{"id":2590,"date":"2017-02-06T22:30:49","date_gmt":"2017-02-06T22:30:49","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/wm-biology2\/?post_type=chapter&#038;p=2590"},"modified":"2024-04-26T00:48:37","modified_gmt":"2024-04-26T00:48:37","slug":"evolution-of-humans","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-biology2\/chapter\/evolution-of-humans\/","title":{"raw":"Evolution of Humans","rendered":"Evolution of Humans"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Describe the evolutionary history of humans<\/li>\r\n<\/ul>\r\n<\/div>\r\n<p id=\"fs-idp13304272\">The family Hominidae of order Primates includes the hominoids: the great apes and humans (Figure 1). Evidence from the fossil record and from a comparison of human and chimpanzee DNA suggests that humans and chimpanzees diverged from a common hominoid ancestor approximately six million years ago. Several species evolved from the evolutionary branch that includes humans, although our species is the only surviving member. The term hominin is used to refer to those species that evolved after this split of the primate line, thereby designating species that are more closely related to humans than to chimpanzees. A number of marker features differentiate humans from the other hominoids, including bipedalism or upright posture, increase in the size of the brain, and a fully opposable thumb that can touch the little finger. Bipedal hominins include several groups that were probably part of the modern human lineage\u2014<em data-effect=\"italics\">Australopithecus<\/em>,\u00a0<em data-effect=\"italics\">Homo habilis<\/em>, and\u00a0<em data-effect=\"italics\">Homo erectus<\/em>\u2014and several non-ancestral groups that can be considered \u201ccousins\u201d of modern humans, such as Neanderthals and Denisovans.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"575\"]<img id=\"7\" src=\"https:\/\/openstax.org\/resources\/1d9e05a467acef56105927e0ebaf1be124bc016f\" alt=\"The evolutionary tree shows the relationship between humans and the great apes. All great apes, including baboons, gibbons, orangutans, gorillas, chimpanzees, humans, and human ancestors, belong in the superfamily Hominoidea. Of these great apes, all but baboons and gibbons belong in the family Hominidae. Gorillas, chimpanzees, humans, and human ancestors belong in the subfamily Homininae. Humans and their direct ancestors belong in the tribe Hominini.\" width=\"575\" height=\"969\" data-media-type=\"image\/jpg\" \/> Figure 1. Hominin phylogeny. This chart shows evolutionary relationship among Hominins and hypothesized relation to modern humans. (*still debated phylogeny position).[\/caption]\r\n<p id=\"fs-idp13305673\">Determining the true lines of descent in hominins is difficult. In years past, when relatively few hominin fossils had been recovered, some scientists believed that considering them in order, from oldest to youngest, would demonstrate the course of evolution from early hominins to modern humans. In the past several years, however, many new fossils have been found, and it is clear that there was often more than one species alive at any one time and that many of the fossils found (and species named) represent hominin species that died out and are not ancestral to modern humans.<\/p>\r\n\r\n<h2>Very Early Hominins<\/h2>\r\n<p id=\"fs-idp206150880\">Three species of very early hominids have made news in the late 20th and early 21st centuries:\u00a0<em data-effect=\"italics\">Ardipithecus<\/em>,\u00a0<em data-effect=\"italics\">Sahelanthropus<\/em>, and\u00a0<em data-effect=\"italics\">Orrorin<\/em>. The youngest of the three species,\u00a0<em data-effect=\"italics\">Ardipithecus<\/em>, was discovered in the 1990s, and dates to about 4.4 MYA. Although the bipedality of the early specimens was uncertain, several more specimens of\u00a0<em data-effect=\"italics\">Ardipithecus<\/em>\u00a0were discovered in the intervening years and demonstrated that the organism was bipedal. Two different species of\u00a0<em data-effect=\"italics\">Ardipithecus<\/em>\u00a0have been identified,\u00a0<em data-effect=\"italics\">A. ramidus<\/em>\u00a0and\u00a0<em data-effect=\"italics\">A. kadabba<\/em>, whose specimens are older, dating to 5.6 MYA. However, the status of this genus as a human ancestor is uncertain.<\/p>\r\n<p id=\"fs-idp206150990\">The oldest of the three,\u00a0<em data-effect=\"italics\">Sahelanthropus tchadensis<\/em>, was discovered in 2001-2002 and has been dated to nearly seven million years ago. There is a single specimen of this genus, a skull that was a surface find in Chad. The fossil, informally called \u201cToumai,\u201d is a mosaic of primitive and evolved characteristics, and it is unclear how this fossil fits with the picture given by molecular data, namely that the line leading to modern humans and modern chimpanzees apparently bifurcated about six million years ago. It is not thought at this time that this species was an ancestor of modern humans.<\/p>\r\n<p id=\"fs-idp36109408\">A younger (c. 6 MYA) species,\u00a0<em data-effect=\"italics\">Orrorin tugenensis<\/em>, is also a relatively recent discovery, found in 2000. There are several specimens of\u00a0<em data-effect=\"italics\">Orrorin<\/em>. Some features of\u00a0<em data-effect=\"italics\">Orrorin<\/em>\u00a0are more similar to those of modern humans than are the australopithicenes, although\u00a0<em data-effect=\"italics\">Orrorin\u00a0<\/em>is much older. If\u00a0<em data-effect=\"italics\">Orrorin<\/em>\u00a0is a human ancestor, then the australopithicenes may not be in the direct human lineage. Additional specimens of these species may help to clarify their role.