Vitruvian Man. Leonardo da Vinci. 1490.


Michelangelo. 1512. The Creation of Adam.

A human (Homo sapiens) is an animal that is rational.

By this I believe Aristotle meant that humans are the only animals which set goals for themselves.


1   Study

The study of humans is called anthropology.

2   Properties

Humans use tools to a much higher degree than any other animal, are the only extant species known to build fires and cook their food, as well as the only extant species to clothe themselves and create and use numerous other technologies and arts.

2.1   Urbanization

Most of the world's population moved to cities in the 20th and 21st centuries.

1950: most people lived in rural areas 2007: global urban population = rural population 2050 (projected): urban populations dominant in almost all countries

2.2   Lifestyle


Lifestyle is the typical way of life of an individual, group, or culture.

The term was originally used by Alfred Adler.

Tangible factors relate specifically to demographic variables. A rural environment has different lifestyles compared to an urban metropolis.

2.3   Population


Alasdair Rae. Global Population Density.


The population of the world has more than doubled in just the last 50 years.

Since 1960, child deaths have decreased from 20 million a year to 6 million a year. [7]


Since 1960 to 2000, the average global fertility rate has halved, from an average of 5 children per woman to 2.5 children. [7]

Until the late 1960s, each woman had on average more than 5 children, and at such high fertility rates, population growth is fast. At that time the world population increased by 2 percent every year. [7]

The availability of contraceptives allows parents to have only as many children as they want. And that number changes as people’s income goes up. From decades of demographic research, we know that women decide to have fewer children as they get access to better education and better opportunities in the job market. We also know that when child mortality falls, so that families do not need to fear that their children will die, they consequently decide to have fewer children in the first place. [7]

Most people used to die in their own beds.

On the concept of demographic transition:

Basically when people get better off in the world, they have fewer children. Women are driving this. In the countryside, you have six or seven children because you need that many to manage your subsistence farm and you can't count on any of them making it. In cities, you want kids who had a better job than you did. In the countryside, women have no choice they marry whoever is available. Moving to town gives them freedom, and then decide how many kids she's going to have.

Human population growth is slowing due to urbanization.

Although more children are an asset in the countryside, they are a liability in the city. A global tipping point in urbanization is what stopped the population explosion.

Paul Ehrlich was a professor population biology at Stanford University. His specialty was butterflies_ and co-evolution. In 1968, Ehrlich wrote a book called The Population Bomb along with the `Sierra Club`_ in which he argued that overpopulation would cause mass starvation and societal upheaval. The book was a best seller. The book was published at the peak year of population growth.

The predictions of the book were wrong because it argued that human population would follow a J-curve rather than an S-curve. In reality, human population slowed for cultural reasons (`demographic transition`_) rather than biological ones.

In 1800, one in three children died before they were 5 years old, no matter where they were born in the world. In London, an essential part of household spending even for the poor was burial insurance, as so many of their children could be expected to die.

2.4   Poverty


In 1990, 1.86 billion people were living on less than 1.90 international-$ per day—more than every third person in the world. Twenty-five years later, the number of people living in extreme poverty has more than halved to 706 million, every tenth person. [7]

This is a very large transformation. It means that, on average, every day for the past 25 years 137,000 fewer people were living in extreme poverty than the day before. On every day in the last 25 years there could have been a newspaper headline reading, “The number of people in extreme poverty fell by 137,000 since yesterday.” [7]

This is the statistic I remember: Today every 10th person is living in extreme poverty—706 million people. An unacceptably large number of people. But we should also know that the trend is moving in the right direction. [7]

2.5   Body temperature

Normal human body temperature is 37 degrees Celsius.

Metabolic activity or oxidization of foods results in the production of heat which can be controlled partially by controlling metabolic rate. However, metabolism during various activities of the body generates heat at varying rates. Hence the body must reject heat at the proper rate to keep the body temperature constant.

The mental state and physical operations done by the body are disturbed if the internal body temperature rises or falls beyond its normal range. [8]

Physiological responses at different body temperatures [8]
Body temperature Physiological response
43.3 C Brain damage, fainting, nausea
37.8 C Sweating
37 C Normal
<37 C Shivering
< 32.2 C Speechless
26.5 C Stiff and deformed body
< 26.5 C Irreversible body cooling

When body temperature falls, respiratory activity, particular in muscle tissue, automatically increases and generates more heat. The extreme symptom of this form of body control is shivering (essentially rapid muscle contractions). Studies have shown that shivering can results in a five times increase in metabolism. [8]

The body has separate sensors for detecting hot and cold in the body. Heat sensors, located in the hypothamlus_, send signals when skin temperature is higher than 37 C. Cold sensors, located in the skin, send signals when skin temperature is below 37 C. If impulses from both types of sensors are of the same magnitude, the body feels thermally neutral. If not, one feels warm or cold. [8]

Multiple components contribute to regulating body temperature.

The hypothalamus_ continuously records the temperature of blood and regulates body temperature using pathways of the nervous system. It is stimulated when there a minute change in temperature at any part of the body, say while drinking, eating, or touching hot or cold materials.

The hypothalamus triggers heat controlling mechanisms to increase or decrease heat loss by controlling the flow of blood to the skin, which is increased or decreased by constricting or expanding the blood vessels (vasoconstriction or vasodilatation) within the skin. [8]

Peripheral receptors located in the skin and central receptors in the spinal cord and in and around veins mainly detect cold temperatures. The temperature signals are transmitted to the hypothalamus, where both signals are combined to control heat-producing and heat-conserving reactions of the body. [8]

Blood has high thermal conductivity. When blood flows from the body core to the skin, it transmits heat to the skin. By controlling peripheral blood flow to the skin, the body is able to increase the temperature of the skin to speed up elimination of body heat. [8]

In a hot environment:

  • The blood vessels in the skin dilate, resulting in more blood transferring to the skin, which increases heat loss and decreases body temperature. [8]
  • The heart beats more rapidly to pump blood to the periphery. [8]
  • Sweat secretion.

