The hazard of "just-so stories"

One of the problems with scientific research is there's a sneaky bias that can creep in -- manifesting as explaining a phenomenon a certain way because the explanation lines up with a narrative that seems so intuitive it's not even questioned.

Back in 1978, evolutionary biologist Stephen Jay Gould nicknamed these "just-so stories," after the 1902 book by Rudyard Kipling containing fairy tales about how animals gained particular traits (the most famous of which is "How the Leopard Got His Spots").  Gould was mainly pointing his finger at the relatively new field of evolutionary psychology -- giving straightforward evolutionary explanations for complex human behaviors -- but his stinging criticism can be levied against a great many other fields, too.

The difficulty is, this bias slips its way in because these explanations seem so damned reasonable.  It's not quite like confirmation bias -- where we accept thin corroborative evidence for ideas we already agreed with, and demand ridiculously high standards for counter-evidence that might falsify them.  It's almost like confirmation bias, only backwards -- after hearing it, we experience a "wow, I never knew that!" sort of delight.  We didn't already believe the explanation; but when we find out about it, we respond with open-armed acceptance.

One good example, that I had to contend with every single year while teaching high school biology, was the whole "right-brained versus left-brained personality" thing, which was roundly debunked a long time ago.  It's certainly true that our brains are lateralized, and most of us have a physically dominant hemisphere; also, it's undeniable that some of us are more holistic and creative and others more reductionistic and analytical; and it's also true that the cognitive parts of the right and left brain seem to process information differently.  Putting these three together seems natural.  The truth is, however, that any connection between brain dominance and personality type is tenuous in the extreme.

But it seems like it should be true, doesn't it?  That's the hallmark of a "just-so story."

The reason this topic comes up is a recent paper in the journal Global Ecology and Conservation that challenges one of the most appealing of the "just-so stories" -- that the reintroduction of wolves to Yellowstone National Park caused a "trophic cascade," positively affecting the landscape and boosting species richness and species diversity in the entire region.

The original claim came from research by William Ripple et al., and connected the extirpation of wolves with the corresponding higher survival rate of elk and deer.  This, they said, resulted in overbrowsing of willow and alder, to the point that as older plants died they were not being replaced by saplings.  This, in turn, led to higher erosion into streams, silting of the gravel bottoms required for salmon and trout to spawn, so a drop in fish population.  Last in the chain, this resulted in less food for bears, so a reduction in survival rates for bear cubs, and a decrease in the numbers of grizzly and black bears.

The reintroduction of wolves -- well, supposedly it undid all that.  Within a few years of the establishment of a stable wolf population, the willows and alders rebounded because of higher predation on elk and deer -- leading to a resurgence of trout and salmon and an increase in the bear population.

This all sounds pretty cool, and doesn't it line up with what we'd like to be true?  The eco-minded amongst us just love wolves.  There's a reason they're featured in every wildlife calendar ever printed.

[Image licensed under the Creative Commons User:Mas3cf, Eurasian wolf 2, CC BY-SA 4.0]

It's why I almost hate to tell you about the new paper, by Daniel MacNulty, Michael Procko, and T. J. Clark-Wolf of Utah State University, and David Cooper of Colorado State University.  Here's the upshot, in their own words:

Ripple et al.... argued that large carnivore recovery in Yellowstone National Park triggered one of the world’s strongest trophic cascades, citing a 1500% increase in willow crown volume derived from plant height data...  [W]e show that their conclusion is invalid due to fundamental methodological flaws.  These include use of a tautological volume model, violations of key modeling assumptions, comparisons across unmatched plots, and the misapplication of equilibrium-based metrics in a non-equilibrium system.  Additionally, Ripple et al. rely on selectively framed photographic evidence and omit critical drivers such as human hunting in their causal attribution.  These shortcomings explain the apparent conflict with Hobbs et al., who found evidence for a relatively weak trophic cascade based on the same height data and a long-term factorial field experiment.  Our critique underscores the importance of analytical rigor and ecological context for understanding trophic cascade strength in complex ecosystems like Yellowstone.

MacNulty et al. demonstrate that if you re-analyze the same data and rigorously address these flaws, the trophic cascade effect largely vanishes.  "Once these problems are accounted for, there is no evidence that predator recovery caused a large or system-wide increase in willow growth," said study co-author David Cooper.  "The data instead support a more modest and spatially variable response influenced by hydrology, browsing, and local site conditions."