<\/p>\r\n\r\n<h2>Early Hominins: Genus <em>Australopithecus<\/em><\/h2>\r\n<p id=\"fs-idp37739504\"><em data-effect=\"italics\">Australopithecus<\/em>\u00a0(\u201csouthern ape\u201d) is a genus of hominin that evolved in eastern Africa approximately four million years ago and went extinct about two million years ago. This genus is of particular interest to us as it is thought that our genus, genus\u00a0<em data-effect=\"italics\">Homo<\/em>, evolved from a common ancestor shared with\u00a0<em data-effect=\"italics\">Australopithecus<\/em>\u00a0about two million years ago (after likely passing through some transitional states).\u00a0<em data-effect=\"italics\">Australopithecus\u00a0<\/em>had a number of characteristics that were more similar to the great apes than to modern humans. For example, sexual dimorphism was more exaggerated than in modern humans. Males were up to 50 percent larger than females, a ratio that is similar to that seen in modern gorillas and orangutans. In contrast, modern human males are approximately 15 to 20 percent larger than females. The brain size of\u00a0<em data-effect=\"italics\">Australopithecus\u00a0<\/em>relative to its body mass was also smaller than in modern humans and more similar to that seen in the great apes. A key feature that\u00a0<em data-effect=\"italics\">Australopithecus\u00a0<\/em>had in common with modern humans was bipedalism, although it is likely that\u00a0<em data-effect=\"italics\">Australopithecus<\/em>\u00a0also spent time in trees. Hominin footprints, similar to those of modern humans, were found in Laetoli, Tanzania and dated to 3.6 million years ago. They showed that hominins at the time of\u00a0<em data-effect=\"italics\">Australopithecus\u00a0<\/em>were walking upright.<\/p>\r\n<p id=\"fs-idm76349936\">There were a number of\u00a0<em data-effect=\"italics\">Australopithecus\u00a0<\/em>species, which are often referred to as\u00a0<em data-effect=\"italics\">australopiths<\/em>.\u00a0<em data-effect=\"italics\">Australopithecus anamensis\u00a0<\/em>lived about 4.2 million years ago. More is known about another early species,\u00a0<em data-effect=\"italics\">Australopithecus afarensis<\/em>, which lived between 3.9 and 2.9 million years ago. This species demonstrates a trend in human evolution: the reduction of the dentition and jaw in size.\u00a0<em data-effect=\"italics\">A<\/em>.<em data-effect=\"italics\">\u00a0afarensis\u00a0<\/em>(Figure 2a) had smaller canines and molars compared to apes, but these were larger than those of modern humans. Its brain size was 380 to 450 cubic centimeters, approximately the size of a modern chimpanzee brain. It also had prognathic jaws, which is a relatively longer jaw than that of modern humans. <img class=\"wp-image-2606\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/06222747\/Figure_29_07_04ab-1024x648.jpg\" alt=\" Photo A shows an A. afarensis skull, which is similar in shape but the forehead slopes back and the jaw juts out. Photo A shows a human skull.\" width=\"600\" height=\"380\" \/><\/p>\r\nFigure\u00a02.\u00a0The skull of (a) Australopithecus afarensis, an early hominid that lived between two and three million years ago, resembled that of (b) modern humans but was smaller with a sloped forehead and prominent jaw.\r\n<p id=\"fs-idm76349936\">In the mid-1970s, the fossil of an adult female\u00a0<em data-effect=\"italics\">A<\/em>.<em data-effect=\"italics\">\u00a0afarensis\u00a0<\/em>was found in the Afar region of Ethiopia and dated to 3.24 million years ago (Figure 3). The fossil, which is informally called \u201cLucy,\u201d is significant because it was the most complete australopith fossil found, with 40 percent of the skeleton recovered.<\/p>\r\nIts brain size was 380\u2013450 cubic centimeters, approximately the size of a modern chimpanzee brain. It also had <b>prognathic jaws<\/b>, which is a relatively longer jaw than that of modern humans. In the mid-1970s, the fossil of an adult female <em>A<\/em>.<em> afarensis <\/em>was found in the Afar region of Ethiopia and dated to 3.24 million years ago (Figure\u00a03). The fossil, which is informally called \u201cLucy,\u201d is significant because it was the most complete australopith fossil found, with 40 percent of the skeleton recovered.\r\n\r\n[caption id=\"attachment_2607\" align=\"aligncenter\" width=\"1024\"]<img class=\"size-large wp-image-2607\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/06222837\/Figure_29_07_05-e1486420130541-1024x424.jpg\" alt=\"Partial skeleton is human-like but child-sized.\" width=\"1024\" height=\"424\" \/> Figure\u00a03.\u00a0This adult female <em>Australopithecus afarensis<\/em> skeleton, nicknamed Lucy, was discovered in the mid 1970s. (credit: \u201c120\u201d\/Wikimedia Commons)[\/caption]\r\n\r\n<section id=\"fs-idm22448416\" data-depth=\"2\">\r\n<p id=\"fs-idp111171552\"><em data-effect=\"italics\">Australopithecus africanus\u00a0<\/em>lived between two and three million years ago. It had a slender build and was bipedal, but had robust arm bones and, like other early hominids, may have spent significant time in trees. Its brain was larger than that of\u00a0<em data-effect=\"italics\">A<\/em>.