Saturday, June 27, 2009

Simple and Obvious Truths

In which the blogger begins with invasive Burmese pythons and ends up with beached Viking funeral ships.

English ivy, an invasive
I am somewhat suspicious of the simple truth or the obvious truth (not necessarily mutually exclusive adjectives for truth) because, from my perspective, things in general, nature, life don’t usually work simply or obviously. (I will avoid the endless loop and not suggest that this is a simple and obvious truth.) I also have a tendency to accumulate trees, lots of trees, and, as a result, end up often deep in details, missing the forest entirely.

I was prompted to think about simple truths and obvious truths when I read a fascinating (and, in true New Yorker style, lengthy) article by Burkhard Bilger in which he describes the exotic or invasive fauna, most prominently the Burmese python, that runs rampant in Florida and considered what might and might not be done to arrest its spread (Swamp Things: Florida’s Uninvited Predators, The New Yorker, April 20, 2009). Though the article seemed to strike a death knell for native Florida fauna (and all small dogs), I was brought up short when Bilger wrote the following:
The one statistic that seems to hold true is the rule of ten, described by an English biologist in 1993: one in ten exotics escape into the wild; one in ten of those become established; one in ten established exotics become pests. . . . Invasives can undoubtedly drive natives to extinction, . . . . But most of the time an ecosystem isn't a game of musical chairs. When a new species arrives, it rarely takes another's place. It just finds another spot to sit.

Well, in that single paragraph, there’s a example of the simple truth and also a challenge to a commonly accepted obvious truth.

A Simple Truth

First, a simple truth. A statistical rule of ten is clearly a macro view of the forest, the trees are indistinguishable. Given, say, 1000 invasive species, 10% or 100 will escape; of the escapees, 10% or 10 will become established; and of those species 10% or 1 will become a pest – 0.1% of the original non-native population. Is that a lot or a little? I don’t know. But, it’s so simple, and so easy.

But it’s not quite so simple – there are some trees in this forest. Biologist Mark Williamson, who first calculated it, calls it the tens rule, and he stresses that it needs to be approached with caution. In fact, the tens are really fives to twenties. In other words, the percentages may range from 5 to 20% at each stage. (The Varying Success of Invaders, Mark Williamson and Alastair Fitter, Ecology, Vol. 77, No. 6, p. 1662) Not only does the rule have a fairly broad range of wiggle room, but it also has a number of exceptions (with much higher percentages at some of the different stages – escape, establishment, or becoming a pest) even within the handful of organisms studied and reported on by Williamson and Fitter.

An Obvious (and Simple) Truth

The challenge to an accepted obvious truth in the paragraph quoted above is this argument: An ecosystem may have room, and invasive species that establish themselves may occupy vacant niches, without upsetting native species.

Wait, wait, wait. Isn’t it obviously (and simply) true that invasive species are bad, and natives are good? I mean, just consider that kudzu tidal wave engulfing the woods just down the road. That’s certainly what the Alien Plant Working Group, sponsored by the National Park Service, posits: "Invasive non-native organisms are one of the greatest threats to the natural ecosystems of the U.S. and are destroying America's natural history and identity.” The APWG states, “[E]ach alien plant is one less native host plant for our native insects, vertebrates and other organisms that are dependent upon them.”

And this view is the one promoted by a local group that works to maintain and protect a park close to my home – the park straddles a creek for many miles of its run. This group describes the possible fate of flora in the park in jeremiadic terms similar to those of the APWG – if action isn’t taken now, the several hundred plant species native to this area will be completely displaced by a limited number of invasive non-native species.

Well, this obvious truth may not be so true. This forest is made up of many, many trees. Turns out there’s an ongoing scientific battle over the consequences of species invasion, and whether we should be in continual crisis mode about it, indeed, whether we might have let our emotions override some necessary scientific distance. The debate supports my wariness of the obvious.

Biologists James H. Brown and Dov F. Sax are in the vanguard of the revisionists cautioning about that obvious conclusion concerning invasive species. At the outset, they suggest jettisoning the idea that direct or indirect human agency is a sine qua non for defining an invasive/non-native/exotic/what-have-you species. They question whether we can or should look to a “pristine” past when things were natural or native, because the invasion of alien species “should be viewed in the context of ‘natural’ colonization events that have occurred without human intervention throughout the Earth’s history.” (An Essay on Some Topics Concerning Invasive Species, Austral Ecology, 2004, p. 530) Invasion isn’t a new story, it’s a very old one.

