. ergaster . Turkana Boy's brain was almost fully grown at the time of his death, but its volume (at 880 cc) was only about 130 cc greater than the maximum found in H. habilis , about 500 cc below the average of modern humans. The 130 cc increase from H. habilis becomes much less significant than what could be presumed when the larger body size of Turkana Boy and H. ergaster
14080-410: The face, the woman's body compensated with round breasts. Ashley Montague (1965) proposed that breasts came about as an adaptation for infant feeding for a different reason, as early human ancestors adopted bipedalism and the loss of body hair. Human upright stance meant infants must be carried at the hip or shoulder instead of on the back as in the apes. This gives the infant less opportunity to find
14240-474: The facial structure of Turkana Boy is narrower and longer than that of the other skulls, with a higher nasal aperture and likely a flatter profile of the upper face. It is possible that these differences can be accounted for through Turkana Boy being a subadult, 7 to 12 years old. Furthermore, KNM ER 3733 is presumed to have been the skull of a female (whereas Turkana Boy is traditionally interpreted as male), which means that sexual dimorphism may account for some of
14400-504: The far younger type specimen of H. erectus (950 cc). Another significant fossil was a fossil mandible recovered at Ileret and described by Leakey with the designation KNM ER 992 in 1972 as " Homo of indeterminate species". In 1975, palaeoanthropologists Colin Groves and Vratislav Mazák designated KNM ER 992 as the holotype specimen of a distinct species, which they dubbed Homo ergaster . The name ( ergaster being derived from
14560-517: The female breast in Greece became less common during the first millennium. The popular adoration of female goddesses decreased significantly during the rise of the Greek city states, a legacy which was passed on to the later Roman Empire . During the middle of the first millennium BC, Greek culture experienced a gradual change in the perception of female breasts. Women in art were covered in clothing from
14720-702: The first known usage of the term was before the 12th century. "Breasts" is often used to refer to female breasts in particular, though the stricter anatomical term refers to the same region on members of either sex. Male breasts are sometimes referred to in the singular to mean the collective upper chest area, whereas female breasts are referred to in the plural unless speaking of a specific left or right breast. A large number of colloquial terms for female breasts are used in English, ranging from fairly polite terms to vulgar or slang. Some vulgar slang expressions may be considered to be derogatory or sexist to women. Humans are
14880-674: The first six months of life, and then remains an important source of nutrition, alongside solid foods, until at least one or two years of age. Biomechanical studies have demonstrated that, depending on the activity and the size of a woman's breast, when she walks or runs braless, her breasts may move up and down by 4 to 18 centimetres (1.6 to 7.1 in) or more, and also oscillate side to side. Researchers have also found that as women's breast size increased, they took part in less physical activity, especially vigorous exercise. Few very-large-breasted women jogged, for example. To avoid exercise-related discomfort and pain, medical experts suggest women wear
15040-483: The five-stage Tanner scale . During thelarche , the developing breasts are sometimes of unequal size, and usually the left breast is slightly larger. This condition of asymmetry is transitory and statistically normal in female physical and sexual development. Medical conditions can cause overdevelopment (e.g., virginal breast hypertrophy, macromastia ) or underdevelopment (e.g., tuberous breast deformity , micromastia ) in girls and women. Approximately two years after
15200-568: The foot. Homo ergaster † Telanthropus capensis Broom and Robinson , 1949 † Homo erectus ergaster (Groves and Mazák, 1975) † Homo louisleakeyi Kretzoi, 1984 † Homo kenyaensis Zeitoun, 2000 † Homo okotensis Zeitoun, 2000 Homo ergaster is an extinct species or subspecies of archaic humans who lived in Africa in the Early Pleistocene . Whether H. ergaster constitutes
15360-593: The fossils of Java Man ( H. erectus erectus , more than five thousand miles away). The dating of key Asian H. erectus specimens (including Java Man) is not entirely certain, but they are all likely to be 1.5 million years old or younger. Ubeidiya is also the oldest firmly confirmed site of Acheulean tools (one of the tool industries associated with H. ergaster ) outside Africa, the tools recovered there closely resembling older tools discovered in East Africa. The earliest fossil evidence of Homo in Asia are