<em data-effect=\"italics\">\u00a0afarensis\u00a0<\/em>at 500 cubic centimeters, which is slightly less than one-third the size of modern human brains. Two other species,\u00a0<em data-effect=\"italics\">Australopithecus bahrelghazali\u00a0<\/em>and<em data-effect=\"italics\">\u00a0Australopithecus garhi<\/em>, have been added to the roster of australopiths in recent years. A.\u00a0<em data-effect=\"italics\">bahrelghazali<\/em>\u00a0is unusual in being the only australopith found in Central Africa.<\/p>\r\n\r\n<\/section><section id=\"fs-idp23125440\" data-depth=\"2\"><\/section>\r\n<h2>A Dead End: Genus <em>Paranthropus<\/em><\/h2>\r\n<section id=\"fs-idp23125440\" data-depth=\"2\">\r\n<p id=\"fs-idp17351584\">The australopiths had a relatively slender build and teeth that were suited for soft food. In the past several years, fossils of hominids of a different body type have been found and dated to approximately 2.5 million years ago. These hominids, of the genus\u00a0<em data-effect=\"italics\">Paranthropus<\/em>, were muscular, stood 1.3 to 1.4 meters tall, and had large grinding teeth. Their molars showed heavy wear, suggesting that they had a coarse and fibrous vegetarian diet as opposed to the partially carnivorous diet of the australopiths.\u00a0<em data-effect=\"italics\">Paranthropus<\/em>\u00a0includes\u00a0<em data-effect=\"italics\">Paranthropus<\/em>\u00a0<em data-effect=\"italics\">robustus\u00a0<\/em>of South Africa, and\u00a0<em data-effect=\"italics\">Paranthropus<\/em>\u00a0<em data-effect=\"italics\">aethiopicus\u00a0<\/em>and\u00a0<em data-effect=\"italics\">Paranthropus<\/em>\u00a0<em data-effect=\"italics\">boisei\u00a0<\/em>of East Africa. The hominids in this genus went extinct more than one million years ago and are not thought to be ancestral to modern humans, but rather members of an evolutionary branch on the hominin tree that left no descendants.<\/p>\r\n\r\n<\/section><section id=\"fs-idp79276832\" data-depth=\"2\"><\/section>\r\n<h2>Early Hominins: Genus <em>Homo<\/em><\/h2>\r\n<p id=\"fs-idp81386448\">The human genus,\u00a0<em data-effect=\"italics\">Homo<\/em>, first appeared between 2.5 and three million years ago. For many years, fossils of a species called\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0habilis\u00a0<\/em>were the oldest examples in the genus\u00a0<em data-effect=\"italics\">Homo<\/em>, but in 2010, a new species called\u00a0<em data-effect=\"italics\">Homo gautengensis<\/em>\u00a0was discovered and may be older. Compared to\u00a0<em data-effect=\"italics\">A<\/em>.<em data-effect=\"italics\">\u00a0africanus<\/em>,<em data-effect=\"italics\">\u00a0H<\/em>.<em data-effect=\"italics\">\u00a0habilis\u00a0<\/em>had a number of features more similar to modern humans.\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0habilis\u00a0<\/em>had a jaw that was less prognathic than the australopiths and a larger brain, at 600 to 750 cubic centimeters. However,\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0habilis\u00a0<\/em>retained some features of older hominin species, such as long arms. The name\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0habilis\u00a0<\/em>means \u201chandy man,\u201d which is a reference to the stone tools that have been found with its remains.<\/p>\r\n\r\n<div class=\"textbox\">\r\n\r\nWatch this video about Smithsonian paleontologist Briana Pobiner explaining the link between hominin eating of meat and evolutionary trends.\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=VYSw0EWwNhw\r\n\r\n<\/div>\r\n\r\n[caption id=\"attachment_2608\" align=\"alignright\" width=\"350\"]<img class=\"wp-image-2608\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/06222924\/Figure_29_07_06.jpg\" alt=\"The photo shows a skull that looks similar to a human skull but has prominent brow ridges.\" width=\"350\" height=\"376\" \/> Figure\u00a04.\u00a0<em>Homo erectus<\/em> had a prominent brow and a nose that pointed downward rather than forward.[\/caption]\r\n<p id=\"fs-idm4268128\"><em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0erectus<\/em>\u00a0appeared approximately 1.8 million years ago (Figure 4). It is believed to have originated in East Africa and was the first hominin species to migrate out of Africa. Fossils of\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0erectus\u00a0<\/em>have been found in India, China, Java, and Europe, and were known in the past as \u201cJava Man\u201d or \u201cPeking Man.\u201d\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0erectus\u00a0<\/em>had a number of features that were more similar to modern humans than those of\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0habilis<\/em>.<em data-effect=\"italics\">\u00a0H<\/em>.<em data-effect=\"italics\">\u00a0erectus\u00a0<\/em>was larger in size than earlier hominins, reaching heights up to 1.85 meters and weighing up to 65 kilograms, which are sizes similar to those of modern humans. Its degree of sexual dimorphism was less than in earlier species, with males being 20 to 30 percent larger than females, which is close to the size difference seen in our own species.\u00a0<em data-effect=\"italics\">H<\/em>.\u00a0<em data-effect=\"italics\">erectus<\/em>\u00a0had a larger brain than earlier species at 775 to 1,100 cubic centimeters, which compares to the 1,130 to 1,260 cubic centimeters seen in modern human brains.\u00a0<em data-effect=\"italics\">H<\/em>.