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Hippos Eat Way More Meat than We Thought, and It Can Make Them Sick

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Hippos are huge animals with fearsome tusks and aggressive natures, but they mainly eat plants. Sometimes they attack people and can tangle with crocodiles, sure, but they’re not predators or carnivores. Right?

But a closer look reveals that hippos aren't so herbivorous after all, says biologist Joseph Dudley. Despite their grass-heavy diets and all the adaptations that make them great grazers, hippos have been known to eat their fair share of meat. There are scattered reports by scientists and amateur observers (note: NSFW gory pictures) of hippos attacking, killing, and eating other animals, stealing kills from predators, and scavenging carcasses, including those of other hippos. In a new paper published in the journal Mammal Review, Dudley and his fellow researchers argue that these incidents aren’t as unusual as they seem or isolated to a few animals or populations. They say there’s a pattern of carnivorous behavior in hippo populations across the animal’s entire range—and that behavior has consequences for hippos. 

Evolution has outfitted hippos and other big herbivores for a plant-based diet, and their guts and the microbes that live within them are adapted for fermenting and digesting lots of plant material. That doesn’t mean these herbivores animals can’t add meat to their menu, though. Many can and do. Antelope, deer, and cattle have been known to feed on carrion, birds’ eggs, birds, small mammals, and fish. What might hold most of these animals back from more frequent carnivory, Dudley suggests, isn’t their digestive physiology, but “biomechanical limitations” in securing and ingesting meat. In other words, they aren’t built for taking down prey or biting into flesh. The hippo is another story. 


“Due to its large body size and unusual mouth and dental configurations, the hippo may represent an extreme case in which the predation and scavenging of large mammals by an ungulate species is not constrained by biomechanical factors,” Dudley and his team write. Not only can hippos kill and eat other big animals more easily than other herbivores, the researchers say, the fact that they’re territorial and highly aggressive may facilitate carnivory, putting them in situations where they kill other animals and can get themselves something to eat.

And eat they do. Since Dudley made the first scientific record of carnivory in hippos in 1996, other cases of hippo carnivory and even cannibalism have also been documented. Dudley lists instances where wild hippos have fed on impalas, elephants, kudus, wildebeest, zebras, and other hippos that they either killed themselves or were killed by other predators. Events like these have been seen both during times when carnivory may be a last resort (e.g. droughts when food is scarce), and when it was merely a convenient opportunity, like a mass drowning of wildebeest crossing a river. There are also reports of captive hippos in zoos killing and eating their neighbors, including tapirs, wallabies, flamingoes and pygmy hippos.

“Our scientific records, coupled with those of other investigators and observers, demonstrate that the phenomenon of carnivory by hippos is not restricted to particular individuals or local populations but is an inherent characteristic of the behavioral ecology of hippos,” the team writes.


If that’s the case, then why did it take so long for anyone to figure it out? Part of the blame can fall on conflicting schedules. Hippos are mostly active at night, which means their meals, meat or otherwise, usually go unseen by humans. Their carnivorous ways, Dudley thinks, have simply been overlooked. 

They may also explain why hippos are so susceptible to anthrax and experience higher mortality rates during outbreaks, the researchers say. Hippos, they think, are doubly exposed to the disease because they ingest and inhale bacterial spores on plants and in the soil like other herbivores, and also consume them when feeding on contaminated carcasses. Cannibalism during outbreaks exacerbates the problem. 

That carnivory might make these outbreaks worse in hippo populations has implications for controlling the disease and protecting both animals and humans. During anthrax outbreaks among wildlife, many human illnesses occur because of contaminated “bush meat.” During a 2011 outbreak in Zambia, for example, 511 human cases of anthrax and at least five deaths were linked to people handling and consuming meat from infected hippos. Burying or burning suspected infected animal carcasses is a standard practice during anthrax outbreaks, and the researchers think that this may be especially effective in hippo habitats because it takes infected meat off the menu for both humans and hippos. 

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iStock // Ekaterina Minaeva
Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
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iStock // Ekaterina Minaeva

Jacques Mattheij made a small, but awesome, mistake. He went on eBay one evening and bid on a bunch of bulk LEGO brick auctions, then went to sleep. Upon waking, he discovered that he was the high bidder on many, and was now the proud owner of two tons of LEGO bricks. (This is about 4400 pounds.) He wrote, "[L]esson 1: if you win almost all bids you are bidding too high."

Mattheij had noticed that bulk, unsorted bricks sell for something like €10/kilogram, whereas sets are roughly €40/kg and rare parts go for up to €100/kg. Much of the value of the bricks is in their sorting. If he could reduce the entropy of these bins of unsorted bricks, he could make a tidy profit. While many people do this work by hand, the problem is enormous—just the kind of challenge for a computer. Mattheij writes:

There are 38000+ shapes and there are 100+ possible shades of color (you can roughly tell how old someone is by asking them what lego colors they remember from their youth).