15520-558: The genus Homo , notably relatively long legs which would have made them obligately bipedal. The teeth and jaws of H. ergaster are also relatively smaller than those of H. habilis and H. rudolfensis , indicating a major change in diet. In 1999, palaeoanthropologists Bernard Wood and Mark Collard argued that the conventional criteria for assigning species to the genus Homo were flawed and that early and basal species, such as H. habilis and H. rudolfensis , might appropriately be reclassified as ancestral australopithecines . In their view,
15680-642: The geographical distribution of their descendants and tools matching those in East Africa, fossils of the species are mainly from East Africa in the time range of 1.8 to 1.7 million years ago. Most fossils have been recovered from around the shores of Lake Turkana in Kenya. The oldest known specimen of H. erectus s.l. in Africa (i.e. H. ergaster ) is DNH 134 , a skull recovered in the Drimolen Palaeocave System in South Africa, dated to 2.04 to 1.95 million years ago. The skull
15840-591: The growth and development in early Homo can be drawn from the Mojokerto child , a ~1.4–1.5 million year old ~1-year old Asian H. erectus , which had a brain at about 72–84% the size of an adult H. erectus brain, which suggests a brain growth trajectory more similar to that of other great apes than of modern humans. Both the Gona pelvis and the Mojokerto child suggest that the prenatal growth of H. ergaster
16000-417: The hand') is commonly used to describe the front of the hand, and dorsal is the back of the hand. For example, the top of a dog 's paw is its dorsal surface; the underside, either the palmar (on the forelimb) or the plantar (on the hindlimb) surface. The palmar fascia is palmar to the tendons of muscles which flex the fingers, and the dorsal venous arch is so named because it is on the dorsal side of
16160-436: The human breast is about 2 hertz . Morphologically , the breast is tear-shaped. The superficial tissue layer ( superficial fascia ) is separated from the skin by 0.5–2.5 cm of subcutaneous fat (adipose tissue). The suspensory Cooper's ligaments are fibrous-tissue prolongations that radiate from the superficial fascia to the skin envelope. The female adult breast contains 14–18 irregular lactiferous lobes that converge at
16320-482: The human breast is identical in males and females until puberty . For pubescent girls in thelarche (the breast-development stage), the female sex hormones (principally estrogens) in conjunction with growth hormone promote the sprouting, growth, and development of the breasts. During this time, the mammary glands grow in size and volume and begin resting on the chest. These development stages of secondary sex characteristics (breasts, pubic hair, etc.) are illustrated in
16480-424: The increments and the decrements of the size and volume of a woman's breasts throughout the course of her life. Breast cancer is a cancer that develops from breast tissue. Signs of breast cancer may include a lump in the breast, a change in breast shape, dimpling of the skin, milk rejection , fluid coming from the nipple , a newly inverted nipple, or a red or scaly patch of skin. In those with distant spread of
16640-608: The jaw), nor with the mandible preserved in Turkana Boy, which has markedly different dentition. The most "iconic" fossil of H. ergaster is the KNM ER 3733 skull, which is sharply distinguished from Asian H. erectus by a number of characteristics, including that the brow ridges project forward as well as upward and arc separately over each orbit and the braincase being quite tall compared to its width, with its side walls curving. KNM ER 3733 can be distinguished from KNM ER 3883 by
16800-626: The jaws projecting farther outwards ( prognathism ). Though the jaws and teeth were smaller than those of the average australopithecine and H. habilis , they were still significantly larger than those of modern humans. Since the jaw slanted sharply backwards, it is probable that they were chinless. The overall structure of Turkana Boy's skull and face is also reflected in other H. ergaster skulls, which combine large and outwardly projecting faces with brow ridges, receding foreheads, large teeth and projecting nasal bones. Though Turkana Boy would have been no more than 12 years old when he died, their stature
16960-404: The latter period of pregnancy; at puberty, estrogens , in conjunction with growth hormone , cause permanent breast growth . In females, the breast serves as the mammary gland , which produces and secretes milk to feed infants . Subcutaneous fat covers and envelops a network of ducts that converge on the nipple , and these tissues give the breast its distinct size and globular shape. At
17120-512: The legs. Temporal has a similar meaning to lateral but is restricted to the head. The terms "left" and "right" are sometimes used, or their Latin alternatives ( Latin : dexter , lit. 'right'; Latin : sinister , lit. 'left'). However, it is preferred to use more precise terms where possible. Terms derived from lateral include: Varus (from Latin 'bow-legged') and valgus (from Latin 'knock-kneed' ) are terms used to describe
