In the program "Historically yours" on Europe 1 this Monday, the journalist David Castello-Lopes discusses the technique of dating human corpses.
Thanks to this, it is possible to trace the exact time of a death from a body.
And as improbable as it may seem, our insect friends are of great help to us.
Every day in
Historically yours
, David Castello-Lopes looks back on the origins of an object or a concept.
This Wednesday, he is studying the study of the dating of corpses.
An exercise of very French origin since it is scientists from our country who have developed techniques to be able to trace the precise time of a death.
For this, they notably helped each other with insects.
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Temperature, rigidity and color, three inseparable indices
"How do investigators, when they arrive at a crime scene, to know the exact time of death? This is the question that many scientists are asking and which, little by little, has found answers. First, there are three major changes to the body that take place when someone dies, and they all have Latin names:
algor mortis
,
rigor mortis
and
livor mortis
. For those who have not. Latin in college, translate as 'the temperature of the corpse', 'the rigidity of the corpse' and 'the color of the corpse'.
The first person who codified these notions in an organized way was the Frenchman Alexandre Lacassagne in the 19th century.
He deciphered the steps and the speed it took for the human body to cool down, to turn all hard and all pale.
But we quickly realized that these methods only worked for the first 48 hours.
Our friends the little animals
The question you are asking yourself is therefore to know what to do if it is more than two days old.
Well, we use for that a science with a very soft name called forensic entomology.
But what can that possibly mean?
This is the study of insects that colonize corpses.
Because insects have been known to colonize corpses for hundreds of years.
But the person who made it a science is also French and is called Jean-Pierre Mégnin.
In 1894, he published the first reference book on the subject, called
La Fauna des Cadavres
.
Small example of his research, page 150, not recommended for sensitive souls: 'We examined a severed human head, wrapped in an old woolen petticoat and found at the Bercy freight station.
His cranial cavity contained a remnant of brain forming a one-centimeter layer covered with the droppings of insects that had fed on the rest of the brain. '
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The great theory of Jean-Pierre Mégnin is that the corpses are colonized by successive squads of insects which arrive in an order which is always the same and which always lasts so long.
In fact, it's a bit more complicated.
Depending on the environment, the temperature, the way the person is dressed at the time of death, it all affects the insects that arrive.
Since then, the science of Jean-Pierre Mégnin has been perfected and forensic entomology is still used today.
Fly larvae, the key element
In particular with a fairly reliable method which consists in removing the larvae of the flies which have laid eggs on dead people.
Yes, because at the same temperature, the larvae that develop on corpses grow at a predictable rate specific to the species of fly to which they belong.
Let us take again the example of a corpse found by the scientific police after a murder.
The larvae taken from him measure 13 millimeters.
We also know that it was 15 ° on the day of the murder.
At this temperature we also know that it takes five days for the larvae of this fly to reach the size of 13 millimeters.
Result: the victim has been dead for five days. "