Author Archives: peduus

An Inseparable History: The Coevolution of Stone Tools and the Human Hand

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In thinking about the 2.6 million year history of stone tools, we often discus the ways in which hands shaped stone; but how did the tools they made shape the hands we use today?

Not surprisingly, the ability to make stone tools had a huge effect on the anatomy of the human hand. Individuals whose hands were better suited to making tools were better able to hunt and protect themselves; this made them more evolutionarily fit (able to produce more offspring), leading to an eventual proliferation of the genes involved in the better hand formation. So when stone tools went from simple banged rocks to complex hand-axes around 1.7 million years ago, this reflected not only an intellectual step but a biological one.

An artist's rendition of a member of the species Homo habilis making a tool of the Oldowan type.

An artist’s rendition of a member of the species Homo habilis making a tool of the Oldowan type.

Before this new technology, the fossil record shows that hominin hands had primitive vestige structures. Although Homo habilis (named the “toolmaker” because of the primitive Oldowan tools found in associated strata) had more advanced hands than those of their predecessors the australopithecines, they were not fully modern. Their fingers had a gentle curve like those of the austrolopithicines, and their wrist morphology resembled that of a part-time arboreal species. Despite these primitive traits, the more modern proportions and joint connecting the finger bones to those of the palm allowed Homo habilis to be credited with the invention of stone tools.

For a long time, the hand’s evolution from 1.7 million years ago (when Homo erectus first shows up in the fossil record and shortly before Homo habilis disappears from it 1.4 million years ago) to about 800,000 years ago was a mystery to paleoanthropologists. Hominin fossils are a rare find at best, and small finger bones especially are easily broken in the millennia they spend in the soil before being excavated. Stone tools, on the other hand, are much more easily preserved. During this almost 1 million year gap, stone tool technology advanced greatly, enough to warrant a new name – Acheulean industry. But what morphological difference had made this advancement possible?

Hand axes of the Acheulean type.

Hand axes of the Acheulean type made and used by the species Homo erectus.

 

A recent discovery has shed some light on this question. In 2010, a team of paleoanthropologists led by Fredrick Kyalo Manthi of the National Museums of Kenya found what appeared to be a finger bone in northern Kenya. It was identified as a third metacarpal, the bone that connects the middle finger to the wrist. Using isotope analysis, it was dated to 1.4 million years ago and attributed to the species Homo erectus. What’s  interesting about this bone is the small bump at its base – the styloid – a feature found in modern humans. What seems like a small structural change has huge implications; the styloid helps stabilize the wrist, increasing griping power between the thumb and forefinger. This change was instrumental in the ability to make finer, more precise percussions to the core, resulting in more fine-tuned tools with which Homo erectus became the first multi-continental hominin. None of this would have been possible without the mutual selective pressure between early humanity and its tools.

 

 Sources:

Reardon, Sara. “Stone tools helped shape human hands.” New Scientist, 11 April 2013. http://www.newscientist.com/article/mg21829124.200-stone-tools-helped-shape-human-hands.html#.Um1JMpE7ZuZ

University of Kent. “Stone tools influenced hand evolution in human ancestors, anthropologists say.” ScienceDaily, 8 Mar. 2011. http://www.sciencedaily.com/releases/2011/03/110307101504.htm

Homo habilis image URL: http://earlyman.yolasite.com/resources/homo%20habilis%203.jpg

Hand ax image URL: http://upload.wikimedia.org/wikipedia/commons/thumb/8/87/Biface_Cintegabelle_MHNT_PRE_2009.0.201.1_V2.jpg/640px-Biface_Cintegabelle_MHNT_PRE_2009.0.201.1_V2.jpg

Childhood Archaeology

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When I was a kid, summer weekends meant time at the family country house in Western Massachusetts without any cell phone service, Internet connection, or television. Built on an old 18th century farm, there simply isn’t the infrastructure to support those 21st century luxuries. As it turned out, my inability to watch Saturday morning cartoons was a blessing in disguise.
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Every morning at the crack of dawn I left the house and walked around looking for things. I wandered the lawns and fields and brook looking for things that stuck out from the landscape. I found rusty nails, old bits of tractors and cars, animal bones, bricks, and remains of toppled buildings. I imagined the stories of the items I had found, and like many people who have dug up rusted bits of metal and bone on their property, I thought I had made some pretty important discoveries. “Look!” I thought as I held a rusty piece of farm equipment that I had taken out of the brook that morning in my hand, “this shows so much about those people’s lives!” But what had I really learned? That there had been a farm here? That metal rusted over time? I knew all of those things; I hadn’t learned anything from my precious artifacts.

Like so many “backyard archaeologists” I had failed to see my finds in their archaeological context, forgoing any real knowledge of history I could have acquired from them. It simply didn’t occur to me that to learn anything, I couldn’t just go around picking up pieces of metal and gleaning facts about them Sherlock Holmes style. I should have mapped out the section of the brook, record the artifacts precise location, asked myself more questions that had never occurred to me. Was this artifact in its primary context? Or had it been uncovered and washed down the brook to where I picked it up? Would further excavation have turned up more artifacts and features? Was the user of this tool the same person who built the stonewall that stands 25 feet up the bank? I didn’t ask any of these questions, I simply pictured some farmer from blurred decades and centuries tossing junk into the water.
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As I’ve become more aware of the complexity of the archaeological process, from surface survey to excavation to data analysis, I think of those artifact I found as a child not as individual pieces of rusted junk, but as a trail of bread crumbs; which upon proper analysis could lead to insights about the history of the property and its transformation from working farm to family house. Maybe next summer I’ll excavate the area of the field where a barn burned down in the 1960s. And this time I’ll actually take the steps necessary to learn something valuable from those little pieces of metal I find.