From the moment we die our bodies start to break down. This process of decomposition involves a cascade of chemical processes involving enzymes and bacteria, which steadily digest the body.
No two humans decay in exactly the same way, as a number of factors affect both the rate and sequence of decomposition, including temperature, humidity and alkalinity. But, overall, the process follows the same key stages. Understanding these extraordinary and complex molecular events goes to the very heart of forensic science.
Autolysis and Putrefaction
Decomposition begins just minutes after death. Early changes to the body include a drop in core temperature, stiffening of the limbs known as Rigor Mortis and a pooling of the blood under the pressure of gravity known as Post Mortem Lividity.
The onset of death also triggers a process called Autolysis, or self-digestion, whereby our own enzymes literally turn against us, digesting our cells from the inside out, and causing them to rupture and release fluids. This liquefying process rapidly spreads across the whole body, with the first visible signs appearing as blisters and loosening of the skin, known as 'skin slippage'. As the cells rupture and fluids steadily build up, the body becomes a moist environment, and ideal breeding ground for bacteria and other micro-organisms.
This next stage in the decay process is called Putrefaction. As these micro-organisms break down the soft tissue, they produce a steady build up of gases including ammonia, methane, and carbon dioxide. As these gases accumulate the body becomes increasingly bloated, particularly around the bacteria-rich area of the intestines.
Chemical processes also turn the skin a distinct greenish colour, as sulphur-containing hemoglobin settles in the blood, and bacteria enter the veins creating a visible, dark marbling effect of the skin surface.
Insects
Insects play a major role in decomposition. First on the scene are blowflies, which can detect a dead body within minutes of death - from many miles away. They lay eggs within the first hour, and the blowfly larvae will feed on the tissues and liquids, and in turn a succession of other flies and beetles will appear, collectively breaking down different parts of the soft tissue.
Active Decay and Skeletonisation
In the active decay phase, bacteria and insects continue to break down the body proteins and fats giving the body a deflated and wet appearance, as well as a strong odour.
The final stage of decomposition is skeletonisation, when the flesh has been completely broken down and only dry bone remains. Depending on the environmental conditions, the body may never get to this stage - but instead can become naturally mummified.
Mummification
Mummification occurs most commonly in dry conditions which slow down or arrest the process of putrefaction. Typical features of a mummy include dry, leathery skin that has been completed desiccated. In Ancient Egypt, the desert conditions naturally preserved bodies in this way - before embalmers started to develop the 'artificial' practice using natron salt to dry out the tissues.
But, deserts are not the only place where natural mummies have been found.
Dry, cold environments have also created extraordinary mummies, the most famous being Otzi the Iceman and the 'bog bodies' of Northern Europe, which have been preserved predominantly through a lack of oxygen and acidic environments that tan the tissues.
Although many ancient cultures preserved their dead in various ways, the Egyptians remain the best known and arguably the most successful mummy makers of all.
Their need to preserve the dead was part of a highly complex belief system which maintained that at death an individual's soul was reborn into another stage of existence. Here it would be judged by the gods who would weigh the individual's heart to find out if they had led a good life. If the heart was heavy with sin it was condemned and destroyed, when a second, final death occurred. Yet if their heart was pure, their soul was allowed to pass through into the Afterlife and live forever in a perfect environment, based on the Egyptian landscape. Here the soul could travel around at will, although it still needed to return to its original body which formed its permanent home.
This explains why the Egyptians went to such great lengths to preserve the body after death. This was particularly important in the case of their rulers, the pharaohs, each of whom contained within them a divine soul regarded as the essence of Egypt itself. With this soul maintained and nurtured by special temple rituals during life, it was essential that at death every pharaohs body was perfectly preserved to house this soul, the accumulated powers of which could be accessed in magical rituals to maintain Egypt's well being.
Yet the most perfect levels of preservation were only achieved after centuries of experimentation and a considerable amount of trial and error.
Although the earliest bodies were buried in hollows in the desert, where the hot sand dried the skin and allowed corrosive bodily fluids to drain away, there is evidence that by c.4500 BC some were also wrapped in linen and coated in various oils and resins. These early bodies were often buried facing east toward the rising sun, with their arms and legs drawn up to the body in the 'foetal' position suggesting an early belief in rebirth.
As society developed, the wealthier classes wanted more elaborate burial to reflect their status so began to be buried in purpose-built stone tombs. Yet no longer in direct contact with the hot dry sand, their bodies soon decomposed, leading to the need to remove the internal organs by c.2600 BC. With the previously flexed body now laid out flat to give access to the abdominal area, there is also evidence that the Egyptians had begun to use naturally occurring natron salt as a preservative, in some cases mixing it in water to use as a solution, but most often in its dry form, piled over the body to draw out the body fluids and preserve the skin.
In this way the Egyptians produced mummies for centuries until the dawn of the 18th dynasty c.1500 BC when a new regime brought in dramatic political and religious changes. These changes were even reflected in the way this new dynasty's royal dead were mummified, the life-like results they achieved now resurrected in the mummification of Alan Billis.
Further reading:
John Taylor, Death and the Afterlife in Ancient Egypt, British Museum Press (London), 2001.
Stephen Quirke, Ancient Egyptian Religion, British Museum Press (London), 1992.
Joann Fletcher, The Egyptian Book of Living & Dying, Duncan Baird (London), 2009.
