One down, Five to go…

I hope to post summaries of all my classes from the past semester up here – this is the first one of four.

Man in the Pleistocene

If there is any way to summarize the last seven million years of human prehistory, it is that time has unraveled with surprising slowness punctuated by moments of rapid fastness.  From the moment of first divergence seven million years ago (Sahelanthropus tchadensis) to the most recent non-human hominids (homo heidelburgensis), change has occurred gradually over time. This accretional change is supplemented by moments of disequilibrium forcing rapid evolutionary development. These moments of instability create opportunities for change – not in any teleological sense – but rather windows in time open, created by population pressure, climate change, and catastrophic events,  to force speciation events.

So when do humans and chimps diverge?  We think somewhere on the order of 6-8 mya – one of the newest fossil finds, Ardipithecus Kaddaba dates to around 5.6 mya and has been used to substantiate the “old but complex” argument for the evolution of humans. It appears that while we diverged at this early time,  humans did not leave Africa for at least3 million years, since no hominid predating 2 mya has been found outside of the Africa. These events take place within the Quaternary period (the pleistocene and holocene), although the largest radiation of our pre-hominid ancestors took place much earlier during the Miocene, in the Tertiary period.  Many theories abound as to what pushed our first divergence,  such at the evolution of the hand to knapping related activities, or to the enhanced needs of our brains to adapt to rapidly changing environments. Tools as a driving force in adaptational development was further expounded upon by Raymond Dart, who developed the notion of an “Osteodontokeratic” culture. At around 3 mya, Australopithecines (early hominids) are thought to begin using bone tools, a further elaboration of the “old but complex” way of thinking.  In the 1970’s Don Johanssen discovers the “Lucy” skeleton, Australopithecus afarenesis, finding it to have an apelike body with long upper limbs, curved fingers, a large thoracic skeleton, wide hips, and stubby legs – not at all morphologically similar to anatomically modern humans. At around 2 mya,  we see an expansion in cephalic development and a slow progression towards much larger brain cases.  The earliest example of this, Homo habilis, was a stone tool maker with an australopithecine body but modern head (1.8 mya). Many such early homo species exist, each moving forward in time to appear anatomically modern.  There are H. rudolfensis (1.8), erectus (1.6), heidelburgensis (1), and sapiens (archaic, 200 kya) to contend with.  What I’ve completely elided over is that with habilis, we also have the development of  the first stone tool industry, Oldowan tools at around 2 mya.  Some scholars might associate these early tools with Australopithecus garhi,  but the majority of archaeological data point to habilis.



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Filed under Academic Ramblings, Observations

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