Why are animals so obsessed with food?

Cannibalism in the animal kingdom

Animals quite often eat their own young, siblings or partners. That is part of their survival strategy.

Male polar bears eat polar bear babies. Female spiders eat husbands willing to mate. Chicks peck siblings to death. Many a young animal feeds on its own mother. "20 years ago cannibalism was considered a strange event in the animal kingdom," says Bill Schutt. "In the meantime, numerous researchers have discovered that it occurs quite frequently." Schutt, a zoologist at Long Island University in New York, has therefore written a book on cannibalism. This makes it clear: The combinations of who eats whom are just as diverse in nature as the reasons why animals eat their fellows.

One benefit of cannibalistic behavior can be faster growth. A striking example of this is the tadpole survival strategy of some species of the American paddock toad. The young amphibians live in pools that can dry out quickly. Usually they feed on plankton and turn to toads within 30 days. After a few days, however, balloon-like tadpoles four to five times as large can suddenly appear in the water. Instead of flat chewing surfaces, they develop pointed teeth in their jaws - the tools to eat their petite counterparts. The abundant diet allows them to grow up in just 20 days. It is not yet known which mechanisms turn the tadpoles into cannibals.

In the case of the tiger salamander, on the other hand, whose aquatic larvae also develop elongated teeth in a small percentage and clog their conspecifics, researchers have suspected. The cannibalistic salamander cubs develop when the larvae collide too often, i.e. when their habitat is too narrow.

Shark embryos eat their siblings in the womb

Another reason for cannibalism is common, especially with fish - and quite banal: the animals cannot distinguish their own offspring from their food, which consists of eggs and larvae. With fish, cannibalism is therefore the rule, not the exception. The females sometimes produce millions of eggs, which are fertilized by the males through a cloud of sperm in the water. This type of reproduction only works through mass. Parental care is impossible.

But even with the estimated 90 fish families in which brood care is involved, the adults occasionally eat their offspring. The cichlids are a specialty. In some species, the females protect their fertilized eggs in their mouths. But they also consume a few eggs or even the entire brood over and over again. "Mouthbrooders practice cannibalism mainly because, as we all know, it is impossible to eat a normal meal with a mouth full of eggs," Schutt explains casually.

The most unusual example of a very early type of cannibalism can also be found in fish, sand tiger sharks. The offspring of these sharks mature in the body of the female. The embryos already have well-developed teeth in the womb. They also have big bellies, which the scientists initially believed to be a kind of yolk sac. When they examined the stomach contents, however, they found a surprise: the remains of an average of 19 embryos, victims of a sibling rivalry that is unique in the animal kingdom. In sand sharks, the embryos develop at different times, so that the oldest eat their yolk first and finally the younger siblings - still in the mother's womb. This leaves one young shark per fallopian tube.

In birds, too, chicks can develop at different speeds and many a young serve as a meal for the first hatch. The limiting factor, however, is the beak. The limited opening is one reason sibling cannibalism is not common in birds. Only some species such as birds of prey or owls can handle larger chunks of meat.

The more brood care an animal species does, the less often it eats its young. Nevertheless, even with mammals, some babies fear for their lives. For example, male polar bears also incorporate young animals when there is a lack of food. This behavior has not only been observed since global warming, emphasizes Schutt. In other large mammals, too, males seek the little one after life. If, for example, bears, lions or chimpanzees take over a group, they kill the young that the previous boss fathered.

But sexual cannibalism is most spectacular when, during mating, one partner - usually the male - disappears in the other's stomach. However, this type of eating and being eaten is hardly widespread in the animal kingdom. It occurs almost exclusively in spiders and insects such as the praying mantis. The terrors with their forelegs raised as if in prayer have been a bit chaste behavior since the 19th century. At that time, an insect breeder observed not only that a female had bitten off its partner's head, but also how the decapitated male kept copulating for hours.

