Lizard tails, gecko toes, and Mission: Impossible

In Mission: Impossible! Ghost Protocol (the fourth installment of the series), a memorable scene has the heroic--and nigh-indestructible--Ethan Hunt (Tom Cruise) climbing the outside of the Burj Khalifa, more than 1700 feet above the ground. Because it's Mission: Impossible, Hunt of course has no harness, rope, or other climbing gear--only a pair of adhesive gloves and some rubber-soled shoes. 

When tech wizard Benji (Simon Pegg) is giving Ethan the demo of how the gloves work, he emphasizes that to un-stick the glove from the window, Ethan needs to use a "rolling-off motion." Ethan, being the super-agent he is, quickly masters this rolling motion and proceeds to use the gloves to pull himself up the sheer glass wall of the skyscraper. 

(It probably goes without saying that, of course, one of the gloves' batteries die once he is past the point of no return, requiring him to finish the climb with only one miracle sticky glove, which manages to catch his entire body weight from a free-fall a short time later.)

As with most action movies, willing suspension of disbelief is required to truly appreciate the stunts that punctuate Ghost Protocol at predictable intervals. But in this case, the physics isn't actually that far-fetched: it's likely that the gloves are biomemetic--technology and engineering inspired by the design and/or function of biological systems. In this case, judging by their appearance and Benji's description of how they work, it's a safe assumption that the gloves are based on the biomechanics and biophysics that help geckos, flies, and other small animals scale walls, dangle from ceilings, and perform other impossible missions. 

The climbing abilities of various lizards have been an object of fascination at least since the time of Aristotle, but it's only within the last century or so that we've been able to start building a detailed understanding of how the structure of their feet enables those abilities. With the advent of advanced microscopy, computer modeling, and incredibly sensitive force detection tools, the mechanism of lizard toe adhesion has become more well understood.

A lizard climbing up a wall or across a ceiling has to have a way to "turn on" and "turn off" the stickiness of its feet. Always "on" and the lizard can't move; always "off" and it's stuck (heh) with the limitations of gravity like we poor bipeds. So how does it work? 

As with many seemingly miraculous everyday occurrences, lizards can thank physics for their selectively sticky feet. Like Benji's magic sticky gloves, lizard feet have a differential stress response: they respond differently to tension than to shear forces. When under tension, the adhesive force is strong; but subject it to a shearing or bending force and it weakens enough to detach. The "rolling motion" Ethan uses to un-stick his hand from the Burj Khalifa's glass produces that shearing force, and lizards create a similar type of motion in their feet when they walk. 

The notion of a material that responds differently to different kinds of force shouldn't be too unfamiliar: rope is strong under tension (pulling) but weak under compression or shear (sideways) forces, whereas many kinds of structural materials (girders etc.) are strong under compression but weaker under shear or tension forces. This is one of the reasons why earthquakes, tidal waves, and other disturbances that produce strong shear forces can cause massive amounts of structural damage, even though they generate less total force than the weight of the building itself pressing downward every day. 

But these are all examples of solid objects demonstrating internal strength or weakness, which is a far cry from adhesion (stickiness) between two different objects--and this is where the physics comes in. As it turns out, gecko feet owe their stickiness to the millions of tiny setae (projections) that make up the bottom surface of each toe--more than 14,000 per square millimeter. Because of their microscopic size, each seta experiences tiny, transient molecular forces known as van der Waals forces when it contacts another surface. 

Although van der Waals forces are among the weakest interactions between molecules, they nonetheless can provide a significant amount of adhesive force when applied to the millions of individual setae on each foot. In one clever study, Autumn et al calculated an adhesive force of more than five atmospheres--more than enough to hold a tiny lizard against the ceiling. 

What's especially fascinating about Autumn et al's results is that they were able to demonstrate that the adhesive forces were primarily the result of the size and shape of the setae, rather than their chemical composition: when they created simulated setae out of rubber and polyester resin, they observed the same adhesive properties as were present in the gecko toes. They were also able to demonstrate that the adhesive force increases significantly as the setae get smaller--which may be part of the reason this type of setal structure has been evolutionarily selected in so many climbing lizards.