In a cold environment:

  • Blood vessels in the skin are constricted. [8]
  • The heart slows down which can cause a feeling of lethargy and mental dullness. [8]
  • The `sympathetic nervous system`_ releases catecholamines (norepinephrine and epinephrine_) which increase the metabolic rate of the many tissues of the body and ultimately result in heat generation. In the liver and muscle, these two hormones cause glycogenolysis_. Sympathetic stimulation causes brown fat burning to generate heat by non-shivering thermogenesis_. Vasoconstriction in the peripheral blood vessels is the result of sympathetic stimulation.
  • The heart rate rises, delivering more oxygen to meet the needs of non-shivering thermogenesis. [8]

3   Substance


Rembrandt. 1632. The Anatomy Lesson of Dr. Nicolaes Tulp.


Cross-section of two women.

Human body composition can be studied at the atomic, molecular, cellular, tissue, and whole body level. [6]

The five levels of body composition are interrelated. Information at one level can be translated to another level. This is important as it forms the basis of many techniques used to determine body composition. For example, the amount of bone can be calculated assuming that a certain amount of total body calcium is in the skeletal tissue after determining the amount of calcium in the body.

There are multiple techniques for measuring body composition. The techniques can be described in terms of direct, indirect, and doubly indirect methods. Direct techniques measure body composition without or with minor assumptions. Indirect techniques do so with assumptions, which may not be valid in the given situation. Doubly indirect methods rely on a statistical relationship between easily measurable body parameters and the body component of interest (e.g. measuring body fat from skin-fold thickness). [6]

Direct methods include carcass analysis and in vivo neutron activation analysis (IVNAA). Carcass analysis involves dissecting tissues, weighing them, and then performing chemical analysis. The data on the chemical composition of only a five male and one female cadaver form the basis for the assumptions that normally used in indirect methods. [6]

3.1   Atomic level

Many chemical elements are found in the human body. Oxygen, carbon, hydrogen_, nitrogen_, calcium, and phosphorus_ are the most abundant and together account for more than 98% of body weight (oxygen: 61%, carbon: 23%, hydrogen: 10%, nitrogen 2.6%, calcium: 1.4%, phosphorus: 0.8%). This information was initially based on chemical analysis of carcasses, but today the information can also be obtained by in vivo neutron activation analysis. [6]

The average human body has enough iron in it to forge a metal nail that is 3-inches long, enough sulfur to kill all fleas on a dog, enough carbon to make 900 pencils, enough potassium to fire a toy cannon, enough fat to make 7 bars of soap, and enough phosphorous to make 2,200 match heads.

3.2   Molecular level

The chemical elements in the human body are bound in molecules. The main compartments are water, lipids, proteins, minerals, and carbohydrates. The total amount of water in the body is high, and can be as high as 60-70% of total bodyweight depending on the body fat content. Total body water can be divided into intracellular water and extracellular water. The ratio of the two is an important health parameter that is distributed in many diseases. [6]

Lipids appear in the human body in different forms. Essential structural lipids such as phospholipids_ (cell membranes) and sphingomyelin (nervous system) form only a minor part of the total lipids in the body. The nonessential lipids, most triglycerides_ or triacylglycerol (fat) are the most abundant. They are the energy store of the adult human body, insulate against cold, and protect vital organs against mechanical damage. [6] In a healthy adult, the amount of amount of body fat varies between 10% and 25% in men and between 15% and 35% in women. [6]

Body protein varies between 10% and 15%. It is higher in males than in females as males generally have more muscles. There is no protein storage in the body.

The amount of minerals in the body varies between 3% and 5% again dependent on body fat. Calcium and phosphorus_ are the two main minerals. They are found mainly in bones. Carbohydrates are found in the boud as glucose (blood sugar) and glycogen_, a polysaccharide in muscle and liver cells that serves as a short-term energy store. The amount of carbohydrates in the body rarely exceeds 500g. [6]

3.3   Cellular level

At the cellular level, body composition can be described in terms of body cells mass, extracellular fluids, and extracellular solids. The body cell mass includes the cells with all their contents, such as water, proteins and minerals. Extracellular fluid contains about 95% water, which is plasma in the intravascular space and interstitial fluid in the extravascular space. Extracellular solids are mainly proteins (e.g. collagen) and minerals (bone minerals and soluble minerals in the extracellular fluid). [6]

3.4   Surface anatomy


The standard anatomical position, with terms of relative location noted.

Humans have a head, neck, torso, two arms and hands and two legs and feet.

The general framework of the body is built up mainly as a series of bones, however, in certain regions, by pieces of cartilage; the bony part of the framework constitutes the skeleton. [1]

In humans, anterior refers to the "front" of the individual, and, posterior, refers to the "back". "Anterior" and "posterior" can also be used as relative terms. Thus, the eyes are posterior to the nose, but anterior to the back of the head in humans.

3.4.1   Lower extremity   Hip

The groin areas are the two creases at the junction of the torso with the legs, on either side of the pubic area. The hip adductor muscles that make up the groin consist of the adductor brevis, adductor longus, adductor magnus, gracilis, and pectineus.   Leg


The leg is the inferior part of the lower extremity between the knee and the ankle.   Thigh


The thigh is the area between the pelvis and the knee.

The thigh consists of a single bone, the femur, and the quadriceps.

The single bone in the thigh is called the femur. This bone is very thick and strong (due to the high proportion of cortical bone), and forms a ball and socket joint at the hip, and a condylar joint at the knee.

3.5   Organ systems

3.5.1   The cardiovascular system

The cardiovascular system consists the heart, blood, and blood vessels.

Blood accounts for roughly 8% of body weight in the human body. Males have 5-6 L of blood and women have 4-5 L. If 1.5L of blood are lost, unconsciousness may occur. Death becomes a risk at 40% blood loss.

3.5.2   The digestive system

Gastroenteritis is an illness that may cause nausea_, vomiting, and diarrhea. It is sometimes called "stomach flu". You will being to feel better in 1 to 2 days. You can care for your self at home by:

  • Take any prescribed antibiotics as needed
  • Drinking fluids to prevent dehydration. Drink fluids in frequent, small amounts; too much too fast can cause vomiting.
  • Eat only mild foods such as dry toast, yogurt, applesauce, bananas, and rice. Avoid spicy and high fat food.