The consequences Brown and Sax suggest are certainly much more complicated than the APWG’s assertion that every invading alien plant species displaces a native species. They review the arguments about whether different ecosystems are capable of absorbing more animal and plant species, whether and how invasions might lead to increased biodiversity in a system, etc. The answers aren’t clear cut and don’t seem to fall uniformly on one side or the other. The consequences of a species invasion can be devastating, but not necessarily so. The villain in the piece isn’t always a villain. Indeed, a New York Times article on the revisionists in this debate was entitled “Friendly Invaders.” (Article by Carl Zimmer, The New York Times, September 8, 2008)

Getting Paleontology into the Mix

When I read about the tens rule, I initially wondered whether what the fossil record might say about it. I recognize that this is a quintessentially naive question. There’s a degree of precision (even within its fudge factors) to the tens rule unlikely to be reflected in the fossil record (that is, if the rule itself is really a reflection of nature).

Still, as Brown and Sax write, “The fossil record shows many episodes of massive invasions and extinctions . . . .” Further, there have been invasions of ecosystems by non-native species throughout the history of life on Earth. And it need not be on a massive scale. “[T]hroughout the past, individual species dispersed across existing biogeographical barriers to invade new continents and islands, oceans and lakes. These independent colonization events were sporadic and infrequent, but over the millennia of the Earth’s history, their numbers were large and their impact on global biodiversity was great.” (p. 531) In the final analysis, species invasion hasn’t been the exclusive work of human agents, and this period’s natives aren’t the previous period’s natives.

With invasive species, the truth may not be quite so obvious or simple.

Beached Viking Funeral Ships

I have read a little bit of the biogeographical literature on the dispersion of species over the Earth’s history – where species end up and why – and am quite taken by some of its extremely clever terminology. Among the avenues through which fauna might move into new areas are corridors (paths offering little obstruction to dispersion), filter bridges (avenues that don’t result in free flow, some species move across these bridges, others don’t), and sweepstakes routes (dispersal where, like the lottery, the odds are very long against success – think islands in the middle of an ocean). (See Bringing Fossils to Life: An Introduction to Paleobiology, by Donald Prothero, 1998, Chapter 9)

But, for me, the best names are those coined by paleontologist Malcolm C. McKenna in describing how plate tectonics can account for some of the dispersal of species. There are the Noah’s arks created when pieces of land masses break off and move across water to join different land masses. Species catch a ride.

My favorite describes a mechanism that’s actually a cheat when it comes to species dispersal. McKenna described beached Viking funeral ships (how glorious) occurring when traveling land masses, carrying their fossil record, collide with other land masses and deposit that fossil record some place unexpected. These are invasions of the long dead, the fossilized. According to Prothero (on whose descriptions of McKenna’s terms I’ve relied), one example of this process at work is the presence in North America of Cambrian European trilobite fossils, and the presence in Scotland of North American trilobite fossils.

Malcolm McKenna, who died last year, had been curator of vertebrate paleontology at the American Museum of Natural History and geosciences professor at Columbia University. The publication in 1997 of Classification of Mammals capped a lengthy career studying fossil mammals. According to his New York Times obituary, McKenna’s legacies include the one that is left by most fossil collectors: “Until almost the end, he was still bringing home fossils, his wife said. Another scientist is classifying the mammal fossils piled up in the basement of their house.” (Malcolm McKenna, 77, Fossil Seeker, Dies, by John Noble Wilford, The New York Times, March 10, 2008)

Yellow-crowned Night Heron chicks born at the extreme northern edge of their range -- not invasives . . . yet.

Friday, June 19, 2009

The Spider Web of Scientific Nomenclature, or How I Started With a Shark and Ended Up in Australia by Way of the French Revolution

"Nomenclature is a preface to understanding." Richard Fortey (Trilobite: Eyewitness to Evolution, 2000, p. 29)

In which the blogger concludes that a 1939 coup against the shark genus name Corax may have been unjustified, builds a mountain out of a mole hill, is easily distracted, and considers a Trilby hat.

This post is another in the series I’ve written on scientific names, their science and art.

