Rich Lenski continues his demolition of Michael Behe’s new book

February 23, 2019 • 1:15 pm

As you probably know from reading this site, ID creationist Michael Behe has a new book coming out this week: Darwin Devolves: The New Science About DNA That Challenges Evolution (note the unclear antecedent, which could be either “New Science” or “DNA”). Various scientists have weighed in, none of them positively, and there’s been considerable criticism by biologists Nathan Lents, Joshua Swamidass, and Rich Lenski, including a damning review in Science.

Lents continued his criticism on The Human Evolution Blog (see here, here and here) and Lenski, whom Behe attacked strongly in the book, promised a three-part rebuttal of Behe’s ideas on his own website, Telliamed Revisited, which is now being extended (see here and here for Lenski’s parts 1 and 2).

Yesterday Lenski put up part 3 (screenshot below), which is an expansion of earlier criticism by Lents on whether a gene likely involved in the adaptive evolution of polar bears—a gene concerned with fat metabolism—was really “broken” or “damaged”.

One of Behe’s major theses in the book is that evolution is self-limiting, as, he argues, nearly all adaptations are based on damaged genes, and when a gene is damaged or inactivated, it can accumulate more mutations that eventually render it functionless and unable to revive. Thus, he concludes, evolution by natural selection runs itself into the ground. ~~God~~ An Intelligent Designer then has to step in to make things right.

Behe is wrong. Indeed, although we have examples of adaptive evolution based on inactivated genes, we also have many that don’t involve “broken genes”, and as long as a reasonable number of mutations involve changes in gene function or regulation, or things like gene duplication, chimeric genes, and so on, Behe’s claim holds no water.

One of the genes that Behe claimed was inactivated during adaptive evolution of polar bears from ancestral brownish bears was ApoB, which regulates the amount of fat in the blood. Behe claimed in his book that the gene’s evolution in polar bears involved many “inactivating” mutations. Lents pointed out that there was no evidence for this; on the contrary, even the authors of the paper analyzing the sequence of that gene found evidence that some of those substitutions were not involved in breaking the gene, but improved its function.

Behe replied, calling Lents an “incompetent reviewer” (without even giving his name!) and presenting some data that, he said, showed that the ApoB substitutions were “possibly damaging” or “probably damaging.

That was a mistake, for, as Lents showed, Behe was duplicitous in his reply, having omitted from his table all the mutations that the authors’ algorithm said were “benign”. Lents is charitable about this, but I can see no explanation except that Behe left out data inimical to his hypothesis. And that seems misleading and deceptive. As I said, Lents is kinder to Behe than I would have been:

In Behe’s defense, he doesn’t explicitly say that he’s presenting the whole Table. So he isn’t lying exactly. Instead, he says that he is presenting “the relevant information” from the Table. I find this deeply misleading. This whole discussion is about the nature of adaptive mutations in the evolution of species and Behe’s arguments is that most of them are damaging. By presenting only the mutations that are predicted to fit that argument, he is intentionally leaving out evidence that is contrary to his position.

After all, what is the purpose of showing the chart at all? To show that some mutations that drove polar bear evolution are damaging? He didn’t need a chart to make that point and no one would argue with that. I suspect that if the unaltered Table S7 gave the impression that the overwhelming number of adaptive mutations were damaging, Behe would have shown the whole thing.

In reality, Table S7 does not give that impression at all, and so he slices it up with surgical precision so that he can present “the relevant information,” that is, the information that appears to support his position. And, at least when it comes to APOB, even the selectively edited information probably doesn’t support his position either, regardless of what the predictive algorithm says, as I (and the study’s authors!) explain above.

The evolution of polar bears is the opening story of Behe’s book, the example he uses to describe his concept of “devolution.” But if you actually consult the data itself, it tells a very different story than Behe does.

Lenski’s new post (click on screenshot), goes into the polar bear gene in detail, and also explains how scientists determine whether a mutation in a gene is advantageous, benign, or damaging—not an easy matter when all you have is its DNA sequence.