I was prescribed in September 2018:

  • Diocycolmine 20mg tablets. Used to treat gastrointestinal (GI) spasms and irritable bowel syndrome.
  • Ondansetron ODT (Generic for Zofran ODT) 4mg tablets to treat my nausea.

3.5.6   The integumentary system

The integumentary system is the organ system that protects the body from various kinds of damage, such as loss of water or abrasion from outside. It consists of skin, hair, feathers_, hooves_, and nails_.

3.5.8   The muscular system


The muscular system is the organ system that permits movement of the body, maintains posture, and circulates blood throughout the body. It consists of skeletal muscle, smooth muscle and cardiac muscle and is controlled through the nervous system.

There are over 600 muscles in the human body.   The anterolateral region of the neck

static/images/muscles_of_the_neck.gif   The lateral cervical muscles

The lateral muscles are trapezius_ and the `sternocleidomastoid muscle`_.

The trapezius is a large superficial muscle that extends longitudinally from the occipital bone to to the lower thoracic vertebrate and laterally to the spine of scapula. Its function are to move the scapula and support the arm.

The trapezius resembles a trapezium_.

The trapezius has three functional regions: the superior region (descending part), which supports the weight of the arm; the intermediate region (transverse part), which retracts the scapulae; and the inferior region (ascending part), which medially rotates and depresses the scapulae.

The Sternocleidomastoid muscle (SCM) passes obliquely across the side of the neck. It is thick and narrow at its central part, but broader and thinner at either end. [1]

Its named is derived from the fact that it originated at the manubrium_ of the sternum_ (sterno-) and the clavicle_ (cleido-), and has an insertion at the `mastoid process`_ of the `temporal bone`_ of the skull_.

The primary actions of the muscle are rotation of the head to the opposite side and flexion of the neck.

It arises from the sternum and clavicle by two heads. The medial or sternal head is a rounded fasciculus, tendinous in front, fleshy behind, which arises from the upper part of the anterior surface of the manubrium sterni, and is directed upward, lateralward, and backward. The lateral or clavicular head, composed of fleshy and aponeurotic fibers, arises from the superior border and anterior surface of the medial third of the clavicle; it is directed almost vertically upward. The two heads are separated from one another at their origins by a triangular interval, but gradually blend, below the middle of the neck, into a thick, rounded muscle which is inserted, by a strong tendon, into the lateral surface of the mastoid process, from its apex to its superior border, and by a thin aponeurosis into the lateral half of the superior nuchal line of the occipital bone. [1]   The trunk


The abdomen (from Latin "belly") is the part of the body between the diaphragm and the pelvis.

The abdominal muscles consists of three layers. The deepest layer is the transverse abdominals, which wrap around the trunk horizontally like a belt. They provide compression that supports the spine.

The internal obliques wrap diagonally from the front of the ribs of the back of the pelvis.

The external obliques interlock with the ribs and run diagonally to the pelvis. These muscles are visible in males as a pelvis crease.

Underneath the external obliques sits the rectus abdominis (the "square abdominal"), a paired muscle running vertically. The parallel muscles are separated by the linea alba (Latin for "white line"). The muscle is divided into eight segments, but six are more commonly visible in people with low body fat.   Upper extremity   Biceps

The biceps brachii is a two-head muscle that lies on the upper arm between the shoulder and the elbow.


The long head (red) and short head (green).

The biceps muscle has two heads: the short head and the long head. Both heads arise on the scapula and join to form a single muscle belly which is attached to the upper forearm.


While the biceps crosses both the shoulder and elbow joints, its main function is at the latter where it flexes the forearm at the elbow and supinates the forearm.


To train a muscle optimally, you have to fully contract it. For your biceps, that means your elbow must be fully flexed and supinated. Barbell curls and alternating dumbbell curls are great exercises for this.   Triceps

The Triceps Brachii is situated on the back of the arm, extending the entire length of the dorsal surface of the humerus. It is of large size, and arises by three heads (long, lateral, and medial), hence its name. [1]


The long head (red), lateral head (yellow), and medial head (green).

The long head arises by a flattened tendon from the infraglenoid tuberosity of the scapula, being blended at its upper part with the capsule of the shoulder-joint; the muscular fibers pass downward between the two other heads of the muscle, and join with them in the tendon of insertion. [1]

The lateral head arises from the posterior surface of the body of the humerus, between the insertion of the Teres minor and the upper part of the groove for the radial nerve, and from the lateral border of the humerus and the lateral intermuscular septum; the fibers from this origin converge toward the tendon of insertion. [1]

The medial head arises from the posterior surface of the body of the humerus, below the groove for the radial nerve; it is narrow and pointed above, and extends from the insertion of the Teres major to within 2.5 cm. of the trochlea: it also arises from the medial border of the humerus and from the back of the whole length of the medial intermuscular septum. Some of the fibers are directed downward to the olecranon, while others converge to the tendon of insertion. [1]

The long head starts (originates) on the scapula (shoulder blade). The lateral and medial heads both start on the humerus. All three heads then come together to a single tendon and attach (insert) on to the ulna.

Different muscle fiber types make up different heads of the muscle.

The medial Head is primarily made up of small type I fibers (“slow twitch” muscle fibers, which are used in lower intensity exercises. These fibers are involved in muscular endurance/high rep training). The lateral head is predominantly made up of large type IIb fiber types (“fast twitch” muscle fibers, which are used during high intensity exercise. This fiber type is involved in high force, power, and speed generation.) The long head is made up of a mixture of both types of fibers.


The function of the triceps is to extend the elbow.

Due to the diversity in muscle fibers that make up the triceps, it is very important to train them in low, medium, and high rep ranges to attain maximal growth (the medial head is used primarily for light/high rep exercises, the lateral head for heavy/low rep exercise, and the long head is used for all exercises).

Overhead movements target the long head, pushdowns target the lateral head.   Deltoids

The deltoid muscle (so called because it it in the shape of the Greek letter Delta) is the muscle forming the rounded contour of the shoulder.


