Rhino Horn: Cure or Curse?

by Brian Dunning
March 14, 2017

Today we're heading into South Africa, where grim-faced game rangers ride in their Land Cruisers clutching Vektor R4 assault rifles. They're on the hunt for poachers, who are, somewhere in the brush, illegally killing rhinos at the rate of more than three a day. Poaching is, by far, the most profitable industry in the nation by each of several metrics. What could drive people to want rhino horns so badly they'll kill for them? It's a subject that's rife with misinformation — including, most likely, a lot of what you think you know about it.

This global demand for rhino horn was brought into stark focus in March of 2017 when a crime was committed that shocked everyone, as it was as horrible as it was unexpected. Poachers broke into a wildlife preserve called Thoiry Zoo just outside of Paris sometime during the night and killed Vince, a 4-year-old white rhino. Vince was shot three times in the head and his front horn was chainsawed off. The much smaller second horn was only partially cut through.

At the time, rhino horn on the black market — often bought and sold using untraceable Bitcoin cryptocurrency — was running about $25,000/lb (€51,000/kg). That's about 40% more than gold. We don't know the weight of what was taken from Vince, but the white rhino's front horn is the largest of the rhino family. Its weight averages 4 kg (8.8 lbs). This means it's likely the poachers netted over $225,000 (€215,000) from that one horn alone. Bold poaching in the suburbs of a major European city like Paris becomes a lot more believable when you consider that nearly a quarter million dollars of gold was just sitting there, virtually unguarded. Who would have thought that a wildlife preserve would need bank vault level security?

These particular poachers played with extraordinarily high stakes. Killing of a species on the IUCN Red List, plus the trafficking of ivory of an animal killed after 1975 (which includes the rhino horn), together carried a maximum criminal penalty of four years in jail plus a fine of up to €750,000, according to a French newspaper. (The Red List is a list of threatened species maintained by the International Union for Conservation of Nature and Natural Resources. The white rhino's status is "near threatened" which is one step above "least concern". The white rhino is the least threatened of the five main species.)

Why would these criminals take such a gamble? As most anyone with even a passing familiarity with the issues knows, the rhino horn trade — like so many others that chip away at the populations of endangered species — is driven almost entirely by the enormous cash flow of the East Asian alternative medicine industry.

In pre-scientific China, the 16th century herbologist Li Shizhen wrote the Compendium of Materia Medica, the seminal encyclopedia of herbal medicine — at the time, the best that could be done before much was known about the human body and no correct information at all was known about the germ theory of disease. Anything you read on this subject in English will tell you that Li listed many uses of rhino horn in the Compendium — for treating everything from headaches, to fever, to rheumatism, to snakebites, to possession by evil spirits. I tried to verify this, but was only able to find references to antelope horn and water buffalo horn. If Li Shizhen can be taken as authoritative, rhino horn had not yet entered the traditional Chinese medicine lexicon by that time.

The first reference in the literature that I could find was in a much later work, a 1987(!!) compilation called the Shen Nong Ben Cao Jing, or Divine Farmer's Materia Medica. This book has an impossibly convoluted history, so I'll grant it as fact that rhino horn did have earlier mentions in writings that don't survive. This later book is said to have come down from oral traditions stretching back as far as 221 BCE, compiled into a book at some point, but which was then lost; and any number of authors over the centuries wrote their own versions of it from their own notions. This 1987 version is also available in searchable English text, and aside from two other brief mentions, here is the extent of what it has to say on rhino horn, called xi jiao:

It mainly kills gu toxins, demonic influx, and spiritual matters. It keeps off malign qi and ill matters, expels evils, and resolves hundreds of toxins.

Given that it's a 200-page book, this doesn't suggest that rhino horn is anywhere near as important as we all seem to think it is to traditional Chinese medicine. In fact the president of the UK Association of Traditional Chinese Medicine told Nature magazine in 2011 that its use was always very limited, not only because it's rare and expensive, but because it has few clinical applications.

And neither has it ever been considered an aphrodisiac or a treatment for male impotence. That is purely the invention of 20th century Western authors, yet still quite the popular urban legend.

To find a medical use for rhino horn from past centuries, it turns out that we needn't look either so far to the East or so far back in time. An 1889 issue of The Pharmaceutical Journal and Transactions includes a French article discussing the merits of various methods of coating pills with keratin in order to protect the medicines they contain from the stomach acids. Where does this keratin come from?

Under the name "keratin" are designated certain products obtained by exhausting different horny tissues, such as bristles, nails, horn, feathers and epidermal tissue, successively with ether, alcohol, water and dilute acids.

