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Lecture 28 - Hominin Adaptations

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Esteban Parra

ANT203Y5 – BiologicalAnthropology Lecture 28 – March 6, 2014 Quiz next Thursday: - Book chapter 7-9. Look at them carefully (chapter 7) that is devoted to growth development in humans HomininAdaptations - The first split happened 12-16 mya with the Orangutans - Then the gorillas split from 6-8 mya - Then closely after, the Chimps and humans split around 5-7 mya Traditional Classification - This is the incorrect from the cladistics point of view - In the traditional classification, it is not only the phylogenetic history - This is not correct from the evolutionary point of view New Classification More Consistent with Current Evidence - Hominidae now encompasses all the great apes and humans - Now all member of the human family are called hominin because they are from the tribe “Hominini” Important NoteAbout Nomenclature that will be used in this Course - In the remaining lectures of this course we will refer to the members of the human lineage as “hominins”, following the cladistic classification. - However, you should be aware that the term “hominids”, is still used quite often. ANT203Y5 – BiologicalAnthropology Lecture 28 – March 6, 2014 What is a Hominin? - So you found a fossil! - And you can date it with some of the methods described before…. - Next problem arises…. o Is it a hominin fossil? Some Times, it is not easy to know! - The closer you are to the time of the last common ancestor between chimps and humans (7-5 m.y ago), the more difficult to clearly assign the fossil to the hominin lineage. o Salaranthropis andAurori were the earliest fossil evidence we have of human. But we only have one fossil (bone) for each type, so it is hard to tell whether they were from the human lineage or from the primate lineage. What Makes Us a Hominin? - Many scientists have pointed to these three diagnostic traits…. - Bipedal locomotion. - Large brain size. - Toolmaking behavior Hominin Traits - However, now it is known that two of these traits, large brain size and toolmaking, appeared relatively late in hominin evolution. - The first hominins had small brain size, and the first evidence of lithic industries have been dated around 2.5 m.y. ago, several m.y. later than the first hominin fossils. - In contrast, there is evidence of bipedalism in the earliest stages of hominin evolution. Bipedal Locomotion - Great apes use bipedal locomotion from time to time…. - However, only hominins among primates use erect bipedalism as the primary form of locomotion. So, Why Did We Become Bipedal? - There are many hypotheses attempting to explain the origin of bipedalism. - At the moment, there is no clear answer to this question…. The “Savanna” Hypothesis - During the late Miocene period, the climate changed inAfrica, becoming cooler and drier. o Apes radiated dramatically during the Micocene o There was warming, so the tropical forest expanded, and then you could see apes everywhere. But later in the Miocene, the climate changed and become cooler and drier - Large forests began to shrink, and gave way to increased grasslands (Savanna). - In the past, many anthropologists had considered this ecological change critical for the adoption of bipedalism. o It became more difficult to find food (search for farther distance) ANT203Y5 – BiologicalAnthropology Lecture 28 – March 6, 2014 - The Savanna environment imposed new challenges, such as increased difficulty finding food, need to travel longer distances, hotter temperatures and greater vulnerability to predators. - This environmental context favored the adoption of bipedalism as the main form of locomotion. Problem with the Savanna Hypothesis - Recent findings challenge this interpretation. - The earliest generally accepted hominin, Ardipithecus ramidus, lived in wet forests and woodlands, but were already bipedal. Still Trying to Find an Explanation - Thus, it is not yet clear what selective factors favored the adoption of bipedalism. Alist of possible factors in indicated in the next slide. - More research is clearly needed, as well as more information on early hominins, to better understand their anatomy, habitat and behavior (present information based on limited findings). Some Hypotheses - Carrying (tools, food) - Energy efficiency o The human type of bipedalism is more efficient than the type of bipedalism of chimps and gorillas - Habitat variability
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