The anterior (red), lateral (green), and posterior (blue) parts of the deltoid.

The deltoid originates in three distinct sets of fibers often refers to as "heads": the anterior, the middle, and the posterior. The anterior deltoid originates on the anterior surface of the clavicle_. The middle or lateral deltoid originates on the acromion and spine of the scapula. The posterior deltoid originates on the spine of the scapula. All three heads join together on the humerus_. [2]


The primary function of the deltoid is to abduct the arm which occurs when all heads of the deltoid contract at the same time. The secondary function is to prevent the dislocation of the humerus when lifting heavy loads. [2]

Each head of the deltoid also has a specific function. The anterior deltoid abducts the shoulder when the arm is externally rotated, the lateral deltoid abducts the shoulder when the arm is internally rotated, and the posterior deltoid extends the shoulder.

The anterior deltoid is primarily used to abduct the shoulder when the arm is externally rotated, flexes the arm at the shoulder, and internally rotates the arm. The lateral deltoid is primarily used to abduct shoulder when the arm is internally rotated. The posterior deltoid is primarily used to extend the arm at the shoulder. [2]


To maximize deltoid development, it is important to train each individual head optimally. A typical deltoid workout should include one exercise for each part of the muscle.   Lower extremity

The muscles of the lower extremity are subdivided into groups corresponding with the different regions of the limb. [1]   Muscles of the thigh   The anterior femoral muscles (quads)


The Sartorius, the longest muscle in the body, is narrow and ribbon-like; it arises by tendinous fibers from the anterior superior iliac spine and the upper half of the notch below it. It passes obliquely across the upper and anterior part of the thigh, from the lateral to the medial side of the limb, then descends vertically, as far as the medial side of the knee, passing behind the medial condyle of the femur to end in a tendon. This curves obliquely forward and expands into a broad aponeurosis, which is inserted, in front of the Gracilis and Semitendinous, into the upper part of the medial surface of the body of the tibia, nearly as far forward as the anterior crest. The upper part of the aponeurosis is curved backward over the upper edge of the tendon of the Gracilis so as to be inserted behind it. An offset, from its upper margin, blends with the capsule of the knee-joint, and another from its lower border, with the fascia on the medial side of the leg. [1]

The Quadriceps femoris (Quadriceps extensor) includes the four remaining muscles on the front of the thigh. It is the great extensor muscle of the leg, forming a large fleshy mass which covers the front and sides of the femur. It is subdivided into separate portions, which have received distinctive names. One occupying the middle of the thigh, and connected above with the ilium, is called from its straight course the Rectus femoris. The other three lie in immediate connection with the body of the femur, which they cover from the trochanters to the condyles. The portion on the lateral side of the femur is termed the Vastus lateralis; that covering the medial side, the Vastus medialis; and that in front, the Vastus intermedius. [1]

The quadriceps ("quads") is a large muscle group that includes the four prevailing muscles on the front of the thigh. It the great extensor muscle of the knee, forming a large fleshy mass which covers the front and sides of the femur.

The quads consists of the rectus femoris, the vastus lateralis, the vastus medialis, and the vastus intermedius.

The Rectus femoris is situated in the middle of the front of the thigh; it is fusiform in shape, and its superficial fibers are arranged in a bipenniform manner, the deep fibers running straight down to the deep aponeurosis. It arises by two tendons: one, the anterior or straight, from the anterior inferior iliac spine; the other, the posterior or reflected, from a groove above the brim of the acetabulum. The two unite at an acute angle, and spread into an aponeurosis which is prolonged downward on the anterior surface of the muscle, and from this the muscular fibers arise. The muscle ends in a broad and thick aponeurosis which occupies the lower two-thirds of its posterior surface, and, gradually becoming narrowed into a flattened tendon, is inserted into the base of the patella. [1]

The Vastus lateralis (Vastus externus) is the largest part of the Quadriceps femoris. It arises by a broad aponeurosis, which is attached to the upper part of the intertrochanteric line, to the anterior and inferior borders of the greater trochanter, to the lateral lip of the gluteal tuberosity, and to the upper half of the lateral lip of the linea aspera; this aponeurosis covers the upper three-fourths of the muscle, and from its deep surface many fibers take origin. A few additional fibers arise from the tendon of the Glutæus maximus, and from the lateral intermuscular septum between the Vastus lateralis and short head of the Biceps femoris. The fibers form a large fleshy mass, which is attached to a strong aponeurosis, placed on the deep surface of the lower part of the muscle: this aponeurosis becomes contracted and thickened into a flat tendon inserted into the lateral border of the patella, blending with the Quadriceps femoris tendon, and giving an expansion to the capsule of the knee-joint.

The Vastus medialis and Vastus intermedius appear to be inseparably united, but when the Rectus femoris has been reflected a narrow interval will be observed extending upward from the medial border of the patella between the two muscles, and the separation may be continued as far as the lower part of the intertrochanteric line, where, however, the two muscles are frequently continuous.

The Vastus medialis (Vastus internus) arises from the lower half of the intertrochanteric line, the medial lip of the linea aspera, the upper part of the medial supracondylar line, the tendons of the Adductor longus and the Adductor magnus and the medial intermuscular septum. Its fibers are directed downward and forward, and are chiefly attached to an aponeurosis which lies on the deep surface of the muscle and is inserted into the medial border of the patella and the Quadriceps femoris tendon, an expansion being sent to the capsule of the knee-joint.

The Vastus intermedius (Crureus) arises from the front and lateral surfaces of the body of the femur in its upper two-thirds and from the lower part of the lateral intermuscular septum. Its fibers end in a superficial aponeurosis, which forms the deep part of the Quadriceps femoris tendon. [1]

All four quadriceps are powerful extensors of the knee joint. They are crucial in walking, running, jumping and squatting.   The medial femoral muscles (adductors)

Deep muscles of the medial femoral region. [1]

The adductors are the muscles of the groin.