The idea that large numbers of setae may have a survival advantage in some species is supported by the genomic work of Liu et al, who used genetic data to construct phylogenetic trees showing the evolution of a number of different lizard species. Their results showed that Gekko japonicus, the Schlegel's Japanese gecko, contain more copies of genes for the proteins that form setae than do other lizard species who have fewer setae per unit area. 

In other words, the species that have lots of very tiny setae have more copies of the gene than the species with fewer, larger setae or no setae at all, and the density of setae is closely related to the species' habit: G. japonicus is a typical gecko, with sticky feet that it uses to climb trees and walls and catch prey, and it has the most copies of the gene and the largest setal density; Anolis carolinensis, the green anole, has fewer copies of the gene and a lower setal density, but still demonstrates some wall-climbing ability; and Alligator sinensis, the Yangtze alligator, has only two copies of the gene and no setae--it lives primarily in water and does not climb. These patterns, together with the inferred timing of the genetic differentiation between the species, support the hypothesis that selection pressure drove the increase in the number of setae (and correspondingly stickier feet).  

Liu et al also investigated the evolutionary history of another well-known trait of many lizard species: caudal autotomy, or the ability to "shed" a still-wriggling tail to distract predators and buy time for an escape. Species that have this ability, such as G. japonicus and An. carolinensis, show positive selection pressure for genes associated with wound healing and cell growth, whereas species that don't shed their tails lack those positively selected genes. 

And now we come full-circle, because it turns out that there are a lot of similarities between the physics of gecko toes and the physics of tail autotomy: both rely on the characteristic strong-under-tension-but-weak-under-shear strain responses associated with the microscopic interfaces between surfaces. 

Just as a gecko's foot is covered in millions of tiny setae, which generate adhesive forces, the point at which its tail connects to its body also contains large numbers of tiny pillars of muscle that hold the tail in place but also allow for its quick release. At the point where it detaches during autotomy, the tail contains a roughly conical arrangement of tiny, mushroom-shaped pillars. The "cone" shape at the end of the tail interfaces with a corresponding "socket" shape on the lizard's body--in other words, the tail attaches to the body the way a phone cable attaches to its charging socket. 

Unlike a charging cable, though, the lizard's tail attachment is quite strong under tension--it won't detach if it's pulled straight backward away from its body. This helps prevent the tail from falling off under regular lizard behavior. But if the lizard moves its tail in just the right type of side-to-side motion, its tail separates from its body. 

Baban et al used a biomemetic fracture model to elucidate how this works in detail. They demonstrated that the geometry of the tail-body attachment, along with the specific type of motion the lizard uses to initiate detachment, allows a "fracture plane" to propagate through the tail attachment surface. As the plane propagates, the tail muscles detach from their corresponding partners in the lizard's body, and eventually the entire tail has detached.

By creating silicon-based models of the tail and its attachment socket, Baban et al were able to demonstrate that the arrangement of the micropillars contributes to the tail's behavior under different kinds of stress. In most situations, the flexibility and nanoscale adhesion between the micropillars and their corresponding sockets helps to stop any incipient fractures from propagating. As Ghatak describes in a summary of the Baban article, the flexibility ensures the stresses never build up enough to cause the tail to detach completely.

It's probably unlikely that Ethan Hunt will ever dangle from the Tokyo Skytree by a detachable rope-tail...but one never knows. 

Autumn, Kellar, Metin Sitti, Yiching A. Lang, Anne M. Peattie, Wendy R. Hansen, Simon Sponberg, Thomas W. Kenny, Ronald Fearing, Jacob N. Israelachvili, and Robert J. Full. 2002. "Evidence for van der Waals adhesion in gecko setae." Proc. Natl. Acad. Sci. 99 (19): 12252-12256. https://doi.org/10.1073/pnas.192252799.

Baban, Navajit S., Ajymurat Orozaliev, Sebastian Kirchhof, Christopher J. Stubbs, and Yong-Ak Song. 2022. "Biomimetic fracture model of lizard tail autotomy." Science 375 (6582): 770-774. https://doi.org/10.1126/science.abh1614.  

