Natures wonders: feigning death to save oneself (Introduction)

by David Turell , Tuesday, September 14, 2021, 21:00 (956 days ago) @ David Turell

It called Thanatosis, and the prime example is the possum:

https://aeon.co/essays/animals-wrestle-with-the-concept-of-death-and-mortality?utm_sour...

"The opossum’s death display, also known as thanatosis, is an excellent demonstration of this, not because of what it tells us about the opossum’s mind, but because of what it shows us about the minds of her predators: animals such as coyotes, racoons, dogs, foxes, raptors, bobcats and large snakes. In the same way that the appearance of the stick insect tells us something about how her predators see the world, and which sorts of objects they avoid eating, the opossum’s thanatosis reveals how common the concept of death is likely to be among the animals that feed on her.

***

"Many animals, when they feel threatened, go into a kind of paralysis that reduces the probability of being preyed upon. This is known as tonic immobility and can be found in a wide range of species, from insects to humans. While tonic immobility is a simple behaviour that operates at a superficial level – in some species it can even be accompanied by an increase in heart rate – in thanatosis, the animal not only stays still but actively imitates the characteristics of a corpse. Although thanatosis might have evolved from tonic immobility, it’s much more than a mere paralysis: the animal is feigning death.

***

"Thanatosis as an anti-recognition mechanism works by making the prey appear unpalatable to the predator. In principle, this could ride on a simple disgust mechanism, since thanatosis is often accompanied by urination and defecation, or by other chemical defences, such as the frogs’ ammonia-like breath, which the predator might find yucky. According to this interpretation, the success of thanatosis would not involve the predator conceptualising anything about the prey’s corpse-like appearance. Instead, the animal in thanatosis would just appear disgusting.

***

"This does not mean that opossums themselves necessarily have a concept of death, or that they behave this way with the intention of being mistaken for a corpse. On the contrary, it appears to be a genetically inherited behaviour that does not require any learning and that is triggered automatically upon the detection of certain stimuli. What this does mean, however, is that the predators’ concept of death was the likely selection pressure that shaped these displays. Maybe opossums lack a concept of death, but we can be pretty sure that the animals who intended to feed on them throughout their evolutionary history did tend to have one. (my bold)

***

"The distribution of thanatosis in the animal kingdom points to how extended the concept of death is likely to be in nature. We find elaborate forms of thanatosis in some species of amphibians, reptiles, birds and mammals. Its widely extended yet patchy presence in the phylogenetic tree suggests that thanatosis appeared in these different species through convergent evolution. These are species that are not closely related, so they would not have inherited their thanatosis from a common ancestor, but, rather, the presence of similar selection pressures in their different habitats would have made this behaviour appear independently in these different taxa. The concept of death, far from being a uniquely human feat, is a fairly common trait in the animal kingdom.

"We humans like to think of ourselves as a unique species. However, little by little, all those traits that we have been relying on to ground this uniqueness have been falling, as the science advances and reveals the staggering diversity and complexity of animal minds and behaviour. We now have solid evidence of culture, morality, rationality, and even rudimentary forms of linguistic communication. The concept of death should also be counted among those characteristics to which we can no longer resort to convince us of how very special we are. It is time to rethink human exceptionalism, and the disrespect for the natural world that comes with it."

Comment: The Darwin-laced article assumes these mechanisms appeared under selection pressure because it works!!! No idea of how any animal using this trick decided upon it. The article is filled with descriptions of semi-possum behaviors, all instinctual (note my bold). It tries to assume predators recognize death, but that is not the same as understanding the concept of dying or being dead by the acting possum. The final paragraph is the standard Darwinian attack on our exceptionalism. The article strains to make a comparison with humans who 'freeze' when frightened or startled. What the possum does is amazing and I've observed it on our ranch. Our dog scared her, she flushed her uterus of unfinished babies and went 'dead'.