The Adductor longus, the most superficial of the three Adductores, is a triangular muscle, lying in the same plane as the Pectineus. It arises by a flat, narrow tendon, from the front of the pubis, at the angle of junction of the crest with the symphysis; and soon expands into a broad fleshy belly. This passes downward, backward, and lateralward, and is inserted, by an aponeurosis, into the linea aspera, between the Vastus medialis and the Adductor magnus, with both of which it is usually blended. [1]

The Adductor brevis is situated immediately behind the two preceding muscles. It is somewhat triangular in form, and arises by a narrow origin from the outer surfaces of the superior and inferior rami of the pubis, between the Gracilis and Obturator externus. Its fibers, passing backward, lateralward, and downward, are inserted, by an aponeurosis, into the line leading from the lesser trochanter to the linea aspera and into the upper part of the linea aspera, immediately behind the Pectineus and upper part of the Adductor longus. [1]

The Adductor magnus is a large triangular muscle, situated on the medial side of the thigh. It arises from a small part of the inferior ramus of the pubis, from the inferior ramus of the ischium, and from the outer margin of the inferior part of the tuberosity of the ischium. Those fibers which arise from the ramus of the pubis are short, horizontal in direction, and are inserted into the rough line leading from the greater trochanter to the linea aspera, medial to the Glutæus maximus; those from the ramus of the ischium are directed downward and lateralward with different degrees of obliquity, to be inserted, by means of a broad aponeurosis, into the linea aspera and the upper part of its medial prolongation below. The medial portion of the muscle, composed principally of the fibers arising from the tuberosity of the ischium, forms a thick fleshy mass consisting of coarse bundles which descend almost vertically, and end about the lower third of the thigh in a rounded tendon which is inserted into the adductor tubercle on the medial condyle of the femur, and is connected by a fibrous expansion to the line leading upward from the tubercle to the linea aspera. At the insertion of the muscle, there is a series of osseoaponeurotic openings, formed by tendinous arches attached to the bone. The upper four openings are small, and give passage to the perforating branches of the profunda femoris artery. The lowest is of large size, and transmits the femoral vessels to the popliteal fossa. [1]   Muscles of the leg

The calf muscle consists of the soleus muscle and the gastrocnemius muscle.

The gastrocnemius is a powerful superficial bipennate muscle that is in the back part of the lower leg. It is primarily involved in running, jumping and other "fast" movements of leg, while to a lesser degree involved in walking and standing. This is due to the large degree of white muscle fibers present in the gastrocnemius. This is as opposed to the soleus, which has a larger degree of red muscle fibers and is the primarily activated muscle during the action of standing still, as has been through EMG studie

3.5.11   The respiratory system

Model of a lung.

As you pull down, the air in the bottle spreads out to fill the new space and thus becomes less dense. The air outside the bottle then fills the ballon simply by flowing from high to low pressure in order to rebalance the system.

When we inhale, our diaphragm moves downwards and our ribcage expands, enlarging the chest cavity and creating a lower air pressure inside our lungs. Air flows in due to the pressure difference.

Exhaling is largely a matter of relaxing the muscles used to inhale.

3.5.12   The skeletal system


A skeleton of a human.

The skeleton (from Greek σκελετός, skeletos "dried up") is the body part that forms the supporting structure of an organism and provides protection for the body's internal organs.

In the human body at birth, there are over 270 bones,[1] but many of these fuse together during development, leaving a total of 206 separate bones in the adult. The largest bone in the body is the thigh-bone (femur) and the smallest is the stapes in the middle ear.

The point where bones connect to one another is called a joint, and this connection is made mostly by ligaments (along with the help of muscles).

The study of the skeletal system is called osteology.


The skeleton may divided into the trunk and the limbs. [1]

In most vertebrates, the main skeletal component is referred to as bone.   Lower extremity

The major (long) bones of the human leg are the femur (thighbone), tibia (shinbone), and fibula (the smaller, rear calf bone). The patella (kneecap) is the bone in front of the knee.   Hip bone

The hip bone is a large, flattened, irregularly shaped bone, constricted in the center and expanded above and below. [1]

Three of the bones of the pelvis fuse into the hip bone in adults.   Pelvis

The pelvis, so called from its resemblance to a basin, is a bony ring, interposed between the movable vertebræ of the vertebral column which it supports, and the lower limbs upon which it rests; it is stronger and more massively constructed than the wall of the cranial or thoracic cavities, and is composed of four bones: the two `hip bones`_ laterally and in front and the sacrum and coccyx behind. [1]

The ischium forms the lower and back part of the hip bone. The ischial tuberosity is a large swelling posteriorly on the superior ramus of the ischium_.

4   Properties

Language is a universal property of humans.

5   Growth


Human body proportion changes with age.

6   Classification

7   Behavior

Human behavior is studied as part of psychology.

Affectation is behavior, speech, or writing that is artificial and designed to impress.

For example, the pitch of voices of many gay men disappears when recovering from anesthesia, indicating that their pitch is conditioned rather than physical.

8   Homeostasis

8.1   Thermoregulation

Despite variety between humans, every body has a healthy body temperature between 97°F (36.1°C) to 99°F (37.2°C), centering on 98.6F because temperature can drastically affect how proteins work; higher temperatures can render proteins completely non-functional (thinking of denaturing the proteins of an egg when cooking it), if not outright destroying them. A narrow temperature range provides the best performance for the body's proteins. This temperature is maintained by the hypothalamus_, which tries to keep the body at peak performance: in that narrow temperature range.

Similarly, many cellular functions have narrow ranges -- electrolytes such as potassium, sodium, magnesium and metabolic levels like pH, carbon dioxide, sodium bicarbonate, all have very narrow ranges that can cause significant malfunctions and death if outside of these ranges.

Except for fish, cold-blooded animals (e.g. insects and reptiles_) often get lethargic when it's chilly too.

8.2   Salt regulation

The saline usually used in IV drips for rehydration is close to isotonic - that is, the amount of 'salt' is approximately the same as what's in the blood stream. This prevent 'diluting' the blood (i.e. causing hyponatraemia etc) and/or causing excessive fluid redistribution to the various compartments.

In a way, it's similar to how sports drinks can have some salt in them without causing dehydration.