Lenski points out that the algorithm used by the real scientists who did the ApoB study is unable to detect adaptive changes that improve the function of the protein: it is limited to detecting “benign”, “possibly damaging” or “probably damaging” mutations. Not only did Behe leave out the “benign” mutations, but didn’t bother to mention that the algorithm can’t show changed or improved function for any mutations. And I call that duplicitous. Here’s Lenski’s take; the emphases are his.

The program simply cannot detect or suggest that a protein might have some improved activity or altered function.

The authors of the paper recognized these limiting assumptions and their implications for the evolution of polar bears. In fact, they specifically interpreted the APOB mutations as follows (p. 789): “… we find nine fixed missense mutations in the polar bear … Five of the nine cluster within the N-terminal βα1 domain of the APOB gene, although the region comprises only 22% of the protein … This domain encodes the surface region and contains the majority of functional domains for lipid transport. We suggest that the shift to a diet consisting predominantly of fatty acids in polar bears induced adaptive changes in APOB, which enabled the species to cope with high fatty acid intake by contributing to the effective clearance of cholesterol from the blood.” In a news piece about this research, one of the paper’s authors, Rasmus Nielsen, said: “The APOB variant in polar bears must be to do with the transport and storage of cholesterol … Perhaps it makes the process more efficient.” In other words, these mutations may not have damaged the protein at all, but quite possibly improved one of its activities, namely the clearance of cholesterol from the blood of a species that subsists on an extremely high-fat diet.

It appears Behe either overlooked or ignored the authors’ interpretation. Determining whether those authors or Behe are right would require in-depth studies of the biochemical properties of the protein variants, their activities in the polar bear circulatory stream, and their consequences for survival and reproductive success on the bear’s natural diet. That’s a tall order, and we’re unlikely to see such studies because of the technical and logistical challenges. The point is that many proteins, including ApoB, are complex entities that have multiple biochemical activities (ApoB binds multiple lipids), the level and importance of which may depend on both intrinsic (different tissues) and environmental (dietary) contexts. In this example, Behe seems to have been too eager and even determined to describe mutations as damaging a gene, even when the evidence suggests an alternative explanation.

Now this may seem an arcane discussion about protein function, but if you’ve gathered anything from this post, Lenski’s post, and Lents’s posts, it should be that Behe has not been intellectually honest in treating the data in a key example used to make his case that natural selection nearly always relies on broken genes. But what do you expect from a creationist who’s deeply religious and who’s counting on the data to make the case for God?

I’m told that Behe really believes the kind of palaver he uses to make the case for “irreducible complexity” and Intelligent Design. But really, how can you leave out data and distort the conclusions of others, without being conscious of what you’re doing? One might almost conclude that Behe is lying for God.

Lenski isn’t done with taking Behe to the woodshed yet: as he says, “I initially planned to write three posts, but it will now be more than that, as I delve deeper into several issues.” Behe’s tuchas is going to be smarting after this!

Human Phylogeography

February 23, 2019 • 11:33 am

by Greg Mayer

For the spring semester, my colleague Dave Rogers and I are teaching a seminar class entitled “Human Phylogeography.” Phylogeography is the study of the history of the genetic variation, and of genetic lineages, within a species (or closely related group of species), and in the seminar we are looking at the phylogeography of human populations. DNA sequencing now allows a fine scale mapping of the distribution of genetic variation within and among populations, and, remarkably, the ability to sequence ancient DNA from fossil remains (including Neanderthals). The seminar is based primarily on a close reading of David Reich’s (2018) Who We Are and How We Got Here (published by OUP in the UK).

A Krapina, Croatia, Neanderthal woman, photo by Jerry.