17280-448: The level of the fourth cervical vertebra may be abbreviated as "C4", at the level of the fourth thoracic vertebra "T4", and at the level of the third lumbar vertebra "L3". Because the sacrum and coccyx are fused, they are not often used to provide the location. References may also take origin from superficial anatomy , made to landmarks that are on the skin or visible underneath. For example, structures may be described relative to
17440-437: The levels of circulating estrogen decline. The adipose tissue and milk glands also begin to wither. The breasts can also become enlarged from adverse side effects of combined oral contraceptive pills . The size of the breasts can also increase and decrease in response to weight fluctuations. Physical changes to the breasts are often recorded in the stretch marks of the skin envelope; they can serve as historical indicators of
17600-491: The loss of body hair could have occurred significantly earlier than H. ergaster . Though skin impressions are unknown in any extinct hominin, it is possible that human ancestors were already losing their body hair around 3 million years ago. Human ancestors acquired pubic lice from gorillas about 3 million years ago, and speciation of human from gorilla pubic lice was potentially only possible because human ancestors had lost most of their body hair by this early date. It
17760-401: The main body, terms to describe position need to refer to an animal when it is in its standard anatomical position . This means descriptions as if the organism is in its standard anatomical position, even when the organism in question has appendages in another position. This helps avoid confusion in terminology when referring to the same organism in different postures. In humans, this refers to
17920-458: The mean difference between male and female individuals. The dimensions of a 1.8 million years old adult female H. ergaster pelvis from Gona , Ethiopia suggests that H. ergaster would have been capable of birthing children with a maximum prenatal (pre-birth) brain size of 315 cc, about 30–50 % of adult brain size. This value falls intermediately between that of chimpanzees (~40 %) and modern humans (28%). Further conclusions about
18080-492: The menstrual cycle, the breasts are enlarged by premenstrual water retention and temporary growth. The breasts reach full maturity only when a woman's first pregnancy occurs. Changes to the breasts are among the first signs of pregnancy. The breasts become larger, the nipple-areola complex becomes larger and darker, the Montgomery's glands enlarge, and veins sometimes become more visible. Breast tenderness during pregnancy
18240-456: The mouth and teeth. This is because although teeth may be aligned with their main axes within the jaw, some different relationships require special terminology as well; for example, teeth also can be rotated, and in such contexts terms like "anterior" or "lateral" become ambiguous. For example, the terms "distal" and "proximal" are also redefined to mean the distance away or close to the dental arch , and "medial" and "lateral" are used to refer to
18400-526: The name for an adaptive grade of human fossils from throughout Africa and Eurasia. Though Tattersall concluded that the H. ergaster material represents the fossils of a single clade of Homo , he also found there to be considerable diversity within this clade; the KNM ER 992 mandible accorded well with other fossil mandibles from the region, such as OH 22 from Olduvai and KNM ER 3724 from Koobi Fora, but did not necessarily match with cranial material, such as KNM ER 3733 and KNM ER 3883 (since neither preserves
18560-512: The neck down, including female goddesses like Athena , the patron of Athens who represented heroic endeavor. There were exceptions: Aphrodite , the goddess of love, was more frequently portrayed fully nude, though in postures that were intended to portray shyness or modesty, a portrayal that has been compared to modern pin ups by historian Marilyn Yalom . Although nude men were depicted standing upright, most depictions of female nudity in Greek art occurred "usually with drapery near at hand and with
18720-557: The nipple during breastfeeding. Volatile compounds in these secretions may also serve as an olfactory stimulus for the newborn's appetite. The dimensions and weight of the breast vary widely among women. A small-to-medium-sized breast weighs 500 grams (1.1 pounds) or less, and a large breast can weigh approximately 750 to 1,000 grams (1.7 to 2.2 pounds) or more. In terms of composition, the breasts are about 80 to 90% stromal tissue ( fat and connective tissue ), while epithelial or glandular tissue only accounts for about 10 to 20% of