On the other hand, the salt water you're probably thinking of is something like sea water, which is hypertonic. Although drinking it doesn't really 'harm us' per se, it doesn't rehydrate us. This is because urine has to be excreted in order to maintain osmolarity.

Certain receptors detect when there's too much 'salt' in the blood and concentrated urine is excreted (bringing the osmolarity back down to normal). However, there's a limit to how concentrated our kidneys can make urine, so the amount of water we gained from drinking sea water is less than the amount of urine that had to be excreted - thus increasing the level of dehydration.

9   Lifespan


Causes of death, 2015. Global Burden of Disease Study (GBD) 2015.


10   History

Over past 126,000 years, as humans showed up on new continents, they wiped out the `Ice Age`_ megafauna_.

10.1   Theories

10.1.1   Great Man theory

The history of the world is but the biography of great men. - Thomas Carlyle

Popular in the 1840s. Criticized in 1860 by Herbert Spencer.

Related to trait theory.

Related out Outlier by Gladwell.

10.1.2   Zeitgeist

Opposed to great man theory.

Related to paradigm.

If Charles Darwin had not lived, his theory of evolution would still have been published. The British naturalist, Alfred Wallace, had come to almost exactly the same theory as Darwin concerning natural selection. They jointly presented their idea to the public. If Darwin had not lived there still would have been advocates for evolution produced simply by the zeitgeist of the time period and the spurring of new thoughts and ideas outside of the usual biblical explanations for differential species existence. Zeitgeist of the time shows that natural selection would still have been introduced to the public.

Zeitgeist seems to have support from the fact that many discoveries are found in parallel and independently.

10.1.3   Future

Philosopher Nick Bostrom describes four possible patterns for the future of humanity [4]:

  1. Recurrent collapse, a neverending alternation between prosperity and ruin.
  2. Plateau, the whole world will converge toward a plateau of development similar to the life of the richest countries today. It's unclear this can last without new technology, since stagnation is likely to erupt into conflict.
  3. Extinction, a collapse so devastating that we won't survive it
  4. Takeoff, accelerating takeoff toward a much better future. The most dramatic form of this is called the singularity.

10.2   History

The word "history" generally refers to the time of written evidence. Prehistory, then, is the entire period preceding written records and evidence. This, like the terms Neolithic, Chalcolithic, etc., mean different windows of time in different places. In Egypt and Sumeria, "history" stretches back to nearly 4,000 BC, while in Greece, "history" doesn't start until about 2,500 BC, and we don't understand any of the written records before about 1,500 BC.

Paleolithic, Mesolithic, Neolithic, and Chalcolithic are all specialized terms referring to specific cultural developments, mainly in the use of tools and methods of acquiring food and shelter, so none of these is a generic "catch-all" term you could swap for "prehistoric". These are all a progression of periods in the prehistory or early history of many different cultures, none of which happened at the same time everywhere.

While the civilizations of the Middle East were using bronze as early as 2,000 BC, and were thus then in the Chalcolithic stage of development, the indigenous population of North America were still in the Neolithic stage in 1500 AD.

10.2.1   Pre-history

Humans (Homo sapiens) evolved about 200,000 years ago in Africa. There is significant archeological evidence that controlling fire and cooking food predates this by about 200,000 to 800,000 years. The first species known to have controlled fire and cooked their food is Homo erectus

We do notice an interesting shift in the physiology of the hominin lineage around the time when Homo erectus began to control fire and cook food. Mainly in that brain size began to increase dramatically...therefore it has been hypothesized that the increase in caloric intake associated with a cooked food diet allowed Homo erectus to be able to take some of that extra energy and divert it towards a larger and more powerful brain. Brains require a lot of energy to run, and while prior to Homo erectus we see the beginnings of a trend towards larger brains it kinda plateaus...we think a cooked food diet allowed Homo erectus to take in more calories which in turn took away the roadblock that was preventing further brain growth in that species. Cooked food diets provide more calories than raw diets.

10.2.2   Old world   Postclassical Era (Middle Ages) 400-1450

In the history of Western Europe, the fall in 476 CE of Romulus Augustulus, by some reckonings the last western Roman emperor, is commonly taken as signaling the end of Antiquity and the start of the Middle Ages. (By contrast, Eastern Europe saw a transition from the Roman Empire to the Byzantine Empire, which did not decline until much later.)   The Renaissance

The Renaissance was a period in European history from the 14th century to the 17th century regarded as the cultural bridge between the Middle Ages and modern history. It started as a cultural movement in Italy in the Late Medieval period and later spread to the rest of Europe, marking the beginning of the Early Modern Age.

The intellectual basis of the Renaissance was its own invented version of humanism, derived from the rediscovery of classical Greek philosophy, such as that of Protagoras, who said that "Man is the measure of all things." This new thinking became manifest in art, architecture, politics, science and literature.   Early Modern (1400-1700)

In the mid-15th century, Johannes Gutenberg's invention of modern printing,[24] employing movable type, revolutionized communication, helping end the Middle Ages and usher in the Scientific Revolution

Includes the Age of Enlightenment.

The scientific revolution was the emergence of modern science during the early modern period, when developments in mathematics, physics, astronomy, biology (including human anatomy) and chemistry transformed views of society and nature

According to traditional accounts, the scientific revolution began in Europe towards the end of the Renaissance era and continued through the late 18th century, influencing the intellectual social movement known as the Enlightenment

While its dates are disputed, the publication in 1543 of Nicolaus Copernicus's De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres) and Andreas Vesalius's De humani corporis fabrica (On the Fabric of the Human body) is often cited as marking the beginning of the scientific revolution. By the end of the 18th century, the scientific revolution had given way to the "Age of Reflection".   Protestant Reformation (1517-1648)

The Protestant Reformation was a schism from the Roman Catholic Church initiated by Martin Luther and continued by John Calvin.

Martin Luther published his Ninety-five Theses in 1517 in Germany.   Romanticism

Romanticism (the “Age of Reflection”) was an intellectual movement, 1800–40, that originated in Western Europe as a counter-movement to the late-18th-century Enlightenment.

