Tag Archives: Richard Prum

Structure of color

AGELESS BRILLIANCE: Although the pigment-derived leaf color of this decades-old specimen of the African perennial Pollia condensata has faded, the fruit still maintains its intense metallic-blue iridescence.COURTESY OF P.J. RUDALL [downloaded from http://www.the-scientist.com/?articles.view/articleNo/34200/title/Color-from-Structure/]

AGELESS BRILLIANCE: Although the pigment-derived leaf color of this decades-old specimen of the African perennial Pollia condensata has faded, the fruit still maintains its intense metallic-blue iridescence.COURTESY OF P.J. RUDALL [downloaded from http://www.the-scientist.com/?articles.view/articleNo/34200/title/Color-from-Structure/]

Hard to believe those berries were collected more than four decades ago, according to Cristina Luiggi in her Feb. 1, 2013 article, Color from Structure, for The Scientist magazine. Her focus is on biological nanostructures and it is a fascinating article which I urge you to read in its entirety if you have the time and this kind of thing interests you. As you can see, the pictures are great.

Here are a few excerpts from the piece,

Colors may be evolution’s most beautiful accident. Spontaneous mutations that perturbed the arrangement of structural components, such as cellulose, collagen, chitin, and keratin, inadvertently created nanoscale landscapes that catch light in the most vibrantly diverse ways—producing iridescent greens, fiery reds, brilliant blues, opalescent whites, glossy silvers, and ebony blacks.

Structural colors, in contrast to those produced by pigments or dyes, arise from the physical interaction of light with biological nanostructures. These color-creating structures likely developed as an important phenotype during the Cambrian explosion more than 500 million years ago, when organisms developed the first eyes and the ability to detect light, color, shade, and contrast. “As soon as you had visual predators, there were organisms that were either trying to distract, avoid, or communicate with those predators using structural coloration,” says Yale University evolutionary ornithologist Richard Prum.

Ever since, structural coloration has evolved multiple times across the tree of life, as a wide range of organisms developed ways to fine-tune the geometry of some of the most abundant (and often colorless) biomaterials on Earth, engineering grooves, pockets, and films that scatter light waves and cause them to interfere with each other in ways we humans happen to find aesthetically pleasing.

Here’s why color derived from structure doesn’t fade, from Luiggi’s article,

Pigments and dyes are molecules that produce colors by the selective absorption and reflection of specific wavelengths of electromagnetic radiation. Structural colors, on the other hand, rely exclusively on the shape of the material and not its chemical properties. While pigments and dyes degrade and their colors fade over time, some types of structural coloration, which rely on the same materials that make up tree bark, insect exoskeletons, and claws or nails, can persist hundreds, thousands, and even millions of years after the death of the organism.

Structural color can be found in a lot of plant life,

Although there are only a handful of known examples of structural colors in fruits, there are plenty to be found in the leaves and petals of plants. Within every family of flowering plants, there is at least one species that displays structural colors.

“The presence of structural colors, especially in flowers, is likely used by pollinators to spot the position of the flower and to recognize it better,” Vignolini [Silvia Vignolini, a physics postdoc at the University of Cambridge] explains. But in some plants, the evolutionary purpose of structural coloration is harder to pin down. The leaves of the low-lying tropical spikemoss Selaginella willdenowii, for example, produce blue-green iridescence when young and growing in the shade, and tend to lose the structural coloration with age and when exposed to high levels of light. The iridescence is achieved by cells in the leaves’ upper epidermis, which contain a few layers of cellulose microfibrils packed with different amounts of water. This ultrastructure is often absent in the leaves of the same species growing in direct sunlight. Researchers hypothesize that the spikemoss turns off its iridescence by changing the water content of the leaves’ cell walls, says Heather Whitney, a research fellow at the University of Bristol who studies iridescence in plants.

This capability is not limited to plants. Insects (jewel beetles and the morpho butterfly are often cited) and fish also have evolved to include structural color as protective or attractive devices, from Luiggi’s article,

The brightest living tissues on the planet are found in fish. Under ideal conditions, for example, the silvery scales of the European sardine and the Atlantic herring can act like near-perfect mirrors—reflecting up to 90 percent of incoming light. It is an irony of nature that these shiniest of structures are not meant to be flaunted, but are intended as camouflage.

“When you’re out in the open water, if you drop down below 10 to 30 meters, in any direction you look, the intensity of light is the same,” explains Nicholas Roberts, a physicist at the University of Bristol who specializes in bio-optics. At that depth, a perfect reflector, or mirror, would seem invisible, because light is equally reflected from all sides and angles.