Although rarely under that rubric, human phylogeography has been a frequent topic of discussion here at WEIT, by Jerry, Matthew, and myself, including our several discussions of Neanderthals (or Neandertals) and Denisovans. So it may be of interest for WEIT readers to follow along. Below the fold I’ve placed the course syllabus, which includes the readings, and links to many newspaper articles of interest, and online postings, including many here at WEIT, and also from John Hawks Weblog, a site we’ve recommended on a number of occasions when discussing human evolution. (The newspaper links appear as images; just click to go to the story.) We just finished our third meeting, and I’ve been quite impressed by the students’ discussion and writing. We’re fortunate to have some students from anthropology or with some anthro background.

Please read along with us, or browse what seems interesting below. If you have questions or comments, post them here, and I’ll be looking in.

Continue reading “Human Phylogeography” →

Mathematician John Lennox embarrasses himself by trying to reconcile Christianity and science

February 23, 2019 • 10:30 am

Reader Alexander called my attention to this item in the Science Focus section of the BBC. (Note that it’s in the science section, not the “religion” section!) It’s a 33-minute podcast interview with John Lennox, whose Wikipedia page says this (my emphasis, and yes, that’s THE Templeton Foundation, which now has a damn Oxford College named after it):

John Carson Lennox (born 1943) is a Northern Irish mathematician specialising in group theory, a philosopher of science and a Christian apologist. He is Emeritus Professor of Mathematics at the University of Oxford and an Emeritus Fellow in Mathematics and Philosophy of Science at Green Templeton College, Oxford University. He is also an Associate Fellow of the Saïd Business School.

. . . Lennox has been part of numerous public debates defending the Christian faith, including debates with Christopher Hitchens, Michael Shermer, Richard Dawkins, Lawrence Krauss, Peter Atkins, Victor Stenger, Michael Tooley, Stephen Law, and Peter Singer.

Green Templeton College resulted from a merger in 2008 between Green College and Templeton College, and here are the facts (my emphasis):

The college was founded in 1965 as the Oxford Centre for Management Studies. The College was based at Egrove Park in Kennington, south of Oxford. Its buildings were opened in 1969, and were awarded listed status in 1999.

It was renamed Templeton College in 1983 as a result of a donation from Sir John Templeton, in honour of his parents, Harvey Maxwell and Vella Handly Templeton. The intention was to raise professional standards in British management. The endowment was one of the largest endowments ever made to a British educational establishment. Initially a “society of entitlement” in the University, Templeton College began admitting graduate students in 1984 and became a full graduate college of the University by Royal Charter in 1995.

The podcast interview with Lennox is below (click on the link), though you may not get through much of it before your digestive system goes awry.

The podcast notes:

With science providing more and more insights into the workings of the Universe, many people have turned their backs on religion entirely. Why invoke a God to explain the world, the argument goes, when science does a perfectly good job? Professor John Lennox, however, begs to differ.

Emeritus Professor of Mathematics at the University of Oxford, Lennox is both a scientist and a Christian. In his new book, Can Science Explain Everything? (£7.99, The Good Book Company), Lennox argues that the worldviews of religion and science are not incompatible. In fact, he goes one step further, arguing that science actually points towards the existence of God.

In this episode of the Science Focus Podcast, he speaks to BBC Focus staff writer James Lloyd.

Listen to as much of this podcast as you can stand, and then, perhaps, to the much shorter video below.

Just a few comments. First, note that Lloyd, the interviewer, does ask hard (and good) questions. Lennox wiggles and weasels but ultimately shows his hand. His schtick is to conflate science and religion by taking two familiar paths: changing the definition of “faith” so that scientists are said to have faith, and arguing that science and rationality also point to the existence of God. (That, of course, is the mission of the Templeton Foundation.)

As for the first bit, he notes that science deals with unrepeatable events, like cosmology, and so to investigate them—or to do any science—requires “faith in the rational intelligibility of the universe”. As he says, “In science there’s a mixture of faith and there’s a mixture of investigation and observation and all the rest of it.” In other words, he’s equating science with his Christianity, which, he says, also requires a mixture of faith and empirical evidence.

