Heart attacks and the “Playing Possum” phenomenon – Halloween article
Heart attacks take a considerable toll on the human population and various programmes to reduce the risks of heart failure through special diets and behaviour (saltfree fish and chips, no smoking, daily jogging, yoga exercises etc.) have been advocated. However, we are of course not the only mammals to suffer from coronary diseases and other problems with our vital pump: pigs on the way to the slaughterhouse, animals under stress, enraged or in fear can collapse and die from heart failure. Others -and here we come to the possum part- fake death. They do it so cunningly, instinctively, and convincingly that a predator in search of a fresh meal may not accept the seemingly uninteresting carcass as food. Triggers for predators to be interested in prey often involve prey to move, to struggle and to attempt to get away. If such clues are missing a predator may not react.
“Playing possum” is a widespread survival strategy found in a variety of mammals and in a form of “thanatosis” also amongst innumerous species of insects, spiders and other invertebrates. In the state of faked deaths amongst mammals, the body temperature may fall, blood circulation ceases, the heart beat stops, limbs are flaccid, and sensory reflexes are non-existent. Sometimes regurgitated food around the mouth may be present.
We humans exhibit many animal behaviours during times of fear and stress. We pale, sweat, tremble with fear, get goose-pimples of fright, may be paralysed by impending danger and, according to Viennese Professor A.D. Jonas, we can arrest our heart beat like possums or other animals in times of extraordinary stress. The only part we have trouble with is making our heart go again, waking up from faking death, releasing us from “playing possum”. Prof Jonas suggested that heart attacks may often be no more than an escape behaviour, which we have inherited from our primitive ancestors, but what to our chagrain in the course of evolution we seem to have lost is the ability to start our vital functions again once the danger has passed.
There is no such problem with invertebrates, which may respond to an attack by reducing their body size through coiling up and withdrawing their limbs and by becoming immobile and impervious to stimulation. When the danger has passed they wake up from their state of thanatosis and usually scuttle away quickly. Pill bugs and millipedes are good examples. They roll up into a ball or a spiral and remain motionless until they feel safe; beetles when disturbed and unable to fly away may pretend to be dead and an insect, perhaps a grasshopper, caught in a spider’s web will seek initial refuge by remaining stock still for a while as if to gather their strengths and will then suddenly making a violent attempt to free themselves. On the other hand, orb web spiders when disturbed in their webs may just drop down, entering a state of thanatosis amongst the vegetation or leaf litter, before ascending the safety line to their web again, a silk thread they had left while dropping down.
There is no doubt that deception has a long evolutionary history, that feigning death and “playing possum” can save lives – as long, of course, as Prof. Jonas has pointed out, the bluff does not become permanent.
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2016.
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