Ghatak, Animangsu. 2022. "How does a lizard shed its tail?" Science 375 (6582): 721-722. https://doi.org/10.1126/science.abn4949.

Liu, Yan, Qian Zhou, Yonjun Wang, Longhai Luo, Jian Yang, Linfeng Yang, Mei Liu, Yingrui Li, Tianmei Qian, Yuan Zheng, et. al. 2015. "Gekko japonicus genome reveals evolution of adhesive toe pads and tail regeneration." Nature Communications 6, 10033. https://doi.org/10.1038/ncomms10033.

The mystery of the rotating seeds

If you live in a temperate deciduous climate, you probably know what a maple tree is. And if you’ve been in a maple forest during spring or fall—or, really, any time of year—you’ve probably seen maple seeds. They look a bit like badminton birdies, only flattened: a heavy, solid "nut" at the bottom, with a single "wing" above. The wing helps the seed fly relatively long distances (for a plant)—up to a few kilometers in some cases.

A maple seed. From http://commons.wikimedia.org/wiki/File:Maple-seed.jpg.

Watching a maple seed fly is an interesting experience—they flutter and twist very rapidly. Because they twist and spin as they fall, scientists say they autorotate. In fact, they autorotate quite stably—a factor that allows the wind to carry them far from their parent trees.

Maples aren't the only trees with autorotating seeds—hornbeams, for example, have similar winged seeds. In all of these seeds, the autorotation is thought to help create extra lift on the seed, enabling it to travel farther from the parent tree. (Rambling offspring are a benefit for plants, because plant seedlings compete with surrounding plants for soil nutrients, sunlight, and water. If they land too close to the parent tree, they end up competing with their own parents—which benefits neither parent nor offspring, and therefore is detrimental to the survival of the species.)

Maple seeds and other autorotating seeds produce surprisingly large amounts of lift as they fall, considering how small and relatively slow they are. This is similar to the wings of many insects, which can produce a lot of lift from a relatively small surface area. Insect wings create this lift through the production of a leading edge vortex (LEV)—that is, a maelstrom of disrupted air along the edge of the seed that is "cutting through" the air as the seed falls. (Think of a wing—one edge of it is pushing through the air as it moves forward. The other edge trails along behind. The edge cutting through the air is the leading edge.)

In the 12 June issue of Science, Lentink et al report results of an investigation into the motions of maple seeds as they fall. Because the LEVs generated by insect wings help the insects produce significant lift, the researchers reasoned that maple seeds might produce similar LEVs.

Maple seeds are relatively small, and studying them while they fall can be challenging. This is especially true if one is interested in observing the flow of air over and around the seed as it falls. Therefore, as an initial test, Lentink et al built a scale model of a maple seed that was somewhat larger than a real seed. To make studying the movement of the air over the seed easier, they attached the model seed to a large arm inside a tank of mineral oil.

It may not be immediately clear how putting a model seed in mineral oil can be used to study the flow of air around a real seed. It turns out that this works because air and mineral oil are both fluids—substances that can flow in response to stress (pressure). As it happens, all fluids behave pretty much the same way under specific kinds of stress, provided that their differences in viscosity (resistance to flow, or thickness) are taken into account. The main difference viscosity makes is in the force required to move through the fluid—as you know if you've ever tried to walk under water. The more viscous the fluid, the more force is required to push through it, and the more slowly it returns to its original position. This latter property is the reason that many fluid dynamics studies are performed in oil or water, rather than air: the higher viscosity of a liquid makes observing its flow paths much easier. The path the liquid follows around the object is the same as the path that air would follow, so the results of the study are easily transferred to air.

Lentink et al used digital particle image velocimetry (DPIV) to make an image of the fluid flow around the model seed as it "fell" through the oil. DPIV is a technique that uses laser light, high-speed cameras, and computer integration to determine the velocity (speed and direction) of the fluid moving around an object in various locations. In DPIV, tiny particles are suspended in the fluid. During the experiment, as the fluid is moving, rapid flashes of laser light shine on the fluid, making the suspended particles visible for brief instances. A high-speed camera photographs the particles during each flash. The images are fed into a computer, which analyzes the locations of the particles during each instant. Because the computer knows the location of each particle at specific instances in time, it can calculate the velocity of each particle over time. Once the computer has calculated the velocities of the particles, it can create a three-dimensional image of how they move (and, by extension, how the fluid moves).