For children’s birthday parties, my mother often created an enormous spider web out of yarn in a large room. Each strand of yarn began at the doorway and, in its length, often suspended, crisscrossed the room, and ended connected to a little gift. Each partygoer told hold of the end of an individual strand and, then, chaos ensued as each tried to go where the line led, until (it was hoped by all adults present) each child happily secured a party favor.

That spider web game comes to mind when I try to untangle the history behind some scientific names. The labyrinthine process through which some organisms acquired their scientific names continues to challenge me. In trying to retrace steps through that labyrinth, I grab hold of a piece of yarn and follow it, hoping for clarity, some bright, fixed lines, but, instead, I often find complexity, confusion, ambiguity, and, yes, some welcome surprises. The yarn’s inevitably connected to something, or some things, though not always the expected. Perhaps that’s just life.

Following the Strand of Yarn

In a 1939 article, Gilbert Percy Whitley (1903-1975), renowned Australian ichthyologist, renamed the extinct shark genus Corax as Squalicorax. In a previous post, I explored a bit of the taxonomic history of the Squalicorax genus of sharks, prompted by my attraction to their complex fossilized teeth. I was left pondering why Louis Agassiz in 1843 applied the name Corax to the genus of these sharks (Corax is, after all, Latin or Greek for “Raven” – if I understand the messy Web, the same word is used in both Latin and Greek). Somewhat secondarily, I asked why G.P. Whitley had been moved to rename the genus in 1939.

I have his answer for the second question. I now have a copy of Whitley’s 1939 article, a lengthy and somewhat eclectic compilation of data on many different kinds of sharks – mostly, as far as I can tell, living sharks. In this piece, Whitley asserted,

A new name is necessary for the shark called Corax, because Mr. T. Iredale informs me that Agassiz’ name is preoccupied by Corax Ledru (Voy. Ténériffe, ii., 1810, p. 204), a generic name for the Raven. [Taxonomic Notes on Sharks and Rays, by G.P. Whitley, The Australian Zoologist, 1939, p. 240.]

Believing that a genus of bird already had the name Corax (“preoccupied”), he fashioned the new name Squalicorax, incorporating the old (Squalus is Latin for “fish” or “shark”).

Unseating Agassiz

I wonder about the story behind that small piece of Whitley’s 1939 article. Tom Iredale (1880-1972), Australian ornithologist and conchologist, had long been intimately involved in ornithological nomenclature, having spent several years on the nomenclature committee of the British Ornithologists’ Union. Uncovering something like Ledru’s work was, I guess, par for the course for someone like him who probably relished that kind of arcane discovery. His entry in the Australian Dictionary of Biography is revealing. "Gifted with extraordinary bibliographical ability, he enjoyed astounding scientific gatherings by quoting long references from memory."

So, Iredale found a bit of “incriminating” evidence against the Corax shark genus name and brought it to the attention of his ichthyologist colleague, Whitley, who, perhaps, was not reluctant to overthrow one of Agassiz’s names, since apparently he was no stranger to nomenclature controversy. One biographical piece asserts, “His taxonomy revealed confidence and something of his impish nature: his 'little regard for rules of nomenclature' provoked disagreement and displeasure from international colleagues on more than one occasion.”

So the shark genus Corax fell, replaced by Squalicorax.

Loose Ends

What Whitley concluded is straightforward, unambiguous, so, obviously, case closed.

I’m not so sure.

Whitley’s action seems premised on an understanding that two genera, regardless of their marked divergence in their overall taxonomic identification, cannot have the same genus name. I see sense in that, but I’m unclear about how rigorously that rule, if it is one, is actually applied. The International Commission on Zoological Nomenclature, the arbiter for the process of giving scientific names to different kinds of organisms, extinct and extant, apparently doesn’t consider non-duplication to be an inviolate rule. For instance, in a 2009 opinion (#2220), the ICZN ruled that the names for two kinds of insects Hemerobius elegans Stephens, 1836 (for a European brown lacewing) and Hemerobius elegans Guérin-Méneville, 1844 (for a neotropical green lacewing) could be conserved, reasoning that: “Both names are in current use but are placed in different families and unlikely to ever be treated as congeneric in the future.” (“Congeneric” means “of the same genus.”)