\u00a0<em data-effect=\"italics\">erectus<\/em>\u00a0also had a nose with downward-facing nostrils similar to modern humans, rather than the forward-facing nostrils found in other primates. Longer, downward-facing nostrils allow for the warming of cold air before it enters the lungs and may have been an adaptation to colder climates. Artifacts found with fossils of\u00a0<em data-effect=\"italics\">H<\/em>.\u00a0<em data-effect=\"italics\">erectus<\/em>\u00a0suggest that it was the first hominin to use fire, hunt, and have a home base.\u00a0<em data-effect=\"italics\">H<\/em>.\u00a0<em data-effect=\"italics\">erectus<\/em>\u00a0is generally thought to have lived until about 50,000 years ago.<\/p>\r\n\r\n<h2>Humans: <em>Homo sapiens<\/em><\/h2>\r\n[caption id=\"attachment_2609\" align=\"alignright\" width=\"350\"]<img class=\"wp-image-2609\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/06223001\/Figure_29_07_07.jpg\" alt=\"The illustration shows a very human looking Neanderthal wearing fur and cutting a hide with a stone tool.\" width=\"350\" height=\"263\" \/> Figure\u00a05.\u00a0The <em>Homo neanderthalensis<\/em> used tools and may have worn clothing.[\/caption]\r\n\r\nA number of species, sometimes called archaic\u00a0<em data-effect=\"italics\">Homo sapiens<\/em>, apparently evolved from\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0erectus<\/em>\u00a0starting about 500,000 years ago. These species include\u00a0<em data-effect=\"italics\">Homo heidelbergensis<\/em>,\u00a0<em data-effect=\"italics\">Homo rhodesiensis<\/em>, and\u00a0<em data-effect=\"italics\">Homo neanderthalensis<\/em>. These archaic\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0sapiens<\/em>\u00a0had a brain size similar to that of modern humans, averaging 1,200 to 1,400 cubic centimeters. They differed from modern humans by having a thick skull, a prominent brow ridge, and a receding chin. Some of these species survived until 30,000 to 10,000 years ago, overlapping with modern humans (Figure\u00a05).\r\n<p id=\"fs-idm37516176\">There is considerable debate about the origins of anatomically modern humans or\u00a0<span id=\"term1252\" data-type=\"term\"><em data-effect=\"italics\">Homo sapiens sapiens<\/em><\/span>. As discussed earlier,\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0erectus<\/em>\u00a0migrated out of Africa and into Asia and Europe in the first major wave of migration about 1.5 million years ago. It is thought that modern humans arose in Africa from\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0erectus\u00a0<\/em>and migrated out of Africa about 100,000 years ago in a second major migration wave. Then, modern humans replaced\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0erectus\u00a0<\/em>species that had migrated into Asia and Europe in the first wave.<\/p>\r\n<p id=\"fs-idm43043568\">This evolutionary timeline is supported by molecular evidence. One approach to studying the origins of modern humans is to examine mitochondrial DNA (mtDNA) from populations around the world. Because a fetus develops from an egg containing its mother\u2019s mitochondria (which have their own, non-nuclear DNA), mtDNA is passed entirely through the maternal line. Mutations in mtDNA can now be used to estimate the timeline of genetic divergence. The resulting evidence suggests that all modern humans have mtDNA inherited from a common ancestor that lived in Africa about 160,000 years ago. Another approach to the molecular understanding of human evolution is to examine the Y chromosome, which is passed from father to son. This evidence suggests that all men today inherited a Y chromosome from a male that lived in Africa about 140,000 years ago.<\/p>\r\n\r\n<div class=\"PageContent-ny9bj0-0 iapMdy\" tabindex=\"0\">\r\n<div id=\"main-content\" class=\"MainContent__HideOutline-sc-6yy1if-0 bdVAq\" tabindex=\"-1\">\r\n<div id=\"112cfa1a-5875-4fb6-a870-c71c74409adb\" class=\"chapter-content-module\" data-type=\"page\" data-cnxml-to-html-ver=\"2.1.0\"><section id=\"fs-idp19004672\" data-depth=\"1\"><section id=\"fs-idp59870416\" data-depth=\"2\">\r\n<p id=\"fs-idm37518298\">The study of mitochondrial DNA led to the identification of another human species or subspecies, the Denisovans. DNA from teeth and finger bones suggested two things. First, the mitochondrial DNA was different from that of both modern humans and Neanderthals. Second, the genomic DNA suggested that the Denisovans shared a common ancestor with the Neanderthals. Genes from both Neanderthals and Denisovans have been identified in modern human populations, indicating that interbreeding among the three groups occurred over part of their range.<\/p>\r\n\r\n<\/section><\/section><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/1b28290c-02d9-4202-9dc8-58e71b037558\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Describe the evolutionary history of humans<\/li>\n<\/ul>\n<\/div>\n<p id=\"fs-idp13304272\">The family Hominidae of order Primates includes the hominoids: the great apes and humans (Figure 1). Evidence from the fossil record and from a comparison of human and chimpanzee DNA suggests that humans and chimpanzees diverged from a common hominoid ancestor approximately six million years ago. Several species evolved from the evolutionary branch that includes humans, although our species is the only surviving member. The term hominin is used to refer to those species that evolved after this split of the primate line, thereby designating species that are more closely related to humans than to chimpanzees. A number of marker features differentiate humans from the other hominoids, including bipedalism or upright posture, increase in the size of the brain, and a fully opposable thumb that can touch the little finger. Bipedal hominins include several groups that were probably part of the modern human lineage\u2014<em data-effect=\"italics\">Australopithecus<\/em>,\u00a0<em data-effect=\"italics\">Homo habilis<\/em>, and\u00a0<em data-effect=\"italics\">Homo erectus<\/em>\u2014and several non-ancestral groups that can be considered \u201ccousins\u201d of modern humans, such as Neanderthals and Denisovans.