Using DPIV, Lentink et al identified a very pronounced LEV along the model seed. To confirm that their model seed accurately represents real seeds, they placed real maple seeds in a vertical wind tunnel. They adjusted the wind speed in the tunnel so that it matched the air speed the seeds would experience as they fell. As a result, the seeds hovered in place, but still spun the same way they would if they were actually falling. They recorded the motions of the seeds as they rotated. They were also able to create images of the flow of air around the seeds. The experiments with the real seeds confirmed the results seen in the model studies: maple seeds do, indeed, produce significant LEVs as they fall.

By comparing the maple seeds to other plant seeds, Lentink et al showed that the rotation of the maple seeds, and the resulting development of the LEVs, allows maple seeds to fall more slowly than non-rotating seeds of a similar wing loading (wing loading is the ratio of seed weight to surface area). Therefore, maple trees (or hornbeam trees, or other trees with rotating seeds) can produce heavier seeds (which can contain more food for the embryonic tree), but those seeds can still travel far enough from the parent trees to avoid competition.

Maple and hornbeam trees are not the only organisms to make use of the extra lift provided by LEVs, though. Hovering insects, bats, and possibly some birds also benefit from the production of LEVs along their wing edges. It makes me wonder whether "winged" marine organisms might generate similar vortices along their wings as they "fly" through the water.

Lentink, D., Dickson, W., van Leeuwen, J., & Dickinson, M. (2009). Leading-Edge Vortices Elevate Lift of Autorotating Plant Seeds Science, 324 (5933), 1438-1440 DOI: 10.1126/science.1174196

Good news for paleontologists?

Paleontologists, as most folks know, study fossils (or, more generally, the evidence of past life of any kind). By examining the types and distributions of fossils in rocks of various ages, paleontologists can give us insight into how life on Earth has evolved. Thanks to the study of fossils, we know, for example, that Cambrian oceans were full of trilobites, that the Mesozoic Era was dominated by giant reptiles, and that giant "terror birds" once roamed South America.

Yes, fossils are undoubtedly vital to our understanding of life on Earth. However, although fossils are the only evidence we have for the existence of past life, they have--like all evidence--limitations. Foremost among these is the preservation bias. There's a reason nearly all the fossils you'll see in a museum or private collection are fossils of shells, bones, and teeth: hard parts are much more likely to fossilize than are soft parts.

This means that critters like the sea squirt and the cuttlefish, cute though they may be, are unlikely to appear in the fossil record. Their bodies are entirely (or almost entirely) made of soft tissue, which decays rapidly once they die. About the only way soft tissue can be preserved is through mummification or other direct preservation methods; and they are pretty darned uncommon.

Size and depositional environment also play a role in preservation bias. Larger body parts may be more likely to be preserved and fossilized than are smaller body parts, because it takes large parts longer to break down (thus allowing them more time to be buried and mineralized--although this isn't a hard-and-fast rule). Similarly, critters that die in the water are much more likely to be preserved, because they're more likely to be buried before they decay completely.

Ultimately, preservation bias means that our understandings of life on Earth are inevitably biased toward largeish, ocean-dwelling animals with shells, bones, and/or teeth. This is why we know so much more about trilobites than we do about, say, ancient jellyfish.

Of course, paleontologists acknowledge this problem, and make attempts to compensate for it. One way to try to compensate for preservation bias is to use so-called "live:dead" ratios. For example, suppose in a particular ocean ecosystem 30% of the animals are bivalves, 25% are bony fish, 35% are crustaceans, and 10% are "squishies" such as anemones and jellyfish. That critter composition is known as a "live assemblage" or a "life assemblage" for that ecosystem. (I made up those numbers. They probably bear almost no relation to realistic numbers--and those particular types of critters may not occur together. Just bear with me for the sake of demonstration.) To try to correct for preservation bias, a scientist might count the number of dead critters in each category. (I should note that this type of analysis would be based on numbers of individuals, not numbers of remains--so two clam shells would count as one clam, for example.) This "dead assemblage" or "death assemblage" can then be compared to the life assemblage to figure out relative preservation rates. If, for example, 30% of the living critters are bivalves, but 40% of the remains are bivalve remains, then bivalves would have a higher preservation rate than other critters in the ecosystem.

