Posts Tagged ‘analogy’

What’s sexier than sex and warfare? Taking the “arms race” one turn too far.

Wednesday, March 25th, 2009

Talk about sexy science. How could any science be any sexier than sexual selection?

Then combine sexual selection with “nature’s arms race,” and what do you get?  Science so titillating that even a seasoned science journalist might get a little…carried away.

This was the only explanation I could contrive yesterday morning after I read Nicholas Wade’s latest contribution to the New York Times Tuesday Science section. Only last week I posted about the importance of the arms race analogy to my dissertation research on the history of coevolutionary research. So I was very excited to see Wade’s piece, “Extravagant Results of Nature’s Arms Race,” gracing the cover of the Science Times.

Sexual selection is not really my bag—the evolutionary “arms races” that I write about are between hungry herbivores and unpalatable plants, not males of the same species. But the general concept is the same: offense and defense is heightened over many generations as a result of natural selection for the best-fed herbivore, or the least palatable plant, or, in the case of the sexual selection, the most successful (read: sexiest) male.

Sexual selection is a special case of natural selection where the most successful features do not always seem obviously adaptive. Take the classic example, the peacock’s plumage. Its lavishness makes no sense when you imagine the peacock trying to outrun a tiger. What can be more evolutionarily important than avoiding being eaten? Being sexy, of course. At some point in evolutionary history, females developed a preference for gaudy tails, and since the males with the gaudiest tails were the ones getting the action, more pretty boys in the next generation had gaudy tails. And so on– you get the picture.

This “female choice” type of sexual selection does involve an “arms race” of sorts: Peahens’ preference for gaudy tails escalates even as the gaudiness of male tails escalates—female preference and male success mutually reinforce and drive each other to greater extremes.

But invoking the “arms race” seems a lot more convincing when you are talking about out-and-out evolutionary combat. The second type of sexual selection, “male-male competition” is all about the escalating evolution of better and better weapons. In some species, males actually fight for sex, as with these male elephant seals battling for control of a harem of females. But in other species, it’s enough to look big and scary, to intimidate the other guy before he even tries to fight you. If your antlers are large, you might fight other males and win. But if your antlers are humongous?  You could be king of the lek without ever having to tangle. Possible bonus: Your “armament” may also serve as an “ornament” if females find your big antlers sexy. These University of Minnesota researchers found that lion’s manes did double duty, attracting females AND intimidating other males.

Wade’s Science Times article profiled a recent review paper on the diversification of male animal “weaponry” by Douglas Emlen at the University of Montana.

Dung beetles -- from a nice Discover Mag blog posting about the evolution of female dung beetle horns.

 

For your viewing pleasure, the piece focuses especially on the dramatically beautiful “horns” of dung beetles. And, as in most profiles of sexy science, Wade could not resist taking the next step, pushing toward that ultimate climax of sexy science.

What’s sexier than sex and warfare?

Sex and warfare and humans, of course:
“People have pathetically puny teeth and claws compared with the armaments of other dominant species. This is a sign not of pacific intent but of the fact that they manufacture their weapons.”

In other words, the “arms race” is more than just a metaphor that allows us to comprehend the evolution of elaborate organic weaponry on our own terms, those of technological weaponry. It’s an analogy between human and nonhuman evolved features.

If you read what I wrote about analogies last week, you’ll know that when evolutionary biologists posit such an analogy, they are claiming that evolved tusks and manufactured guns were generated in response to the same selective pressures. They have different evolutionary histories–in this case, the difference is even more extreme, since one has a biological evolutionary history and the other has a cultural evolutionary history.  But they are analogous because they share an adaptive function.

I am most fascinated by analogies like these, which effectively blur the boundary between biological evolution and cultural evolution. But it’s not just the boundary between biology and culture that becomes a bit blurry here. Wade interviewed a primatologist who claimed that it’s “very reasonable to assume that, as humans evolved and our culture became more complex, skills in tool making or other cultural behaviors took over from anatomical traits as ‘markers’ of a male’s competitive skill.”  In other words, the proposed mechanism for such a shift is also kind of hazy.  Claiming that cultural evolution just “took over” from biological evolution is not exactly a substitute for a testable hypothesis.

