Human beings, humans, or Homo sapiens sapiens (Homo sapiens is latin and refers to the wise or knowing human) are bipedal primates in the family Hominidae. DNA evidence indicates that modern humans originated in Africa about 250,000 years ago. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and emotion. This mental capability, combined with an erect body carriage that frees the forelimbs (arms) for manipulating objects, has allowed humans to make far greater use of tools than any other species. Humans currently inhabit every continent on Earth, except Antarctica (although several governments maintain seasonally-staffed research stations there). Humans also now have a continuous presence in low Earth orbit, occupying the International Space Station. The human population on Earth is greater than 6.7 billion, as of July, 2008.

 

 
  Like most primates, humans are social by nature. However, they are particularly adept at utilizing systems of communication for self-expression, exchanging of ideas, and organization. Humans create complex social structures composed of many cooperating and competing groups, from families to nations. Social interactions between humans have established an extremely wide variety of traditions, rituals, ethics, values, social norms, and laws, which together form the basis of human society. Humans have a marked appreciation for beauty and aesthetics, which, combined with the desire for self-expression, has led to innovations such as culture, art, literature and music. 

 

 
 Humans are notable for their desire to understand and influence the world around them, seeking to explain and manipulate natural phenomena through science, philosophy, mythology and religion. This natural curiosity has led to the development of advanced tools and skills; humans are the only currently known species known to build fires, cook their food, clothe themselves, and manipulate and develop numerous other technologies. Humans pass down their skills and knowledge to the next generations through education. 

 

 
 The scientific study of human evolution encompasses the development of the genus Homo, but usually involves studying other hominids and hominines as well, such as Australopithecus. Modern humans are defined as the Homo sapiens species, of which the only extant subspecies - our own - is known as Homo sapiens sapiens. Homo sapiens idaltu (roughly translated as elder wise human), the other known subspecies, is now extinct. Anatomically modern humans first appear in the fossil record in Africa about 130,000 years ago, although studies of molecular biology give evidence that the approximate time of divergence from the common ancestor of all modern human populations was 200,000 years ago. 

 

 
 The closest living relatives of Homo sapiens are the two chimpanzee species: the Common Chimpanzee and the Bonobo. Full genome sequencing has resulted in the conclusion that after 6.5 [million] years of separate evolution, the differences between chimpanzee and human are just 10 times greater than those between two unrelated people and 10 times less than those between rats and mice. Suggested concurrence between human and chimpanzee DNA sequences range between 95% and 99%. It has been estimated that the human lineage diverged from that of chimpanzees about five million years ago, and from that of gorillas about eight million years ago. However, a hominid skull discovered in Chad in 2001, classified as Sahelanthropus tchadensis, is approximately seven million years old, which may indicate an earlier divergence. 

 

 
 The Recent African Origin (RAO), or the - out-of-Africa-, hypothesis proposes that modern humans evolved in Africa before later migrating outwards to replace hominids in other parts of the world. Evidence from archaeogenetics accumulating since the 1990s has lent strong support to RAO, and has marginalized the competing multiregional hypothesis, which proposed that modern humans evolved, at least in part, from independent hominid populations. Geneticists Lynn Jorde and Henry Harpending of the University of Utah propose that the variation in human DNA is minute compared to that of other species. They also propose that during the Late Pleistocene, the human population was reduced to a small number of breeding pairs, no more than 10,000, and possibly as few as 1,000, resulting in a very small residual gene pool. Various reasons for this hypothetical bottleneck have been postulated, one being the Toba catastrophe theory. 

 

 
 Human evolution is characterized by a number of important morphological, developmental, physiological and behavioural changes, which have taken place since the split between the last common ancestor of humans and chimpanzees. The first major morphological change was the evolution of a bipedal locomotor adaptation from an arboreal or semi-arboreal one, with all its attendant adaptations, such as a valgus knee, low intermembral index (long legs relative to the arms), and reduced upper-body strength. 

 

 
 Later, ancestral humans developed a much larger brain – typically 1,400 cm³ in modern humans, over twice the size of that of a chimpanzee or gorilla. The pattern of human postnatal brain growth differs from that of other apes (heterochrony), and allows for extended periods of social learning and language acquisition in juvenile humans. Physical anthropologists argue that the differences between the structure of human brains and those of other apes are even more significant than their differences in size. 