<\/p>\n<div style=\"width: 585px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" id=\"7\" src=\"https:\/\/openstax.org\/resources\/1d9e05a467acef56105927e0ebaf1be124bc016f\" alt=\"The evolutionary tree shows the relationship between humans and the great apes. All great apes, including baboons, gibbons, orangutans, gorillas, chimpanzees, humans, and human ancestors, belong in the superfamily Hominoidea. Of these great apes, all but baboons and gibbons belong in the family Hominidae. Gorillas, chimpanzees, humans, and human ancestors belong in the subfamily Homininae. Humans and their direct ancestors belong in the tribe Hominini.\" width=\"575\" height=\"969\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 1. Hominin phylogeny. This chart shows evolutionary relationship among Hominins and hypothesized relation to modern humans. (*still debated phylogeny position).<\/p>\n<\/div>\n<p id=\"fs-idp13305673\">Determining the true lines of descent in hominins is difficult. In years past, when relatively few hominin fossils had been recovered, some scientists believed that considering them in order, from oldest to youngest, would demonstrate the course of evolution from early hominins to modern humans. In the past several years, however, many new fossils have been found, and it is clear that there was often more than one species alive at any one time and that many of the fossils found (and species named) represent hominin species that died out and are not ancestral to modern humans.<\/p>\n<h2>Very Early Hominins<\/h2>\n<p id=\"fs-idp206150880\">Three species of very early hominids have made news in the late 20th and early 21st centuries:\u00a0<em data-effect=\"italics\">Ardipithecus<\/em>,\u00a0<em data-effect=\"italics\">Sahelanthropus<\/em>, and\u00a0<em data-effect=\"italics\">Orrorin<\/em>. The youngest of the three species,\u00a0<em data-effect=\"italics\">Ardipithecus<\/em>, was discovered in the 1990s, and dates to about 4.4 MYA. Although the bipedality of the early specimens was uncertain, several more specimens of\u00a0<em data-effect=\"italics\">Ardipithecus<\/em>\u00a0were discovered in the intervening years and demonstrated that the organism was bipedal. Two different species of\u00a0<em data-effect=\"italics\">Ardipithecus<\/em>\u00a0have been identified,\u00a0<em data-effect=\"italics\">A. ramidus<\/em>\u00a0and\u00a0<em data-effect=\"italics\">A. kadabba<\/em>, whose specimens are older, dating to 5.6 MYA. However, the status of this genus as a human ancestor is uncertain.<\/p>\n<p id=\"fs-idp206150990\">The oldest of the three,\u00a0<em data-effect=\"italics\">Sahelanthropus tchadensis<\/em>, was discovered in 2001-2002 and has been dated to nearly seven million years ago. There is a single specimen of this genus, a skull that was a surface find in Chad. The fossil, informally called \u201cToumai,\u201d is a mosaic of primitive and evolved characteristics, and it is unclear how this fossil fits with the picture given by molecular data, namely that the line leading to modern humans and modern chimpanzees apparently bifurcated about six million years ago. It is not thought at this time that this species was an ancestor of modern humans.<\/p>\n<p id=\"fs-idp36109408\">A younger (c. 6 MYA) species,\u00a0<em data-effect=\"italics\">Orrorin tugenensis<\/em>, is also a relatively recent discovery, found in 2000. There are several specimens of\u00a0<em data-effect=\"italics\">Orrorin<\/em>. Some features of\u00a0<em data-effect=\"italics\">Orrorin<\/em>\u00a0are more similar to those of modern humans than are the australopithicenes, although\u00a0<em data-effect=\"italics\">Orrorin\u00a0<\/em>is much older. If\u00a0<em data-effect=\"italics\">Orrorin<\/em>\u00a0is a human ancestor, then the australopithicenes may not be in the direct human lineage. Additional specimens of these species may help to clarify their role.<\/p>\n<h2>Early Hominins: Genus <em>Australopithecus<\/em><\/h2>\n<p id=\"fs-idp37739504\"><em data-effect=\"italics\">Australopithecus<\/em>\u00a0(\u201csouthern ape\u201d) is a genus of hominin that evolved in eastern Africa approximately four million years ago and went extinct about two million years ago. This genus is of particular interest to us as it is thought that our genus, genus\u00a0<em data-effect=\"italics\">Homo<\/em>, evolved from a common ancestor shared with\u00a0<em data-effect=\"italics\">Australopithecus<\/em>\u00a0about two million years ago (after likely passing through some transitional states).