18880-444: The nipple or the purchase to cling on to the mother's body hair. The mobility of the nipple on a large breast in most human females gives the infant more ability to find it, grasp it and feed. Other suggestions include simply that permanent breasts attracted mates, that "pendulous" breasts gave infants something to cling to, or that permanent breasts shared the function of a camel's hump , to store fat as an energy reserve. In women,
19040-448: The nipple-areola complex. Approximately 75% of the lymph from the breast travels to the axillary lymph nodes on the same side of the body, while 25% of the lymph travels to the parasternal nodes (beside the sternum bone). A small amount of remaining lymph travels to the other breast and to the abdominal lymph nodes. The subareolar region has a lymphatic plexus known as the "subareolar plexus of Sappey". The axillary lymph nodes include
19200-419: The nipple. The 2.0–4.5 mm milk ducts are immediately surrounded with dense connective tissue that support the glands. Milk exits the breast through the nipple, which is surrounded by a pigmented area of skin called the areola. The size of the areola can vary widely among women. The areola contains modified sweat glands known as Montgomery's glands . These glands secrete oily fluid that lubricate and protect
19360-472: The only mammals whose breasts become permanently enlarged after sexual maturity (known in humans as puberty ). The reason for this evolutionary change is unknown. Several hypotheses have been put forward: A link has been proposed to processes for synthesizing the endogenous steroid hormone precursor dehydroepiandrosterone which takes place in fat rich regions of the body like the buttocks and breasts. These contributed to human brain development and played
19520-480: The onset of puberty (a girl's first menstrual cycle ), estrogen and growth hormone stimulate the development and growth of the glandular fat and suspensory tissues that compose the breast. This continues for approximately four years until the final shape of the breast (size, volume, density) is established at about the age of 21. Mammoplasia (breast enlargement) in girls begins at puberty, unlike all other primates, in which breasts enlarge only during lactation. During
19680-565: The origins of H. ergaster are obscured by the fact that the species marks a radical departure from earlier species of Homo and Australopithecus in its long limbs, height and modern body proportions. Though a large number of Pleistocene tools have been found in East Africa, it can not be fully ascertained that H. ergaster originated there without further fossil discoveries. It is assumed that H. ergaster evolved from earlier species of Homo , probably H. habilis . Though populations of H. ergaster outside of Africa have been inferred based on
19840-400: The outer surface of the organism. For example, in skin , the epidermis is superficial to the subcutis . These two terms, used in anatomy and embryology , describe something at the back ( dorsal ) or front/belly ( ventral ) of an organism. The dorsal (from Latin dorsum 'back') surface of an organism refers to the back, or upper side, of an organism. If talking about
20000-402: The outside of the left or right side of the body toward the inside) or "mediolateral"(from the inside of that side of the body toward the outside. The same logic is applied to all planes of the body and, thus top-to-bottom or bottom-to-top X-ray projections are known as "superoinferior" and "inferosuperior," respectively. However, within the diagnostic imaging industry, for this particular example,
20160-422: The pectoral (chest), subscapular (under the scapula), and humeral (humerus-bone area) lymph-node groups, which drain to the central axillary lymph nodes and to the apical axillary lymph nodes. The lymphatic drainage of the breasts is especially relevant to oncology because breast cancer is common to the mammary gland, and cancer cells can metastasize (break away) from a tumor and be dispersed to other parts of
20320-829: The perception of a woman's body and sexual attractiveness . Breasts, especially the nipples, can be an erogenous zone . The English word breast derives from the Old English word brēost ('breast, bosom') from Proto-Germanic * breustam (breast), from the Proto-Indo-European base bhreus– (to swell, to sprout). The breast spelling conforms to the Scottish and North English dialectal pronunciations. The Merriam-Webster Dictionary states that " Middle English brest , [comes] from Old English brēost ; akin to Old High German brust ..., Old Irish brú [belly], [and] Russian bryukho ";
20480-450: The period of 1.7 to 1.4 million years ago, though a broader time range is possible. Though fossils are known from across East and Southern Africa, most H. ergaster fossils have been found along the shores of Lake Turkana in Kenya. There are later African fossils, some younger than 1 million years ago, that indicate long-term anatomical continuity, though it is unclear if they can be formally regarded as H. ergaster specimens. As
