What is a human?

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This image shows a Singpho couple in traditional costume, Arunachal Pradesh, India. Credit: ahinsajain.

Humans (Homo sapiens),[1][2] the only living members of the genus Homo, are mammals of the primate order originally from Africa, where they reached anatomical modernity about 200,000 years ago and began to exhibit full behavioral modernity around 50,000 years ago.[3]

Theoretical humans[edit]

Young Ibans, or Sea Dayaks, certainly look very fine in gala dress. Credit: Charles Hose.

"[O]ne of the major ongoing questions for scientists investigating human evolution [is] "the lack of a satisfactory biological definition of our own species, Homo sapiens," Curnoe said."[4]

The human condition encompasses the unique and believed to be inescapable features of being human.

It can be described as the irreducible part of humanity that is inherent and not dependent on factors such as gender, race or class. It includes concerns such as the meaning of life, the search for gratification, the sense of curiosity, the inevitability of isolation, or anxiety regarding the inescapability of death.

The humanities are a set of disciplines and fields that help us to understand the nature of the human condition and the broader cultural and social arrangements that make up human lives.

The human condition is the subject of such fields of study as philosophy, theology, sociology, psychology, anthropology, demographics, evolutionary biology, cultural studies, and sociobiology. The philosophical school of existentialism deals with core issues related to the human condition including the ongoing search for ultimate meaning.

Physiology[edit]

The image shows a Bantu couple in 1908. Credit: Thomas Athol Joyce and Northcote Whitridge Thomas.{{free media}}

"The larynx, or voice box, sits lower in the throat in humans than in chimps, one of several features that enable human speech. Human ancestors evolved a descended larynx roughly 350,000 years ago. We also possess a descended hyoid bone — this horseshoe-shaped bone below the tongue, unique in that it is not attached to any other bones in the body, allows us to articulate words when speaking."[5]

"[T]he changes made in our pelvis for moving on two legs ... [and] [t]he lumbar curve in the lower back, which helps us maintain our balance as we stand and walk" are the physiology necessary for upright posture.[6] The construction of the human pelvis differs from other primates, as do the toes. As a result, humans are slower for short distances than most other animals, but are among the best long-distance runners in the animal kingdom.[7]

"[H]umans [have] thinner, shorter, lighter hairs [than] our hairier ape cousins."[8] Although humans appear hairless compared to other primates, with notable hair growth occurring chiefly on the top of the head, underarms and pubic area, the average human has more hair follicles on his or her body than the average chimpanzee. The main distinction is that human hairs are shorter, finer, and less heavily pigmented than the average chimpanzee's, thus making them harder to see.[9]

"[W]e don't have opposable big toes on our feet. ... we can bring our thumbs all the way across the hand to our ring and little fingers. We can also flex the ring and little fingers toward the base of our thumb."[10]

"[O]ur extraordinary brain ... [gives] us the ability to reason and think on our feet beyond the capabilities of the rest of the animal kingdom"[11] Humans are characterized by having a [encephalization] large brain relative to body size, with a particularly well developed neocortex, prefrontal cortex and temporal lobes, making them capable of abstract reasoning, language, introspection, problem solving and culture through social learning.

"[Most of us wear clothing, a fact that makes us unique in the animal kingdom"[12]

"The human ability to control fire would have brought a semblance of day to night, helping our ancestors to see in an otherwise dark world and keep nocturnal predators at bay. The warmth of the flames also helped people stay warm in cold weather, enabling us to live in cooler areas. And of course it gave us cooking, which some researchers suggest influenced human evolution — cooked foods are easier to chew and digest, perhaps contributing to human reductions in tooth and gut size."[13] Humans are the only extant species known to build fires and cook their food, as well as the only known species to clothe themselves and create and use numerous other technologies and arts.