This is of course bogus. We don’t have faith in the rational intelligibility of the universe: we try to find out if the universe is intelligible, and if it obeys rules. It does, because we can make predictions based on the ubiquity of those rules. An intelligible universe, then, is not an article of faith but a conclusion based on observation of repeated patterns and fulfilled predictions. It’s like having “faith” that the sun will rise tomorrow. And that is very different from religious faith. (See here for more of my take on this issue.)

As far as “science” supporting Christianity, Lennox argues that the grounding principle of Christianity—the existence of a divine Jesus who was resurrected—is strongly supported by history. Here are some of my notes and transcribed quotes:

“Christianity is a rational faith, but when it comes to the historical side, then we use the kind of abductive inference we use in historical science.”

Ancient historians produce “very powerful evidence”; they are “very sure of . . . most of the basic facts of Jesus’s life and so on.”

And, says Lennox, Christianity also makes sense: The God and Christ explanations make sense of what we discover because an explosion of science occurred under Galileo, Kepler and Newton, “all of whom were religious”.

That’s also bogus. There were also Jews, Hindus, Muslims and atheists who made profound scientific discoveries, not to mention the “pagan” Greeks. The faith of someone who makes a discovery is not evidenced by the nature of that discovery. Kepler’s laws no more buttress Christianity than does the structure of DNA (determined by two atheists) show that there is no God. What science does show is that we make discoveries by assuming there is no God, and that adding the assumption of a God has never pushed science forward one iota—except to the limited extent that some religionists may be inspired to do science by their religious faith. But of course that doesn’t show there is a God. These days, of course, most accomplished scientists are atheists, and we don’t need God to make further progress.

Lennox also sees, beyond the copious “historical evidence for Jesus” (is he aware that it’s limited to what’s in the Bible?), further evidence for God and Jesus based on his “experience.” He regards this “experiential evidence” as quasi-scientific. For instance, Lennox asserts that “Christ’s claims can be inductively tested”. Jesus said, argues Lennox, that He would return, and “if we trusted Him as Saviour and Lord then we would experience forgiveness, peace and inner harmony and power to deal with life.” And, says Lennox, he’s seen that happen over and over again in people who have accepted Jesus. Ergo, PROOF! (Of course, you can cite examples of people who have said they gained inner harmony and forgiveness from accepting the tenets of Islam, Hinduism, or Judaism, or even atheism, but somehow Lennox forgets that.)

Finally, Lennox claims that miracles do occur, and that there are at least three times God intervened in nature beyond reviving Jesus: the Big Bang (he doesn’t think it could happen naturalistically), the origin of life, and the evolution of humans. He seems to accept the rest of evolutionary biology, but argues, like a true Intelligent Design proponent, that the origin of life and the evolution of humans either couldn’t happen naturalistically and thus involved the hand of God. This kind of human exceptionalism is a trademark of the ID/creationist Discovery Institute.

Why did the BBC put this on? And if they did, why don’t they have ME on to argue that science and religion are incompatible? I’m here, Mr. Lloyd!

Altogether, for a smart professor, Lennox makes some remarkably weak and almost humorously stupid arguments. But this is how religion distorts the rationality of wish-thinkers. Lennox is a serious wish thinker. You can get a precis of his ideas in this three-minute video:

As for Lennox’s debates against atheists, here are three videos. I haven’t watched any of them, but will look in.

Lennox vs. Hitchens

Lennox vs. Dawkins

Lennox vs. Singer

Caturday felid trifecta: Cat weight-control device; vets save a frozen, ice-covered cat; shelters for homeless cats in Ecuador

February 23, 2019 • 9:00 am

Here’s a device, “Little Cat”, that purports to help your tubby moggie lose weight; it apparently comes from Korea, and I can’t find out how much it costs. You can operate it from your phone with an app, and the speeds are up to 72 rpm, which may be a bit fast for even a fit cat! Also, since the cat never catches the laser dot, it’s bound to get frustrated. And if your cat is going to chase a laser dot, why not just get a laser pointer instead of this wheel?

No, I don’t think this is a good buy, but who knows?