\u00a0<em data-effect=\"italics\">Australopithecus\u00a0<\/em>had a number of characteristics that were more similar to the great apes than to modern humans. For example, sexual dimorphism was more exaggerated than in modern humans. Males were up to 50 percent larger than females, a ratio that is similar to that seen in modern gorillas and orangutans. In contrast, modern human males are approximately 15 to 20 percent larger than females. The brain size of\u00a0<em data-effect=\"italics\">Australopithecus\u00a0<\/em>relative to its body mass was also smaller than in modern humans and more similar to that seen in the great apes. A key feature that\u00a0<em data-effect=\"italics\">Australopithecus\u00a0<\/em>had in common with modern humans was bipedalism, although it is likely that\u00a0<em data-effect=\"italics\">Australopithecus<\/em>\u00a0also spent time in trees. Hominin footprints, similar to those of modern humans, were found in Laetoli, Tanzania and dated to 3.6 million years ago. They showed that hominins at the time of\u00a0<em data-effect=\"italics\">Australopithecus\u00a0<\/em>were walking upright.<\/p>\n<p id=\"fs-idm76349936\">There were a number of\u00a0<em data-effect=\"italics\">Australopithecus\u00a0<\/em>species, which are often referred to as\u00a0<em data-effect=\"italics\">australopiths<\/em>.\u00a0<em data-effect=\"italics\">Australopithecus anamensis\u00a0<\/em>lived about 4.2 million years ago. More is known about another early species,\u00a0<em data-effect=\"italics\">Australopithecus afarensis<\/em>, which lived between 3.9 and 2.9 million years ago. This species demonstrates a trend in human evolution: the reduction of the dentition and jaw in size.\u00a0<em data-effect=\"italics\">A<\/em>.<em data-effect=\"italics\">\u00a0afarensis\u00a0<\/em>(Figure 2a) had smaller canines and molars compared to apes, but these were larger than those of modern humans. Its brain size was 380 to 450 cubic centimeters, approximately the size of a modern chimpanzee brain. It also had prognathic jaws, which is a relatively longer jaw than that of modern humans. <img loading=\"lazy\" decoding=\"async\" class=\"wp-image-2606\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/06222747\/Figure_29_07_04ab-1024x648.jpg\" alt=\"Photo A shows an A. afarensis skull, which is similar in shape but the forehead slopes back and the jaw juts out. Photo A shows a human skull.\" width=\"600\" height=\"380\" \/><\/p>\n<p>Figure\u00a02.\u00a0The skull of (a) Australopithecus afarensis, an early hominid that lived between two and three million years ago, resembled that of (b) modern humans but was smaller with a sloped forehead and prominent jaw.<\/p>\n<p id=\"fs-idm76349936\">In the mid-1970s, the fossil of an adult female\u00a0<em data-effect=\"italics\">A<\/em>.<em data-effect=\"italics\">\u00a0afarensis\u00a0<\/em>was found in the Afar region of Ethiopia and dated to 3.24 million years ago (Figure 3). The fossil, which is informally called \u201cLucy,\u201d is significant because it was the most complete australopith fossil found, with 40 percent of the skeleton recovered.<\/p>\n<p>Its brain size was 380\u2013450 cubic centimeters, approximately the size of a modern chimpanzee brain. It also had <b>prognathic jaws<\/b>, which is a relatively longer jaw than that of modern humans. In the mid-1970s, the fossil of an adult female <em>A<\/em>.<em> afarensis <\/em>was found in the Afar region of Ethiopia and dated to 3.24 million years ago (Figure\u00a03). The fossil, which is informally called \u201cLucy,\u201d is significant because it was the most complete australopith fossil found, with 40 percent of the skeleton recovered.<\/p>\n<div id=\"attachment_2607\" style=\"width: 1034px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2607\" class=\"size-large wp-image-2607\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/06222837\/Figure_29_07_05-e1486420130541-1024x424.jpg\" alt=\"Partial skeleton is human-like but child-sized.\" width=\"1024\" height=\"424\" \/><\/p>\n<p id=\"caption-attachment-2607\" class=\"wp-caption-text\">Figure\u00a03.\u00a0This adult female <em>Australopithecus afarensis<\/em> skeleton, nicknamed Lucy, was discovered in the mid 1970s. (credit: \u201c120\u201d\/Wikimedia Commons)<\/p>\n<\/div>\n<section id=\"fs-idm22448416\" data-depth=\"2\">\n<p id=\"fs-idp111171552\"><em data-effect=\"italics\">Australopithecus africanus\u00a0<\/em>lived between two and three million years ago. It had a slender build and was bipedal, but had robust arm bones and, like other early hominids, may have spent significant time in trees. Its brain was larger than that of\u00a0<em data-effect=\"italics\">A<\/em>.<em data-effect=\"italics\">\u00a0afarensis\u00a0<\/em>at 500 cubic centimeters, which is slightly less than one-third the size of modern human brains. Two other species,\u00a0<em data-effect=\"italics\">Australopithecus bahrelghazali\u00a0<\/em>and<em data-effect=\"italics\">\u00a0Australopithecus garhi<\/em>, have been added to the roster of australopiths in recent years. A.\u00a0<em data-effect=\"italics\">bahrelghazali<\/em>\u00a0is unusual in being the only australopith found in Central Africa.<\/p>\n<\/section>\n<section id=\"fs-idp23125440\" data-depth=\"2\"><\/section>\n<h2>A Dead End: Genus <em>Paranthropus<\/em><\/h2>\n<section id=\"fs-idp23125440\" data-depth=\"2\">\n<p id=\"fs-idp17351584\">The australopiths had a relatively slender build and teeth that were suited for soft food. In the past several years, fossils of hominids of a different body type have been found and dated to approximately 2.5 million years ago. These hominids, of the genus\u00a0<em data-effect=\"italics\">Paranthropus<\/em>, were muscular, stood 1.3 to 1.4 meters tall, and had large grinding teeth. Their molars showed heavy wear, suggesting that they had a coarse and fibrous vegetarian diet as opposed to the partially carnivorous diet of the australopiths.