{"id":4314,"date":"2019-06-17T17:53:04","date_gmt":"2019-06-17T17:53:04","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/chapter\/2-5-the-human-animal-3\/"},"modified":"2023-11-30T17:47:57","modified_gmt":"2023-11-30T17:47:57","slug":"2-5-the-human-animal-3","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/chapter\/2-5-the-human-animal-3\/","title":{"raw":"2.5 The Human Animal","rendered":"2.5 The Human Animal"},"content":{"raw":" \r\n\r\n \r\n\r\n[caption id=\"attachment_5920\" align=\"aligncenter\" width=\"289\"]\"Figure Figure 2.5.1 Selfie!<\/em>[\/caption]\r\n

Primate Pals<\/h1>\r\nFigure 2.5.1 Humans and monkeys share an evolutionary past.\u00a0 Humans belong to the animal kingdom, which includes small organisms \u2014 like insects \u2014 and larger organisms, like humans and monkeys. From genes to morphology to behavior, humans and monkeys are similar in many ways because they share an evolutionary past. Humans and monkeys also both belong to the order [pb_glossary id=\"5599\"]Primate[\/pb_glossary]<\/strong>,\u00a0which means\u00a0they have more traits in common with each other than with\u00a0insects.\r\n
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How Humans Are Classified<\/h1>\r\n<\/div>\r\n\r\n[caption id=\"attachment_200\" align=\"alignright\" width=\"295\"]\"A Figure 2.5.2 This taxonomic diagram shows how our Homo sapiens species is classified.<\/em>[\/caption]\r\n\r\nYou probably know that modern humans\u00a0are members of\u00a0the\u00a0species\u00a0Homo sapiens<\/a>.<\/em>\u00a0But what is our place in nature? How is our\u00a0species classified? A simple\u00a0classification\u00a0is represented in the taxonomic diagram\u00a0below, along with some representative characteristics.\r\n
\r\n\r\nLet's start at the bottom of the chart, with the\u00a0<\/span>kingdom. Among other animal characteristics, humans can move on their own,\u00a0so they\u00a0are placed in the animal\u00a0<\/span>kingdom. Further, humans belong to the animal phylum known as\u00a0<\/span>chordates, because we have a backbone.\u00a0<\/span>The human animal\u00a0has\u00a0<\/span>hair\u00a0and milk glands, so we are placed in the class of mammals. Within the mammal class, humans are placed in the primate order.<\/span>\r\n\r\n<\/div>\r\n
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Humans as\u00a0Primates<\/h1>\r\n<\/div>\r\nLiving members of the [pb_glossary id=\"5599\"]primate[\/pb_glossary] <\/strong>order include monkeys, apes, and humans. At some point in the distant past, we shared ape-like ancestors with all of these modern groups of primates. We share between 93 and 99 per cent of our DNA sequences with them, which provides hard evidence that we have relatively recent common ancestors. Besides genes, what traits do we share with other primates?\r\n\r\nPrimates are considered generalists among the mammals. A\u00a0[pb_glossary id=\"5755\"]generalist[\/pb_glossary]<\/strong>\u00a0is an organism that can\u00a0thrive in a wide variety of environmental conditions. Generalists also make use of a variety of different\u00a0resources; for example, they consume many types of food.\u00a0Although primates exhibit a wide range of characteristics, there are several traits shared by most primates.\r\n

Primate Traits<\/h2>\r\n[caption id=\"attachment_196\" align=\"alignright\" width=\"300\"]\"A Figure 2.5.3 The capuchin monkey shows manual dexterity common to primates.<\/em>[\/caption]\r\n\r\nPrimates have pentadactylism, or five digits (fingers or toes) on each extremity (hand or foot). The fingers and toes have nails instead of claws and are covered with sensitive tactile pads. The thumbs (and in many species, the big toes, as well) are opposable, which means they can be brought into opposition with the other digits, allowing both a power grasp and a precision grip. You can see these features of the primate extremities in the capuchin monkey pictured in Figure 2.15.\r\n
\r\n\r\nThe five fingers, opposable thumb, and other primate features of the hand give this capuchin monkey great manual dexterity. This is the primary reason these primates are trained to assist quadraplegic human beings with daily tasks.\r\n\r\n<\/div>\r\nThe primate body is generally semi-erect or erect, and primates have one of several modes of\u00a0locomotion, including walking on all four legs (quadrupedalism), vertical clinging and leaping, swinging from branch to branch in trees (brachiation), or walking on two legs (bipedalism, which today only applies to humans).\u00a0The primate shoulder girdle has a collar bone (clavicle), which is associated with a wide range of motion of the upper limbs.\r\n\r\nRelative to other mammals, primates rely less on their sense of smell. They have a reduced snout and relatively small area in the brain for processing olfactory (odor) information. Primates rely more on their sense of vision, which shows several improvements over that of other mammals. Most primates can see in colour. Primates also tend to have large eyes with forward placement in a relatively flat face. This results in an overlap of the visual fields of the two eyes, allowing stereoscopic (or three-dimensional) vision. Other indications of the importance of vision to primates is the protection given the eyes by a complete bony eye socket and the large size of the occipital lobe of the brain, where visual information is processed.\r\n\r\n[caption id=\"attachment_197\" align=\"alignleft\" width=\"300\"]\"Several Figure 2.5.4 Crab-eating macaques use a variety of stones as tools to kill and crush crabs in order to get the meat inside the shells.