Dazzling stripes are a way of deterring flies. Photo: Getty
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How the zebra got its stripes

A method for dodging predators? A means of social interaction? Or a way of getting rid of flies?

Zebras' stripes have baffled biologists since Charles Darwin. Many hypotheses have been proposed regarding their purpose but, despite hundreds of years of study, there remains disagreement.

In an attempt to end the debate, researchers have pitted various models against each other and systematically analysed data from past studies. Their results reveal the one reason zebras have stripes: to ward off flies.

A handful of ideas regarding zebras’ stripes have found some support among biologists. One proposed that the dark and light bands change how air flows around a zebra’s body and helps in heat management, which could go a long way in the hot tropical areas that zebras live in.

Another proposed the stripes were used by zebras as a way of social interaction. They may use them to identify other zebras and for bonding as a group in the wild.

A third proposal suggested zebras used the stripes as camouflage. While stripes are clearly visible in the day, there some thought that it helped at dawn, dusk, and in the night.

All these ideas were shot down when tested rigorously. Two others, however, remained intriguing.

The first was that the stripes were used to dodge predators. It is called the “motion dazzle hypothesis”, and it suggests predators are confused by zebras' stripes and cannot understand their movement. Research published in the journal Zoology in 2013 used a simulated visual system to show that zebra stripes do interfere with visual perception. But this is a difficult hypothesis to test in the field.

Martin Stevens at the University of Exeter has researched the motion dazzle hypothesis by getting human subjects to catch moving stripy objects on a computer. “It’s an artificial experimental system,” he admitted.

The second proposal was that stripes helped keep flies at bay. Zebras are especially susceptible to biting flies due to their geographic spread. These flies, which include the tsetse fly, stomoxys stable flies, and tabanid biting flies, are particularly prevalent in areas with high temperature and humidity – exactly the areas where zebras are normally found.

Bites from these flies can be nasty and, quite literally, draining. About thirty flies feeding for six hours on just one horse can draw as much as 100mL of blood. Usually the flies can number in the hundreds around one animal.

Zebras have shorter hair than other equids – the family that includes horses, donkeys and zebras – which may also increase their susceptibility to attack. Also, four diseases which are fatal to equids have been found in Africa. This could mean that investing in anti-biting defenses such as stripes is especially important for zebras compared to non-African equids.

It is possible that the dazzle effect acts on flies, rather than larger predators, and deter them from biting. “Stripes clearly have a number of functions,” Stevens said, “and these could be interacting in zebras.”

Revealing maps

In the new research, just published in Nature Communications, Tim Caro and his colleagues at the University of California in Davis, didn’t perform experiments. Instead they used ecological and observational data on zebras' geographical locations and related factors. It is the first time that a comparative approach has been applied to find the reasons for zebras' characteristic colouration. Caro thinks his findings may have nailed the answer at last.

Caro looked at seven species of equids and scored them for number and intensity of stripes. Just to be sure, they tested all five hypotheses regarding zebra stripes' use: camouflage, predator avoidance, heat management, social interaction, and warding off flies. The extent of overlap between the geographic distribution of striped equids with each of these five measures was calculated.

E. greyvi, E. burchelli and E. zebra have stripes on all their bodies. Other equids don’t. Caro, Izzo, Reiner, Walker and Stankowich

“The results were a shock to me,” said Caro. Of these five proposals, only warding off flies had statistical support. He had not expected such a clear-cut answer to the question. As the map shows, the only places where flies and equids live together are areas that are populated by striped equids.

The exact mechanism by which stripes deter flies remains unknown, but experimental studies performed by researchers at Lund University in 2012 have found support for this proposal. They created striped surfaces and stuck glue on them. Based on the number of flies on the surfaces with different thicknesses of stripes, they concluded that these flies stayed away from stripes as thin as those found on zebras.

“As is normal in science you get a solution that asks more questions,” Caro said. It is time to hand the problem over to vector biologists, who can understand the susceptibility of horses to biting flies.

In Darwin’s days, people didn’t consider animal colouration with respect to fitness advantages. “People thought that animal colouration existed simply to please humans or was caused directly by the environment,” Caro said.

Darwin “would be delighted” that researchers are now considering animal colouration as a functional trait, he said. We might not have all the answers regarding zebra stripes – but it seems we may be looking through the right lens.

The ConversationThis article was originally published on The Conversation. Read the original article.

Jake Paul via YouTube
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We should overcome our instinct to mock Jake Paul’s school shooting video

The urge to mock the ex-Disney star diminishes the victims he speaks to and ignores the good YouTubers can do.  

It’s very “darkest timeline”. Ex-Disney star Jake Paul (brother of vlogger Logan Paul, who infamously filmed the dead body of a suicide victim) has created a 22-minute documentary about the Parkland school shooting in which he greets Florida senator Marco Rubio with the words “Hey, what’s up man?” and doesn’t mention gun control once. 

Paul – who has previously made headlines for setting fire to a swimming pool – goes on to ask the politician: “I think like a lot of people think passing laws is super easy, can you explain some of the struggles around, uh, passing laws?”

It’s hard to not immediately balk at the documentary, which was released yesterday and has since been widely mocked by the press and individual journalists. Critics note that Paul doesn’t mention gun reform within the YouTube video, and many mock his conduct towards Rubio. Others accuse the video of being an insincere PR move, particularly as Paul has previously fetishised guns on his YouTube channel – and has a tattoo of a gun on his thigh.

