I deliberately held off mentioning HUMANS in that list, both because there’s another thread running on this and because technically and artistically in origami we’re not quite there yet. Still, I’ve had a sentiment very similar to the one about animals with regard to humans too. Namely: that there is something about folded paper, maybe its impermanence, thinness, vulnerability, refoldability—which makes sculpting in it more appropriate for human subjects (even if still technically harder) than sculpting in clay, stone, wood or metal. Those traditional solid materials all seem to freeze or kill or falsely eternalize & raise what they represent, while paper stays at the same level--just as warm, as frail, as free and as alive.
But as to the supposed gulf with birds and lizards, flowers and horses and things---I’ve had pretty sharp shifts of opinion about this. On the one hand, I left off origami animal design for almost a dozen years out of dissatisfaction with its artistic or expressive potential. (Too soon as I now think, having seen the work of e.g. Komatsu and Roman Diaz). And got back into origami only when I could find a road into human figuration and expression, or the faint beginnings of one.
On the other hand: there is so much principled affinity between what makes things attractive or evocative in the animate and even inanimate world, and this applies to human beings too. The laws of evocation or ‘signalling’ are much more tightly bound than is usually acknowledged. A male mallard with its iridescent head is imitating the colors of the sky at sunset; this for all we know was already found attractive by (a desideratum for) a long line of its female ancestors. A bit more obviously, it was the insects who taught the first angiosperms to produce the extravagant and exquisite forms of flowers---all in line with insect tastes and fantasies. (Tastes which somehow connect with ours despite 600 million years of distinct evolution, and a common ancestor with quite rudimentary vision.) Some insects even went a step further: they began to demand of their mates the same visual qualities they had long been insisting on from flowers. The result was----the Butterfly.
This sort of fusion or merger of signals and forms has not passed by us humans, either. Look for a moment at these random wave shapes, which I made a while back from brown paper.
http://www.saadya.net/Curvigami/sand-curves.jpg
They look a little like patterns of sand on a beach or dunes carved by the wind; or maybe like hills in the distance just before sunset. Now, some of this shaded-curve effect is visible in the human body too: in the nape of the neck, or the space under the shoulder-blades on the back of a child. Those soft sand-shadows, that provoke so infinite a tenderness. Here the body has picked up the compassion of a landscape, or maybe projects onto the landscape a softness it already knows.
In short, let’s not be too hasty in dismissing traditional paperfolding--or the haunting crispness, presentness and fragility its best animal forms have--even as we struggle to widen the lexicon for human origami figuration.