***********

From both ScienceAlert and news.com.au, we have the chilling but ultimately happy story of a rescued cat. The moggie in question, one Fluffy from Montana, was an indoor/outdoor cat whose owners, having gone away for a bit, found it frozen and covered with ice balls:

Fluffy’s owners, who did not want to be identified [JAC: no surprise!], found her covered in thick chunks of ice and snow near their home last week. They scooped her up and immediately drove her to the vet, which is probably what saved her life.

“She was frozen,” said Andrea Dutter, executive director of the Animal Clinic of Kalispell.

A photo!

It wasn’t a rock-solid kind of frozen. But her body temperature was below what the clinic’s thermometers could read — 90 degrees. A cat’s normal internal body temperature is 101 degrees.

“We immediately began to warm her up,” Dutter said. “Warm water, heating pads, hot towels . . . within an hour she started grumbling at us.”

Staff warmed the cat using towels, cage warmers and intravenous fluids. Fluffy is normally a little crabby, so when she began growling after about an hour, Clark knew she would be fine, he said.

“These crabby cats are survivors,” Clark said.

And now Fluffy is okay. I hope the owners learned a lesson. More photos from the AP:

Fluffly thawing out:

Lazarus revived!

***********

From Designboom we have the story of a developing project in Ecuador in which street cats are provided with spiffy designer shelters to protect them from dogs and other outdoor dangers. Architects have put up this shelter in Babahoyo, Ecuador, and it seems to work.

A translation from the Spanish:

The refuge of 60 square centimeters is built of wood, protected against water and rain by small eaves, that help to have cross ventilation. a tray for food is placed next to the water. in the end, the shelters bring the idea of consciousness, a responsible city that welcomes and learns to live next to animals while they achieved in finding their home.

The locals even provide food and water, as you can see in the video below. This is a prototype, but let’s hope that these will spread across the country (or other countries):

h/t: Michael, Tom, Stephen

Readers’ wildlife photos

February 23, 2019 • 7:30 am

I saw a photo of a coyote (Canis latrans) on Stephen Barnard’s Facebook page, and asked him if I could use it. He said yes, but told me that I may have published one or more of these several years ago. So be it; I don’t remember, and I bet most readers either don’t or have come aboard since then. Stephen’s notes:

I’m pretty sure you’ve posted my coyote photos from three years ago. It was a winter of a vole population explosion and the coyotes were numerous and well fed. She was enamored of Deets — tried to get him to play and generally fool around — but she never crossed the creek, to my relief.

Anyway, here are some photos of her three years ago, across the creek, flirting with my Border Collie.

One request for any readers: No comments, please, about how dangerous coyotes are to dogs. I’m much more worried about mountain lions.

Saturday: Hili dialogue

February 23, 2019 • 6:30 am

It’s ~~Caturday~~ Saturday, February 23, 2019, and National Banana Bread Day. That comestible has one thing going for it: it’s not zucchini bread, which is what they feed people in Hell.

Today in Russia, Turkmenistan, Belarus, Kyrgyzstan, Kazakhstan and Tajikistan, it’s Defender of the Fatherland Day, celebrating the date in 1918 when the first mass draft into the Red Army took place.

On this day in 1455, it’s the “traditional date for the publication of the Gutenberg Bible, the first Western book printed with movable type.” (Wikipedia). On February 23, 1836, the Siege of the Alamo began in San Antonio, Texas. In 1896, according to Wikipedia, “Charles Martin Hall produced the first samples of man-made aluminium, after several years of intensive work. He was assisted in this project by his older sister, Julia Brainerd Hall.” On February 23, 1898, Émile Zola was imprisoned in France for his famous “J’Accuse” letter defending Dreyfus and accusing the French government of antisemitism and railroading Dreyfus into prison.

On this day in 1903, Cuba leased Guantànamo Bay to the U.S.—in perpetuity. That decision was deeply regretted when Castro took over. Exactly fourteen years later, the February Revolution began in St. Petersburg with demonstrations by workers. And a decade later than that, in 1927, Werner Heisenberg wrote a letter to Wolfgang Pauli describing his “uncertainty principle” for the first time. In 1941, plutonium was first produced by Glenn T. Seaborg.