In any case, whether or not you think this is a reasonable assumption, you have to admit that it’s very compelling. Analogies are compelling—that’s why they are so useful.  They motivate us to make analytical leaps that, in the best of scientific circumstances, may also be empirically verified.

Sometimes those gravity-defying leaps also defy logic, however. Even a seasoned science journalist like Nicholas Wade may be seduced by sexy analogies into making such a logic-defying leap.

Wade analogizes between the organic “weaponry” featured in Dr. Emlen’s paper and a samurai helmet or a crossbow. So far, so good—these could make sense within the context of sexual selection.

Then, suddenly, Wade leaps into the geopolitical domain of the “menacing tanks and rockets that paraded through Red Square in Moscow in the days of the Soviet Union.” This is where the allure of the arms-race analogy becomes dangerous. Was the Cold War a result of sexual competition? Is the “the advent of chemical, biological and nuclear arsenals” really relevant to a piece on male-male competition?

The arms-race analogy has been scientifically productive, helping biologists imagine a series of evolutionary interactions that mimic the military escalation of the Cold War.  But when it leads us to relate sexual selection to global politics, it has probably overreached the limits of its utility. And when this overreaching happens on the cover of the Science Times, we must take pause.

Evocative analogies are powerful tools and—just like that nuclear arsenal—they should be used only with the greatest of caution.

Make an analogy between humans and cockroaches and then read this posting.

Friday, March 13th, 2009

At this moment in my dissertation work, I am transcribing my two-hour interview with ecologist Daniel H. Janzen.  In early December 2007 I flew to Philly and stayed there for one night, interviewing Janzen in his office at the University of Pennsylvania just 6 hours before I flew back to Toronto.  Clearly, I have waited far too long to transcribe the interview, which is typical of me.  I am always excited to rediscover what I learned during an interview.  Somehow I manage to forget almost everything we discussed in the minute after an interview ends—it’s as if my intense relief that it’s over triggers some sort of spontaneous amnesia.  So there are always many pleasant (and some excruciatingly embarrassing) surprises awaiting me.  But I find the process of the transcription totally grueling.  I really try to get every “um” and “ah” and grammatically disastrous sentence recorded for posterity, and this requires a lot of rewinding.  In the case of Janzen, who sprints from topic to topic in a rusty Minnesotan accent, rarely pausing for the insertion of a period or comma, my rate of transcription slows down considerably.  Not to mention that there are so many more words per minute in this interview.  I am 1 hour and 36 minutes into this interview and I have a 15-page transcript already.

There is a lot of good stuff here.  There’s an absolutely incredible story about botanist G. Ledyard Stebbins, who purportedly slept through Janzen’s thesis defense, but woke up just in time to compare the ants that Janzen studied to the chemical defenses that other plants produce, which protect them against attack by herbivorous insects.

At that moment, Stebbins gave Janzen what would become one of his most persuasive analogies.

My (point-and-shoot) pics of ant acacias from Santa Rosa National Park in Costa Rica (2006)

My (point-and-shoot) pics of ant acacias from Santa Rosa National Park in Costa Rica (2006)

Some background will help you understand this analogy.  Janzen’s dissertation research in Mexico exhaustively detailed the mutualistic relationship between “bull’s-horn” acacias and acacia ants.  As a graduate student in entomology at Berkeley, his first notion was just to study these ants—why were they so bizarrely fond of these prickly acacia trees?  It was by chance, or at least “serendipity,” that his attention shifted to the relationship between the ants and the acacia tree.  In his thesis, he concluded that there is a real mutual reliance between the two species.  The ants cannot live without the acacias: they take shelter and breed in the acacia’s oversized thorns and feed from the plant’s nectaries and Beltian bodies (little nutritive tabs that grow at the leaftips of the acacia).  Conversely, acacias that grow without a resident ant population rarely thrive. Without the ants to fight off other insects and the choking lianas that like to drape themselves across other plants, the acacia falls prey to both herbivory and competition with other plants.