<\/em>[\/caption]\r\n\r\nPrimates are noted for their relatively large brains, high degree of intelligence, and complex behaviors. The part of the brain that is especially enlarged in primates is the cerebrum, which analyzes and synthesizes sensory information and transforms it to motor behaviors appropriate to the environment. Primates tend to have longer lifespans than most other mammals. In particular, there is a lengthening of the prenatal period and the postnatal period during which infants depend on adults, providing an extended opportunity for learning among juveniles. Most primates live in social groups. In fact, primates are among the most social of animals. Depending on the species, adult nonhuman primates may live in mated pairs or in groups with hundreds of members. Humans and some nonhuman primates can also make and use tools. The crab-eating macaques pictured below provide examples of tool use in nonhuman primates.\r\n
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Life in the Trees<\/span><\/h2>\r\n<\/div>\r\n\r\n[caption id=\"attachment_228\" align=\"alignright\" width=\"300\"]\"Image Figure 2.5.5 Primates evolved adaptations which suited them to life in the trees.<\/em>[\/caption]\r\n\r\nScientists think that many primate traits are adaptations to an arboreal (or tree-dwelling) lifestyle. [pb_glossary id=\"239\"]Primates[\/pb_glossary]<\/strong> are thought to have evolved in trees, and the majority of primates still live in trees. For life in the trees, the sense of vision trumps the sense of smell, and three-dimensional (3D) vision is especially important for grasping the next branch or limb. Having mobile limbs, a good grip, and manual dexterity are matters of life and death when one lives high above the ground. While some modern primates are mainly terrestrial (ground dwelling) rather than arboreal, all primates possess adaptations for life in the trees.\r\n\r\n[caption id=\"attachment_202\" align=\"alignleft\" width=\"300\"]\"A Figure 2.5.6 This map shows the present worldwide distribution of nonhuman primates.<\/em>[\/caption]\r\n\r\nThe map to the left shows the present distribution of nonhuman primates around the world.\u00a0Tropical\u00a0forests in Central and South America are home to many species of monkeys, including the squirrel monkey pictured\u00a0above. Old World\u00a0tropical\u00a0forests in Africa and Asia are home to many other species of monkeys, including the crab-eating macaque pictured\u00a0above, as well as all modern apes.\r\n
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Humans as Hominids<\/h1>\r\n<\/div>\r\n\r\n[caption id=\"attachment_203\" align=\"alignleft\" width=\"195\"]\"A Figure 2.5.7 Orangutan mother and child.<\/em>[\/caption]\r\n\r\nWho are our closest relatives in the primate order? We are placed in the family called\u00a0Hominidae.<\/em>\u00a0Any member of this family is called a\u00a0[pb_glossary id=\"5898\"]hominid[\/pb_glossary].\u00a0<\/strong>Hominids include four living genera: chimpanzees, gorillas, orangutans, and humans. Among these four genera are just seven living species: two in each genera, except humans, with our sole living species,\u00a0Homo sapiens.\u00a0<\/em>The orangutan mother pictured cradling her child shows how similar these hominids are to us.\r\n\r\nHominids are relatively large, tailless primates, ranging in size from the bonobo (or pygmy chimpanzee) \u2014 which may weigh as little as 30 kg (66 lb) \u2014 to the eastern gorilla, which may weigh over 200 kg (440 lb). Most modern humans fall somewhere\u00a0within\u00a0that range. In all species of hominids, males are somewhat larger and stronger, on average, than females, but the differences may not be\u00a0significant. Except for humans, hominids are mainly quadrupedal, although they can get around bipedally if need be to gather food or nesting materials.\u00a0Humans are the only habitually bipedal species of living hominids.\r\n\r\nThe Human Genus<\/span>\r\n\r\nWithin the hominid family, our species is placed in the genus\u00a0Homo.<\/strong><\/em>\u00a0Our species,\u00a0Homo sapiens,<\/em>\u00a0is the only living species in this genus. Several earlier species of\u00a0Homo<\/em>\u00a0existed, but have since gone extinct, including the species\u00a0Homo erectus.<\/em>\r\n
\r\n\r\nBy about 2.8 million years ago, early\u00a0<\/span>Homo<\/em>\u00a0species such as\u00a0<\/span>Homo erectus<\/em>\u00a0were probably nearly as efficient at bipedal\u00a0<\/span>locomotion<\/span>\u00a0as modern humans. Relative to quadrupedal primates, they had a broader pelvis, longer legs, and arched feet. However, from the neck up, they were still quite different from us. They typically had bigger jaws and teeth, a sloping forehead, and a relatively small brain.<\/span>\r\n\r\n<\/div>\r\n
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Homo sapiens<\/em><\/h2>\r\n<\/div>\r\n\r\n[caption id=\"attachment_208\" align=\"alignright\" width=\"200\"]\"The Figure 2.5.8 Turkana Boy is the name given to a nearly complete skeleton of a Homo erectus (Homo ergaster) youth who lived at c. 1.5 to 1.6 million years ago. This specimen is the most complete early human skeleton ever found.<\/em>[\/caption]\r\n\r\nDuring the roughly 2.8 million years of the evolution of the\u00a0Homo<\/em>\u00a0genus, the remaining features of\u00a0Homo sapiens<\/em>\u00a0evolved. These features include:\r\n