Atomic Nerds

So in the last post, I mentioned in a footnote that while giant pandas have adapted to a bamboo-intensive diet completely unlike that of other bears*, this might not have been the most sensible choice for them as a species. I said that matter deserved its own post. Several said I should write that. I am nothing if not eager to please.

The panda’s most famous “problem”- that they are extremely difficult to breed in zoos because the males have disproportionately small penises and no instinctive knowledge of sex, and the females have a very short estrus period- aren’t really problems for wild pandas. In the wild, a cub would spend years with its mother; in the Chinese breeding programs most zoos try to follow because they have such a smaller comparative amount of knowledge of how to breed them in captivity, cubs may be taken from their mother as young as six months to ensure that she goes into another cycle as soon as possible. In other words, in the wild a male cub can expect to pick up sexual behavior by watching and learning- which is actually how a number of other species operate, including elephants and rhinoceri, for whom mating carries logistical problems on a scale roughly equivalent to figuring out how to park one tank on top of another and then separate them again without damage. Likewise, the short estrus period is pretty much status quo for bears across the world, and the proportionately small genitalia are also not uncommon in other species, including the gorilla, and no one has accused them of being unable to breed. Pandas aren’t the world’s most efficient breeders, but they can do it a lot better in the wild than in zoos.

Almost all of the panda’s real problems stem from its diet: all bamboo, all the time. Other bears are omnivores- fish, meat, fungus, berries, insects, roots… and especially for smaller bears like black bears, grasses and forbs**. Contrary to campers’ usual imagination, for a black bear life is mostly vegetarian***. The panda has done this one better: it has exchanged a life of constantly rummaging around trying to find grubs, berries, and meat for feeding on what were at one time seemingly endless forests of incredibly abundant food… bamboo. On the face of it, this is not a problem, it’s a smart fitness choice- and in the short term, it was, for all the reasons that are obvious.

The problem is that pandas are not all THAT much changed from being bears. Unlike other herbivores, they have short guts without much in the way of dedicated bacterial colonies to extract nutrition from the bamboo. Unlike other herbivores, they have no ability to move their jaws from side to side to efficiently grind plant foods. (You can see this same carnivoran jaw structure in your cat or dog- notice how they try to chomp everything to pieces instead of chewing as we know it?) The massive jaw muscles they had to develop to chew up a woody plant like bamboo also required their skull to grow in a way that essentially closes off any potential development of this capability, too. Like other herbivores that subsist exclusively on grasses, they are large- being big and round is the most efficient shape for conserving heat, and if you’re a mammal, most of the calories you eat go toward maintaining your body temperature. Unlike most other herbivores that subsist exclusively on grasses, they can’t digest what they eat very efficiently, so they have to conserve energy; like another herbivore I’ve written about in the past, they have virtually no energy to spare and spend as little of their time possible moving, which is one reason they’re not the world’s most enthusiastic about socializing and mating.

The problems of their diet don’t stop there. They don’t do another sensible thing that other bears do- hibernating through winter’s months of poor food supply- because they can’t. The nutrition they get from bamboo is completely inadequate to building up the necessary supplies of body fat required to hibernate for a few months; therefore, this animal that moves as little as possible is forced to spend a great deal of energy migrating up or down mountains every season in order to find places where the bamboo is still growing lushly enough to sustain it. More than that, it makes reproduction difficult in a way totally unrelated to their sex lives- the bamboo is also a poor diet both for sustaining pregnancy and producing nutritious milk after birth. Therefore, baby pandas are born at a far earlier stage of development than other bear cubs- they are famously tiny and fragile, and they will take quite awhile to grow to a reasonable size- a panda cub is three months old before it can even walk, and a year old before it has a full set of teeth. Bear in mind, this is based on pandas being fed a comparatively rich zoo diet that includes as much meat and fruit as the animals will take (they prefer bamboo)- for wild pandas it’s likely to be considerably slower. The panda does have some compensations, first in the form of delayed implantation of fertilized embryos that allows the mother about two months of latitude to “time” a birth after a mating for the time when the bamboo is youngest and richest, and extremely powerful maternal instincts that need no learning curve****. These are enough to keep the panda going as a species, but not to give it much resilience against difficult changes- like, say, encroachment of human habitation on those suddenly not so endless forests of bamboo.

Pandas aren’t, as some intelligent design proponents like to claim*****, an “unfit” species. They had a wide open, unexploited ecological niche, and they radiated into it, established a monopoly on it for large animals, and they even managed to survive an ice age in it. What they aren’t is a species likely to last all that long on a geological time scale; specialization, especially specializations with such large costs, tend to be the ultimate death knell for a species. Exploiting nascent island ecosystems is also a way for a species to thrive for awhile, but becoming an island species- which often entails losing a lot of expensive capabilities like flight, body size, and alertness and aggression- is essentially suicide in terms of a lineage that survives across the epochs. It may yet turn out that an omnivore from a carnivore lineage going fully herbivorous is a mistake of similar proportions.

*You may have some recollection of a old bit of trivia that pandas aren’t actually bears. There was a taxonomic tug-of-war dating back to the nineteenth century about whether they were, in essence, smallish bears or really large raccoons, based on observations of many morphological similarities to another creature classified as a Procyonid (raccoon family). In more recent years, multiple molecular studies have effectively resolved the debate: giant pandas are bears and red pandas are procyonids. The morphological and behavioral similarities are convergent evolution due to the shared diet.

**This is a fancy botanical term for a class of plants that gardeners are familiar with both as “the wildflowers I’m trying to grow” and “the weeds in my wildflower garden”. Dandelions are forbs, as are other small, non-woody flowering plants that aren’t grasses or shrubs.

***Right in line with campers’ fears and driving the dump bear phenomenon, black bears are VERY eager to opportunistically seize on protein and fat-rich foods- they’re incompetent predators, but hungry for meat all the same. Outside of human influence they get it from carrion. Unlike polar or brown bears, which ARE competent predators and may kill you for food, the black bear will just kill you in the process of trying to steal your hamburger or out of fear.

****Unlike our ancestors. For a lot of primates, it’s rare for the firstborn infant to survive its mother’s ineptitude.

*****Yes, really. They claim the panda’s so screwed up it’s proof evolution, with its reliance on “survival of the fittest”, can’t possibly have produced it and God must have. They never seem to go into the theological implications of God creating such a supposedly hapless animal; sure, they’re cute and all, but wouldn’t that make the Divine Creator something of a sadist?

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