How Does Mummification Work? Removing the Water Decay Needs

Decomposition begins immediately and proceeds in two overlapping ways. Autolysis is self-digestion: cells stop maintaining themselves, their enzymes leak out and begin breaking down surrounding tissue, which is why organs with high enzyme content, particularly the gut and pancreas, deteriorate first. Putrefaction follows, driven by bacteria, overwhelmingly the ones already present in the intestine, which spread through the body and produce the gases and the characteristic changes of advanced decay. Both processes require liquid water, both proceed faster at higher temperatures, and putrefaction is greatly accelerated by oxygen and by insect activity, since blowflies locate a body within minutes and their larvae consume soft tissue rapidly. Preservation therefore means interrupting one or more of these requirements, and the three routes available are drying, cold, and chemical conditions that kill or inhibit bacteria, which between them account for every preserved body ever found.

The Egyptian process was refined over three thousand years and the developed version, described by Herodotus and confirmed by examination of bodies, followed a consistent sequence:

• •Removal of the brain, usually through the nose with a hooked instrument, since it decays fast and was not thought important
• •Removal of the internal organs through an incision in the left side, with the lungs, liver, stomach and intestines preserved separately in canopic jars under the protection of four deities, while the heart was left in place as the seat of thought and judgement
• •Packing and covering the body with natron, a naturally occurring mixture of sodium carbonate and bicarbonate from the Wadi Natrun, which is both strongly drying and antibacterial, for around forty days
• •Cleaning, and treatment with resins, oils and spices, which sealed the surface against moisture and added fragrance
• •Packing the cavities to restore shape, sometimes with linen, sawdust or sand, and in later periods inserting artificial eyes
• •Wrapping in many layers of linen with amulets placed at specific points, a process taking days and consuming enormous quantities of cloth
• •The whole undertaking was reported as taking about seventy days, and simpler and cheaper versions were available for those who could not afford the full procedure

Nature produces preserved bodies through each of the same mechanisms without any intention. Desiccation in hot dry conditions is the oldest route, and predynastic Egyptian burials directly in hot sand produced naturally dried bodies, which is very likely what gave Egyptians the idea; the irony is that the elaborate coffins of later periods, by separating the body from the sand, made artificial preservation necessary. Freezing preserves through cold and dryness, as in Otzi, the man found in an Alpine glacier who died around 3300 BCE, and the Inca children found on Andean summits. Bogs preserve through acidity, cold and oxygen-free water, tanning the skin while dissolving the bones. Salt does it by drawing out water, as with the miners preserved in an Iranian salt mine. Anoxic dry conditions in caves and crypts produce mummies across the world, including in Sicily and in the Guanajuato cemetery in Mexico. The Chinchorro of coastal Chile were producing artificial mummies around 5000 BCE, about two thousand years before the Egyptians.

Ancient remains are now examined with methods that leave them intact, which matters because earlier generations unwrapped mummies at public parties and destroyed them. Computed tomography reconstructs the interior in three dimensions, revealing packing, amulets, injuries and diseases, and has established that atherosclerosis was common in ancient Egyptians, undermining the assumption that it is purely a modern disease. Ancient DNA recovered from teeth and bone gives ancestry and relationships, and has resolved family questions in royal burials. Isotopes in hair and bone record diet and geographic origin, so a body can indicate where a person lived in their final months. Stomach contents give a last meal, and in bog bodies with striking precision. Parasites, pathogens and pollen can all be recovered. The ethical questions have grown alongside the techniques, with museums reconsidering the display of human remains, the use of the word mummy in favour of naming the person where known, and the claims of descendant communities over bodies held in collections far from where they were taken.

Decay is driven by the body's own enzymes and by intestinal bacteria, both of which need liquid water, so preservation means drying, freezing or creating conditions bacteria cannot tolerate. Egyptian embalmers removed the brain and most organs, packed the body in natron for about forty days, sealed it with resins and wrapped it, taking around seventy days in total. Nature does the same accidentally through desert sand, glaciers, acidic bogs, salt and dry crypts, and the Chinchorro of Chile were mummifying bodies two thousand years earlier.