 

 
 Other significant morphological changes included: the evolution of a power and precision grip; a reduced masticatory system; a reduction of the canine tooth; and the descent of the larynx and hyoid bone, making speech possible. An important physiological change in humans was the evolution of hidden oestrus, or concealed ovulation, which may have coincided with the evolution of important behavioural changes, such as pair bonding. Another significant behavioural change was the development of material culture, with human-made objects becoming increasingly common and diversified over time. The relationship between all these changes is the subject of ongoing debate. 

 

 
 The forces of natural selection continue to operate on human populations, with evidence that certain regions of the genome display directional selection in the past 15,000 years. 

 

 
 This description from WikiPedia, 3rd August 2008: http://en.wikipedia.org/wiki/Homo_sapiens

 

Kidneys of humans filter impurities by use of a dual membrane system.

       
  "Using a system based on the human body's kidneys - the ultimate in water recycling technology - Singapore and Orange County, CA have developed schemes that will use a dual membrane process to recycle domestic waste water (sewage) to levels that approach the quality of distilled water. Like the kidney, these recycling plants use two membranes, one with larger holes to remove micro-organisms such as protozoa and bacteria that cause infection, while the second separates salt from water." (Courtesy of the Biomimicry Guild)

  Learn more about this functional adaptation.

 

The circulatory system of humans prevents blood loss from wounds by sending platelets to block the hole.

   
  "Just as the human circulatory system sends platelets to a wound to prevent blood loss, oil pipelines can now transport special polymers that 'clot' oil at the site of a leak. Drawn by the pressure of the escaping liquid, these polymers press against the opening and form a temporary seal. Because each 'platelet' is electronically tagged, engineers can determine the exact location of a leak, and can repair the pipeline while it continues to operate. The technology, called Advanced Technology for Leak Location and Sealing System (ATLLASTM), works in any pressurized flow system. In addition to oil pipelines, it may prove useful in the water and chemical industries." (Courtesy of the Biomimicry Guild)

  Learn more about this functional adaptation.

 

Skin of humans serves multiple functions (sensing, healing, actuation, etc.) because of integrated components that all work together.

       
  "Nature offers numerous examples of materials that serve multiple functions. Biological materials routinely contain sensing, healing, actuation, and other functions built into the primary structures of an organism. The human skin, for instance, consists of many layers of cells, each of which contains oil and perspiration glands, sensory receptors, hair follicles, blood vessels, and other components with functions other than providing the basic structure and protection for the internal organs. These structures have evolved in nature over eons to the level of seamless integration and perfection with which they serve their functions." (Bar-Cohen 2006:310)
  Learn more about this functional adaptation.

 

Neurons aid organisms in reacting to environmental stimuli because they collaborate to sense the environment, share information, and filter unimportant information

       
  "Feng Zhao, a computer scientist at Xerox's Palo Alto Research Center, proposes equipping machinery and structures with 'collaborating sensors' reminiscent of neurons. These sensors would respond adaptively to the physical environment, infer the needs of their human operators, share information within the network, and filter out unimportant details. A building or piece of equipment containing these sensors would behave almost organically." (Courtesy of the Biomimicry Guild)
  Learn more about this functional adaptation.

 

Alveoli in lungs improve gas exchange by increasing the surface area of the lungs.

   
  "Our lungs are the functional interface between us and the atmosphere. The capacity of a pair of lungs is about 6 liters, but this modest volume, divided among three hundred million alveoli, is bounded by a surface of 50-100 square meters, about the floor area of a large classroom." (Vogel 2003:47)
  Learn more about this functional adaptation.

 

The blood of humans distributes oxygen through the body via hemoglobin with adjustable oxygen affinity.

   
  "Nature has evolved in ways that, at the molecular scale, make inventive and elegant uses of chemistry. To take an example more or less at random, the use of allosteric effects by haemoglobin to fine-tune the protein's affinity for oxygen in different environments is exquisite. Imagine trying to design from first principles a system with haemoglobin's oxygen-sensitive oxygen affinity—there is not at all an obvious solution, and the engineer's answer would be likely to involve a cumbersome system of sensors and switches." (Ball 2002:15)
  Learn more about this functional adaptation.