20640-458: The radical differences between H. ergaster and earlier Homo and australopithecines, it is unclear whether australopithecines were significantly more sexually diamorphic than H. ergaster or modern humans. Skeletal evidence suggests that sexes in H. ergaster differed no more in size than sexes in modern humans do, but a 2003 study by palaeoanthropologists Philip L. Reno, Richard S. Meindl, Melanie A. McCollum and C. Owen Lovejoy suggested that
20800-408: The rest of their energy requirements. Multiple reasons make a fully meat-based diet in H. ergaster unlikely, the most prominent being that African ungulates (the primary prey available) are relatively low in fat and that high meat diets demand increased intake of water, which would have been difficult in an open and hot environment. Modern African hunter-gatherers who rely heavily on meat, such as
20960-570: The river god Hapy who was considered to be responsible for the annual overflowing of the Nile . Female breasts were also prominent in Minoan art in the form of the famous Snake Goddess statuettes, and a few other pieces, though most female breasts are covered. In Ancient Greece there were several cults worshipping the "Kourotrophos", the suckling mother, represented by goddesses such as Gaia , Hera and Artemis . The worship of deities symbolized by
21120-410: The rounded shape of a woman's breast evolved to prevent the sucking infant offspring from suffocating while feeding at the teat; that is, because of the human infant's small jaw, which did not project from the face to reach the nipple, they might block the nostrils against the mother's breast if it were of a flatter form (compare with the common chimpanzee ). Theoretically, as the human jaw receded into
21280-403: The same embryological tissues. Anatomically, male breasts do not normally contain lobules and acini that are present in females. In rare instances, it is possible for very few lobules to be present, this makes it possible for some men to develop lobular carcinoma of the breast. Normally, males produce lower levels of estrogens and higher levels of androgens , namely testosterone , which suppress
21440-413: The same was also true for the significantly earlier Australopithecus afarensis . Sexual dimorphism is difficult to measure in extinct species since the sex of fossils is usually not determinable. Historically, scientists have typically measured differences between the extreme ends (in terms of size and morphology) of the fossil material attributed to a species and assumed that the resulting ratio applies to
21600-442: The skull, the dorsal side is the top. The ventral (from Latin venter 'belly') surface refers to the front, or lower side, of an organism. For example, in a fish, the pectoral fins are dorsal to the anal fin , but ventral to the dorsal fin . The terms are used in other contexts; for example dorsal and ventral gun turrets on a bomber aircraft. Specific terms exist to describe how close or far something
21760-402: The small volume of its braincase (600 cc), the form of the middle and upper face and the lack of an external nose. The mixture of skulls at Dmanisi suggests that the definition of H. ergaster (or H. erectus ) might most appropriately be expanded to contain fossils that would otherwise be assigned to H. habilis or that two separate species of archaic humans left Africa early on. In addition to
21920-719: The southern end of the Red Sea or along the Nile Valley , but there are no fossil hominins known from either region in the Early Pleistocene. The earliest Homo fossils outside Africa are the Dmanisi skulls from Georgia (dated to 1.77–1.85 million years old, representing either early H. ergaster or a new taxon, H. georgicus ), three incisors from Ubeidiya in Israel (about 1.4 to 1 million years old) and
22080-661: The species and what it should encompass. Some researchers, such as palaeoanthropologist Ian Tattersall in 2013, have questioned H. erectus since it contains an "unwieldly" number of fossils with "substantially differing morphologies". In the 1970s, palaeoanthropologists Richard Leakey and Alan Walker described a series of hominin fossils from Kenyan fossil localities on the eastern shore of Lake Turkana . The most notable finds were two partial skulls; KNM ER 3733 and KNM ER 3883 , found at Koobi Fora . Leakey and Walker assigned these skulls to H. erectus , noting that their brain volumes (848 and 803 cc respectively) compared well to
22240-418: The species. A nearly complete fossil, interpreted as a young male (though the sex is actually undetermined), was discovered at the western shore of Lake Turkana in 1984 by Kenyan archaeologist Kamoya Kimeu . The fossils were described by Leakey and Walker, alongside paleoanthropologists Frank Brown and John Harris, in 1985 as KNM-WT 15000 (nicknamed "Turkana Boy"). They interpreted the fossil, consisting of