It will be interesting to see if there’s any future discussion of the giant squid in the context of structural color since, according to very recent research (as per my Feb. 1, 2013 posting), it appears to be covered in gold leaf when observed in its habitat.

Luiggi’s article starts with an ornithologist and circles back in a discussion about the difficulty of creating nanostructures, soft matter condensed physics, and birds,

To create structural colors, organisms must master architecture at the nanoscale—the size of visible-light wavelengths. “But it turns out that biology doesn’t do a good job of creating nanostructures,” Prum says.

Instead, organisms create the initial conditions that allow those nanostructures to grow using self-organizing physical processes. Thus, organisms exploit what’s known as soft condensed matter physics, or “the physics of squishy stuff,” as Prum likes to call it. This relatively new field of physics deals with materials that are right at the boundaries of hard solids, liquids, and gases.

“There’ve been huge advances in this field in the last 30 years which have created rich theories of how structure can arise at the nanoscale,” Prum says. “It has been very applicable to the understanding of how structural colors grow.”

Soft condensed matter physics has been particularly useful in understanding the production of the amorphous nanostructures that imbue the feathers of certain bird species with intensely vibrant hues. The blue color of the male Eastern bluebird (Sialia sialis), for example, is produced by the selective scattering of blue light from a complex nanostructure of b-keratin channels and air pockets in the hairlike branches called feather barbs that give the quill its lift. The size of the air pockets determines the wavelengths that are selectively amplified.

While there’s better understanding of the mechanisms involved in structural color, scientists are a long way from replicating the processes, from the article,

“The three-dimensional nature of the structures themselves is just so complex,” says Vukusic. [physicist Peter Vukusic, a professor of natural photonics at the University of Exeter, UK] “Were it to be a simple periodic system with a regular geometry, you could easily put that into a computer model and run simulations all day. But the problem is that they are never perfectly periodic.”

This article is open access so, as I noted earlier, all you need is the time. As of my Feb. 6, 2013 posting, there was some new research announced about scientists making observations about the structural color in peacock feathers and applying some of those ideas to develop better resolution in e-readers.

Art/Sci: Survival of the beautiful

Peafowl flaring its feathers. Credit: Jebulon

Thanks to Wikipedia and Jebulon for this image to illustrate this story about a special event in New York titled, Survival of the Beautiful, Feb. 25, 2012.  (I took my inspiration from the event poster.) From the event’s home page,

Why did the peacock’s tail so trouble Charles Darwin?  Natural selection could not explain it, so he had to contrive a whole new theory of sexual selection, which posited that certain astonishingly beautiful traits became preferred even when not exactly useful, simply because they appealed to the opposite sex, and specifically so in each case.  And yet the parallels in what gets preferred at different levels of life suggest that nature may in fact favor certain kinds of patterns over others.  Visually, the symmetrical; colorwise, the contrasting and gaudy; displaywise, the gallant and extreme.  Soundwise, the strong contrast between low note and high, between fast rhythm and the long clear tone. For that matter, plenty of beauty in nature would seem to arise for reasons other than mere sexual selection: for example, the mysterious inscriptions on the backs of seashells, or the compounding geometric symmetries of microscopic diatoms, or the live patterns pulsating across the bodies of octopus and squid.

Humans see such things and find them astonishingly beautiful: are we wrong to experience Nature in such terms?  Far greater than our grandest edifices and epic tales, Nature itself nevertheless seems entirely without purposeful self-consciousness or self-awareness.  Meanwhile, though we ourselves are as nothing compared to it, we still seem possessed of a parallel need to create.  So: can we in fact create our way into better understanding of the role of beauty in the vast natural world?  David Rothenberg recently published a book on these themes, Survival of the Beautiful (Bloomsbury, 2011), and many of the protagonists he encountered on his quest will join him on stage at the Cantor Film Center to debate the question of whether nature’s beauty is actual, imaginary, useful, excessive, or perhaps even entirely beside the point.

What a great event to publicize a book! The schedule reveals some very interesting guests, including Vancouver-based rapper, Baba Brinkman,



10:45 am
DAVID ROTHENBERG and JARON LANIER offer a musical and conceptual introduction.

11:00 am
GAIL PATRICELLI on building a fembot bowerbird to study how male bowerbirds woo females through elaborate dancing and decorating rituals; drawing on her example, RICHARD PRUM explains why everyone misses the point of sexual selection except him.

12:00 pm
OFER TCHERNICHOVSKI responds to Prum’s claim by way of introducing
CHRISTINE ROESKE, a postdoc in his lab, who, veritably haunted
by the beauty of the nightingale’s song, nevertheless tries to subject it to scientific analysis.

12:45 pm
ANNA LINDEMANN, Prum alum turned performance artist, enacts her Theory of Flight.

