How Were Shells Used as Money? A Currency With Real Advantages

Anything serving as money has to satisfy a set of practical requirements, and the shells used most widely met them unusually well. It must be durable, and these shells are hard and essentially do not decay. It must be portable, and they are light for their value. It must be divisible in the sense of coming in convenient units, and they are naturally uniform in size. It must be difficult to counterfeit, and a shell of a particular species from a particular region cannot be manufactured. And its supply must be limited, which held as long as the sources were distant and controlled. Those properties are why they were adopted independently in several places rather than by imitation.

The geography of the trade is specific and revealing:

• •Cowrie shells from the Maldives and a few other Indian Ocean sources supplied most of the world's supply
• •They circulated as currency across West Africa, in parts of India and China, and in the Pacific
• •Values were reckoned in strings and bags of standard counts rather than individually
• •Chinese characters relating to money and value incorporate the shell sign, recording early use
• •In several regions they coexisted with metal currency, handling small transactions
• •Other shell currencies existed independently, including wampum in northeastern North America

The system collapsed when European shipping removed the natural limit on supply. Traders discovered that shells obtainable cheaply in the Indian Ocean commanded high value in West Africa, and imported them in enormous quantities as ballast and as trade goods, with imports running into thousands of tonnes over the nineteenth century. The predictable result was severe inflation, with the quantity of shells needed for a given purchase rising many times over a few decades, which destroyed the currency's usefulness and the savings held in it. Colonial administrations then demonetised it in favour of imperial coinage. The episode is a clean natural experiment in monetary economics, since the supply shock is documented and the price response followed as theory predicts.

Setting the shells beside other commodity currencies clarifies what made them work. Salt was used across several regions and is durable enough when dry and useless when wet. Cattle served widely and are the origin of several words relating to wealth, and they are not divisible without destroying the value. Cloth strips circulated in West Africa and in Asia and wear out. Metal bars and rings preceded coinage and required weighing at every transaction, which is what stamping a coin removes. Large carved stone discs on one Pacific island functioned as money without being moved at all, with ownership transferring by agreement, including for one famously lost at sea and still counted. Each of these satisfies some of the requirements well and fails others, which is what the shells did unusually well overall.

The case corrects several assumptions about what money is. It shows that a currency need not be issued by a state, since these circulated with no issuer at all and their value rested on convention and on scarcity. It shows that intrinsic usefulness is not required, since the shells had no substantial use beyond ornament. It demonstrates that the quantity theory relating supply to prices operates outside modern economies. And it illustrates that a currency's stability depends on the cost of obtaining more, which is the same property that made gold work and that fiat currencies replace with institutional restraint. The wampum case shows the same pattern, with European manufacture of counterfeits and mass production collapsing its value within decades.

The shells were durable, portable, naturally uniform, impossible to counterfeit and limited in supply, which is why several regions adopted them independently. Almost all came from a small number of Indian Ocean sources. European shipping removed the supply limit, importing thousands of tonnes and producing severe inflation that destroyed the currency within decades.