Drama broke out at Leipzig Zoo, Germany, on Monday when a lioness called Kigali ate her two young cubs without any apparent explanation.
The cubs were just 3 days old and hadn't yet been named. A spokesperson from Leipzig Zoo told Deutsche Welle that Kigali was grooming the pair when she apparently snapped – and ate them.
This might sound like it flies in the face of the natural order – after all, shouldn't a parent do all they can to protect the lives of their children and thus their genes? But it's more common than you might think.
In 2013, Khali the sloth bear shocked keepers at the Smithsonian's National Zoo when she bent over and ate her newborn cub straight after giving birth. Not long afterward, she ate the second of her three cubs. Like Kigali, it seemingly appeared out of the blue.
Worried she might strike again, keepers took the third and final cub to the zoo's animal hospital, where they discovered she was ill. They suspected this had also been true of her siblings, hence Khali's sudden case of the munchies.
One reason often giving for this example of infanticide is ill-health, specifically that of the baby. Rearing offspring – particularly during the nursing stage – can take up a lot of valuable resources. If an infant is unlikely to survive to adulthood, it might be in the mother's interest to dispose of the unhealthy child and conserve her resources for those in better health – or move on the next.
If there is a lack of resources and it is a choice of her or the infant, she might decide she is better off cutting her loss and improving her chances of surviving to a time when breeding circumstances are more favorable. It is eerily efficient – and appears almost psychopathic in the seeming lack of empathy or parental care, but nature is cruel and resources are precious.
To stop the rotting carcass from drawing the attention of any nearby predators, the mother may choose to eat the infant and so dispose of any evidence, Tony Barthel, a mammal curator at Smithsonian's National Zoo, told National Geographic in 2014.
Male animals also take part in infanticide, but they do it for very different reasons. To boost their own chances of reproductive success and destroy the competition, male animals may kill children born from different fathers. A male dolphin, for example, might try to separate a female from her calf before killing said calf. The female will become fertile again, thus increasing his chances of mating and producing viable offspring with her.
These incidents aren't exceptions. The practice of animal infanticide – whether it is carried out by the males or females of the species – is incredibly common. In fact, Elise Huchard from the Centre for Evolutionary and Functional Ecology estimates it occurs in roughly 25 percent of mammals, not to mention many species of fish, insects, reptiles, and amphibians. These species tend to live in groups where a small troupe of males dominates the reproductive activity, yet cannot necessarily hold onto their top position for very long. Think: lions and Chacma baboons.
In many instances, animals have adapted their mating and rearing strategy as a result. In Chacma baboons, females use their promiscuity to confuse male baboons over the identity of the father. In human society, it's the opposite – some scientists believe monogamy evolved in humans as a solution to the problem of male-instigated infanticide.
As for Kigali, keepers cannot confirm if her actions were motivated by survival of the fittest instincts. Because she ate the cubs, it is not possible to perform an autopsy to check their health.