It's kind of a shame, isn't it?  Definitely one of those "it'd be nice if it were true" things.  It'll be interesting to see how Ripple et al. respond.  I'm reminded of a video on astronomer David Kipping's wonderful YouTube channel The Cool Worlds Lab about his colleague Matthew Bailes -- who in 1990 announced what would have been the first hard evidence of an exoplanet, and then a few months later had to retract the announcement because he and his co-authors had realized there'd been an unrecognized bias in the data.  Such admissions are, naturally, deeply embarrassing to make, but to Bailes's credit, he and his co-authors Andrew Lyne and Setnam Shemar owned up and retracted the paper, which was certainly the honest thing to do.

Here, though -- well, perhaps Ripple et al. will be able rebut this criticism, although having read both papers, it's hard for me to see how.  We'll have to wait and see.

Note, too, that MacNulty et al. are not saying that there's anything wrong with reintroducing wolves to Yellowstone -- just that the response of a complex system to tweaking a variable is going to be, well, complex.  And we shouldn't expect anything different, however much we like neat tales of How the Leopard Got His Spots.

So that's today's kind of disappointing news from the world of science.  How we have to be careful about ideas that have an immediate intuitive appeal.  Just keep in mind physicist Richard Feynman's wise words: "The first rule in science is that you must not fool yourself -- and you are the easiest person to fool."

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Pack mentality

As hard as it may be to imagine, dogs -- yes, all of them -- are the domesticated descendants of gray wolves.

Well, it's hard for me to imagine, anyhow.  I have three dogs whose wolf ancestry is, shall we say, rather well hidden.

This is Jethro.  He's half Plush Toy and half Dust Bunny.

This is Guinness, who is a full-blooded Tennis Ball Retriever.  He is also a very dapper gentleman.

And this is Rosie, who has had just about enough of your shit.

None of them, let's say, exactly screams out "Alpha Wolf of the Deep Forest Pack."  But nevertheless, all three of them descend from wolves that were domesticated by our distant ancestors something like twenty thousand years ago, in an encounter that went something like this:

Wolf (snarling): I will terrorize your villages, decimate your livestock, and eat your children!

Early human:  We have sofas, peanut butter, and squeaky toys.

Wolf:  ... I'm listening

What's fascinating is that despite a lot of selective breeding since then, wolves and dogs are still cross-fertile.  It's yet another example of how we think we have a good definition for the word species, then we keep finding exceptions, or at least situations that leave you thinking, "Wait... those are the same species?"  But yes: by the canonical definition of species -- a population whose members are capable of interbreeding and producing fertile offspring -- dogs and wolves are the same species.

And new research by a team from the American Museum of Natural History and the Smithsonian Institution has found something even more astonishing; since domestication, dogs have been backcrossed to wolves multiple times, meaning that since domestication, wolf genetics has been reintroduced into dog lineages over and over.

Not always how you'd expect, either.  It isn't just "big dogs = lots of recent wolf ancestry, small dogs = not so much."  Mastiffs and Saint Bernards both show close to zero reintroduced wolf DNA.  Even chihuahuas have more (at around 0.2%).  The highest amount, unsurprisingly, is amongst the breeds associated with pulling sleds -- huskies, malamutes, Samoyeds, and Greenland dogs.  But most dog breeds have somewhere between two and five percent recent wolf ancestry, even the ones you might not suspect.

What's also fascinating is that the amount of recent wolf ancestry correlates strongly to personality.  Breeds were given descriptors by dog breeders and owners, and a significant pattern emerged.  Low recent wolf ancestry correlated to a breed being described as “friendly,” “eager to please,” “easy to train,” “courageous,” “lively,” or “affectionate.”  High wolf ancestry breeds were more likely to be described as “suspicious of strangers,” “independent,” “dignified,” “alert,” “loyal,” “reserved,” or “territorial.”

John Heywood's comment that what's bred in the bone comes out in the flesh apparently applies to dogs as well as humans.

It makes me wonder about how wolfy my own dogs are.  Jethro, I suspect, is pretty low on the scale.  High wolf ancestry is also correlated with intelligence, and -- to put not too fine a point on it -- Jethro has the IQ of a tuna salad sandwich.  I suspect Guinness is on the high end, because he's part husky, and also checks off most of the boxes for the personality traits of high wolf ancestry dogs.  Rosie is mostly Australian cattle dog, and she's probably in the middle.  All I know is that she's extremely sweet, stubborn as hell, and can give you a reproachful look that makes you feel like you have disappointed not only her, but all of her ancestors.