Identical genus and species names for lacewings from two different genera . . . . Hmm, maybe, we could have kept Corax for the shark. Would anyone have thought that the shark genus Corax was congeneric with a Corax bird genus?

What else does Whitley’s Squalicorax entry in his article offer for our consideration? Well, might there may be something interesting to discover if we blow off the layer of dust that covers volume II of Voyage aux iles de Ténériffe, La Trinité, Saint-Thomas, Sainte-Croix et Porto-Ricco, . . . . (Voy. Ténériffe), other than how variable the spelling of place names has been?

Not surprisingly, we have at hand the usual bubbly brew of the relevant and interestingly irrelevant. This is the volume that, according to Iredale, showed the genus name Corax was preoccupied. Published in 1810 and written by André Pierre Ledru et al., it reports the natural history findings from a voyage to the Canary Islands and the West Indies in the late 1790s. In this volume, Ledru described a raven-like bird which he spotted on the voyage. With its crossed beak, he named it Corax crucirostra.

(Ledru (1761-1825) merits an aside. He was ordained as a priest when the French Revolution broke out – not a great career path at that moment. But, he did what he had to do in order to survive, ultimately forsaking the priesthood when the Revolution turned against religion, and, in another wise move, getting out of France for awhile by serving as a botanist on the 1796-1798 voyage of discovery.)

Back to the issue at hand, it’s not clear to me whether or how long the name Corax crucirostra was used. A century later (and some 30 years before Whitley), it was clearly considered invalid. In a 1904 article, Robert Ridgway, the Curator of the Division of Birds at the U.S. National Museum (Smithsonian Institution), asserted that Corax crucirostra was one of several synonyms for Corvus leucognaphalus, the latter, according to Ridgway’s entry, having been named in 1800 (yes, it precedes the 1810 publication by Ledru). Under scientific nomenclature, synonyms aren’t names that can be substituted for one another (as common usage would have it), rather they are invalid names and shouldn’t be used. According to Ridgway, Corvus leucognaphalus was this bird’s valid name.

Were Iredale and Whitley simply unaware of Ridgway’s publication? Am I missing something here? I’m coming to believe that there might not really have been any preoccupying of the Corax genus name, after all.

(By the way, nothing has changed in the intervening century. Corvus leucognaphalus is the valid name for the presently extant White-Necked Crow, a bird in serious decline and confined primarily to parts of Haiti and the Dominican Republic.)

Then there’s the small matter of Whitley’s choice of a word. He calls Corax a “generic name for the Raven.” Is he using “generic” as in the “genus name” for that bird? If so, I find that very confusing, since Linnaeus named the Common Raven, Corvus corax – the genus isn’t Corax. Perhaps Whitley meant a “common” or “plain vanilla” name for Raven, which seems right given the definition of “Corax” in Greek and Latin. If so, should the common usage of “Corax” carry weight in an argument against retaining it for the scientific name of a shark genus?

Not that it makes any difference, but, I’m left unconvinced by Whitley’s conclusion that Corax needed to be replaced. Still, I enjoyed spinning the yarn and I’m pretty sure Whitley and Iredale enjoyed their roles.

Other Finds from the Spider Web
My piece of yarn in this spider web of scientific nomenclature, unlike the birthday version, connected me to multiple gifts, not just an explanation of the name change. Whitley and Iredale are impressive figures, each with a substantial body of publications and memorialized in the scientific names of various fish and birds, among other animals.

Then there’s this wonderful group picture from 1950. The inscription on the reverse of this picture reads as follows:

13/3/50. Dear Major Whittell, another for your Rogues' Gallery. Left to right: G.P. Whitley, T.A. Everitt (Hon. Sec. R.Z.S.N.S.W.), A.J. Moran (Cairns, Q. naturalist), Tom Iredale, Alex Chisholm. No woder [sic] the traffic was held up in sydney when this photo was taken a week or two ago. Regards Gilbert P. Whitley

[Permission to post this group picture provided by the National Library of Australia, picture on the Web at: Full citation information provided below.]
Whitley is the grinning one without a hat; Iredale is the one facing the camera head on and smiling. This picture draws me in, capturing a period in time when hats and three-piece suits were de rigueur, though, in this instance, the bare-headed Whitley flouted the convention, perhaps in keeping with his “impish” character. Iredale wore his hat at a charming and cocky angle. There is a confidence in their posture and in the look on their faces. Is Whitley tapping his foot? Impatience?