Potential problems with this method are probably obvious: How do you know which types of modern environments to compare ancient remains to? How do you know that preservation rates in remains are the same as fossilization rates? How do you know preservation rates for different types of critters are the same today as they were then? What happens if the ecosystem changes rapidly--do the death assemblages still accurately reflect the life assemblages?

In the May 22 issue of Science, Western and Behrensmeyer present data that may help to address the last two of these questions. They used a 40-year record from the Amboseli ecosystem in Kenya to study the relative preservation rates for large mammal (15 kg-4000 kg) bones. Previous studies have shown that the life and death assemblages for these mammals are similar at specific points in time; that is, at a given time, the proportions of different species in the life assemblage are similar to those in the death assemblage.

A variety of factors have caused the Amboseli environment to change quite rapidly since the 1960s. Woodlands have shrunk, grasslands have expanded, and swamps have doubled in size. These environmental changes, in addition to direct human actions, have substantially affected the mammal populations in Amboseli during that time. The ratios of different types of organisms--grazers vs. browsers, for example--have changed as a result, and overall species diversity has declined.

Bone and live animal surveys were conducted during two time periods: 1975-1976 and 2002-2004. The bones studied during those times could be separated into subintervals based on how long ago the animal died; this allowed the researchers to divide the samples into four subintervals (1964-1969, 1970-1976, 1993-1998, and 1999-2004). They also used census data to determine the numbers of live animals in various groups during those same time intervals.

For each of the time periods, the researchers compared the proportions of different organisms in the life assemblages with those in the death assemblages. They used these data to determine how well the death assemblages "track" or represent the life assemblages. What they found is pretty interesting:

Statistically significant correlations between live populations and bone counts for the different time intervals indicate that organisms that make up a larger fraction of a living community also make up a proportionally larger fraction of the bone assemblage for that community. In other words, at least for this ecosystem, you can use the death assemblage as a pretty direct proxy for the life assemblage--if 50% of the individuals represented by the death assemblage are medium-sized grazers, then you can infer that about 50% of the organisms in the ecosystem (on average) over the time period you're looking at were medium-sized grazers. You can also use the death assemblages to study how populations in the ecosystem changed over time; the ratios of grazers to browsers in the death assemblages roughly paralleled those in the life assemblages for the same time period. They were able to distinguish changes in population composition over time scales as small as 5 years; they were even able to "predict" ecological structure from the death assemblages (and those predictions were largely confirmed by the life assemblages).

Western & Behrensmeyer's data could be very useful for paleontologists, particularly large-vertebrate paleontologists; the data suggest that bone distributions in death assemblages can be used to infer population and community structures for ancient ecosystems. With some assumptions about ecolosystem properties, bone assemblages can also be used to infer other properties of ancient ecosystems, such as species richness and productivity.

Obviously, these data have limitations; Amboseli is a relatively dry terrestrial ecosystem populated by relatively large mammals, so it's not clear whether the same correlations apply to marine ecosystems, wetter (or drier) terrestrial ecosystems, or to those inhabited primarily by smaller organisms or invertebrates. Additionally, because all of the remains studied were relatively recent (40 years isn't long enough to produce fossilization or even significant burial in most terrestrial ecosystems), it's not clear how the processes of preservation, burial, and fossilization might affect the death assemblages. (Although they do note that partially buried bones--a "pre-fossil" assemblage--seem to show the same correlations as unburied remains.) But studies like these are still very important in determining the error bars (accuracy) of ecosystem studies based on fossil assemblages.

Their data also suggest that studies of death assemblages in modern ecosystems can be of use to scientists studying the effects of human actions and other phenomena, as well as to those wishing to confirm (or obtain) estimates of vertebrate population sizes and compositions.

Western, D., & Behrensmeyer, A. (2009). Bone Assemblages Track Animal Community Structure over 40 Years in an African Savanna Ecosystem Science, 324 (5930), 1061-1064 DOI: 10.1126/science.1171155

If the Egyptians had only known...

