Eating their own kind is quite common throughout the world of animals, ranging from unicellular to humans.. He writes this entomologist from the University of California at Davis (USA) Jay Rosenheim and his colleagues in a new review of the journal Ecology, Science reports..

However, cannibalism is a risky way to eat.. If you have claws and teeth, then so do your fellow tribesmen.. Female praying mantises are notorious for biting off the heads of much smaller males during mating.. In addition, they sometimes engage in deadly combat with females of equal weight.. “I saw how one female gnawed off the leg of another,” says Rosenheim, “and then the female, who lost her leg, somehow managed to kill the other”.

Cannibalism is also dangerous in terms of infections. Many pathogens are host-specific, so if a cannibal eats an infected companion, they risk catching the same disease..

One of the most famous examples is the spread of a deadly brain disease that struck the Fore Indians of New Guinea in the 1950s.. The locals call it " In science, it is known as " Kuru raged in the Fore tribe, where a funeral ritual was practiced by eating the brain and flesh of a deceased relative. As soon as the ritual was over, the incidence of kuru began to disappear..

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In their review, Rosenheim and colleagues point to certain hormones - octopamine in invertebrates and adrenaline in vertebrates - that seem to be associated with levels of cannibalism.. As the crowding of individuals of the same species increases, and food becomes scarce, the amount of these hormones increases dramatically, and hungry animals attack everything they can grab with their jaws, legs or claws..

The study also shows how certain conditions cause some young amphibians, such as tiger salamanders and spadefoot toads, to turn into supercannibals.. When the pond is overflowing with their larvae, the tadpoles, some mutate and become super cannibals, gaining mass and growing powerful jaws.. Similar cannibal forms are also found in other arthropods and vertebrates..

But in most cases, the end result of cannibalism is positive: a non-excessive and healthier population.. For this reason, Rosenheim avoids viewing cannibalism as barbaric.. “When we think of human cannibalism, we recoil,” he writes.. “But cannibalism is one of the key factors contributing to the preservation of the natural balance.”.

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