22400-414: The suckling of her baby, the mother's brain secretes oxytocin . High levels of oxytocin trigger the contraction of muscle cells surrounding the alveoli, causing milk to flow along the ducts that connect the alveoli to the nipple. Full-term newborns have an instinct and a need to suck on a nipple, and breastfed babies nurse for both nutrition and for comfort. Breast milk provides all necessary nutrients for
22560-460: The surfaces of the hand and what is the "anterior" or "posterior" surface. The term "anterior", while anatomically correct, can be confusing when describing the palm of the hand; Similarly is "posterior", used to describe the back of the hand and arm. This confusion can arise because the forearm can pronate and supinate and flip the location of the hand. For improved clarity, the directional term palmar (from Latin palma 'palm of
22720-429: The terms "cranial" (towards the head) and "caudal" (towards the tail, or, downwards, away from the head) are known interchangeable alternatives to the previous two projection terms. Combined terms were once generally hyphenated, but the modern tendency is to omit the hyphen. Anatomical terms describe structures with relation to four main anatomical planes : The axes of the body are lines drawn about which an organism
22880-404: The terms often is context-sensitive. Much of this information has been standardised in internationally agreed vocabularies for humans ( Terminologia Anatomica ) and animals ( Nomina Anatomica Veterinaria ). Different terms are used for groups of creatures with different body layouts, such as bipeds (creatures that stand on two feet, such as humans) and quadrupeds . The reasoning is that
23040-403: The time H. ergaster could use for resting, socialising and travelling. Though this would have been possible, it is considered unlikely, especially since the jaws and teeth of H. ergaster are reduced in size compared to those of the australopithecines, suggesting a shift in diet away from fibrous and difficult-to-chew foods. Regardless of energy needs, the small gut of H. ergaster also suggests
23200-481: The time of H. ergaster , this behaviour had probably resulted in the development of true hunter-gatherer behaviour, a first among primates. H. ergaster was an apex predator . Further behaviours that might first have arisen in H. ergaster include male-female divisions of foraging and true monogamous pair bonds. H. ergaster also marks the appearance of more advanced tools of the Acheulean industry, including
23360-537: The torso proportions of H. ergaster implies a relatively small gut, which means that energy needs might not necessarily have been higher in H. ergaster than in earlier hominins. This is because the earlier ape (and australopithecine) gut was large and energy-expensive since it needed to synthesize fat through fermenting plant matter, whereas H. ergaster likely ate significantly more animal fat than their predecessors. This would have allowed more energy to be diverted to brain growth, increasing brain size while maintaining
23520-408: The true earliest representative of Homo was H. ergaster . Au. africanus Au. garhi H. habilis H. rudolfensis H. ergaster H. erectus H. antecessor H. heidelbergensis H. neanderthalensis H. sapiens Since its description as a separate species in 1975, the classification of the fossils referred to H. ergaster has been in dispute. H. ergaster
23680-437: The type specimen of H. erectus , in 2013, Ian Tattersall concluded that referring to the African material as H. ergaster rather than "African H. erectus " was a "considerable improvement" as there were many autapomorphies distinguishing the material of the two continents from one another. Tattersall believes it to be appropriate to use the designation H. erectus only for eastern Asian fossils, disregarding its previous use as
23840-474: The volume of the breasts. The tissue composition ratios of the breast also vary among women. Some women's breasts have a higher proportion of glandular tissue than of adipose or connective tissues. The fat-to-connective-tissue ratio determines the density or firmness of the breast. During a woman's life, her breasts change size, shape, and weight due to hormonal changes during puberty , the menstrual cycle , pregnancy , breastfeeding, and menopause . The breast
24000-460: The women's health and ability to grow and carry them in her life. Prospective mates can then evaluate the genes of a potential mate for their ability to sustain her health even with the additional energy demanding burden she is carrying. The zoologist Desmond Morris describes a sociobiological approach in his science book The Naked Ape . He suggests, by making comparisons with the other primates, that breasts evolved to replace swelling buttocks as