I’m not sure I can explain fully how and why, but the picture of G.P. Whitley and his colleagues reminds me of another, a very personal one, one of my maternal grandfather.

Each of these pictures captures a moment that is now long gone, yet tantalizingly recent. I know these people and what happened to them. Though the one of my grandfather is probably from a period earlier than 1950, there are essential similarities. The hat and three-piece suit are the fashion. By God, that same confident, cocky air radiates from my grandfather.

His inscription to my mother on the reverse is:
Happy whistling bare foot boy or sumthin'
Your Dad

Full Citation for Group Picture
PIC/5989/190 LOC Album 1094/2
Group portrait of G.P. Whitley, T.A. Everitt, A.J. Moran, Tom Iredale and Alex Chisholm, March 1950 [picture].
1950. 1 photograph : b&w ; 14 x 8.5 cm.
Part of G.M. Mathews collection of portraits of ornithologists [picture]. 1900-1949.

Friday, June 12, 2009

Venturing Into Poetry

Britain’s new poet laureate is Carol Ann Duffy, the first woman poet laureate – huzzah! Her new position is a largely thankless job with the expectation (which she might not honor) that poems will be written about such scintillating things as events in the lives of the members of the royal family. In its article on this appointment, the New York Times included this poem entitled “Mrs Darwin” –

7 April 1852
Went to the Zoo
I said to him — Something about that chimpanzee over there
reminds me of you

A ditty, somewhat amusing, and presumably part of Duffy's volume of poems about the unsung women behind the men. Initially, I was prepared to dismiss this poem as frivolous and wholly incorrect. I mean, by 1852, Charles Darwin’s thinking on evolution had long since gelled and Emma Darwin knew it intimately, so if Duffy is playing for a laugh by suggesting Emma Darwin was responsible for the genesis of Darwin’s theory then, it’s just plain misguided.

Yet, as I thought about this poem and considered other comments on it, I found a little more. Perhaps Duffy’s Emma Darwin is teasing her husband by tossing a mild barb in his direction, anticipating a criticism of his theory. Adam Gopnik in a recent book (Angels and Ages: A Short Book About Darwin, Lincoln, and Modern Life, 2009, p. 106) speculates that she may have acted as a sounding board for his ideas, bringing a faith-based perspective to bear on them. Or is Duffy being ironic in attributing to Emma some responsibility for Darwin’s theory, given that that was not something she, Emma, would ever claim?

Ultimately, I wonder if what I question about the poem is the tone of the voice. It’s too light. None of this seems to be something Emma Darwin would tease her husband about. Among the proffered explanations for Darwin’s long delay in bringing his magnum opus to publication was his concern about the pain it would bring to religious believers, including his beloved wife. She also took his lack of faith quite seriously. In one letter, she gently chided him for letting his science push aside his own religious faith,

May not the habit in scientific pursuits of believing nothing till it is proved, influence your mind too much in other things which cannot be proved in the same way, and which, if true, are likely to be above our comprehension?
(Another reason suggested for the long delay in publication is that very trait of wanting such full proof. Ironically, On the Origin of Species was published without it.)

I find that Duffy’s venture in this direction (that is, natural history) frees me to extend my amateur reach in her direction (that is, poetry). What follows is a poem of mine, inspired by, but certainly not faithful to, an incident described by Stephen Jay Gould in an essay entitled “In a Jumbled Drawer” (in the collection entitled Bully for Brontosaurus, 1991).

One 19th Century Afternoon in the Museum of Comparative Zoology

A drawer of calcite-eyed stone trilobites
On table in museum Agassiz.
A careless stroke of sweeping broom, and flights
Of ancient “bugs” into the floor’s debris.
Like dice, they’re rolled into their drawer anew,
Slip-slotted in a cabinet’s dark space.
Inside, a century they rest, askew,
Until discovered out of proper place.
The human thrust – diminish chaos – seize
The flux, impose our own intelligence.
The drawer with care restored. A full reprise?
No. Learning’s not held in dusty suspense.
This science is not kind to what’s thought known,
Upsets drawers, genera all on its own.

