Starting in the Holocene period after the last Ice Age, we see a significant increase in the building of shell mounds as noted by anthropologist Katherine Szabo:
From about 17 000 years ago until about 7000 years ago the sea steadily rose as the ice of the last glacial maximum melted, inundating many areas of land that were previously dry. It is at this time that we see an increase in the number of sites with shell midden deposits. This has been an archaeological talking point over the last few decades - why did people start intensively exploiting marine resources at this time?
Some researchers have called this phase the "mega-midden" period because of the vast size of shell mounds created.
Shell mound builders in coastal Vietnam and probably also in Sundaland began expanding with the rapid rise in sea levels during the Holocene. One particular culture of Hoabinhian affinity developed an advanced fishing and sea/aquatic mammal hunting culture.
They made earthenware perforated spindle whorls for fishing nets, and also similar-looking earthenware net sinkers. They used whole shells, particularly cowries, for various purposes including as burial goods. Among the notable types found are Cypraea moneta (money cowrie), Cypraea tigris (tiger cowry) and Cypraecassis rufa (red helmet).
They made beads of shell and also apparently in some places of opaque glass. Jade/nephrite tools appear in regions associated with the culture. and less frequently tools made of shell.
The Nusantao, most likely Malayo-Polynesian or Proto-Malayo-Polynesian speakers, established distant settlements in areas explored earlier by others including their Proto-Austronesian ancestors. These events occured initially during the Mesolithic-Neolithic transition period, which I believe in this case is linked with earlier edge-grinding practices.
Some researchers have commented negatively on shellfish gatherers as people who acquired low status, and have characterized shellfish as a secondary protein source inferior to land-based game.
However, these concepts may be overly-simplified. Some shellfish today, for example, such as lobster are among the most expensive sources of high-quality protein and are generally thought of elite food. Oysters have a similar reputation and the oyster shell was conceived in Roman myth as the throne of the goddess Venus. Indeed, shellfish collection among fishing cultures is generally performed by women, while men take to the seas to fish and hunt.
One thing that modern research has shown is that shellfish and marine fish are
much higher, sometimes by many fold, in brain-specific fats as compared to meat and other protein sources.
For thousands of years shells, albeit of the non-edible kind, were used as money over most of the world throughout. Indeed, if we look at many cultures, the rise of status-based civilization is often linked with the sea-coasts, and in some cases with peculiar people depicted as amphibious humans.
I've suggested that these marine humans were none other than the Nusantao, whose sea-based lifestyle may have seemed peculiar to other observers. By virtue of their long-range travel, these people had a major impact by transferring ideas to and fro, and also because they had an inter-related economic and spiritual agenda.
Paul Kekai Manansala