21-year-old Jake Paul talks and conducts himself like a child, which is what makes the video immediately jarring (“I just wanna become homies with them and just be there for them,” he says of the Parkland survivors he is about to meet). There is a vacant – almost dumb – expression on his face when he speaks with Rubio, leading the viewer to question just how much the YouTube star understands. But this is precisely the value of the video. Paul is a child talking to an audience of children – and talking to them on their terms.

YouTube doesn’t disclose the exact demographics of a YouTuber’s audience, but fan videos and Paul’s comment section reveal that most of his 14 million subscribers are young children and teens. Paul is introducing these children to a politician, and the video is edited so that Rubio’s claims don’t go unchecked – with footage of the senator being criticised by Parkland survivors playing in between shots of Paul and Rubio’s chat.

Paul (admittedly unintentionally) asks the senator questions a child might ask, such as “Is there anything that people can look forward to? Is there anything new that you’re working on?”. Although this might be jarring for adults to watch, the comment section of Paul’s video reveals it is already positively affecting his young audience.

“Definitely going to speak out now,” writes one. Another: “I shared this to my Mum and asked her to show the head teacher so everyone do that as well.” Childishness is still transparently at play – one commenter writes “Plzzz Stop the Guns… it hurts my feeling I’m crying… 1 like = 10 Pray to Florida” – but this too shows that Paul has introduced new concepts to kids previously more concerned with online pranks and viral fame.

Of course, it’s easy to see how this might be a cynical move on Paul’s part. Yet how can we demand more from YouTubers and then criticise them when they deliver it? Paul’s video is far from perfect, but engaging children in genuine discussions about current affairs is a commendable move, one far superior to his prior acts. (Paul previously caused controversy by telling a fan from Kazakhstan that he “sounds like you’re just going to blow someone up”, and his diss-track “It’s Everyday Bro” is third most disliked video on YouTube). Like it or not, Paul has an incredible influence over young people – at least he is finally using it for good.

Paul’s video has also undeniably helped at least one teen. “It’s just easier to talk about what’s going on with someone like you than a doctor or someone,” Jonathan Blank – a Parkland survivor – tells the YouTuber in the video. Later, his mother praises Paul through her tears. “It was the best therapy for my son,” she says, “You didn’t have an agenda, you cared.”

Other Parkland survivors are angry at the media’s response to the video. Kyle Kashuv – also interviewed in the documentary – has tweeted multiple times since the video’s release. “Media has the utter audacity to mock my classmates and Senator Rubio for doing the interview ON MY REQUEST AND THE REQUEST OF TWO OTHER STUDENTS,” he wrote.  

“If you mock a video where my classmates, that witnessed their friends get murdered in cold blood, are crying and putting their hearts on their sleeve, be prepared to be hit back twice as hard.”

Kashuv differs from the most famous group of Parkland survivors, as the teen supports the STOP School Violence Act over national gun reform. Yet the teen’s politics do not make his thoughts or feelings less valid, or his voice less important in the conversation. While critics note Paul spoke little of gun reform in his video (instead he suggested that schools have bullet proof glass and Instagram should flag pro-gun posts), the YouTuber later tweeted to clarify his stance.

“Gun Reform changes we need in my opinion,” he wrote. Paul went on to suggest that anyone who wants to buy a gun should be 21, go through a six month training course, and have a mental health evaluation. He also tweeted that gun shows should be banned and there should be a “30 day wait period after purchase to receive firearm”.

This isn’t to say, of course, that Paul is right, or has all the answers, or is even equipped to discuss this topic sensitively. Yet his promise to pay for busses to the March for Our Lives demonstration in Washington DC, alongside the fact he didn’t monetise his YouTube documentary, speak of someone at least trying to do some good. “We all want the same thing and that’s to make schools safe,” he says in the video. Although he gives Rubio and the STOP School Violence Act a platform, he is dismissive of their impact.

“Kind of why I wanted to make this video in the first place is to activate parents and kids within their own schools and communities, that’s the way things are going to get done the fastest. We don’t to wait for hundreds of people in Washington DC to pass the laws,” he says.

Though the description to Paul’s video was most likely written by a far-more savvy PR, it’s hard to disagree with. “I vow to be part of the solution and utilise my platform to raise awareness and action across the board, but we cannot focus on one issue, we must actively discuss and make progress on them all,” it reads.

The criticism of Paul smacks of the old media sneering at the new media, galled and appalled that a 21-year-old YouTuber would dare wade into politics and do so less than perfectly. Concerns about propriety and morality are a veil to disguise a pervasive distaste for YouTube stars. Criticisms that his suggested solutions are stupid ignore the fact that it’s not his job to reform society. It’s like having a go at Sesame Street for not criticising Theresa May.

YouTubers might not be the idols that adults wish teenagers had, but we can’t change that. What we can do is encourage viral stars to engage with important issues, and not mock them when they do so less than brilliantly. Jake Paul may not be a good person – it might even be a stretch to describe the video as “good”. But the YouTuber made an effort that should be commended, not mocked. 

Amelia Tait is a technology and digital culture writer at the New Statesman.