According to legend, one of the way the Egyptians were punished in the time of Moses was with a swarm of locusts.

Locusts are insects that look a bit like big grasshoppers. They're a classic example of what's called phenotypic plasticity. An organism's phenotype is basically its observable characteristics--behavior, color, size, etc. (Phenotype is the outward expression of genotype; genotype is the specific group of alleles that an organism has. Most--all? I'm not sure--genes have at least two alleles, or "flavors." The classic example is, of course, Mendel's peas; the gene that controls flower color in pea plants has two alleles, purple and white. A pea plant's flower-color genotype is the particular combination of alleles that it has; its flower-color phenotype is the particular color of flower it produces.)

Organisms such as locusts that demonstrate phenotypic plasticity can undergo significant changes in behavior, appearance, etc due to changes in their surrounding environment. Locusts are a classic case because the change is so dramatic. If you take two locusts and put them in a box, they will pretty much avoid each other--that is, assuming they're demonstrating the "solitarious" phenotype. This is pretty much the default position for locusts; most of the time, they hang out by themselves (not a lot of singles bars in their neighborhoods, I guess).

Now if you had put, say, 20 or 30 solitarious locusts in that box and shut them in for a couple of hours, they would be quite changed when you opened the box. They would be swarming together, and they would have changed in appearance (from kind of boring and green to a rather striking, Steelers-like combination of yellow/tan and black...sorry, couldn't help it). They would be demonstrating the "gregarious" phenotype.

Solitarious (top) and gregarious (bottom) desert locusts. Image from Dr. Tim Matheson, University of Leicester

Locusts in the gregarious phase are the stuff of legend. These are the critters that mow crops down to the roots and blacken the skies. (Presumably, the Egyptians crowded their locusts.)

The cause of the transition from solitarious to gregarious has been known for a while, at least in broad strokes: being in the presence of lots of other locusts makes a locust more gregarious. In a recent article in Science, Anstey et al identify the mechanism that triggers the transformation.

There are two different sets of stimuli that can make a locust more friendly: mechanical and "cephalic." Mechanical stimulation involves being jostled by other locusts; in contrast to most humans, most locusts become more friendly when strangers stroke their legs. Cephalic stimulation involves the sight and smell of other locusts; locusts apparently have really great makeup and cologne. Both types of stimuli cause the locust's central nervous system (CNS) to produce (what else?) serotonin. (Yes, that serotonin.)

Previous researchers established that serotonin levels are higher in locusts undergoing the solitarious-to-gregarious transition. Anstey et al set out to determine the limits of this relationship. They did four main experiments: first, they figured out whether artificial stimulation of the individual sensory pathways could stimulate serotonin production and gregariousness. Then, they tested whether serotonin antagonists (i.e., chemicals that block the action of serotonin) could prevent the onset of gregarious behavior. Third, they determined whether artificially increasing serotonin levels was enough to induce gregariousness. Finally, they determined whether giving the locusts a serotonin precursor (i.e., a chemical that is easily converted to serotonin) increased their sensitivity to environmental stimuli.

In the first experiment, the researchers either stroked the hind legs of solitarious locusts, stimulated the nerve connecting the legs to the CNS directly, or put the locusts in a cage that allowed them to see and smell (but not touch) other locusts. In all cases, the locusts switched from solitarious to gregarious, and serotonin levels increased, suggesting that either type of stimulation is sufficient to induce gregariousness.

Next, they injected some of the locusts with serotonin antagonists (they also, of course, injected others with just saline--this was the control group). After the injections, the treated locusts (the ones that received the antagonist) were significantly less responsive to stimuli than the control locusts; treated locusts did not become gregarious, even when exposed to stimuli that caused the control locusts to boogie down. This relationship showed that inhibiting the action of serotonin prevents the "phase change."

In the third experiment, Anstey et al applied serotonin directly to the locusts' nerves (again, they also used a control group that received just saline). They also injected a third group of locusts with a serotonin agonist (i.e., a chemical that increases the activity of serotonin--the opposite of an antagonist). The treated locusts became much more friendly, but the control locusts remained aloof. In other words, just increasing serotonin levels (without actual stimuli) can make solitarious locusts more gregarious.

