How do parasite flukes like the lancet liver fluke know it’s night time, know how to control it’s host, find grass, etc?


How do these parasites know how to control their hosts to walk to grass and climb up it but only at night. Or, in some cases with crickets, how to find a body of water. These require some thinking wouldn’t it? It’s not just randomly triggering the nervous system it’s deliberate acts it seems like.

In: 8

They don’t “know”.

It is a common misconception that evolution has goals, and that animals evolve to achieve those goals.

Evolution is random. But some random things work better than other random things. And the better working things get to reproduce. Those children get their own randomness, some of which is better, and some of which is worse. And the process repeats. Through this process, over thousands/millions of generations, some very complex processes and species can form. But they were formed randomly.

Parasites that “control” their hosts are not sitting in the hosts brain with a joystick saying “go outside and do this”. They have no idea what the host is doing. They have no ideas at all, as they are far below sentience.

They release (or cause to be released) hormones, or affect nerves/brain in a way that causes the animal to do something (random). Maybe the animal dies on the spot. Maybe it feels hot. Maybe it feels hungry. Maybe it gets the runs. The parasites that happened to evolve in a way that influences the host to behave in a way that helps the parasite, allows that strain of parasites to reproduce more successfully.

The fact that the parasite isn’t truly in control is moot to the host. It does what it does.

So, lets take the Ophiocordyceps camponoti-floridani fungus, which can create “zombie ants”. Infected ants climb to a high branch, bite, never let go, and starve to death. But then they are eaten by a passing bird or something, get pooped out later, and the fungus spreads. The fungus is completely non intelligent. It has no thoughts or knowledge of anything. (Unless there is something we really don’t know about fungus). So you could imagine incremental steps in this funguses evolution to get us here. The first step maybe causes hunger. “Bite plants”, “bite plants up high”. “don’t let go”, etc. Each step is an improvement over the last, so the fungus that evolved to trigger that step propagates and takes over. But the fungus isn’t giving orders, and the ant isnt following them. The ant is blindly responding to stimuli with its responses influenced by the fungus, due to its brain/body being affected.

Note that Humans are possibly susceptible to this kind of thing too. Toxiplasmosis, a parasite in cats (and most mammals) can infect humans. In cats, it causes rats/mice to be attracted to the scent of cats (or cat urine), thus being eaten by the cat, and infecting the cat. For humans, it can cause problems during pregnancy, but there are also some studies indicating it may affect human behavior for those infected. Infection with Toxoplasmosis has been found in some studies to be associated with promiscuity in women, and lack of grooming in men. Its also been linked with schizophrenia in some studies. This may be the origin of the popular “crazy cat lady” stereotype. (Its easy to find articles about this in popular media, and even studies, but do note that the studies are show rather weak results with many confounding variables so the proceeding statements should be taken with a big grain of salt – after all, its difficult to run an ethical study with randomized controls saying “hey, we are going to infect you with this parasite and see if it changes your behavior”)

/r/ExplainLikeImPHD answer :