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1 Am I a Monkey?
- Johns Hopkins University Press
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Am I a Monkey? Iam a primate. Monkeys are primates, but humans are not monkeys. Primates include monkeys, apes, and humans. Humans are more closely related by descent to apes than to monkeys. That is, the apes are our first cousins, so to speak, while the monkeys are our second or third cousins. Among apes we are most closely related to the chimps, less so to the gorillas, and even less to the orangutans. The human lineage separated from the chimp lineage about 6 or 7 Ma (million years ago). We know about these matters in three ways: by comparing living primates, including humans, with each other; by discovery and investigation of fossil remains of primates that lived in the past; and by comparing their DNA, proteins, and other molecules. DNA and proteins give us the best information about how closely related we are to each of the primates and they to each other. But to learn how human lineage changed over time as our ancestors became more and more humanlike, we have to study fossils. Darwin’stheoryofevolutionassertedthathumansandapes share common ancestors, which were not human. His contemporaries questioned where the “missing link” was, the intermediate organism between apes and humans. Darwin pub- 4 AB Am I a Monkey? lished his best-known book, The Origin of Species, in 1859; in 1871, he published The Descent of Man, which extends the theory of evolution to humans; he died in 1882. Primates that were ancestors to humans after our lineage separated from the chimp lineage are called hominids (or hominins). At the time of Darwin’s death, no hominid fossils ancestral to modern humans were known, although he was persuaded that they would eventually be found. The first hominid fossil was discovered in 1889 by a Dutch physician, Eugene Dubois, on the island of Java. It consisted of a femur and a small cranium. Because he was expert in human anatomy, Dubois knew that these fossils belonged to an individual with bipedal gait; the femur was very similar to the femur of a modern human. But the capacity of the small cranium was about 850 cc (cubic centimeters), which could hold a brain weighing somewhat less than 2 pounds (a pound is 454 grams, equivalent to 454 cc), while the cranium of a modern human is about 1,300 cc (with a brain of about 3 pounds). The fossil discovered by Dubois was from an individual who lived about 1.8 Ma and is now classified in the species Homo erectus. Our own species is called Homo sapiens. The “missing link” is no longer missing. The fossil from Java was the first one, but hundreds of fossil remains belonging to hundreds of individual hominids have been discovered in the twentieth and twenty-first centuries in Africa, Asia, and Europe and continue to be discovered at an accelerated rate. These fossils have been studied and dated using radiometric and other methods. Some fossil hominids are very different from others, as well as from humans, and are classified in different species. The record of fossil hominids that lived at [35.175.246.88] Project MUSE (2024-03-29 13:03 GMT) Am I a Monkey? AB 5 different times shows that several changes occurred through time in the lineage of modern humans. One change was increase in body size; another was increase in cranial capacity (and brain size). The species names are sometimes exotic, referring in some cases to the place where the fossils were found or their morphological characteristics and determined in others by the whim of the discoverers. The oldest known fossil hominids are 6 to 7 million years old, come from Africa, and are known as Sahelanthropus and Orrorin. Their anatomy indicates that they were predominantly bipedal when on the ground, but they had very small brains. Ardipithecus lived about 5.5 Ma, also in Africa. Numerous fossil remains from diverse African origins are known of Australopithecus, a hominid that appeared about 4 Ma. Australopithecus had an upright human stance but a cranial capacity of about one pound, comparable to that of a gorilla or chimpanzee and about one-third that of modern humans. The skull of Australopithecus displayed a mixture of ape and human characteristics—a low forehead and a long, apelike face but teeth proportioned like those of humans. Other early hominids partly contemporaneous with Australopithecus include Kenyanthropus and Paranthropus; both had comparatively small brains, although some species of Paranthropus had larger bodies. Paranthropus represents a side branch of...