“Again, this makes great sense from a materials science point of view,” says Van Orden. “It may be that a certain thickness of matrix has to be there as a buffer against insults. If the fibers were abutted together without a buffer, and you broke one, you could break them all.” This way, the keratin matrix acts like the mortar in abalone shell; it interrupts cracks coming from the side, and the stress is redistributed, giving the horn torsional strength.
But what does this design buy the rhino? Daniel tells me that cow rhinos wave, joust, and stab with their horns to protect their calves from attack. Bulls use it to drive off interlopers in territorial disputes, and all rhinos use it for digging in the ground. To be able to do all this, rhino horn has to possess strength when pushed from the tip as well as from the side. This head-on strength is called compressive, and building a spicule shaped like a porcupine quill is a great way to achieve it. Van Orden shows me a close-up of a horn fracture, in which the tips of the quill-like spicules are all bent. “Here’s where the compressive strength comes in—instead of being flat topped, and taking all the pushing energy directly, it’s tipped with a point. The point simply bends or breaks, but doesn’t transmit the load all the way down. There’s a lesson we should apply right now to our composites, which are rarely blessed with both compressional and torsional strength.”
What has Daniel and Van Orden really excited is a third trait of rhino horn that our materials don’t possess—the ability to heal. The evidence of self-healing was hiding in the beautiful Polaroid picture. “If you look closely, you’ll see a crack that has infilled with polymer, essentially healing over,” says Daniel. “But as a biologist, I considered this impossible, because as far as we know, there are no living cells in the horn—only dead tissue. Or so we thought. The idea that there might be something alive in the horn opened the possibility that we could take a sample of those cells and try growing, through tissue culture techniques, a horn in vitro.”
In search of living cells, Daniel went to an exotic-animal breeding facility in Texas to perform a needle biopsy on a rhino. “The veterinarian agreed to call me when he was going to do a checkup, because they don’t like to anesthetize the animals very often. I flew down there, took the horn sample, and then placed it into a liquid growing medium. If keratinocytes [cells] had been present, they would have grown out into that medium. Unfortunately, that didn’t happen. Now I’m waiting for another rhino to need its shots so I can fly down for another biopsy.”
In the meantime, Daniels and Van Orden are investigating other options for making a horn facsimile. “Say the healing isn’t caused by living cells,” says Daniels. “Say instead that the material for the infilling is cannibalized from somewhere nearby. Say a portion of the horn depolymerizes [breaks down into its building blocks], flows to the crack, then repolymerizes to fill in the gap. That got us thinking—maybe we could do something similar. Maybe we could depolymerize rhino keratin and induce it to reassemble around a core of rhino hair.”
Daniel’s idea is to practice on something like horsehair. Horses have two types of hair—the rough tail hair that is used for violin bows, and the softer hair of the coat. First he would depolymerize the coat hair into a liquid, then lay the tail hairs side by side in the liquid solution and put it under pressure. The keratin would, it’s hoped, polymerize around the nucleus of the larger fibers, forming connectors that gather all the hairs together.
The same sort of technique is already being done with bone, says Van Orden. “A dental surgeon can take bone and treat it so that just the hydroxyapatite is left. To build up the jawbone foundation beneath an implant, for instance, they’ll cut open a patient’s jaw and put in this hydroxyapatite. When the person’s bone cells come in contact with this hydroxyapatite, they say, ‘Hey, we forgot to calcify this!’ and they’ll make new bone in that spot. We’re hoping that our liquefied horsehair cells might see the tail hairs and say, ‘Oh, hair tissue. We forgot to gather all this together.’ If it works with horsehair, we’ll do the same thing with rhino keratin—we’ll provide the hair, the keratin, and the right conditions and say, ‘Structure yourself!’ ”
Although it seems like a blue-sky idea to grow rhino horns from scratch this way, it may not be. “Heck,” says Van Orden with her trademark enthusiasm. “If you told us thirty years ago we’d be putting graphite fibers in a resin matrix, it would have seemed farfetched. Today we’re playing doubles tennis with composites like this.”