In their final experiment, the researchers determined whether increasing the ability of the locusts to produce serotonin would cause them to become more gregarious after only a small amount of stimulation. Typically, a solitarious locust has to hang out with other locusts for a couple of hours before putting on its party shoes. However, when solitarious locusts were injected with a serotonin precursor, 30 minutes of exposure was enough to get them dancing.

There's some hope that these results might lead to new possibilities for locust control. Individually (i.e., in the solitarious phase), locusts aren't too much of a problem--no more so than, say, grasshoppers, really. It's only when they start to swarm that they become economically disastrous. If a way could be found to prevent locusts from become gregarious, even when crowded, then locust swarms could be controlled. (Too late for Rameses, of course.) Such possibilities are still in the future--currently, there is no locust-specific serotonin antagonist that can be applied appropriately--but it does give some hope.

Until then, there is one thing we can definitely conclude: keep the locusts away from the Prozac!

Anstey, Michael L., Stephen M. Rogers, Swidbert R. Ott, Malcolm Burrows, and Stephen J. Simpson, 2009. "Serotonin mediates behavioral gregarization underlying swarm formation in desert locusts." Science 323: 627-630. doi 10.1126/science.1165939

Stevenson, P.A., 2009. "The key to Pandora's box." Science 323: 594-595. doi 10.1126/science.1169280

(Yes, I know this isn't quite 1,000 words. But it's pretty darned close!)

Book Review: Tested

(First, an apology: Sorry for the long delay in posts. I blame the holidays. Sorry if my hiatus has caused problems for either of the people who ever visit...)

I don't remember a lot about third grade. I remember even less about how I was taught reading and math in third grade. In math, I remember that we did a lot of Mad Minutes. (For those unfamiliar with the concept, a Mad Minute is a 30-problem math test that students try to complete in--you guessed it--one minute. The problems start out easy--for example, I think Mad Minute 1-1 is multiplication by 1--and get progressively harder. A Mad Minute minimally tests mathematical skill; it's more a test of a student's ability to memorize a list of 30 numbers and write them down in one minute.)

In reading, I remember we used a basal reader (although I didn't know that's what it was called), and that we were put into reading groups, each of which got a different reader. (I was in a group called the "Odd Balls," so named because there was only one boy in the group. I think the groups were roughly homogeneous in terms of level--certainly the others in my group were among the higher students in the class.) I remember we also did a lot of writing: short stories, poems, etc.

If I had attended third grade at Tyler Heights Elementary in Maryland, I would have learned math by rote. I would have learned to read by reading the same passage each day for a week and answering the same types of questions over and over again. I could have gone to another classroom and heard their teacher saying pretty much the same thing my teacher was saying, because all the teachers would have been reading from the same teacher guide, and their district curricula would have dictated when they would move from one topic to another. I would have learned how to write 3-4 sentence Brief Constructed Responses to standardized questions (such as, "What features of the instructions make them easy for third-graders to follow?"), but I would have done almost no other writing. And I would have spent most of the year learning how to take the Maryland State Assessment (MSA).

At least, that's what the third graders profiled in Tested: One American School Struggles to Make the Grade, by Linda Perlstein, experienced. In Tested, Perlstein describes a (school) year in the life of the third grade at Tyler Heights Elementary in Annapolis. Tyler Heights was listed as a "failing" school under No Child Left Behind (NCLB). In one year, they turned their test scores around and had an MSA pass rate of more than 75%. The school was widely touted in the press as a "success story," which is what caught Perlstein's attention. In Tested, Perlstein attempts to answer the questions "How did Tyler Heights turn its scores around?" and "What do those test scores mean?"

Tyler Heights was praised as a success story largely because most people expected it to keep failing. Most of the students at Tyler Heights are poor and non-white; many of them are homeless, have absent parents, or do not get adequate food at home. (The school serves both breakfast and lunch to its students to help ensure that most students get at least two good meals a day.) The school receives so much Title 1 money that it sometimes has trouble spending it all. Many of its students don't show up for school; some of them show up when school is closed, because their parents don't pay attention to closures. In short, it fulfills every stereotype of a failing school.