On February 23, 1945, in Iwo Jima, the famous photo of “raising the flag” took place when a Navy corpsman and U.S. marines raised an American flag atop Mount Suribachi during the battle for the island. Wikipedia describes the scene (my emphasis):

Rosenthal put his Speed Graphic camera on the ground (set to 1/400 sec shutter speed, with the f-stop between 8 and 11 and Agfa film) so he could pile rocks to stand on for a better vantage point. In doing so, he nearly missed the shot. The Marines began raising the flag. Realizing he was about to miss the action, Rosenthal quickly swung his camera up and snapped the photograph without using the viewfinder. Ten years after the flag-raising, Rosenthal wrote:

Out of the corner of my eye, I had seen the men start the flag up. I swung my camera and shot the scene. That is how the picture was taken, and when you take a picture like that, you don’t come away saying you got a great shot. You don’t know.

Sergeant Genaust, who was standing almost shoulder-to-shoulder with Rosenthal about three feet away, was shooting motion-picture film during the second flag-raising. His film captures the second event at an almost-identical angle to Rosenthal’s shot. Of the six flag-raisers in the picture – Ira Hayes, Harold Schultz (identified in June 2016), Michael Strank, Franklin Sousley, Rene Gagnon, and Harlon Block – only Hayes, Gagnon, and Schultz (Navy corpsman John Bradley was incorrectly identified in the Rosenthal flag-raising photo) survived the battle. Strank and Block were killed on March 1, six days after the flag-raising, Strank by a shell, possibly fired from an offshore American destroyer and Block a few hours later by a mortar round. Sousley was shot and killed by a Japanese sniper on March 21, a few days before the island was declared secure.

Several photographers were present, but the iconic photo was taken by Joe Rosenthal, who won a Pulitzer Prize for it (and no, it wasn’t posed or faked). It is the photo on which the Marine Corps Memorial, across the Potomac from Washington D.C. is based

Once again: Why do zebras have stripes? (And once again the answer: it’s the flies, stupid!)

February 22, 2019 • 11:15 am

Over the past three years I’ve written about research, mostly by Tim Caro’s group, dealing with the perpetual question: “Why do zebras have stripes?” (See earlier posts here, here, and here.) There used to be lots of hypotheses, including confusing predators like lions, aiding thermoregulation, camouflaging these equids, keeping groups together, and so on, but research has demolished these hypotheses one by one (for example, striped animals are no more camouflaged to predators than are solid-colored animals.)

Rather, evidence has been accumulating that stripes help deter biting flies, particularly tabanid flies (horseflies) and tsetse flies that not only draw blood but, more dangerously, carry disease that can kill zebras. It’s been shown, for instance, that the ranges of striped equids all fall within the ranges of biting flies, and that these flies can carry diseases like equine influenza, African horse sickness, equine infectious anaemia, and trypanosomiasis, all fatal. Other evidence is that tabanids appear averse to landing on striped patterns, as well as the evidence against the alternative hypotheses mentioned above.

Now, however, we have more direct evidence from Caro and his colleagues in a paper published in PLoS ONE. Click on the screenshot below, or get a free pdf here (the reference is at bottom).

What the authors did here was look at the behavior of horseflies around zebras and different-colored horses, all in a pasture in Somerset in the UK. They also dressed up the horses in zebra suits as well as in monochrome white or black suits, and watched the behavior of tabanids around the equids and the behavioral responses of zebras and horses to flies. Here’s a horse in a zebra suit from the experiment:

There were a number of sub-studies, and I’ll give the results briefly. The conclusion that tabanids are averse to crawling on striped patterns seems pretty solid.

Direct observations of flies. These were done by observers watching equids and flies directly, and also by video that could follow the trajectory of flies as they approached zebras and horses.