Thirty years ago, there were many, many more rhinos than there are today. No matter how far-fetched or whatever else may come from this research in terms of composite innovations, any attempts to stop rhino slaughter will be well worth the effort. In fact, it’s one of the best uses of biomimicry I can imagine. This time, we’re learning to imitate an animal not to save ourselves (directly) but to save another species from “an end to birth.” It’s biomimicry come full circle, a glimpse of the good we could do with this new science if we choose to.
That sets me thinking about which agencies, or which foundations, have had the foresight to sponsor this type of research. When I ask Daniel and Van Orden, they lock eyes across the table and simultaneously make the hand sign for zilch. Their rhino horn work has received no official funding. For now, their quest is a labor of love and conscience, a pro bono for Rufus and the thinning herds whose horns alone, strong as they are, cannot protect them now.
CHAPTER 5
HOW WILL WE HEAL OURSELVES?
EXPERTS IN OUR MIDST: FINDING CURES LIKE A CHIMP
Nature is the supreme chemist. With all due respect to the brilliance of chemists, I don’t think a chemist could dream up a molecule like Taxol. [Taxol, a promising new cancer drug, is found in the bark of the Pacific yew tree (Taxus brevifolia) in the Pacific Northwest.]
—GORDON CRAGG, chief of the natural products branch,
National Cancer Laboratory, Frederick, Maryland
What matters is that we swallow our hubris and start acknowledging that animals have many things to teach us.
—RICHARD WRANGHAM, MICHAEL HUFFMAN, KAREN STRIER,
and ELOY RODRIGUEZ, zoopharmacognosy pioneers
Kenneth Glander’s office at the Duke University Primate Center in Durham, North Carolina, has a perfectly round, high-dome ceiling that feels like it might be thatched, and that an African village might be right outside. Instead, the back door leads to the Carolina piney woods, a humidor of coniferous spice and old, fuming leaves. In the morning drizzle, Glander tilts back his head, catching sparkling drops on the drooping handles of his waxed mustache. In the uppermost canopy of trees, small balls of fur curl up against the rain: five hundred lemurs, some of the most painfully endangered primates in the world. Aye-ayes, sifakas, and other prosimians are being bred in this arboreal ark in the event that they become completely zeroed out in the wild. Part of Glander’s mission as ark director is to see to it that they keep themselves healthy.
But these woods are half a world away and vegetatively different from the lemurs’ home in Madagascar. “It took me five years to convince people you could let these animals roam in these woods without fear of them poisoning themselves on our mushrooms. Even though people die from eating mushrooms all the time, I had a hunch these primates were smarter than that.”
Primates are smarter than that, and so are elephants, bears, birds, and even insects. Wild things live in a chemically charged world, and their goal in life is to pick their way through the maze of poisons and find a packet of energy or perhaps a dose of curative. We humans were once as omnivorous as they, able to pick and choose between the good, the bad, and the bitter.
Today, we are beginning to return to wild places to search for new drugs and new crops (or wild genes to add spunk to our old standbys). Given our domesticated and dulled senses of taste and smell, however, we now screen the forest for promising plants in a time-consuming way. Instead of innately sensing the best, we collect it all and painstakingly sort through it. Given the rapid acceleration of plant ex
tinctions, we no longer have time for this buckshot approach.
There are more than four hundred thousand plants and as many unique chemicals that we have yet to explore as possible medicines or foods. Before they’re all gone, say the biomimics practicing “biorational” drug and crop discovery, we need to consult the talented taste buds of wild connoisseurs and fur-covered pharmacists. They have, after all, been “native to this place” for millions of years longer than even our most astute agronomists or medicine men. They know what to eat and what to avoid, what will make them sick, delay the birth of an offspring, give them energy, or arrest a case of diarrhea. They are the experts we have been too arrogant to consult. Now, in this era of massive loss and little time for screening, we are beginning to tap them on their furry, scaled, feathered, and exoskeletoned shoulders and ask, “What’s that you’re eating?”
CHEMICAL WARFARE, PASSIONFLOWER STYLE
In order to appreciate the gustatory talent these wild experts possess, it helps to focus your mind on a fine hallucination. Think of yourself as a plant, rooted in place, unable to switch your tail or twitch your flanks. You are the succulent object of desire for countless microbes, insects, and animals that can’t photosynthesize their own food. You may parry their attacks with leathery leaves, thorns, or perhaps burrowing nettles, but your warfare of choice is chemical.