In the meantime, scientists have relativized the male devouring behavior of the praying mantis. According to this, starved females mainly eat their husbands in captivity. Males willing to mate are not so sure about each other in nature either. They approach a partner with extreme caution so that she does not mistake her for a prey. And why headless male praying mantis continue to breed is explained by the researchers in a similar way to the phenomenon of a headless chicken running around. After all, in the case of the praying mantis, the male can still release his sperm before he dies.

The "copulatory suicide" is worthwhile for the males

This is also often the case with slaughtered male spiders. Researchers have long wondered where the evolutionary advantage lies for the males who allow themselves to be eaten. In the case of the Australian red-backed spider, they found that the cannibalized males had mated longer and were thus able to fertilize twice as many eggs as those that ran away. In addition, females who had eaten their sexual partner were less likely to reconnect with other males. The "copulatory suicide" is also not too big a victim. After all, the males of the red-backed spider die after sex anyway because their sexual organs are torn off during copulation and they are mortally wounded.

Males of other spider species do not give up without a fight. In some cases they have developed sophisticated strategies to outsmart voracious females. So some males of the black widow tie up their partner with a spider thread. And thick-jawed spider members use their specially trained jaws to block the wife's jaw during sexual intercourse. On the other hand, males of the real spider simply only approach the chosen one when it has hunted another prey.

While females are generally more prone to cannibalism, there are also cases where they are the victims - of their young. The cellar spider first cares for its newly hatched offspring by laying so-called trophic eggs. These are eggs that are used exclusively for nutrition and that, for example, also present ladybugs or snails to their brood. After the first molt, however, young cellar spiders need more food. Then the mother spider calls her flock of children to her by knocking on the web. The young come and eat them alive.

Bill Schutt: Cannibalism - A Perfectly Natural History, Algonquin Books of Chapel Hill


Human cannibalism

In times of need, humans eat humans. Some examples.

100,000 years ago Neanderthals probably ate their fellows. This suggests bone finds from caves in northern Spain, southern France and Croatia. The early human remains had been worked with blades, as had the bones of red deer.

450 BC Chr. The Greek historian Herodotus mentions that straws were distributed in a starving troop to kill and eat the loser. It is said that this is what the soldiers of the Persian king Cambyses are supposed to have done when they moved to Egypt.

1492 Christopher Columbus coined the term “cannibal”. In his logbook, he describes that captured Indians from the Caribbean islands feared their neighbors, the "Canibs" or "Canima". These were considered cannibals. Whether there were cannibalistic customs in the New World has not been historically proven.

Late 19th century The Fore people in Papua New Guinea have a strange disease: Kuru. Those affected laugh confusedly, lose their balance, can no longer swallow and die. It was not until the 1950s / 60s that researchers found the cause: During funeral rituals, people ate infected brains of the deceased and became infected with prions.

1941/44 Hitler has Leningrad surrounded by his troops in order to starve the population. The trapped eat rats, leather soles, lick glue from book spines. During the 900 days or so, up to 1.5 million people perish. In the first winter, the Russian authorities registered 1,000 cases of cannibalism.

1959/60 The famines in China are a consequence of Mao Zedong's disastrous agricultural plans. An estimated 25 million people die. The population partly falls back on human flesh. In the province of Anhui alone, 1,289 cases of cannibalism have been documented. People in China eat meat from their own kind over and over again throughout history.

1960s Centuries later, the Brazilian tribe of Wari stopped the funeral ritual of consuming the dead down to the last finger bone. Family members by marriage showed their condolences to the relatives by eating the corpse.

1972 Plane crash over the Andes with 45 people on board. Twelve died instantly, five injured died in the first night, and more died in an avalanche. The rest of them hold out in the snow at minus 40 degrees. They eat from the dead, some of whom were their friends. After more than 70 days, 16 survivors are rescued.

2001 Armin Meiwes, the Rotenburg cannibal, kills a 43-year-old man. The two found each other on the Internet. The perpetrator is obsessed with eating human flesh, the other wants to be eaten. The cannibal first cuts off the victim's penis, which both of them consume together, and then stabs the 43-year-old. He eats its meat for months.

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