\u00a0<em data-effect=\"italics\">Paranthropus<\/em>\u00a0includes\u00a0<em data-effect=\"italics\">Paranthropus<\/em>\u00a0<em data-effect=\"italics\">robustus\u00a0<\/em>of South Africa, and\u00a0<em data-effect=\"italics\">Paranthropus<\/em>\u00a0<em data-effect=\"italics\">aethiopicus\u00a0<\/em>and\u00a0<em data-effect=\"italics\">Paranthropus<\/em>\u00a0<em data-effect=\"italics\">boisei\u00a0<\/em>of East Africa. The hominids in this genus went extinct more than one million years ago and are not thought to be ancestral to modern humans, but rather members of an evolutionary branch on the hominin tree that left no descendants.<\/p>\n<\/section>\n<section id=\"fs-idp79276832\" data-depth=\"2\"><\/section>\n<h2>Early Hominins: Genus <em>Homo<\/em><\/h2>\n<p id=\"fs-idp81386448\">The human genus,\u00a0<em data-effect=\"italics\">Homo<\/em>, first appeared between 2.5 and three million years ago. For many years, fossils of a species called\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0habilis\u00a0<\/em>were the oldest examples in the genus\u00a0<em data-effect=\"italics\">Homo<\/em>, but in 2010, a new species called\u00a0<em data-effect=\"italics\">Homo gautengensis<\/em>\u00a0was discovered and may be older. Compared to\u00a0<em data-effect=\"italics\">A<\/em>.<em data-effect=\"italics\">\u00a0africanus<\/em>,<em data-effect=\"italics\">\u00a0H<\/em>.<em data-effect=\"italics\">\u00a0habilis\u00a0<\/em>had a number of features more similar to modern humans.\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0habilis\u00a0<\/em>had a jaw that was less prognathic than the australopiths and a larger brain, at 600 to 750 cubic centimeters. However,\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0habilis\u00a0<\/em>retained some features of older hominin species, such as long arms. The name\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0habilis\u00a0<\/em>means \u201chandy man,\u201d which is a reference to the stone tools that have been found with its remains.<\/p>\n<div class=\"textbox\">\n<p>Watch this video about Smithsonian paleontologist Briana Pobiner explaining the link between hominin eating of meat and evolutionary trends.<\/p>\n<p><iframe loading=\"lazy\" id=\"oembed-1\" title=\"Dietary Detective: Smithsonian Scientist Briana Pobiner\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/VYSw0EWwNhw?feature=oembed&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<\/div>\n<div id=\"attachment_2608\" style=\"width: 360px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2608\" class=\"wp-image-2608\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/06222924\/Figure_29_07_06.jpg\" alt=\"The photo shows a skull that looks similar to a human skull but has prominent brow ridges.\" width=\"350\" height=\"376\" \/><\/p>\n<p id=\"caption-attachment-2608\" class=\"wp-caption-text\">Figure\u00a04.\u00a0<em>Homo erectus<\/em> had a prominent brow and a nose that pointed downward rather than forward.<\/p>\n<\/div>\n<p id=\"fs-idm4268128\"><em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0erectus<\/em>\u00a0appeared approximately 1.8 million years ago (Figure 4). It is believed to have originated in East Africa and was the first hominin species to migrate out of Africa. Fossils of\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0erectus\u00a0<\/em>have been found in India, China, Java, and Europe, and were known in the past as \u201cJava Man\u201d or \u201cPeking Man.\u201d\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0erectus\u00a0<\/em>had a number of features that were more similar to modern humans than those of\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0habilis<\/em>.<em data-effect=\"italics\">\u00a0H<\/em>.<em data-effect=\"italics\">\u00a0erectus\u00a0<\/em>was larger in size than earlier hominins, reaching heights up to 1.85 meters and weighing up to 65 kilograms, which are sizes similar to those of modern humans. Its degree of sexual dimorphism was less than in earlier species, with males being 20 to 30 percent larger than females, which is close to the size difference seen in our own species.\u00a0<em data-effect=\"italics\">H<\/em>.\u00a0<em data-effect=\"italics\">erectus<\/em>\u00a0had a larger brain than earlier species at 775 to 1,100 cubic centimeters, which compares to the 1,130 to 1,260 cubic centimeters seen in modern human brains.\u00a0<em data-effect=\"italics\">H<\/em>.\u00a0<em data-effect=\"italics\">erectus<\/em>\u00a0also had a nose with downward-facing nostrils similar to modern humans, rather than the forward-facing nostrils found in other primates. Longer, downward-facing nostrils allow for the warming of cold air before it enters the lungs and may have been an adaptation to colder climates. Artifacts found with fossils of\u00a0<em data-effect=\"italics\">H<\/em>.\u00a0<em data-effect=\"italics\">erectus<\/em>\u00a0suggest that it was the first hominin to use fire, hunt, and have a home base.\u00a0<em data-effect=\"italics\">H<\/em>.\u00a0<em data-effect=\"italics\">erectus<\/em>\u00a0is generally thought to have lived until about 50,000 years ago.<\/p>\n<h2>Humans: <em>Homo sapiens<\/em><\/h2>\n<div id=\"attachment_2609\" style=\"width: 360px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2609\" class=\"wp-image-2609\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/06223001\/Figure_29_07_07.jpg\" alt=\"The illustration shows a very human looking Neanderthal wearing fur and cutting a hide with a stone tool.