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Evolution doesn't care about ethics - it cares about surviving and getting your alleles out there as much as possible. From that perspective, cannibalism can seem like a pretty good idea to some creatures. Hank introduces us to three different types of animal cannibalism, and tells us about some of the species that practice them.

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 Introduction


There are few things that humans can agree on, but one is nobody likes a cannibal. For years popular convention held that animals eating their own kind was some kind of extreme behavior usually under stressful conditions, severe hunger, or mental short-circuits.

And while this can be true in recent years scientist have begun to look at animal cannibalism through new eyes. And they've learned that sometimes eating your neighbor or even members of your family, makes pretty good evolutionary sense. 

[Intro Music]

Evolution doesn't care about ethics; it cares about surviving and getting your alleles out there as much as possible, and from that perspective, cannibalism can seem like a pretty good idea to some creatures. It's convenient, it limits your competition for food, territory, and breeding rights, and it provides some extra nutrition!

But of all the ways animals choose to dine on their own kind, there are a few strategies that take the practice to the extreme.

 Method 1


For example certain species of shark, like the Sand Tiger, get a jump on their competition before they are even born. Sand Tiger sharks practice Intrauterine Cannibalism, also known as Oophagy, or Adelphophagy.

Now Oophagy, or "egg-eating" occurs when an embryo snacks on unfertilized eggs passing through their mother's uterus. Adelphophagy literally translates into "brother eating" and for sharks it involves a battle royale among twenty embryos in the womb, in which they eat each other until just one big one remains! What?

Well actually two pups end up remaining because the mother has two uteri. So, the two survivors can't actually get at each other: good strategy.

If your wondering how we came to learn about this nasty business, you'll have to thanks shark biologist, Stewart Springer. In the late 1940s, Springer was poking around in the lady parts of a Sand Tiger, when he had the bejesus scared out of him by a chomp to the hand. 

 Method 2


Sexual Cannibalism often occurs when a female kills and consumes her male suitor before, during, or after an attempt to copulate. While this is par for the course in certain Praying Mantis, Scorpion, and some species of spider, Black Widow, I'm looking at you! It doesn't mean that some male suitors wouldn't prefer to get away uneaten and, you know, go about their day. Maybe pick up a few more ladies and eat some flies. 

Not so for the Australian Redback Spider, who takes parental investment to the extreme! After an elaborate courtship dance of frenzied flips, shimmies, and hopefully successful insemination, a Redback will voluntarily present his tasty abdomen directly in front of his lady love with true, suicidal, Shakespearean flare.

Why? Well, he's about 200x smaller than this lady and he knows he may never run into another female again. Evolutionary speaking, he just wants to pass on his genes. So if he can do his little dance well enough to hold her attention while he injects his sperm into her receptors and then further occupy her time by providing her with a meal, then he has greatly increased his chances his babies and not another suitor's that will hatch. Making his death worth it in the end.

 Method 3


Finally, Filial Cannibalism occurs when a parent eats some, or all of their offspring, either to thin their brood so they can focus of fewer healthier progeny, or to cut their losses under stressful conditions and get back into the dating game. 

But one animal has turned the tables on hungry parents. Caecilians, not to be confused with these guys, are the least known member of the amphibian class, which include Frogs, Toads, and Salamanders. 

These tropical ground-dwelling, limbless critters look pretty much like earthworms, but they can grow as large as snakes. Not much is known about their diet, but recently scientists made a peculiar discovery among two Caecilian species.

For about three months after her babies hatch, a mother will repeatedly feed them from her very flesh. Her outer layer of skin swells and glistens with extra fatty lipids, where upon her ravenous rugrats dive in and quickly devour her skin raw with their specialized, temporary, hook little teeth.

Like a real-life Prometheus, it takes mom about three days to recover and regenerate the next meal. And in doing so, earns what should really be a really nice mother's day gift. 

So, you see, while the subject of human cannibalism remains macabre, it turns out that it isn't so taboo in the animal kingdom. In fact, some biologist wonder why more species don't eat their own kind. 

 Ending


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