In any case, this is all an excellent example of introgression -- where populations that initially come from a common ancestry are repeatedly backcrossed to the wild type.  And that, plus twenty thousand years of selective breeding, is why we have the great variety of dogs we have.

But you'll have to excuse me.  Guinness wants to play ball.  I wonder if "extremely demanding and will not take no for an answer" is a wolf trait?

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Rebuilding the web

One of the (many) ways people can be shortsighted is in their seeming determination to view non-human species as inconsequential except insofar as they have a direct benefit to humans.

The truth, of course, is a great deal more nuanced than that.  One well-studied example is the reintroduction of gray wolves to Yellowstone National Park, something that was opposed by ranchers who owned land adjacent to the park, hunters who were concerned that wolves would reduce numbers of deer, elk, and moose for hunting, and people worried that wolves might attack humans visiting the park or the area surrounding it.  The latter, especially, is ridiculous; between 2002 and 2020 there were 489 verified wolf/human attacks worldwide, of which a little over three-quarters occurred because the animal was rabid.  Only eight were fatal.  The study, carried out by scientists at the Norwegian Institute for Nature Research, stated outright that the risks associated with a wolf attacking a human were "non-zero, but far too low to calculate."

Fortunately, wiser heads prevailed, and the wolf reintroduction went forward as scheduled, starting in 1996.  The results were nothing short of spectacular.  Elk populations had skyrocketed following the destruction of the pre-existing wolf population in the early twentieth century, resulting in such high overgrazing that willows and aspens were virtually eradicated from the park.  This caused the beaver population to plummet, as well as several species of songbirds that depend on the insects hosted by those trees.  The drop in the number of beaver colonies meant less damming of streams, resulting in small creeks drying up completely in summer and a resultant crash of fish populations.

In the years since wolves were reintroduced, all of that has reversed.  Elk populations have returned to stable numbers (and far fewer die of starvation in the winter).  Aspen and willow groves have come back, along with the beavers and songbirds that depend on them.  The ponds and wetlands are rebuilding, and the fish that declined so precipitously have begun to rebound.

All of which illustrates the truth of the famous quote by naturalist John Muir: "When we try to pick out anything by itself, we find it hitched to everything else in the Universe."

The reason this all comes up is a recent story in Science News about a project that should give you hope; the restoration of mangrove forests in Kenya.  You probably know that mangroves are a group of trees that form impenetrable thickets along coastlines.  They've been eradicated in a lot of places -- particularly stretches of coast with sandy shores potentially attractive to tourists -- resulting in increased erosion and drastically increased damage potential from hurricanes.  A 2020 study found that having an intact mangrove buffer zone along a coast decreased the damage to human settlements and agricultural land from a direct hurricane strike by an average of 24%.

[Image is in the Public Domain courtesy of NOAA]

The Kenyan project, however, was driven by two other benefits of mangrove preservation and reintroduction -- carbon sequestration and increased fish yields.  Mangrove swamps have been shown to be four times better at carbon capture and storage as inland forests, and their tangled submerged root systems are havens for hatchling fish and the plankton they eat.  The restoration has been successful enough that similar projects have been launched in Mozambique and Madagascar.  A UN-funded project called Mikoko Pamoja allows communities that are involved in mangrove restoration to receive money for "carbon credits" that then can be reinvested into the community infrastructure -- with the result that the towns of Gazi and Makongeni, nearest to the mangrove swamps and responsible for their protection, have become economically self-sufficient.

I have the feeling that small, locally-run projects like Mikoko Pamoja will be how we'll save our global ecosystem -- and, most importantly, realizing that species having no immediately obvious direct benefit to humans (like wolves and mangroves) are nevertheless critical for maintaining the health of the complex, interlocked web of life we all depend on.  It means taking our blinders off, and understanding that our everyday actions do have an impact.  I'll end with a quote from one of my heroes, the late Kenyan activist Wangari Maathai: "In order to accomplish anything," she said, "we must keep our feelings of empowerment ahead of our feelings of despair.  We cannot do everything, but still there are many things we can do."

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