"Humans are the only species known to blush, a behavior Darwin called "the most peculiar and the most human of all expressions." It remains uncertain why people blush, involuntarily revealing our innermost emotions. The most common idea is that blushing helps keep people honest, benefiting the group as a whole."[14]

"Humans must remain in the care of their parents for much longer than other living primates. The question then becomes why, when it might make more evolutionary sense to grow as fast as possible to have more offspring. The explanation may be our large brains, which presumably require a long time to grow and learn."[15] The human life span can be split into a number of stages: infancy, childhood, adolescence, young adulthood, adulthood and old age. The lengths of these stages, however, have varied across cultures and time periods. Compared to other primates, humans experience an unusually rapid growth spurt during adolescence, where the body grows 25% in size. Chimpanzees, for example, grow only 14%, with no pronounced spurt.[16]

"Most animals reproduce until they die, but in humans, females can survive long after ceasing reproduction. This might be due to the social bonds seen in humans — in extended families, grandparents can help ensure the success of their families long after they themselves can have children."[17] Humans are one of the few species in which females undergo menopause. It has been proposed that menopause increases a woman's overall reproductive success by allowing her to invest more time and resources in her existing offspring and/or their children (the grandmother hypothesis), rather than by continuing to bear children into old age.[18][19]

Human DNA[edit]

Main source: Human DNA
A couple from Tanzania in 2015. Credit: David cheyo.{{free media}}

"[H]uman DNA has millions of on-off switches and complex networks that control the genes' activities. ... [A]t least 80% of the human genome is active, which opposed the previously held idea that most of the DNA are useless."[20]

Homo sapiens neanderthalensis[edit]

This is an image of a skull of Neanderthal. Credit: Catherine Brahic.
This abstract cave carving is possibly the first known example of Neanderthal rock art. Credit: Stewart Finlayson.

"Neanderthals (or Neandertals) are our closest extinct human relatives. [They may have been] a subspecies [Homo sapiens neanderthalensis]. Our well-known [...] fossil kin lived in Eurasia 200,000 to 30,000 years ago, in the Pleistocene Epoch. [...] they used tools, buried their dead and controlled fire, among other intelligent behaviors."[21]

"Neanderthals came to Europe some 300,000 years ago. They hunted big game with stone tools. Their territory spanned Europe and Asia. They left distinctive "Mousterian" artefacts."[22]

"Work on material from Italy seems to show human settlers pushing Neanderthals out (see maps). Mousterian tools were common there 45,000 years ago, when human-made Uluzzian material first appeared. By 44,000 years ago, humans were sharing Italy with a dwindling Neanderthal population. By 42,000 years ago, the Neanderthals were gone."[22]

"Around 39,000 years ago, a Neanderthal huddled in the back of a seaside cave at Gibraltar, safe from the hyenas, lions and leopards that might have prowled outside. Under the flickering light of a campfire, he or she used a stone tool to carefully etch what looks like a grid or a hashtag [in the image at the right] onto a natural platform of bedrock."[23]

"This was intentional — this was not somebody doodling or scratching on the surface."[24]

"Neanderthals might have behaved more like Homo sapiens than previously thought: They buried their dead, they used pigments and feathers to decorate their bodies, and they may have even organized their caves."[23]

"Art is something else — it's an indication of abstract thinking."[24]

"In Gorham's Cave, Finlayson and colleagues were surprised to find a series of deeply incised parallel and crisscrossing lines when they wiped away the dirt covering a bedrock surface. The rock had been sealed under a layer of soil that was littered with Mousterian stone tools (a style long linked to Neanderthals). Radiocarbon dating indicated that this soil layer was between 38,500 and 30,500 years old, suggesting the rock art buried underneath was created sometime before then."[23]

"Gibraltar is one of the most famous sites of Neanderthal occupation. At Gorham's Cave and its surrounding caverns, archaeologists have found evidence that Neanderthals butchered seals, roasted pigeons and plucked feathers off birds of prey. In other parts of Europe, Neanderthals lived alongside humans — and may have even interbred with them. But 40,000 years ago, the southern Iberian Peninsula was a Neanderthal stronghold."[23]

"Modern humans had not spread into the area yet."[24]