10.2.3   Late Modern

By the 18th century, the accumulation of knowledge and technology, especially in Europe, had reached a critical mass that brought about the Industrial Revolution.

Industrial revolution to the present.

10.2.4   The Enlightenment (1715 - 1789)

The Enlightenment was an intellectual movement which dominated the world of ideas in Europe in the 18th century. The Enlightenment included a range of ideas centered on reason as the primary source of authority and legitimacy, and came to advance ideals such as liberty, progress, tolerance, fraternity, constitutional government, and separation of church and state.

The most influential publication of the Enlightenment was the Encyclopédie (Encyclopaedia). Published between 1751 and 1772 in thirty-five volumes, it was compiled by Denis Diderot, Jean le Rond d'Alembert (until 1759), and a team of 150 scientists and philosophers and it helped spread the ideas of the Enlightenment across Europe and beyond.

10.2.5   Romantic era (1800 - 1850)

Romanticism (also the Romantic era or the Romantic period) was an artistic, literary, musical and intellectual movement that originated in Europe toward the end of the 18th century and in most areas was at its peak in the approximate period from 1800 to 1850. Romanticism was characterized by its emphasis on emotion and individualism as well as glorification of all the past and nature, preferring the medieval rather than the classical. It was partly a reaction to the Industrial Revolution, the aristocratic social and political norms of the Age of Enlightenment, and the scientific rationalization of nature.

10.2.6   Contemporary

On 9 August 1945, an atom bomb fell on Nagasaki in Japan, bringing WWII to a close.

11   Further reading

12   References

[1](1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19) Henry Gray. Anatomy of the Human Body.
[2](1, 2, 3) Thats_Justice. Deltoids 101: An Anatomical Guide to Training.
[3]Mark Rippetoe. 2005. Starting Strength.
[4]Peter Thiel, Blake Masters. 2015. Zero to One: Notes on startups, or how to build the future.
[6](1, 2, 3, 4, 5, 6, 7, 8, 9) Paul Deurenberg. 2009. Body Composition.
[7](1, 2, 3, 4, 5, 6, 7) Max Roser. June 26, 2018. Memorizing these three statistics will help you understand the world.
[8](1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) A.K.Roy Choudhury, P.K. Majumdar, and C. Datta. 2011. Woodhead Publising Limited. Factors affecting comfort: human physiologic and the role of clothing.

One of the most surprising, and perhaps confounding, facts of charity in America is that the people who can least afford to give are the ones who donate the greatest percentage of their income. In 2011, the wealthiest Americans—those with earnings in the top 20 percent—contributed on average 1.3 percent of their income to charity. By comparison, Americans at the base of the income pyramid—those in the bottom 20 percent—donated 3.2 percent of their income. The relative generosity of lower-income Americans is accentuated by the fact that, unlike middle-class and wealthy donors, most of them cannot take advantage of the charitable tax deduction, because they do not itemize deductions on their income-tax returns.

'But why? Lower-income Americans are presumably no more intrinsically generous (or “prosocial,” as the sociologists say) than anyone else. However, some experts have speculated that the wealthy may be less generous—that the personal drive to accumulate wealth may be inconsistent with the idea of communal support. Last year, Paul Piff, a psychologist at UC Berkeley, published research that correlated wealth with an increase in unethical behavior: “While having money doesn’t necessarily make anybody anything,” Piff later told New York magazine, “the rich are way more likely to prioritize their own self-interests above the interests of other people.”

In a series of controlled experiments, lower-income people and people who identified themselves as being on a relatively low social rung were consistently more generous with limited goods than upper-class participants were. Notably, though, when both groups were exposed to a sympathy-eliciting video on child poverty, the compassion of the wealthier group began to rise, and the groups’ willingness to help others became almost identical.

If Piff’s research suggests that exposure to need drives generous behavior, could it be that the isolation of wealthy Americans from those in need is a cause of their relative stinginess? Patrick Rooney, the associate dean at the Indiana University School of Philanthropy, told me that greater exposure to and identification with the challenges of meeting basic needs may create “higher empathy” among lower-income donors. His view is supported by a recent study by The Chronicle of Philanthropy, in which researchers analyzed giving habits across all American ZIP codes. Consistent with previous studies, they found that less affluent ZIP codes gave relatively more. round Washington, D.C., for instance, middle- and lower-income neighborhoods, such as Suitland and Capitol Heights in Prince George’s County, Maryland, gave proportionally more than the tony neighborhoods of Bethesda, Maryland, and McLean, Virginia. But the researchers also found something else: differences in behavior among wealthy households, depending on the type of neighborhood they lived in. Wealthy people who lived in homogeneously affluent areas—areas where more than 40 percent of households earned at least $200,000 a year—were less generous than comparably wealthy people who lived in more socioeconomically diverse surroundings. It seems that insulation from people in need may dampen the charitable impulse.Go Wealth affects not only how much money is given but to whom it is given. The poor tend to give to religious organizations and social-service charities, while the wealthy prefer to support colleges and universities, arts organizations, and museums. Of the 50 largest individual gifts to public charities in 2012, 34 went to educational institutions, the vast majority of them colleges and universities, like Harvard, Columbia, and Berkeley, that cater to the nation’s and the world’s elite. Museums and arts organizations such as the Metropolitan Museum of Art received nine of these major gifts, with the remaining donations spread among medical facilities and fashionable charities like the Central Park Conservancy.

But our charity system is also fundamentally regressive, and works in favor of the institutions of the elite. The pity is, most people still likely believe that, as Michael Bloomberg once said, “there’s a connection between being generous and being successful.” There is a connection, but probably not the one we have supposed.

Why the Rich Don't Give to Charity KEN STERNMAR 20 2013, 9:50 PM ET


What best distinguishes our species is an ability that scientists are just beginning to appreciate: We contemplate the future. Our singular foresight created civilization and sustains society. It usually lifts our spirits, but it’s also the source of most depression and anxiety, whether we’re evaluating our own lives or worrying about the nation.

