Welcome to the newest edition of The Why. “Why are giant panda cubs so tiny?” Good question. (OK, it’s a little “Facebook-cutesy” but again it beats answering those questions about some of your odder intimate inquiries. Seriously? We thought a “Bear Claw” was something you bought at Dunkin Donuts, mmmkay?)
For those not in the know, the tiny panda cubs at the National Zoo in Washington, D.C. have caused a lot of concern. Our guest speaker, Joel Achenbach contributor to The Washington Post online notes that the “tiny, hairless, squeaky, utterly helpless, butter-stick-sized creatures are supposed to live outside mama’s womb and eventually grow into adorable giant pandas.”
But why are giant panda cubs so tiny? It’s because bear babies are like human babies. Achenbach confirms this and says: “The key word to remember is ‘altricial’.”
Don Moore, a senior scientist at the National Zoo and an expert on mammals notes: “It’s a fancy word that means pretty much helpless.” Achenbach confirms that it is true that both human babies and panda cubs are born “on the altricial side.”
He continues: “A giant panda is a bear. Bear cubs are extremely altricial in general. Of the placental mammals, Moore said, the panda has the tiniest babies in comparison to the size of the mother. The size ratio can be as small as 1 to 900.”
OK but why are giant panda cubs so tiny? It’s the bamboo diet and their metabolism, right? We wrote about that earlier.
Achenbach agrees explaining: “A giant panda . . . has evolved to eat a diet primarily of bamboo, a woody grass that is hard to digest. To adapt to this rather spartan diet, giant pandas have evolved a low metabolism. They sit around a lot.”
He continues: “This low metabolism means the female’s blood-oxygen level is relatively low. That tiny panda cub actually has a better shot at survival if it can breathe fully oxygenated air — and so being outside in the world is better than being inside the mother. Moreover, the kind of fatty acids that the cub needs can’t be passed from the mother to the cub through the placental barrier.”
Moore adds: “In order to get the fatty acids to the baby, to make the baby grow faster, they can’t go across the placenta, but they can go out in the milk.” Thus it’s more efficient to give birth to tiny cubs to grow “outside the womb.”
Achenbach concludes that giant panda cubs are tiny because “carnivores can ‘afford’ to give birth to more altricial babies in a cave or den, and to raise their babies there. Bears can use their body reserves to nourish a growing fetus during a short gestation, and then can use different body reserves to nourish an altricial newborn with their fatty milk.”
Why are giant panda cubs so tiny? Now you know.
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