"More than 50 stone-tool incisions were needed to mimic the deepest line of the grid, and between 188 and 317 total strokes were probably needed to create the entire pattern."[23]

"It's very basic. It's very simple. It's not a Venus. It's not a bison. It's not a horse."[25]

"There is a huge difference between making three lines that any 3-year-old kid would be able to make and sculpting a Venus."[25]

"My own feeling is that if Neanderthals regularly used symbols, and given their longtime occupation throughout large parts of the Old World, we probably would have found clearer evidence by now."[26]

Scientists need "more than a few scratches — deliberate or not — to identify symbolic behavior on the part of Neanderthals."[26]

"Symbols, by definition, have meanings that are shared by a group of people, and because of that, they are often repeated. By itself, this is a unique example and without any intrinsic meaning … the question is not 'Could it be symbolic?' but rather 'Was it symbolic?' And to demonstrate that, it would be very important to have repeated examples."[26]

Neanderthals had an average brain size of 1500 cm3.[27] Another source puts brain sizes from three localities as Spy I 1,305 ml, Spy II 1,553 ml, and Djebel Ihroud I 1305 ml.[28]

Hypotheses[edit]

Main source: Hypotheses
  1. Human DNA has been around for at least 4 x 106 b2k.

See also[edit]

References[edit]