In the following months, Mattheij built a proof-of-concept sorting system using, of course, LEGO. He broke the problem down into a series of sub-problems (including "feeding LEGO reliably from a hopper is surprisingly hard," one of those facts of nature that will stymie even the best system design). After tinkering with the prototype at length, he expanded the system to a surprisingly complex system of conveyer belts (powered by a home treadmill), various pieces of cabinetry, and "copious quantities of crazy glue."

Here's a video showing the current system running at low speed:

The key part of the system was running the bricks past a camera paired with a computer running a neural net-based image classifier. That allows the computer (when sufficiently trained on brick images) to recognize bricks and thus categorize them by color, shape, or other parameters. Remember that as bricks pass by, they can be in any orientation, can be dirty, can even be stuck to other pieces. So having a flexible software system is key to recognizing—in a fraction of a second—what a given brick is, in order to sort it out. When a match is found, a jet of compressed air pops the piece off the conveyer belt and into a waiting bin.

After much experimentation, Mattheij rewrote the software (several times in fact) to accomplish a variety of basic tasks. At its core, the system takes images from a webcam and feeds them to a neural network to do the classification. Of course, the neural net needs to be "trained" by showing it lots of images, and telling it what those images represent. Mattheij's breakthrough was allowing the machine to effectively train itself, with guidance: Running pieces through allows the system to take its own photos, make a guess, and build on that guess. As long as Mattheij corrects the incorrect guesses, he ends up with a decent (and self-reinforcing) corpus of training data. As the machine continues running, it can rack up more training, allowing it to recognize a broad variety of pieces on the fly.

Here's another video, focusing on how the pieces move on conveyer belts (running at slow speed so puny humans can follow). You can also see the air jets in action:

In an email interview, Mattheij told Mental Floss that the system currently sorts LEGO bricks into more than 50 categories. It can also be run in a color-sorting mode to bin the parts across 12 color groups. (Thus at present you'd likely do a two-pass sort on the bricks: once for shape, then a separate pass for color.) He continues to refine the system, with a focus on making its recognition abilities faster. At some point down the line, he plans to make the software portion open source. You're on your own as far as building conveyer belts, bins, and so forth.

Check out Mattheij's writeup in two parts for more information. It starts with an overview of the story, followed up with a deep dive on the software. He's also tweeting about the project (among other things). And if you look around a bit, you'll find bulk LEGO brick auctions online—it's definitely a thing!

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200 Health Experts Call for Ban on Two Antibacterial Chemicals
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In September 2016, the U.S. Food and Drug Administration (FDA) issued a ban on antibacterial soap and body wash. But a large collective of scientists and medical professionals says the agency should have done more to stop the spread of harmful chemicals into our bodies and environment, most notably the antimicrobials triclosan and triclocarban. They published their recommendations in the journal Environmental Health Perspectives.

The 2016 report from the FDA concluded that 19 of the most commonly used antimicrobial ingredients are no more effective than ordinary soap and water, and forbade their use in soap and body wash.

"Customers may think added antimicrobials are a way to reduce infections, but in most products there is no evidence that they do," Ted Schettler, science director of the Science and Environmental Health Network, said in a statement.

Studies have shown that these chemicals may actually do more harm than good. They don't keep us from getting sick, but they can contribute to the development of antibiotic-resistant bacteria, also known as superbugs. Triclosan and triclocarban can also damage our hormones and immune systems.

And while they may no longer be appearing on our bathroom sinks or shower shelves, they're still all around us. They've leached into the environment from years of use. They're also still being added to a staggering array of consumer products, as companies create "antibacterial" clothing, toys, yoga mats, paint, food storage containers, electronics, doorknobs, and countertops.

The authors of the new consensus statement say it's time for that to stop.

"We must develop better alternatives and prevent unneeded exposures to antimicrobial chemicals," Rolf Haden of the University of Arizona said in the statement. Haden researches where mass-produced chemicals wind up in the environment.

The statement notes that many manufacturers have simply replaced the banned chemicals with others. "I was happy that the FDA finally acted to remove these chemicals from soaps," said Arlene Blum, executive director of the Green Science Policy Institute. "But I was dismayed to discover at my local drugstore that most products now contain substitutes that may be worse."

Blum, Haden, Schettler, and their colleagues "urge scientists, governments, chemical and product manufacturers, purchasing organizations, retailers, and consumers" to avoid antimicrobial chemicals outside of medical settings. "Where antimicrobials are necessary," they write, we should "use safer alternatives that are not persistent and pose no risk to humans or ecosystems."

They recommend that manufacturers label any products containing antimicrobial chemicals so that consumers can avoid them, and they call for further research into the impacts of these compounds on us and our planet.