While tonic immobility has clear de

While tonic immobility has clear defence functions, when it comes to thanatosis, biologists can’t agree on its concrete advantages and the reasons why it would have been favoured by natural selection. Why would an animal who wants to avoid being eaten pretend that she’s already dead? The problem is that thanatosis is unusually complex behaviour and must be distinguished from simple tonic immobility, since it’s very costly. That is, there has to be a good evolutionary reason for animals to develop thanatosis above and beyond tonic immobility. There are several hypotheses, but all postulate thanatosis as either an anti-recognition or an anti-subjugation mechanism. For our purposes, regardless of which hypothesis is true, all we need is to postulate a concept of death in the deceived predators in order to successfully explain the evolutionary emergence of thanatosis. Let’s go through these hypotheses.