(1:00 – 1:30 pm:  Break)


2:00 pm
PHILIP BALL shows how chemistry and physics might trump biology in their ability to account for formal natural beauty.  TYLER VOLK deploys his concept of metapatterns to explain how 3 realms and 13 steps (from quarks to culture) make us who we are.

3:00 pm
We know how Science is regularly said to influence Art, but SUZANNE ANKER
explores the flow in the other direction.  DAVID SOLDIER and VITALY KOMAR revisit
their classic elephant art experiment, asking whether we can learn anything about art by
teaching animals to make it.

4:00 pm
Composer DAVID DUNN details his proposal to use music to
save the forests of the American West from destruction by pine bark beetles.
DAVID ABRAM on how synaesthesia (the blending of the senses) might help us
feel our way into the experience of another animal.

(5:00 – 5:30 pm:  Break)


5:30 pm
Digital artist SCOTT SNIBBE recounts how he helped morph
Björk’s love of science into the Biophilia app.

6:15 pm
BABA BRINKMAN, direct from off-Broadway, performs
a special version of The Rap Guide to Evolution.

7:00 pm
JARON LANIER explains why if squid only had childhoods,
they would rule the world.
LAURIE ANDERSON evokes some of her journeys along
the borderlands of nature and culture.

(Times listed above are approximate at best.)

The event is being hosted by the New York Institute for the Humanities and the New Jersey Institute of Technology. The event, which is open and free to the public (due to funding from the Alfred P. Sloan Foundation), will be held at New York University.

Here’s more information about the presenters, from the (sigh) undated news release,

Jaron Lanier is one of the pioneers in virtual reality. His book You Are Not a Gadget is an international bestseller and he was named one of the 100 most influential people in the world by Time Magazine in 2010.

Gail Patricelli is associate professor of evolution and ecology at the University of California Davis.  She specializes in the study of acoustic communication in birds, and is the inventor of the fembot bowerbird.

Richard Prum is professor of evolutionary biology at Yale, and a specialist on the evolution of feathers and the role of beauty in sexual selection.  He received a MacArthur Fellowship in 2009.

Ofer Tchernichovski is associate professor of animal behavior at CUNY, where he studies songbird learning by recording every single sounds baby birds make when learning to sing.

Christina Roeske is postdoctoral associate in biology at the CUNY laboratory for animal behaviour, where she is focusing on the structure of complex birdsongs.

Anna Lindemann is visiting assistant professor of art at Colgate University.  She is a multimedia artist and composer whose works are based on evolutionary/developmental (Evo Devo) biology.

Philip Ball is a science writer and formerly an editor at Nature.  His many books include Natures Patterns: Shape- Flow-Branches; The Music Instinct; and Critical Mass.

Tyler Volk is professor of biology and science director of environmental studies at NYU and author of Metapatterns, CO2 Rising, and other books.

Suzanne Anker is chair of the Fine Arts Department at the School of Visual Arts, and the co-author with Dorothy Nelkin of The Molecular Gaze: Art in the Genetic Age.  She recently built a bio-art lab at SVA, just opened for the spring 2012 semester.

David Soldier is a composer who has collaborated with elephants, zebra finches, and, together with Komar and Melamid, written the best and worst songs in the world.  In his other life as David Sulzer he is professor of neuroscience at Columbia.

Vitaly Komar, together with Alex Melamid, is known for trying to paint the best and worst paintings in the world, and for his work with with elephants in Thailand.  He was one of the first Russian-exile artists to receive a grant from the National Endowment for the Arts.

David Dunn is a composer, sound artist, and theorist, who has lately discovered a new way to listen inside of trees that may radically change the way we manage the forest destruction wrought by the pine bark beetle.

David Abram, cultural ecologist and philosopher, is the award-winning author of Becoming Animal and The Spell of the Sensuous. Described as as “daring” and “truly original” by Science, his work has helped catalyze the burgeoning field of ecopsychology.

Scott Snibbe is a media artist and researcher into interactivity.  His works are in the permanent collection of the Whitney and MOMA, and he has collaborated with James Cameron and Björk.

Baba Brinkman is a Canadian rap artist, writer, actor, and tree planter. He is best known for his award-winning shows The Rap Canterbury Tales and The Rap Guide to Evolution, which interpret the works of Chaucer and Darwin for a modern audience.

Laurie Anderson is one of the most celebrated performance artists in the world.  She is the inventor of the tape-bow violin and sometimes alters her voice to a low baritone to perform as Fenway Bergamot.  She was awarded the Gish Prize in 2007, and is a Fellow of the New York Institute for the Humanities at NYU.

