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 <title>Early Hominins: Genus <emphasis effect="italics">Australopithecus</emphasis></title>
-<para id="fs-idp37739504"><emphasis effect="italics">Australopithecus</emphasis> (“southern ape”) 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 <emphasis effect="italics">Homo</emphasis>, evolved from a common ancestor shared with <emphasis effect="italics">Australopithecus</emphasis> about two million years ago (after likely passing through some transitional states). <emphasis effect="italics">Australopithecus </emphasis>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 <emphasis effect="italics">Australopithecus </emphasis>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 <emphasis effect="italics">Australopithecus </emphasis>had in common with modern humans was bipedalism, although it is likely that <emphasis effect="italics">Australopithecus</emphasis> also 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 <emphasis effect="italics">Australopithecus </emphasis>were walking upright.</para><para id="fs-idm76349936">There were a number of <emphasis effect="italics">Australopithecus </emphasis>species, which are often referred to as <emphasis effect="italics">australopiths</emphasis>. <emphasis effect="italics">Australopithecus anamensis </emphasis>lived about 4.2 million years ago. More is known about another early species, <emphasis effect="italics">Australopithecus afarensis</emphasis>, 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. <emphasis effect="italics">A</emphasis>.<emphasis effect="italics"> afarensis </emphasis>(<link target-id="fig-ch29_07_04"/>a) 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. In the mid-1970s, the fossil of an adult female <emphasis effect="italics">A</emphasis>.<emphasis effect="italics"> afarensis </emphasis>was found in the Afar region of Ethiopia and dated to 3.24 million years ago (<link target-id="fig-ch29_07_05"/>). The fossil, which is informally called “Lucy,” is significant because it was the most complete australopith fossil found, with 40 percent of the skeleton recovered.</para><figure id="fig-ch29_07_04"><media id="fs-idp97597168" 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.">
+<para id="fs-idp37739504"><emphasis effect="italics">Australopithecus</emphasis> (“southern ape”) 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 <emphasis effect="italics">Homo</emphasis>, evolved from a common ancestor shared with <emphasis effect="italics">Australopithecus</emphasis> about two million years ago (after likely passing through some transitional states). <emphasis effect="italics">Australopithecus </emphasis>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 <emphasis effect="italics">Australopithecus </emphasis>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 <emphasis effect="italics">Australopithecus </emphasis>had in common with modern humans was bipedalism, although it is likely that <emphasis effect="italics">Australopithecus</emphasis> also 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 <emphasis effect="italics">Australopithecus </emphasis>were walking upright.</para><para id="fs-idm76349936">There were a number of <emphasis effect="italics">Australopithecus </emphasis>species, which are often referred to as <emphasis effect="italics">australopiths</emphasis>. <emphasis effect="italics">Australopithecus anamensis </emphasis>lived about 4.2 million years ago. More is known about another early species, <emphasis effect="italics">Australopithecus afarensis</emphasis>, 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. <emphasis effect="italics">A</emphasis>.<emphasis effect="italics"> afarensis </emphasis>(<link target-id="fig-ch29_07_04"/>a) 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. In the mid-1970s, the fossil of an adult female <emphasis effect="italics">A</emphasis>.<emphasis effect="italics"> afarensis </emphasis>was found in the Afar region of Ethiopia and dated to 3.24 million years ago (<link target-id="fig-ch29_07_05"/>). The fossil, which is informally called “Lucy,” is significant because it was the most complete australopith fossil found, with 40 percent of the skeleton recovered.</para><figure id="fig-ch29_07_04"><media id="fs-idp97597168" alt="Photo A shows an A. afarensis skull, which is similar in shape but the forehead slopes back and the jaw juts out. Photo B shows a human skull.">
 <image mime-type="image/jpg" src="../../media/Figure_29_07_04ab.jpg" width="475"/>
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 <caption>Australopithicene and modern human skulls. The skull of (a) <emphasis effect="italics">Australopithecus afarensis</emphasis>, 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, larger teeth, and a prominent jaw.</caption></figure><figure id="fig-ch29_07_05"><media id="fs-idp114323744" alt="Partial skeleton is human-like but child-sized.">