Microbes, Parasites, and Behaviour: Why the Human Body Does Not Speak with One Voice
From a mouse that loses fear of cat smell to the gut microbiome, real studies show that organisms living inside the body can tune a host's behaviour in their own favour. The article follows the three steps of that argument and asks what happens when small shifts repeat across millions of people.
Read in Vietnamese →A 2020 scientific review returned to a result that laboratories have reproduced for decades: a mouse infected with Toxoplasma gondii loses its fear of cat smell, and some infected rodents even turn back toward it. Toxoplasma is a one-celled parasite. It reproduces sexually only inside cats, while mice and many other animals serve as stopovers on the route. For the parasite, a mouse that stops fearing cats is a mouse that gets caught sooner, and the life cycle closes there. This detail does not belong to horror fiction. It is a reproductive advantage that experiments can measure.
The experiment carries a large idea with it. A very small living thing can tune the behaviour of a much larger host in a direction that serves its own route through the world. The parasite does not need to drive the host mad or weaken it. One switch inside the defensive-response system is enough to make the host walk into danger on its own.
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