Environmental Engineering Reference
In-Depth Information
Ultimately, all life on Earth is supported by the relationship between the sun and
autotrophic organisms, as the energy stored in their cells is transferred to other organisms
in the food chain. At the end of its life, every organism enters what is called the detritus
chain: its biomass is decomposed by insects and bacteria. As a result, the complex organic
molecules, full of chemical energy, that make up the organism return to the soil as simple
inorganic molecules that can be recycled into biomass by autotrophs. In this way, all life is
part of an energetic flux. The irony of our recent 'discovery' of recycling as an approach to
waste management is that all the processes on which our lives depend involve the principle
of recycling. When herbivores eat grass or carnivores eat herbivores, they consume part of
the solar energy stored in biomass via photosynthesis. The atoms that comprise our body
belonged just a few days ago to another living organism, and perhaps a few years ago to
another human being.
1.6 From Rubbing Sticks to Splitting Atoms: The History of
Human Energy Use
According to the American biophysicist Alfred Lotka, any organism or organic system
will tend to increase in size and complexity as long as there is enough available energy.
Mould, for example, will spread over a piece of moist bread as long as there is space
available and organic material from which to recover energy. Once this energy source is
exhausted, the mould dies and is itself consumed by bacteria. Humans, like all animals,
are heterotrophs, obtaining our energy by ingesting organic compounds. The astonishing
reproductive success of our species is largely attributable to our consistent ability to
discover new sources of energy and to optimise their use.
BetweensevenandsixmillionyearsagothedominantvegetationinEastAfricachanged
from woody forest to savannah. Formerly tree-dwelling primates were forced to adapt to
lifeonopengrasslands.Evolutionaryscientistshaveidentifiedthisasthemomentwhenthe
earliest stageofthehumanline(knownashominids)divergedfromtheevolutionary lineof
apes (Pollard 2009 ). The change in environment forced the first major evolutionary change
in the history of humankind: the development of upright gait (Lovejoy 1988 ; McHenry
2009 ; Wong 2006 ). The major advantage of walking upright was that it freed up the
front limbs for other uses. The evolution of the human hand with its opposable thumbs
allowed us to grasp and hold objects, leading to another great evolutionary achievement:
the manufacture and use of tools.
Scientists have interpreted the use of tools as a key indicator of intelligence, yet tool
usage was probably as much a cause as an effect of greater brain power. As early humans
experimented with more complex and intricate tools, they came to rely more on cognitive
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