The non-video observations showed that there was no significant difference in the rates at which horseflies circled zebras versus horses, or touched them briefly, but significantly fewer flies landed on zebras than on horses. The probability of this occurring by chance, while significant, was not very impressive (p = 0.041). This could, however, reflect a differential behavior of the animals, for horses respond to flies by twitching their skin while zebras more often switched their tails (and ran away). Perhaps skin-twitching helps deter landing.

The videos showed that the trajectories of flies approaching zebras differed from that approaching horses: flies approached the horses more slowly, and decelerated very little while approaching zebras, so that they simply bumped into the zebras rather than landing on them. This difference in the proportion of approaching flies that landed was highly significant (p < 0.0001). Further, flies flew away from zebras significantly faster than from horses.

Further, once landed, a tabanid spent considerably more time on the horse than on the zebra: 10.1 versus 1.2 seconds respectively. This again is significant at the 0.01 level, but it’s not clear whether this reflected differential behavior of the equids toward flies (e.g., skin twitching versus tail switching).

Experiment with colored coats on horses. This is the most convincing part of the results. They used cloths of three types, as shown in the diagram, and you can see that the rate of horseflies landing on the cloths or touching the clothes was significantly lower (p < 0.0001) for the striped coat versus the white or black coat, with the latter two not differing from each other. In contrast, there was no difference in the rate of flies touching or landing on the horse’s heads, which were not covered by the cloth. That shows that the pattern is probably what’s important. (Sample sizes are given in the figure; they are not large.)

The upshot: Stripes don’t appear to deter tabanids at a distance, but, once close to the horse or zebra, appear to deter landing. The authors say that tabanids find equids at a distance using odor rather than visual ues, so this is understandable.

In the case of the horse-coat experiment and of the comparison of horses versus zebras, tabanids don’t land as often on stripes as on solid colors, and, once landed, they spend less time on zebras then on horses. The flies also do not decelerate so much when approaching zebras, perhaps because they don’t see a striped substrate as an appropriate place to land.

The conclusion is that if you have stripes, you’re more likely to deter flies from landing or, if they land, less likely to get bitten and thus to get any diseases carried by the flies. As the authors note,

In summary, multiple lines of evidence indicate that stripes prevent effective landing by tabanids once they are in the vicinity of the host but did not prevent them approaching from a distance. In addition, zebras appear to use behavioural means to prevent tabanids spending time on them through constant tail swishing and even running away. As a consequence of both of these morphological and behavioural defenses, very few tabanids are able to probe for a zebra blood meal as evidenced by our data.

Now we still don’t really know what it is about stripes that deter flies or drive them away. Perhaps their visual system gets confused or flummoxed. But the coincidence of the ranges of striped equids and biting flies (see here) is pretty remarkable, and supports this experiment in suggesting that stripes evolved in equids to protect them from the bites of disease-carrying flies. I’ll put up those range maps again, which are historical rather than present-day ranges (after all, selection for stripes operated in the past), and here’s what I wrote about them:

Here’s the association between the historical (not present!) ranges of equids and of tabanids and tsetse flies; equids at top (zebra ranges striped!) and flies at bottom. Note that tsetse flies (Glossina) aren’t found outside Africa. E. kiang is an unstriped wild ass, E. africanus is the African wild ass, having thin stripes on its legs, E. hemionus is the onager, an unstriped wild ass, and E. ferus przewalskii is Prezewalski’s horse, a rare wild horse thought to be the closest living relative of the domestic horse.

The correspondence is pretty good, although not perfect, since flies live in some areas where zebras don’t. The crucial observation, though, is that biting flies always occurred in areas where zebras lived.

Note, too, that unstriped equids don’t generally coexist with either kind of fly, though the African wild ass, which does have thin striping on its legs, does live in areas with horseflies.

__________

Caro, T., Y. Argueta, E. S. Briolat, J. Bruggink, M. Kasprowsky, J. Lake, M. J. Mitchell, S. Richardson, and M. How. 2019. Benefits of zebra stripes: Behaviour of tabanid flies around zebras and horses. PLOS ONE 14:e0210831.

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