A more apt name for our species would be Homo prospectus, because we thrive by considering our prospects. The power of prospection is what makes us wise. Looking into the future, consciously and unconsciously, is a central function of our large brain, as psychologists and neuroscientists have discovered — rather belatedly, because for the past century most researchers have assumed that we’re prisoners of the past and the present.

Behaviorists thought of animal learning as the ingraining of habit by repetition. Psychoanalysts believed that treating patients was a matter of unearthing and confronting the past. Even when cognitive psychology emerged, it focused on the past and present — on memory and perception.

But it is increasingly clear that the mind is mainly drawn to the future, not driven by the past. Behavior, memory and perception can’t be understood without appreciating the central role of prospection. We learn not by storing static records but by continually retouching memories and imagining future possibilities. Our brain sees the world not by processing every pixel in a scene but by focusing on the unexpected.

Our emotions are less reactions to the present than guides to future behavior. Therapists are exploring new ways to treat depression now that they see it as primarily not because of past traumas and present stresses but because of skewed visions of what lies ahead.

Some of our unconscious powers of prospection are shared by animals, but hardly any other creatures are capable of thinking more than a few minutes ahead. Squirrels bury nuts by instinct, not because they know winter is coming. Ants cooperate to build dwellings because they’re genetically programmed to do so, not because they’ve agreed on a blueprint. Chimpanzees have sometimes been known to exercise short-term foresight, like the surly male at a Swedish zoo who was observed stockpiling rocks to throw at gawking humans, but they are nothing like Homo prospectus.

If you’re a chimp, you spend much of the day searching for your next meal. If you’re a human, you can usually rely on the foresight of your supermarket’s manager, or you can make a restaurant reservation for Saturday evening thanks to a remarkably complicated feat of collaborative prospection. You and the restaurateur both imagine a future time — “Saturday” exists only as a collective fantasy — and anticipate each other’s actions. You trust the restaurateur to acquire food and cook it for you. She trusts you to show up and give her money, which she will accept only because she expects her landlord to accept it in exchange for occupying his building.

The central role of prospection has emerged in recent studies of both conscious and unconscious mental processes, like one in Chicago that pinged nearly 500 adults during the day to record their immediate thoughts and moods. If traditional psychological theory had been correct, these people would have spent a lot of time ruminating. But they actually thought about the future three times more often than the past, and even those few thoughts about a past event typically involved consideration of its future implications.

When making plans, they reported higher levels of happiness and lower levels of stress than at other times, presumably because planning turns a chaotic mass of concerns into an organized sequence. Although they sometimes feared what might go wrong, on average there were twice as many thoughts of what they hoped would happen.

While most people tend to be optimistic, those suffering from depression and anxiety have a bleak view of the future — and that in fact seems to be the chief cause of their problems, not their past traumas nor their view of the present. While traumas do have a lasting impact, most people actually emerge stronger afterward. Others continue struggling because they over-predict failure and rejection. Studies have shown depressed people are distinguished from the norm by their tendency to imagine fewer positive scenarios while overestimating future risks.

They withdraw socially and become paralyzed by exaggerated self-doubt. A bright and accomplished student imagines: If I flunk the next test, then I’ll let everyone down and show what a failure I really am. Researchers have begun successfully testing therapies designed to break this pattern by training sufferers to envision positive outcomes (imagine passing the test) and to see future risks more realistically (think of the possibilities remaining even if you flunk the test).

Most prospection occurs at the unconscious level as the brain sifts information to generate predictions. Our systems of vision and hearing, like those of animals, would be overwhelmed if we had to process every pixel in a scene or every sound around us. Perception is manageable because the brain generates its own scene, so that the world remains stable even though your eyes move three times a second. This frees the perceptual system to heed features it didn’t predict, which is why you’re not aware of a ticking clock unless it stops. It’s also why you don’t laugh when you tickle yourself: You already know what’s coming next.

Behaviorists used to explain learning as the ingraining of habits by repetition and reinforcement, but their theory couldn’t explain why animals were more interested in unfamiliar experiences than familiar ones. It turned out that even the behaviorists’ rats, far from being creatures of habit, paid special attention to unexpected novelties because that was how they learned to avoid punishment and win rewards.

The brain’s long-term memory has often been compared to an archive, but that’s not its primary purpose. Instead of faithfully recording the past, it keeps rewriting history. Recalling an event in a new context can lead to new information being inserted in the memory. Coaching of eyewitnesses can cause people to reconstruct their memory so that no trace of the original is left.

The fluidity of memory may seem like a defect, especially to a jury, but it serves a larger purpose. It’s a feature, not a bug, because the point of memory is to improve our ability to face the present and the future. To exploit the past, we metabolize it by extracting and recombining relevant information to fit novel situations.

This link between memory and prospection has emerged in research showing that people with damage to the brain’s medial temporal lobe lose memories of past experiences as well as the ability to construct rich and detailed simulations of the future. Similarly, studies of children’s development show that they’re not able to imagine future scenes until they’ve gained the ability to recall personal experiences, typically somewhere between the ages of 3 and 5.

Even when you’re relaxing, your brain is continually recombining information to imagine the future, a process that researchers were surprised to discover when they scanned the brains of people doing specific tasks like mental arithmetic. Whenever there was a break in the task, there were sudden shifts to activity in the brain’s “default” circuit, which is used to imagine the future or retouch the past.

This discovery explains what happens when your mind wanders during a task: It’s simulating future possibilities. That’s how you can respond so quickly to unexpected developments. What may feel like a primitive intuition, a gut feeling, is made possible by those previous simulations.

Your brain engages in the same sort of prospection to provide its own instant answers, which come in the form of emotions. The main purpose of emotions is to guide future behavior and moral judgments, according to researchers in a new field called prospective psychology. Emotions enable you to empathize with others by predicting their reactions. Once you imagine how both you and your colleague will feel if you turn down his invitation, you intuitively know you’d better reply, “Sure, thanks.”

TIL most Koreans don't produce body odor due to large scale dominance of the gene ABCC11. As a consequence, deodorant is a rare commodity.

Apes do not ask questions, even when they learn sign language. They don't seem to realize other entities can know things they don't.