Perlstein got permission from the school to essentially live in the building for an entire school year. She was allowed to interview students, parents, teachers, and administrators, and to report her observations and interviews. It's hard to believe that such freedom would be granted in this day and age, but the result is as exceptional as one would hope: Perlstein's book is informative, well written, and gripping. Her descriptions of day-to-day life at Tyler Heights are vivid; I could almost hear some of the students' and teachers' voices by the end of the book.

The story Perlstein tells in Tested is one that probably will not surprise most educators: Tyler Heights got its scores up by drilling students every day on how to answer the questions they would most likely see on the MSA. The only types of questions they ever saw were those that were similar to MSA questions; the only content they covered was content within the testable limits of the Maryland Voluntary State Curriculum (which isn't really voluntary, since the MSA is based on it, and thanks to NCLB, students have to pass the MSA for a school to continue to receive funding).

The book focuses primarily on the reading curriculum (possibly because it's harder to argue about how to write a test that truly tests students' ability to do math). Tyler Heights uses a program specifically designed to raise students' test scores; because most reading tests focus exclusively on reading comprehension, students spend almost no time writing, reading for fun, or doing any of the other things that help get kids excited about reading. (At one point in the book, Perlstein relates a situation in which students who had finished an exam early were reading silently at their desks. The teacher was told that students who finish early must go back and continue working on their answers; they were not to read "fun books" outside of designated time slots.)

As would many educators (okay, maybe I'm inflating myself a bit, but someone who writes textbooks and lessons is still an educator, right?), I found the stories Perlstein tells about a typical Tyler Heights third grade day disturbing. The curriculum seemed designed to drum out of students any vestige of curiosity they might have; the reading curriculum certainly was unlikely to instill in any child a love of reading, or an ability to write coherently. It's especially disturbing because one could argue that these kids are the ones most in need of that kind of inspiration.

But although I found the stories disturbing, sadly, they did not surprise me. It doesn't take a rocket scientist to predict that if most of a school's funding (or even a significant portion of it) is based on whether students pass a standardized test, that school is probably going to focus on giving students as much practice on that test as possible. (There's a good reason most students' scores on the SAT increase the second time they take the test: practice, as they say, makes perfect.)

Don't get me wrong; I don't necessarily think the administration at Tyler Heights made a bad choice in implementing the programs they have. As long as NCLB controls funding and public perception of school success, schools will continue to focus on getting kids to pass the test at any cost. And in a community with almost no parental support for education (percent attendance at parent-teacher night at Tyler Heights rarely reaches double digits), there aren't a lot of ways to get those test scores up other than drill, drill, drill. But just because I understand the administration's decision doesn't mean I think all is well in schools like Tyler Heights (because I'm sure there are hundreds of schools around the country in a similar situation). Of course, I could go off on a long, long rant about my thoughts on public education today--but this is supposed to be a book review, so I'll stop there.

Tested should be required reading for anyone curious about the effects of NCLB (or high-stakes testing in general) or the realities of teaching in a low-income, urban school district. Heck, they should put it on the mandatory reading list for the U.S. Department of Education. (Do they even have one of those? If they don't, they should!) But when you do read it, be prepared to be disturbed and saddened (and a little inspired, too).

Tested: One American School Struggles to Make the Grade
Linda Perlstein
Henry Holt and Co., 2007 (1st edition); Holt Paperbacks, 2008 (Reprint)
ISBN 978-0805080827 (hardcover), 978-0805088021 (paperback)

1000 words

One of my favorite lazy-Saturday-afternoon-with-a-book book series is Lillian Jackson Braun's The Cat Who.... In one of them (I can't remember which), she makes reference to an activity that the main character's English teacher used to have him do: pick a topic from a dictionary or encyclopedia and write 1000 words on that topic.

I think this is a pretty cool idea, and an interesting way to practice writing without going back over the same topics over and over again.

So, I am going to try to start doing that. I will post the results here. We'll see how it goes! With any luck, I'll learn some interesting things, and you'll get more interesting posts.