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Thursday, 31 October 2019

What happens after death?

Myths persist that death is somehow toxic or disgusting – a myth that dates back to before the theory of disease, when a common idea was that breathing the air of the dead could shorten your life. But modern research has shown this simply isn’t true: you can’t catch death, and dead bodies and the changes that happen to them are actually quite clean and safe. Natural decomposition processes allow a body to break down into its component parts, feed a plethora of insect life, and return the nutrients stored in it to soil.

Skull via Jakub T. Jankiewicz on flickr.
So where did the idea come from? Partly, it’s due to hysteria. When the origin of diseases were unknown, it was natural for people to grapple at ideas and desperately try to science themselves to safety. But ultimately, taking steps to distance themselves from death didn’t help reduce their chances of illness, so science moved on. Another factor is necromones, the odours of death. Necromones are the decomposition products of corpses that animals of the same species have a strong alarm response to. Necromones have been well established in some insect communities, where the oleic and linoleic acids produced by dead crustaceans and hexapods alert other members to the death and initiate gathering or fleeing behaviours. It’s also believed that necromones initiate fleeing in sharks, and might affect humans to a lesser degree. There’s no denying decaying human bodies smell horrible, but are they more horrible to us than other decaying animal bodies?

And what does happen to our bodies when they die? The answer is it’s very complex and we still don’t understand it fully. Primarily, two processes take over: the one whereby the microbes within our bodies start to eat us, and the one whereby bugs from the world around us start to eat us. Yummy.

There may be as many as 10 times as many microbial cells in the body as human cells, and they don’t necessarily die when we do. So what do they do? Well, they start eating our bodies.

Bacteria via Geralt (Pixabay)
The fate of the microbiome after death is less understood than the microbiome whilst we’re alive. However, we do know that the microbiome supports natural decomposition, and has even been proposed as a forensic tool for estimating time since death, or postmortem interval (PMI). Once death takes place, oxygen inside the body is depleted, and cell autolysis takes place: cells self-digest and break themselves up, releasing macromolecules that gut microflora can feed on. And those microflora? They go to town. Interestingly, research has shown that, over time, the richness of human gut bacterial communities significantly increases and, at the same time, the diversity decreases[1]. This “dynamic decomposition” is a process still little understood by forensic science yet, if reliable and predictable, could be invaluable for future development of the field.

Something not too dissimilar also happens with bugs. Although entomotoxicology is not a new field, it has recently emerged as a new field in forensic science. Insects and other arthropods, drawn by the odours of autolysing cells and digestion by the microbiome, populate bodies minutes to months after death, and as such what's there, how many, and how they behave can be instrumental in establishing time of death. Insects also serve as reliable alternate specimens for toxicological analyses once tissues and fluids have been devoured (because the toxins are in their bodies now, not the dead body!). As such, researchers are keen to learn more about them and, in particular, events that may disrupt their normal turn up times and rates of development, such as toxins or where a body is buried.

Insect via Pixabay
Early research has shown entomology may be predictably affected by chemicals found in the body just before death – especially toxins. This means the populations and variations across insects and bugs found in decaying corpses could indicate how the person died and give new information about how trace chemical compounds affect decomposition rates essential for accurate time of death analysis. Most recent into the area is currently carried out in graveyards, which can be problematic because of the inclusions of embalming chemicals, makeup, coffin sealants, and all that. Being able to correct for these factors could also provide better data and entomotoxicological estimations in the future.

It sounds like the bugs are in the know. 

References
why don't all references have links?

[1] DeBruyn, Jennifer M., and Kathleen A. Hauther. ‘Postmortem succession of gut microbial communities in deceased human subjects.’ PeerJ 5 (2017): e3437.

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