Friday, August 1, 2014

From the Forest to the Garden - How Climate Change Forged Human Nature

How many of us have heard the story of Adam and Eve and the “Garden of Eden”? I wonder how a Tabloid newspaper would headline this story?  Hmm, something like... “God Discovers Naked Couple in Garden.”

I love the way that the story situates us in  the “garden”  and I really appreciate the uncanny way  that Genesis manages to touch all the bases of  human nature:   walking, pair bonding, egalitarianism, and language.

And,  as I have already pointed out, the story portrays Adam and Eve as naked. Their eventual recognition that they should cover up comes when they disobey God and eat from the fruit of the tree of knowledge. Note that Adam and Eve cover themselves with the leaves of the fig tree. One of the deep things about this story is how the images of the tree of knowledge and the leaves of the fig tree take us back to our pre-origins in the forest.
So at some point, maybe two million or so years ago, but long after we left the forest,  we lost a lot of body hair and we developed sweat glands. (the apes don’t have them, you know)  Consequently we developed a greater need for drinking water  compared to apes, which tied us to reliable sources of fresh water big-time.  Imagine trying to get enough water from puddles in the rain forest, especially if those forests were dying back.   

   Shedding the fur was a human evolutionary adaptation to climate change.  Check one  for Genesis.  


So what is human nature anyways?  Let’s say, you’re hiking along a trail, looking for a place to camp. It will need to have trees, open spaces and a nice view of water…Or, you’re a billionaire and want to buy the perfect match of house and landscape.  It will need to have trees, open spaces and a nice view of water.  Choice real estate means location, location, location.  

Anthropologist, Clive Finlayson,  in his book,  The Improbable Primate (c. 2014) tells us that for millions of years humankind and hominids have preferred to live “in areas close to fresh water with trees and open spaces nearby.”    The hominid line that branched off from the great apes six million years ago, left the forest to live permanently in this sort of environment, which existed all over the earth and was alternately encouraged and then checked  by periods of glaciation and interglacials.   Open spaces, some trees,  and a water view.  That’s the garden.   Check two for Genesis.    

But six million years ago a group of Apes did not decide -”Hey Dudes, let’s start walking on our hind legs.   We’ll look more dignified and be able to make cool gadgets and carry them around with us.”  So, why did those furry little hominids start walking then?  

For aeons of time the big rainforests were like a green supermarket for apes.  Everything a group of primates needed was near-at-hand.  fruits, tubers, veggies, leaves, herbs, nesting materials, etc.

The trees were great protection against predators like the big cats, and there were lots more of them in those days - sabre tooth tigers…We’re talking real bad cats.  Those big cats could make mincemeat out of our ancestors.  Cats can climb trees but they have to have low hanging branches.  Apes can climb up any old kind of tree, the point being that having access to trees and being able to sleep in them high in the forest canopy keeps apes safer from predators.

So why did hominids start walking when the apes stayed in the forest?  According to Finlayson, it was climate change.  Six million years ago the ice ages became more severe.  The huge African equatorial rainforests  were shrinking and grasslands,  savannas,  and  deserts were getting larger.

 The major glaciation events of the Pleistocene era created a drier, cooler world with more water locked up in ice and less liquid fresh water available.  That meant that your basic body of fresh water was getting smaller and further between.  That meant that the ability to walk distances in the open, to follow game and search for permanent and seasonal water holes was an asset.

Even though it was riskier to be walking out in the open it sometimes meant the difference between dying of thirst or survival.  If big sections of forests died out because of the climate change, then the ability to walk distances would have benefited the first hominids.

In Darwin’s Theory of Evolution, changes in a species’ environment cause selective pressures on the reproductive success of different individuals that make up that species. Over time, this differential in reproductive success, if accompanied by periods of isolation from the parent species, can lead to speciation.

  The apes that  stayed in the forest,  evolved over time into Chimpanzees and Bonobos. But six million years ago the forest was shrinking, and water was getting scarcer.  

Walking  had a tremendous evolutionary potential, basically, the ability to quickly open access  to the many different environments that existed in places around the world.

To recap:  Walking was an advantage for the first hominids because glaciation up north made the climate drier, which shrunk the African rain forests and created a lot more deserts and grasslands, with bodies of fresh water only available at greater distances from each other.  The behavioural adaptation of walking on our hind legs opened up a cornucopia of new environments to hominids for the first time,  which allowed the first humans to migrate out of Africa and to populate the rest of the world. Tune in next week when I explain how.  

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