 

The fingertips of humans are extremely sensitive to fine textures, in part due to the unique dermal ridges found on each fingertip.

     
  "Human fingertips, probably the most sensitive skin areas in the animal world, can distinguish between a smooth glass surface and one bearing grooves only 63,000 mm deep…The flexibility of the skin, together with the fine ridges, enable the fingers to grip objects and manipulate them. The pattern of dermal ridges is unique to each individual human being, and even to each finger…" (Foy and Oxford Scientific Films 1982:77)
  Learn more about this functional adaptation.

 

Lubricating synovial fluid in joints protects from friction via a brush-like phase of charged macromolecules.

   
  "It is proposed that the extremely efficient lubrication observed in living joints arises from the presence of a brush-like phase of charged macromolecules at the surface of the superficial zone. This phase forms when charged macromolecules, including lubricin, superficial-zone protein, and aggrecan, cross the interface between the superficial zone and the synovial cavity as they are secreted into the synovium from within the bulk of the cartilage, and, in particular, the feasibility of such brush-like surface-phases is examined in some detail. The molecular mechanisms for the reduction in friction are proposed to be similar to those recently revealed using surface force balance studies on lubrication by charged brushes." (Klein 2006:691)
  Learn more about this functional adaptation.

 

The skin of humans protects from water loss in part due to fibrous structural proteins (keratins) and cross-linking.

   
  "The vertebrate integument represents an evolutionary compromise between the needs for mechanical protection and those of sensing the environment and regulating the exchange of materials and energy. Fibrous keratins evolved as a means of strengthening the integument while simultaneously providing a structural support for lipids, which comprise the principal barrier to cutaneous water efflux in terrestrial taxa…How do the structural features of keratin influence its resistance to water movement? Generally, structural features that alter the free volume (equivalent to pores or channels) should alter the permeation of water molecules accordingly. Resistance to diffusion is affected by the molecular mass of side chains and tends to increase with cross-linking beyond certain critical levels (Lieberman et al., 1972)…The stability of cross-linkages is dependent on a large number of intermolecular forces, including covalent, ionic, and hydrogen bonding in addition to van der Waals attractive forces between non-polar amino acid side chains. All of these act to influence the mobility and free volumes of the structure…Studies of human skin have indeed demonstrated that gradients of water exist in the stratum corneum (Warner et al., 1988; Bommannan et al., 1990; Caspers et al., 2001; Bouwstra et al., 2003a). Fourier transform infrared spectroscopy has demonstrated that free water content in stratum corneum is greater in central regions relative to superficial and deeper cell layers at moderate levels of hydration (57%–87%, w/w), whereas at higher levels of hydration (300% w/w) water swells corneocytes in a direction perpendicular to the skin surface except for the deepest cell layers adjacent to the viable epidermis (Bouwstra et al., 2003a). While the mechanism excluding free water from the deeper cell layers of stratum corneum is not understood, it is speculated to play a role in preventing dehydration of the viable epidermis. In relatively dry conditions (18%–26% w/w), only bound water is present in the stratum corneum (Bulgin and Vinson, 1967; Hansen and Yellin, 1972; Bouwstra et al., 2003a)." (Lillywhite 2006:202, 212, 213)
  Learn more about this functional adaptation.

 

The aortic valve in vertebrate hearts allows the tissue to expand under high pressures by having elastic properties.

   
  "THE human aortic valve consists of three cusps made of relatively inelastic, muscle-free material about 0.15 mm thick. It opens and shuts about once a second, and withstands a pressure difference of 100 mm of mercury when closed. It usually functions for 70 yr without failure, and works so efficiently that very little blood is regurgitated at each pulse. In order to support this large pressure difference, the cusps must close simultaneously in all operating conditions and should not touch the wall of the aorta, for considerable reversed flow would then be required to close the valve. This action suggests a fluid dynamic control mechanism which positions the cusps away from the wall of the aorta, so that the slightest reversed flow will close the valve." (Bellhouse and Bellhouse 1968:86)
  Learn more about this functional adaptation.

 

The spongy bones of humans handle stress efficiently via the distribution of fine strands called trabeculae.