\" width=\"350\" height=\"263\" \/><\/p>\n<p id=\"caption-attachment-2609\" class=\"wp-caption-text\">Figure\u00a05.\u00a0The <em>Homo neanderthalensis<\/em> used tools and may have worn clothing.<\/p>\n<\/div>\n<p>A number of species, sometimes called archaic\u00a0<em data-effect=\"italics\">Homo sapiens<\/em>, apparently evolved from\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0erectus<\/em>\u00a0starting about 500,000 years ago. These species include\u00a0<em data-effect=\"italics\">Homo heidelbergensis<\/em>,\u00a0<em data-effect=\"italics\">Homo rhodesiensis<\/em>, and\u00a0<em data-effect=\"italics\">Homo neanderthalensis<\/em>. These archaic\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0sapiens<\/em>\u00a0had a brain size similar to that of modern humans, averaging 1,200 to 1,400 cubic centimeters. They differed from modern humans by having a thick skull, a prominent brow ridge, and a receding chin. Some of these species survived until 30,000 to 10,000 years ago, overlapping with modern humans (Figure\u00a05).<\/p>\n<p id=\"fs-idm37516176\">There is considerable debate about the origins of anatomically modern humans or\u00a0<span id=\"term1252\" data-type=\"term\"><em data-effect=\"italics\">Homo sapiens sapiens<\/em><\/span>. As discussed earlier,\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0erectus<\/em>\u00a0migrated out of Africa and into Asia and Europe in the first major wave of migration about 1.5 million years ago. It is thought that modern humans arose in Africa from\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0erectus\u00a0<\/em>and migrated out of Africa about 100,000 years ago in a second major migration wave. Then, modern humans replaced\u00a0<em data-effect=\"italics\">H<\/em>.<em data-effect=\"italics\">\u00a0erectus\u00a0<\/em>species that had migrated into Asia and Europe in the first wave.<\/p>\n<p id=\"fs-idm43043568\">This evolutionary timeline is supported by molecular evidence. One approach to studying the origins of modern humans is to examine mitochondrial DNA (mtDNA) from populations around the world. Because a fetus develops from an egg containing its mother\u2019s mitochondria (which have their own, non-nuclear DNA), mtDNA is passed entirely through the maternal line. Mutations in mtDNA can now be used to estimate the timeline of genetic divergence. The resulting evidence suggests that all modern humans have mtDNA inherited from a common ancestor that lived in Africa about 160,000 years ago. Another approach to the molecular understanding of human evolution is to examine the Y chromosome, which is passed from father to son. This evidence suggests that all men today inherited a Y chromosome from a male that lived in Africa about 140,000 years ago.<\/p>\n<div class=\"PageContent-ny9bj0-0 iapMdy\" tabindex=\"0\">\n<div id=\"main-content\" class=\"MainContent__HideOutline-sc-6yy1if-0 bdVAq\" tabindex=\"-1\">\n<div id=\"112cfa1a-5875-4fb6-a870-c71c74409adb\" class=\"chapter-content-module\" data-type=\"page\" data-cnxml-to-html-ver=\"2.1.0\">\n<section id=\"fs-idp19004672\" data-depth=\"1\">\n<section id=\"fs-idp59870416\" data-depth=\"2\">\n<p id=\"fs-idm37518298\">The study of mitochondrial DNA led to the identification of another human species or subspecies, the Denisovans. DNA from teeth and finger bones suggested two things. First, the mitochondrial DNA was different from that of both modern humans and Neanderthals. Second, the genomic DNA suggested that the Denisovans shared a common ancestor with the Neanderthals. Genes from both Neanderthals and Denisovans have been identified in modern human populations, indicating that interbreeding among the three groups occurred over part of their range.<\/p>\n<\/section>\n<\/section>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_1b28290c-02d9-4202-9dc8-58e71b037558\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/1b28290c-02d9-4202-9dc8-58e71b037558?iframe_resize_id=assessment_practice_id_1b28290c-02d9-4202-9dc8-58e71b037558\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-2590\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>Biology 2e. <strong>Provided by<\/strong>: OpenStax. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\">http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":17,"menu_order":26,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology 2e\",\"author\":\"\",\"organization\":\"OpenStax\",\"url\":\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction\"}]","CANDELA_OUTCOMES_GUID":"51d5b882-c815-4339-828a-0e2fe006efe1, 5e230415-76c8-47da-a4d9-31da1c8c8f69","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-2590","chapter","type-chapter","status-publish","hentry"],"part":148,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/2590","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":12,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/2590\/revisions"}],"predecessor-version":[{"id":8480,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/2590\/revisions\/8480"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/parts\/148"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/2590\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/media?parent=2590"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapter-type?post=2590"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/contributor?post=2590"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/license?post=2590"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}