Animals, which must carry their energy reserves with them, universally
have developed the involved chemistry of fats and fatty acids, for
the sake of the weight reduction, in using a nearly gasoline like
fuel. Stationary plants, for which portability and a high energy-to-mass
ratio are of no advantage, have opted instead for the simplicity
of carbohydrate chemistry. However, animals do make one use of carbohydrates
as an energy reservoir.
They synthesize glycogen (animal starch), which is a more highly
branched version of amylopectin, with branching every 8-10 glucose
units. Glycogen in the liver and muscle tissues serves as a special
rapid access energy store - a buffer between the immediate needs
of the animal and the long-term energy supply in fats.
Thus animals have the best of both worlds, and a good analogy exists
between this energy-storage strategy and currency.
Paper money in Europe was developed in the 1600's to combat the
danger and inconvenience of carrying large amounts of gold and silver
coin from place to place.
The Italians developed the Girobanks ("circulation banks")
to assist the transfer of credit from one city to another, and these
Girobank notes gradually became accepted as substitutes for the
money they represented.
Paper currency was easier to carry than metal, but sometimes was
difficult to use. Persuasion and discounts would be needed to get
currency accepted as payment in out-of-the-way places. A sedentary
businessman could keep all of his wealth in gold and silver.
The traveler would transfer his bulk accounts in bank notes (starch)
for the sake of efficiency, but would be careful to keep small amounts
in coin for immediate use. Glycogen is the metal coinage of animal