The stew of so-called “secondary compounds” that you, the plant, produce are what gives the green world its flavors, fragrances, spices, medicines, and poisons. It is with these chemicals that you bite back—burning, revolting, intoxicating, or even killing those that dare to eat too much of you.
Now focus on another hallucination. Imagine yourself as a wild herbivore confronted with a jungle full of defensive plants, each one doing its best to get you to keep your big square teeth to yourself. It would make a good computer game, actually. Here are the rules: Armed with only your senses, your powers of observation, and your memory, you have to gather your own food. Before moving on to the next level of play—surviving long enough to pass on your genes—you have to garner just the right amounts of vitamins, essential amino acids, proteins, and other nutrients to survive.
It may look like the Garden of Eden out there, but nature’s menu is a minefield. Even if a food doesn’t kill you outright, its secondary compounds can rob you of nourishment. The lineup of plant poisons includes alkaloids, phenolics, tannins, cyanogenic glycosides, and terpenoids, all possessing devilish ways to discourage digestion. Alkaloids such as nicotine and morphine, for instance, interfere with your nervous system. Cyanide (a tannin) and cardiac glycosides dive straight into your muscles, wreaking havoc with your heart rhythm. The respiratory inhibitor in passionflower (cyanogenic glycoside) will literally take your breath away. Or, if you’d like, plant hallucinogens will liberate you from your good sense and get the plant off the hook in the process. (As ecologist Paul Ehrlich says, “If a deer nibbles a hallucinogenic plant and then happily trots off into the arms of a cougar, it is unlikely to return to pester the plant.”)
Other toxins hold nutrients hostage, gridlocking digestion. Tannin, for instance, binds peptides (the building blocks of proteins) so tightly that they can’t be teased out by the digestive enzymes that normally disassemble food. Other toxins work by pinning the arms of these digestive enzymes. Either way, the protein remains unbroken and unused, and you go hungry. The only way to loosen the grip of digestion inhibitors is to heat the offending plant to 100 degrees Celsius, which is why the discovery of fire gave early humans a truly Promethean power. As a wild herbivore, however, you can’t crank up the Jenn-Air range when faced with a suspect plant. You have to detoxify the poisons in plants internally, using your own chemical laboratory. In the end, nutrition becomes a wrestling match between the plant’s chemical profile and your physiology.
Things get really interesting when the plant changes its chemical profile. When stressed by poor soil or moisture loss, for instance, a plant may beef up its chemical arsenal, not wanting to lose even a single leaf. Depending on the terrain, one tree might be fine to eat, while the same species in a patch of poorer soil may hold a bitter harvest. The very act of puncturing a leaf may cause a tree to fight back with an overproduction of toxins—changing its chemistry in as little as forty minutes to protect the rest of its leaves. As a herbivore, you never know what you’re going to get, not from forest to forest, tree to tree, or even from one side of a tree to the other.
Even if your system is equipped to detoxify a toxin, it takes energy to boot offending molecules out of your liver, repair your DNA, launch antioxidant artillery, or shed the poisoned cells in your mouth, stomach, esophagus, intestine, and so on. If you spend more energy breaking down or flushing out a toxin than you receive from the food itself, you could rack up a negative nutrient score. But if you don’t detoxify secondary compounds, they’ll filibuster your digestive system. Either way, you may look like you’re feasting, but you could be steadily starving. And natural selection, which deals harshly with foolish genes and foolish choices, won’t let that go on for long. An out-of-balance diet will eventually weaken you, and those genes (your genes!) will be edited out of the population.
If you want to keep your place in the gene pool, explains Glander, there are at least three dietary strategies you can adopt. You can be a specialist like the eucalyptus-chomping koala—eating one plant that your whole digestive system is dedicated to detoxifying. Or you can be a generalist and eat small amounts of lots of different species, so your body has to detoxify only tiny batches of toxin, spreading out the risk. Or you can do what our primate ancestors did: eat a limited selection of plants but be very picky—selecting only the choicest parts of the plants so that you net more nutrients than toxins.