Keratin, of course, being what rhino horns are nearly entirely composed of. Once the keratin has been dissolved and prepared and used to coat the pills:

Pills coated with a layer of keratin, which is insoluble in the gastric juice, are not dissolved until they reach the intestines, when they come under the action of the alkaline bile which dissolves the keratin.

Fortunately we now have numerous alternatives for such coatings, and no longer need to turn to animal-sourced proteins. But interestingly, it is this same property of keratin that led to another of its popular uses in history. Keratin is stable in a highly acidic environment, like the stomach; but when it encounters a more alkaline environment, it breaks down. It is this quality that led early scientists in a number of cultures to seek out cups made from rhino horn for an unexpected purpose: to detect poisons.

Many popular poisons used by assassins in early history were based on alkaloids, with the most familiar examples being poison hemlock (such as was used to execute Socrates) and the arrow poison curare (first discovered by Europeans when indigenous Americans used it to kill two men of Christopher Columbus' crew). Alkaloids, which are (obviously) alkaline, react with keratin by bubbling off hydrogen sulfide, and can thus be detected when — for example — poisoned wine is poured into a rhino horn cup.

Rhino horn libation cups can be found in museums and they come from all over Europe and Asia. The oldest known are from the Tang dynasty, from the years 618-907. Nobody makes them anymore, of course, so they don't contribute to today's illegal rhino trade.

But where horns are being used, it's problematic, because it is the very fact that the material comes from a rhino which is the desired quality. Chemical substitutes are not wanted. In Yemen, there has long been a tradition of giving curved daggers called jambiya to boys when they reach the age of twelve. The most desirable style of jambiya has a rhino horn handle, and a famous one can be worth hundreds of thousands of dollars. Other materials are used in various styles, but the desire for rhino has a deep cultural tradition profoundly tied to masculinity. So although making new jambiya from rhino horn has been illegal for some time, many knife makers would jump at the chance to acquire some. And enough does still creep in — via that Bitcoin-driven black market — to keep the highest paying (and most discreet) customers happy.

So far we know where rhino horns are not going. They're not going into libation cups or detecting poisoned wine; they're not going to Chinese aphrodisiacs (and never were); they're not going into jambiya; and they're not even going much into traditional Chinese medicine. So where are they going? Why is the rhino trade accelerating? Why has the price of rhino horn skyrocketed to ten times what it was ten years ago? Demand from a single source: a modern alternative cancer treatment in Vietnam.

It started as a rumor in the mid 2000s that some unnamed politician in Vietnam claimed to have been cured of cancer by powdered rhino horn. Almost immediately, wealthy Vietnamese cancer patients offered any price for the miraculous cure. In 2007, 13 rhinos were poached in South Africa. In 2008, following the story of the Vietnamese politician, that number had increased by a factor of more than six, to 83. But it didn't stop there. Each year since the apocryphal politician was miraculously cured, the number of rhinos poached in South Africa alone has climbed, hitting an all-time high of 1,215(!!!) in 2014. The first quarter of 2016, for which the latest data was available, was on track to exceed that.

The first to go was the Javan Rhinoceros. In 2011 it was declared extinct in Vietnam, when the last one was found dead with its horn sawn off. The Sumatran Rhinoceros is likely to follow soon; both species are represented only by double-digit numbers in preserves or in captivity. For ten years, Vietnamese hunters have swamped the applications for legal rhino hunt permits in Africa.

Rhino horn for cancer? So regardless of the ethics, is this something that really works? Not according to traditional Chinese medicine, where it has never been mentioned. And certainly not according to medical science. Rhino horn has never been observed to treat cancer — discounting the one urban legend of the Vietnamese politician. No plausible hypothesis has ever been put forward suggesting a reason for studies, and accordingly, no studies have been done. It wouldn't be either legal or ethical, for one thing. That's not to claim that keratin has no role in cancer therapies. It might; for one example, keratin has been studied as a biomarker that can bind to cancer cells as a potential aid to targeted drug delivery. But keratin is widely available from many sources; there is no reason at all why rhino horn would be involved.

The fact is that the Vietnamese appetite for rhino horn is a pseudoscientific fad, like gluten-free dieting in the Western world. It is the result of poor science literacy combined with a proclivity for anecdotal thinking: "It works because I heard it on the Internet." Think again to those numbers of poached rhinos. Beliefs matter. Pseudoscientific thought patterns are a road that leads nowhere good.

By Brian Dunning
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