  1. Goodman M, Tagle D, Fitch D, Bailey W, Czelusniak J, Koop B, Benson P, Slightom J (1990). "Primate evolution at the DNA level and a classification of hominoids". J Mol Evol 30 (3): 260–6. doi:10.1007/BF02099995. PMID 2109087. 
  2. Hominidae Classification. http://animaldiversity.ummz.umich.edu/site/accounts/classification/Hominidae.html. Retrieved 2006-09-25. 
  3. McHenry, H.M (2009). "Human Evolution". In Michael Ruse & Joseph Travis. Evolution: The First Four Billion Years. Cambridge, Massachusetts: The Belknap Press of Harvard University Press. p. 265. ISBN 978-0-674-03175-3. 
  4. Charles Choi (March 14, 2012). Mysterious Chinese Fossils May Be New Human Species. LiveScience. http://www.livescience.com/19039-human-species-china-cave.html. Retrieved 2012-09-06. 
  5. Techmedia (July 18, 2012). Speech. TechMediaNetwork.com. http://www.livescience.com/15689-evolution-human-special-species.html. Retrieved 2012-09-02. 
  6. Techmedia (July 18, 2012). Upright Posture. TechMediaNetwork.com. http://www.livescience.com/15689-evolution-human-special-species.html. Retrieved 2012-09-02. 
  7. Parker-Pope, Tara (October 27, 2009). The Human Body Is Built for Distance. http://www.nytimes.com/2009/10/27/health/27well.html. 
  8. Techmedia (July 18, 2012). Nakedness. TechMediaNetwork.com. http://www.livescience.com/15689-evolution-human-special-species.html. Retrieved 2012-09-02. 
  9. Why Humans and Their Fur Parted Way by Nicholas Wade, New York Times, August 19, 2003.
  10. Techmedia (July 18, 2012). Hands. TechMediaNetwork.com. http://www.livescience.com/15689-evolution-human-special-species.html. Retrieved 2012-09-02. 
  11. Techmedia (July 18, 2012). Extraordinary Brains. TechMediaNetwork.com. http://www.livescience.com/15689-evolution-human-special-species.html. Retrieved 2012-09-02. 
  12. Techmedia (July 18, 2012). Clothing. TechMediaNetwork.com. http://www.livescience.com/15689-evolution-human-special-species.html. Retrieved 2012-09-02. 
  13. Techmedia (July 18, 2012). Fire. TechMediaNetwork.com. http://www.livescience.com/15689-evolution-human-special-species.html. Retrieved 2012-09-02. 
  14. Techmedia (July 18, 2012). Blushing. TechMediaNetwork.com. http://www.livescience.com/15689-evolution-human-special-species.html. Retrieved 2012-09-02. 
  15. Techmedia (July 18, 2012). Long Childhoods. TechMediaNetwork.com. http://www.livescience.com/15689-evolution-human-special-species.html. Retrieved 2012-09-02. 
  16. Leakey, Richard; Lewin, Roger (1993). Origins Reconsidered: In Search of What Makes Us Human. New York, New York: Anchor Books. ISBN 978-0-385-46792-6. 
  17. Techmedia (July 18, 2012). Life after Children. TechMediaNetwork.com. http://www.livescience.com/15689-evolution-human-special-species.html. Retrieved 2012-09-02. 
  18. Jared Diamond (1997). Why is Sex Fun? The Evolution of Human Sexuality. New York, New York: Basic Books. pp. 167–170. ISBN 0-465-03127-7. 
  19. Peccei, Jocelyn Scott (2001). "Menopause: adaptation or epiphenomenon?" (PDF). Evolutionary Anthropology 10 (2): 47–57. doi:10.1002/evan.1013. http://www.biology.ed.ac.uk/public/conferences/evolbiol2006/papers/Peccei.pdf. 
  20. Bryan McBournie (September 6 2012). Human genome study could unlock the biology of disease. Sigma Xi. http://alquemie.smartbrief.com/servlet/ArchiveServlet?issueid=176C7415-9260-447D-A04F-77F3B17D39AF&sid=5df40ccd%252dcb14%252d46a9%252d9d44%252d2dd7cc2984b5. Retrieved 2012-09-06. 
  21. Jessie Szalay (March 19, 2013). Neanderthals: Facts About Our Extinct Human Relatives. livescience. http://www.livescience.com/28036-neanderthals-facts-about-our-extinct-human-relatives.html. Retrieved 2013-11-15. 
  22. 22.0 22.1 Catherine Brahic (20 August 2014). "Neanderthal demise traced in unprecedented detail". New Scientist. http://www.newscientist.com/article/mg22329831.500-neanderthal-demise-traced-in-unprecedented-detail.html#.U_0oRihORSU. Retrieved 2014-08-26. 
  23. 23.0 23.1 23.2 23.3 23.4 Megan Gannon (02 September 2014). Cave Carving May Be 1st Known Example of Neanderthal Rock Art. LiveScience.com. http://www.livescience.com/47640-abstract-neanderthal-cave-engraving-discovered.html. Retrieved 2014-09-09. 
  24. 24.0 24.1 24.2 Stewart Finlayson (02 September 2014). Cave Carving May Be 1st Known Example of Neanderthal Rock Art. LiveScience.com. http://www.livescience.com/47640-abstract-neanderthal-cave-engraving-discovered.html. Retrieved 2014-09-09. 
  25. 25.0 25.1 Jean-Jacques Hublin (02 September 2014). Cave Carving May Be 1st Known Example of Neanderthal Rock Art. LiveScience.com. http://www.livescience.com/47640-abstract-neanderthal-cave-engraving-discovered.html. Retrieved 2014-09-09. 
  26. 26.0 26.1 26.2 Harold Dibble (02 September 2014). Cave Carving May Be 1st Known Example of Neanderthal Rock Art. LiveScience.com. http://www.livescience.com/47640-abstract-neanderthal-cave-engraving-discovered.html. Retrieved 2014-09-09. 
  27. Gerhard Roth and Ursula Dicke (May 2005). "Evolution of the brain and intelligence". Trends in Cognitive Sciences 9 (5): 250-7. http://www.subjectpool.com/ed_teach/y3project/Roth2005_TICS_brain_size_and_intelligence.pdf. Retrieved 2014-09-23. 
  28. Ralph L. Holloway (1981). "Volumetric and Asymmetry Determinations on Recent Hominid Endocasts: Spy I and II, Djebel Ihroud I, and the Salè Homo erectus Specimens, With Some Notes on Neandertal Brain Size". American Journal of Physical Anthropology 55: 385-93. http://www.columbia.edu/~rlh2/Spy1%262,IrhoudEndos.AJPA1981.pdf. Retrieved 2014-09-23. 

External links[edit]

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