David Rothenberg is the author of Survival of the Beautiful, Thousand Mile Song, Why Birds Sing, and a recording artist with ECM Records.  He is professor of philosophy and music at the New Jersey Institute of Technology, and a Fellow of the New York Institute for the Humanities at NYU.

Between this and the events at the New York Academy of Sciences, it all makes me wish I lived in New York.

It’s a bird. It’s a plane. No, it’s a laser!

I couldn’t resist the Superman reference although it really should have been a Morpho butterfly or a jewel beetle reference since these are two other animals/insects that also display unusual optical properties courtesy of nanoscale structures.

Top: Male eastern bluebird (Sialia sialis, Turdidae). Credit: Ken Thomas (image in public domain). Published in Soft Matter, 2009, 5, 1792-1795. E.R. Dufresne et al., “Self-assembly of amorphous biophotonic nanostructures by phase separation.” Royal Society of Chemistry. http://dx.doi.org/10.1039/B902775K

According to the Oct. 12, 2011 news item on Nanowerk,

Researchers at Yale University are studying how two types of nanoscale structures on the feathers of birds produce brilliant and distinctive colors. The researchers are hoping that by borrowing these nanoscale tricks from nature they will be able to produce new types of lasers—ones that can assemble themselves by natural processes. The team will present their findings at the Optical Society’s (OSA) Annual Meeting, Frontiers in Optics (FiO) 2011, taking place in San Jose, Calif. next week. [It starts Sunday, Oct. 16, 2011.]

Devin Powell, in a May 13, 2011 article for Science News provides some additional detail,

The barbs of these feathers [from bluebirds, blue jays, and parrots] contain tiny pockets of air. Light striking the tightly packed air bubbles scatters, bringing out deep shades of blues and ultraviolet (which birds can see but humans can’t).

“Birds use these structures to create colors that they can’t make in other ways,” says Richard Prum, an  ornithologist at Yale University who discovered the mechanism behind this color.

To make a two-dimensional imitation of a bird feather, Yale physicist Hui Cao and her colleagues punched holes into a thin slice of gallium arsenide semiconductor. The holes were arranged like people in a crowd — somewhat haphazardly but with small-scale patterns that dictate roughly how far each hole is from its neighbor.

“The lesson we learned from nature is that we don’t need something perfect to get control,” says Cao, whose team describes their laser in the May 6 [2011] Physical Review Letters.

The latest work being presented is described this way in an Oct. 2011 news release (why aren’t people putting dates on their news releases????) from the Optical Society of America,

Inspired by feathers, the Yale physicists created two lasers that use this short-range order to control light. One model is based on feathers with tiny spherical air cavities packed in a protein called beta-keratin. The laser based on this model consists of a semiconductor membrane full of tiny air holes that trap light at certain frequencies. Quantum dots embedded between the holes amplify the light and produce the coherent beam that is the hallmark of a laser. The researchers also built a network laser using a series of interconnecting nano-channels, based on their observations of feathers whose beta-keratin takes the form of interconnecting channels in “tortuous and twisting forms.” The network laser produces its emission by blocking certain colors of light while allowing others to propagate. In both cases, researchers can manipulate the lasers’ colors by changing the width of the nano-channels or the spacing between the nano-holes.

What makes these short-range-ordered, bio-inspired structures different from traditional lasers is that, in principle, they can self-assemble, through natural processes similar to the formation of gas bubbles in a liquid. This means that engineers would not have to worry about the nanofabrication of the large-scale structure of the materials they design, resulting in cheaper, faster, and easier production of lasers and light-emitting devices.

Here’s an image of a ‘feather-based laser’,

Top: A laser based on feathers with the sphere-type nanostructure. This laser consists of tiny air holes (black) in a semiconductor membrane; each hole is about 77 nanometers across. (Scale bar = 5 micrometers.) Credit: Hui Cao Research Laboratory / Yale University.

As for the Morpho butterfly and jewel beetle, I last posted about gaining inspiration from these insects (biomimicry) in my May 20, 2011 posting in the context of some anti-counterfeiting strategies.

I first came across some of this work on the optical properties of nanostructures in nature in a notice about a 2008 conference on iridescence at Arizona State University. Here’s the stated purpose for the conference (from the conference page),

A unique, integrative 4–day conference on iridescent colors in nature, Iridescence: More than Meets the Eye is a graduate student proposed and organized conference supported by the Frontiers in Life Sciences program in Arizona State University’s School of Life Sciences. This conference intends to connect diverse groups of researchers to catalyze synthetic cross–disciplinary discussions regarding iridescent coloration in nature, identify new avenues of research, and explore the potential for these stunning natural phenomena to provide novel insights in fields as divergent as materials science, sexual selection and primary science education.