Now, Janzen was not, by any means, the first to turn his attention to this surprising relationship.  Thomas Belt, a 19th-century British mining engineering who worked in Nicaragua for years, called the ants a “standing army” that defends the acacias against their enemies.   Harvard entomologist William Morton Wheeler challenged the claim that the ants were protecting the acacias, writing in the early 20th century that plants needed ants like a dog needs fleas.  Strong words, gentleman!  A raging academic debate that did not subside till Dan Janzen’s paper, “Coevolution of Mutualism Between Ants and Acacias in Central America,” published in the journal Evolution in 1966.

One of the things I’ve always loved about evolutionary biology is the evocative language that biologists use to describe processes and relationships.  Are the ants a “standing army” or a pack of voracious sap-sucking fleas?  Gives you two pretty distinct ecological pictures, right?

The study of coevolution between plants and insects has been built upon suggestive language like this.  This was a field that came into being during the Cold War, so who could really resist using the term “arms race” to describe the back-and-forth evolutionary responses between plants and insects?  Plants escalate their toxic biochemical defenses against hungry herbivorous insects, and insects escalate the tools they use to overcome those defenses.

So, what does it mean to claim that acacia ants function just like the chemical defenses used by other plants to fend off the insects that would eat them?  First, this analogy crosses categories: the ants, organisms in their own right, become (merely?) evolutionary adaptations of the acacias.  The ants are, Janzen would claim, an extension of the plant’s genome—in the same way that human technologies are extensions of our genome (which he also claims).  In essence, then, the ants become an adaptive technology.

But an analogy always operates in two directions.  The reciprocal effect is to grant the chemicals produced by plants a new identity.  The best analogies (just like the best metaphors) associate entities that seem, otherwise, completely dissimilar.  In this case, the analogy between ants and plant chemicals breaks a long-accepted boundary between what animals can do and what plants can do—or, rather, what plants can’t do, passive pieces of green furniture that they are.

I mean, when we talk about animals, we use active verbs.  We see them causing things to happen, acting—in short—with agency, if not intentionality.  Plants, on the other hand, when they’re not simply invisible, don’t tend to act.  They don’t move, they have no sensory organs.  Even when we see them, we don’t think of them as agents.   Even when a plant has an effect on its environment, it appears somehow passive, and the effect is often considered a by-product of some other more planty function.

Coevolutionary analogies, by contrast, make plants and animals equal partners.  More accurately, they’re adversaries. And plants, so long seen as the wallpaper of the world, suddenly become embattled veterans of an ancient chemical war with animals.

This kind of transmission of meaning and agency between plants and animals has real effects on science (this is one of the themes of my dissertation).  It’s one reason that I became so interested in Janzen.  The man analogizes like it’s going out of style.

More importantly, he is very careful to distinguish between “analogy” and “metaphor.”  Janzen does not speak in metaphors, because metaphors make comparisons that could not be literally true.  If he makes a comparison between, say, armyworms gobbling up an entire field of corn and Germany invading Poland, he does not mean this comparison metaphorically.  To him, hungry caterpillars and power-hungry humans are the same thing. The entities interacting are unimportant: locusts or leopards, hummingbirds or humans, it doesn’t matter—only the interactions themselves are important.

Janzen describes this as a fundamentally ecological perspective on the world, but I see it as a fundamentally evolutionary perspective, instead. In evolutionary biology, limbs or organs are analogous when they perform the same biologically adaptive function but have different evolutionary origins.  When Janzen draws an analogy between human warfare and plant-insect warfare, this is also what he means: same adaptive function, different evolutionary origin.

Ants or wild parsnips, humans or cockroaches—we might organize them into different categories, but evolutionarily, they are all subject to the same forces.  It’s part of what gives evolutionary biology its explanatory power.  And also, let’s face it, what makes it so darn fascinating.

This is one good-looking cockroach, right?  Also from Santa Rosa National Park.

This is one good-looking cockroach, right? Also from Santa Rosa National Park.