Emma Darwin's letter is contained in Emma Darwin, a Century of Family Letters, 1792-1896, 1915, p. 174.

Thursday, June 4, 2009


One of the highlights of some paleontological publications, particularly from the 19th century and earlier, are the illustrations of the fossils.

Yes, they are intended to depict the detailed reality of the fossil, still they do more. I am often captured by the light and shadow the artists use to cast these relics of ancient life into three dimensions – the images are not in stark, clinical isolation, rather, they are in a specific place and time. The arrangement of multiple specimens in the same drawing frequently seems to me to be much more than simply utilitarian – they are arranged to strike a balance, each playing off the other.

I’d love to be able to include an image of one of the many images that Joseph Dinkel drew to illustrate Louis Agassiz’s masterwork on fossil fishes (see previous post). Unfortunately, I don’t find any that I’m comfortable reproducing here.

These illustrations are in a category of paleoart that is fundamentally different from the paleoart in which the artist attempts to recreate the appearance of the original living organism and its environment.

Earlier this week, the New York Times ran an article entitled Where Art and Paleontology Intersect, Fossils Become Faces (June 1, 2009, by Donald G. McNeil, Jr.). The article profiles Viktor Deak, a paleoartist whose work is featured prominently in the American Museum of Natural History and has appeared in many publications. Deak is among those artists, grounded in science, who are putting flesh on the fossilized bones and bone fragments from ancient hominids, giving us a vision of what our early ancestor might have looked like. Others include John Gurche, the artist-in-residence at the Museum of the Earth (Paleontological Research Institution, Ithaca, New York).

Deak has created a 78 foot long mural showing human evolution in Ethiopia (the mural is seen and discussed by Deak in the video that accompanies the article on the Times web site). It’s an amazing work of art – as you scan the mural from left to right, you move from the earliest hominids some 6 million years ago, until you reach modern humans. You are also moving across a 24 hour period, from midnight to noon, and back to midnight.

The mural is part of an exhibit entitled “Lucy’s Legacy: The Hidden Treasures of Ethiopia,” currently touring North America. Among the remains of proto-humans in the exhibit is Lucy, the skeleton of an Australopithecus afarensis, some 3.18 million years old.

As much as I like the mural, I find myself in strong disagreement with the author of the Times article, Donald McNeil. He writes, “. . . his mural, a vast Photoshop collage, is more fun to ponder than the bones.”

More fun than the bones? More fun than Lucy? Not a chance. The paleoart created by Deak and others is grand and useful, the art blended with science moves our understanding forward. But, the bones, the fossils, are the essence. Without them, nothing. The fossils are the actual connection to the past, they are the touchstone to which we return if, as our understanding grows, we discover flaws in the vision depicted by this paleoart. The ancient history resides within them. They are what is to be pondered.

To be frank, for me, the murals that adorn museum exhibits are only a backdrop for the real thing.

A Couple of Asides

I must admit that seeing images of Deak at work – taking a cast of a skull fragment, adding clay and other material to complete the skull and to layer on muscle and flesh, inserting artificial eyes, photographing, manipulating the images . . . – all reminded me of the current forensic science police shows and movie animation studios. Makes Deak's work seem less special than it is (I do think it special despite my put-down of murals).

Finally, since Viktor Deak is the focus of the article, the Times, properly, provided a phonetic spelling of Mr. Deak’s name. But, it strikes me as very funny that the Times chose not the first instance of “Deak” in the article beside which to insert the phonetic spelling, but, rather, this sentence: “Mr. Deak (pronounced DAY-ahk) and Xochitl Gomez were married at the Bronx Zoo, in the gorilla grotto.” And, no, it’s not being married in the gorilla grotto that I find amusing.

Credits for Images
The first image of vertebrae is from the Smithsonian Institution's image collection with the following identifying information: James Dwight Dana, Geology, 1849. Oregon Fossils, Plate 17. Smithsonian ID: SIL19-15-023. URL:

The second image of trilobites is from the Smithsonian Institution's image collection with the following identifying information: Joachim Barrande, Systême silurien du centre de la Bohême, 1852. Smithsonian ID: SIL7-240-016. URL:

Final image is a photo of a portion of a mural at the Dinosaur State Park, Rocky Hill, Connecticut. The mural was painted by William Sillin. It depicts a prosauropod in the late Triassic.
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