Physical Anthropology, Part 5

Question 1: Discuss the Miocene epoch hominoids

Answer 1: During the Miocene epoch (~23-5 m.y.a.), early hominoids antecedent to but different from present-day apes evolved. Fossils from the early part of the epoch indicate three species of the Proconsul group in Africa, characterized by dentition similar to current apes but a skeleton more like that of a monkey. Approximately 16 m.y.a. at the start of the middle part of the Miocene epoch, a land bridge developed between Eurasia and Africa providing migratory opportunities. Fossils of protoapes from this time have been discovered in various areas usually coexisting with our genus of Homo erectus. These include the extremely large Gigantopithecus, which probably lived in Asia until about 400,000 years ago. More recent finds from this time period include Pierolapithecus catalaunicus, from about 13 m.y.a. in Spain, which some believe is the last common ancestor to modern great apes including humans; Sahelanthropus tchadensis or Toumai, from about 7 to 6 m.y.a. in Chad, possibly the oldest known human descendant; Orrorin tugenensis, from about 6 m.y.a in Kenya, a bipedal creature with many resemblances to a chimp; and Ardipithecus (discussed elsewhere).

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Question 2: Discuss how bipedalism developed and its significance.

Answer 2: Bipedalism, the ability to walk upright on two feet, is considered the fundamental feature that distinguishes early hominins from apes. The earliest identified and recognized ones belong to the genus Ardipithecus, examples of which have been found in Ethiopia dating from 5.8 to 4.4 m.y.a. Most experts believe that bipedalism developed during the Miocene epoch in some primates because of geological factors more than 5 million years ago. There was a shift toward a cooler, drier climate and more grassland in Africa. There was also a sinking of the Rift Valley and development of mountains in what is present-day Ethiopia, Kenya, and Tanzania. Primates east of this range started using bipedalism in order to navigate the grasslands more easily and view predators, while still sleeping and hiding in trees. Another explanation is that walking upright kept these hominins cooler due to less exposure to solar radiation. To the west of this range, the environment had more trees and was more humid, favoring chimpanzees.

Question 3: Discuss the traits other than bipedalism that characterize hominins

Answer 3: Hominins are the tribe that humans belong to. Early hominins had much smaller brains, similar in size to those of a chimpanzee, than modern humans. Brain size relative to other parts of the anatomy has increased over the ages because of the demands of upright bipedal locomotion. The pelvic and trunk regions need to be smaller for posture. Walking upright makes it difficult to have too large of a pelvic opening. Brain and skull size also became larger because humans have an extended period of childhood dependency. Early hominins had larger back teeth than modern humans because they needed them to chew tough, fibrous vegetation in the grasslands. As humans evolved, dentition has gotten smaller. Early hominins created and used tools, which was facilitated by bipedalism. Use of tools is still unique to hominins.

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