   
  "In some materials, such as metal, stress lines are usually invisible; but in others, including bone, they are often quite easy to see. Some parts of bone are composed of a spongy mesh of very fine strands called trabeculae. In a cross-section of bone the trabeculae can be seen to be orientated to the lines of stress. Where they are most closely packed together, the stress is greatest. It was a section of the top of a human thigh bone that inspired Professor Culmann, a Swiss engineer, to design in 1866, a new crane: he realized that the lines of stress shown by the trabeculae constituted a diagram of how his crane should be designed to cope with similar stress (diagram c)." (Foy and Oxford Scientific Films 1982:35)
  Learn more about this functional adaptation.

 

The muscles of humans flex by the sliding of tethered molecular units over one another.

         
  "Muscle fibers contain comblike arrays of filaments made from chains of the protein actin, with nodes of the myosin protein interdigitated between the combs' teeth. The ends of the filaments are covered with molecular 'motors' that can walk along actin filaments. When this motion is triggered by a nerve signal, the myosin rods become more deeply interdigitated, causing the muscle fiber to shorten." (Courtesy of the Biomimicry Guild)
  Learn more about this functional adaptation.

 

The hairs in human ears convert motion into electrical energy and back in order to amplify sound via the prestin protein.

       
  "A new Cambridge-based venture called IntAct Labs is investigating how to harness the power generating capabilities of life for space applications. It would involve the use of a protein called prestin found in human ear-hair as a means of powering space suits. The protein converts motion into electrical energy -- and if it's augmented with an electricity-conducting microbe, it could form self-healing, semi-living 'skins' that convert Martian wind and even the jogging and walking of astronauts into electricity. Prestin is found in the outer hair cells of the human ear. In the cell membranes of these cells, prestin also converts electrical voltage into motion, elongating and contracting the cell. This movement amplifies sound in the ear." (Courtesy of the Biomimicry Guild)
  Learn more about this functional adaptation.

 

The cochlea of the human ear helps us hear deep vibrations by directing low-frequency waves into the tightest turns of its spiral.

     
  "Deep inside your ear, the pea-size, spiral-shaped cochlea helps translate reverberations from the outside world into neurological signals that we perceive as sound. The cochlea's coil has traditionally been regarded as little more than the body's way of packing a lot of membrane into a small space—a mechanical adaptation that did not affect hearing. Not any more.

Last March a team of engineers found a function for the cochlea's shape. Using a mathematical model, they determined that the tight coil at the cochlea's center steers low-frequency waves into its tightest turns, helping us hear deep vibrations. Previous models had treated sound waves as if they traveled in a straight line, an assumption that failed to take into account how the cochlea's shape affects the waves' path. 'It's the curvature that's critical,' says biophysicist Richard Chadwick at the National Institutes of Health, a collaborator on the project. 'The more the curvature changes, the more focused the energy gets. It's behaving something like a whispering gallery, but even better.'" (Ornes 2006)
  Learn more about this functional adaptation.

 

Smell receptors in the human nose detect smells with the help of a thin mucus layer, which dissolves scents and uses chromatography.

   
  "Humans detect smells using more than 100 million specialised receptors on the roof of the nasal cavity, just behind the bridge of the nose. The complex manner in which multiple receptors react to a molecule is used to identify and differentiate them...the receptors in a human nose are covered in a thin layer of mucus, which helps them detect scents.

"This layer of mucus dissolves scents and separates their components chemically, using chromatography. Different odour molecules then reach receptors at slightly varied times. As a result, the receptors have another way to distinguish between compounds." (Simonite 2007)


"Here, we report on a biologically inspired analytical system that represents a new concept in the field of machine olfaction. Specifically, this paper describes the design and fabrication of a novel sensor system, based upon the principle of 'nasal chromatography', which emulates the human olfactory mucosa. Our approach exploits the physical positioning of a series of broadly tuned sensors (equivalent to the olfactory epithelium) along the length of a planar chromatographic channel (analogous to the thin mucus coating of the nasal cavity) from which we extract both spatial (response magnitude) and temporal (retentive delay) sensor signals. Our study demonstrates that this artificial mucosa is capable of generating both spatial and temporal signals which, when combined, create a novel spatio-temporal representation of an odour. We believe that such a system not only offers improved odour discrimination over a sensor array-based electronic nose, but also shorter analysis times than conventional gas chromatographic techniques." (Gardner et al. 2007:1713)

  Learn more about this functional adaptation.