24160-623: The years, including a massive set of jaws from Indonesia which were perceived to be similar to those of australopithecines and dubbed Meganthropus (now believed to be an unrelated hominid ape ). The discovery of H. floresiensis in 2003, which preserved primitive foot and wrist anatomy reminiscent of that of H. habilis and Australopithecus again led to suggestions of pre- erectus hominins in Asia, though there are no known comparable foot or wrist bones from H. erectus which makes comparisons impossible. The idea that H. ergaster / H. erectus first evolved in Asia before expanding back into Africa
24320-668: Was either a single but variable species, several subspecies divided by time and geography or several geographically dispersed but closely related species. In 2015, paleoanthropologists David Strait, Frederick Grine and John Fleagle listed H. ergaster as one of the seven "widely recognized" species of Homo , alongside H. habilis , H. rudolfensis , H. erectus , H. heidelbergensis , H. neanderthalensis and H. sapiens , noting that other species, such as H. floresiensis and H. antecessor , were less widely recognised or more poorly known. Comparing various African fossils attributed to H. erectus or H. ergaster to Asian fossils, notably
24480-677: Was flat and receding, merging at an angle with the brow ridge above their eyes. A noticeable difference between Turkana Boy and the australopithecines and H. habilis would have been their nose, which would have been similar to that of modern humans in projecting forwards and having nostrils oriented downwards. This external nose may have also been an adaptation towards a warmer climate, since the noses of modern humans are usually cooler than their central bodies, condensing moisture that would otherwise have been exhaled and lost during periods of increased activity. The face of Turkana Boy would have been longer from top to bottom than that of modern humans, with
24640-417: Was greater than expected for a single species when compared to modern humans and chimpanzees , but fell well within the variation expected for a species when compared to gorillas , and even well within the range expected for a single subspecies when compared to orangutans (though this is partly due to the great sexual dimorphism exhibited in gorillas and orangutans). Baab concluded that H. erectus s.l.
24800-454: Was immediately dismissed by Leakey and Walker and many influential researchers, such as palaeoanthropologist G. Philip Rightmire, who wrote an extensive treatise on H. erectus in 1990, continued to prefer a more inclusive and comprehensive H. erectus . Overall, there is no doubt that the group of fossils composing H. erectus and H. ergaster represent the fossils of a more or less cohesive subset of closely related archaic humans. The question
24960-465: Was in need of significant revision. In 2000, French palaeoanthropologist Valéry Zeitoun suggested that KNM ER 3733 and KNM ER 3883 should be referred to two separate species, which she dubbed H. kenyaensis (type specimen KNM ER 3733) and H. okotensis (type specimen KNM ER 3883), but these designations have found little acceptance. Although frequently assumed to have originated in East Africa ,
25120-543: Was notably held by Eugène Dubois , who first described H. erectus fossils in the 19th century and considered the fossils of Java Man, at the time undeniably the earliest known hominin fossils, as proof of the hypothesis. Though the discovery of australopithecines and earlier Homo in Africa meant that Homo itself did not originate in Asia, the idea that H. erectus (or H. ergaster ) in particular did, and then expanded back into Africa, has occasionally resurfaced. Various fossil discoveries have been used to support it through
25280-460: Was similar to that of modern humans but that the postnatal (post-birth) growth and development was intermediate between that of chimpanzees and modern humans. The faster development rate suggests that altriciality (an extended childhood and a long period of dependency on your parents) evolved at a later stage in human evolution, possibly in the last common ancestor of Neanderthals and modern humans. The faster development rate might also indicate that
25440-496: Was substantially weakened by the dating of the DNH 134 skull as approximately 2 million years old, predating all other known H. ergaster / H. erectus fossils. The only well-preserved post-cranial remains of H. ergaster come from the Turkana Boy fossil. Unlike the australopithecines, Turkana Boy's arms were not longer relative to their legs than the arms of living people and the cone-shaped torso of their ancestors had evolved into
25600-476: Was the end result of gradual modifications within a single lineage of hominin evolution. As the perceived transitional form between early hominins and modern humans, H. erectus , originally assigned to contain archaic human fossils in Asia, came to encompass a wide range of fossils covering a large span of time (almost the entire temporal range of Homo ). Since the late twentieth century, the diversity within H. erectus has led some to question what exactly defines
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