Once upon a time, before there were nutritionists or USDA safety inspectors, our primate ancestors knew how to put together a sensible, safe diet. Somehow, they’d learned to shop the supermarkets of the plains, jungles, and seas, avoiding the dangers while cashing in on digestible nuggets of nutrition. In a country where millions are spent each year on diet and nutrition advice, why haven’t we consulted the mammals, birds, and insects that successfully act as their own nutritionists? Might their choices show us what we may have been meant to eat, in a purely biological sense?
SMART EATING: WILD CONNOISSEURS
Strangely enough, not much research has focused on the chemical intricacies of animal food choice. Glander, one of the few primatologists who has published on the subject, devised a way to demonstrate the nutritional common sense of the new guests (Lemur fulus) at his Primate Center. “Before placing them out in the forest, I gave the lemurs ten leaves—leaves from local species like sweet gum that they had never seen before. I made sure there were no outright poisons (not wanting to take any chances with an endangered species), but I did include five leaves that contained digestion inhibitors and five without. After sniffing and puncturing like trained tasters, they spit out the bad and swallowed the good. Their menu was a balanced mix of leaves with the highest digestibility, the highest nutrient content, and the lowest tannin content. We couldn’t have hired a nutritionist to do a better job.”
Glander’s hunch about primate palates was developed while studying the discriminating tastes of mantled howler monkeys (Alouatta palliata)—a tree-dwelling species native to Costa Rica, Panama, and Mexico. He had followed the howlers day after day, watching them move through the jungle like picky eaters at a dinner buffet—eating only certain leaves, or certain parts of leaves from one tree, while ignoring a neighboring tree of the same species. To find out why, he chemically probed both the plants they ate and those they passed over. Turns out the plant material they avoided was either full of alkaloids and condensed tannins (especially virulent protein hoarders) or conspicuously low in protein and unbalanced in amino acid counts. He concluded in his paper: “Howlers are chemically astute; they consistently chose material of the highest nutritive value and passed up the low-value material with secondary compo
unds.”
Katherine Milton, a professor of anthropology at the University of California, Berkeley, would have to agree. She studied howlers on Barro Colorado Island in Panama, examining what age leaves they preferred. In her 1979 study, she found that howlers overwhelmingly preferred young leaves to older ones, perhaps because the young leaves earn them a higher return of energy per unit of weight.
In a 1978 study, Doyle McKey and his colleagues reported a similar cautiousness among black colobus monkeys (Colobus satanus) in the Douala-Eden Reserve in Cameroon. The monkeys in this particular reserve studiously avoided a common tree species that colobus happily ate in other parts of the country. McKey guessed that poor soils at the reserve must have made the native tree species beef up with toxins to protect every hard-won leaf. Sure enough, when he analyzed the avoided leaves in that region, he found them loaded with phenolics, which are digestion inhibitors. The only part of the plant the colobus would eat was the seeds, which were high enough in protein to be worth the trouble of detoxifying.
On the trail of yet another instance of smart eating, Harvard anthropologist Richard Wrangham and his colleague Peter Waterman looked at vervets feeding on acacia trees. The vervets lustily devoured immature leaves, seeds, fruits, and flowers of two species of acacia (Acacia tortilis and Acacia xanthophloea), but when it came to eating the gum, they got picky. Only gum from A. xanthophloea was eaten, while the reddish-brown gum of A. tortilis was completely ignored. Analysis showed that the ignored gum had high levels of condensed tannins and not enough protein to justify the effort. The sought-after gum, on the other hand, was high in soluble carbohydrates and devoid of tannins. A hassle-free wad of energy.
Wild baboons (Papio anubis) of Africa also seem to know how to stretch a feeding dollar. Researchers Andrew Whiten and Dick Bryne of Scotland’s University of St. Andrews found that the baboons preferred plants or plant parts that were high in proteins but low in hard-to-digest fiber and alkaloid toxins. When the baboons had no choice but to eat a high-toxin menu, they made sure they picked individual plants that were also rich in proteins. Plants that were lower in proteins—not worth the trouble—were simply passed over.
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