Saluting the Genius of Darwin

Thomas Porostocky

The New York Times, February 11, 2009, by Nicholas Wade — Darwin’s theory of evolution has become the bedrock of modern biology. But for most of the theory’s existence since 1859, even biologists have ignored or vigorously opposed it, in whole or in part.

It is a testament to Darwin’s extraordinary insight that it took almost a century for biologists to understand the essential correctness of his views.

Biologists quickly accepted the idea of evolution, but for decades they rejected natural selection, the mechanism Darwin proposed for the evolutionary process. Until the mid-20th century they largely ignored sexual selection, a special aspect of natural selection that Darwin proposed to account for male ornaments like the peacock’s tail.

And biologists are still arguing about group-level selection, the idea that natural selection can operate at the level of groups as well as on individuals. Darwin proposed group selection — or something like it; scholars differ as to what he meant — to account for castes in ant societies and morality in people.

How did Darwin come to be so in advance of his time? Why were biologists so slow to understand that Darwin had provided the correct answer on so many central issues? Historians of science have noted several distinctive features of Darwin’s approach to science that, besides genius, help account for his insights. They also point to several nonscientific criteria that stood as mental blocks in the way of biologists’ accepting Darwin’s ideas.

One of Darwin’s advantages was that he did not have to write grant proposals or publish 15 articles a year. He thought deeply about every detail of his theory for more than 20 years before publishing “On the Origin of Species” in 1859, and for 12 years more before its sequel, “The Descent of Man,” which explored how his theory applied to people.

He brought several intellectual virtues to the task at hand. Instead of brushing off objections to his theory, he thought about them obsessively until he had found a solution. Showy male ornaments, like the peacock’s tail, appeared hard to explain by natural selection because they seemed more of a handicap than an aid to survival. “The sight of a feather in a peacock’s tail, whenever I gaze at it, makes me sick,” Darwin wrote. But from worrying about this problem, he developed the idea of sexual selection, that females chose males with the best ornaments, and hence elegant peacocks have the most offspring.

Darwin also had the intellectual toughness to stick with the deeply discomfiting consequences of his theory, that natural selection has no goal or purpose. Alfred Wallace, who independently thought of natural selection, later lost faith in the power of the idea and turned to spiritualism to explain the human mind. “Darwin had the courage to face the implications of what he had done, but poor Wallace couldn’t bear it,” says William Provine, a historian at Cornell University.

Darwin’s thinking about evolution was not only deep, but also very broad. He was interested in fossils, animal breeding, geographical distribution, anatomy and plants. “That very comprehensive view allowed him to see things that others perhaps didn’t,” says Robert J. Richards, a historian at the University of Chicago. “He was so sure of his central ideas — the transmutation of species and natural selection — that he had to find a way to make it all work together.”

From the perspective of 2009, Darwin’s principal ideas are substantially correct. He did not get everything right. Because he didn’t know about plate tectonics, Darwin’s comments on the distribution of species are not very useful. His theory of inheritance, since he had no knowledge of genes or DNA, is beside the point. But his central concepts of natural selection and sexual selection were correct. He also presented a form of group-level selection that was long dismissed but now has leading advocates like the biologists E. O. Wilson and David Sloan Wilson.

Not only was Darwin correct on the central premises of his theory, but in several other still open issues his views also seem quite likely to prevail. His idea of how new species form was long eclipsed by Ernst Mayr’s view that a reproductive barrier like a mountain forces a species to split. But a number of biologists are now returning to Darwin’s idea that speciation occurs most often through competition in open spaces, Dr. Richards says.

Darwin believed there was a continuity between humans and other species, which led him to think of human morality as related to the sympathy seen among social animals. This long-disdained idea was resurrected only recently by researchers like the primatologist Frans de Waal. Darwin “never felt that morality was our own invention, but was a product of evolution, a position we are now seeing grow in popularity under the influence of what we know about animal behavior,” Dr. de Waal says. “In fact, we’ve now returned to the original Darwinian position.”

It is somewhat remarkable that a man who died in 1882 should still be influencing discussion among biologists. It is perhaps equally strange that so many biologists failed for so many decades to accept ideas that Darwin expressed in clear and beautiful English.

The rejection was in part because a substantial amount of science, including the two new fields of Mendelian genetics and population genetics, needed to be developed before other, more enticing mechanisms of selection could be excluded. But there were also a series of nonscientific considerations that affected biologists’ judgment.

In the 19th century, biologists accepted evolution, in part because it implied progress.

“The general idea of evolution, particularly if you took it to be progressive and purposeful, fitted the ideology of the age,” says Peter J. Bowler, a historian of science at Queen’s University, Belfast. But that made it all the harder to accept that something as purposeless as natural selection could be the shaping force of evolution. “On the Origin of Species” and its central idea were largely ignored and did not come back into vogue until the 1930s. By that time the population geneticist R. A. Fisher and others had shown that Mendelian genetics was compatible with the idea of natural selection working on small variations.

“If you think of the 150 years since the publication of ‘Origin of Species,’ it had half that time in the wilderness and half at the center, and even at the center it’s often been not more than marginal,” says Helena Cronin, a philosopher of science at the London School of Economics. “That’s a pretty comprehensive rejection of Darwin.”

Darwin is still far from being fully accepted in sciences outside biology. “People say natural selection is O.K. for human bodies but not for brain or behavior,” Dr. Cronin says. “But making an exception for one species is to deny Darwin’s tenet of understanding all living things. This includes almost the whole of social studies — that’s quite an influential body that’s still rejecting Darwinism.”

The yearning to see purpose in evolution and the doubt that it really applied to people were two nonscientific criteria that led scientists to reject the essence of Darwin’s theory. A third, in terms of group selection, may be people’s tendency to think of themselves as individuals rather than as units of a group. “More and more I’m beginning to think about individualism as our own cultural bias that more or less explains why group selection was rejected so forcefully and why it is still so controversial,” says David Sloan Wilson, a biologist at Binghamton University.

Historians who are aware of the long eclipse endured by Darwin’s ideas perhaps have a clearer idea of his extraordinary contribution than do biologists, many of whom assume Darwin’s theory has always been seen to offer, as now, a grand explanatory framework for all biology. Dr. Richards, the University of Chicago historian, recalls that a biologist colleague “had occasion to read the ‘Origin’ for the first time — most biologists have never read the ‘Origin’ — because of a class he was teaching. We met on the street and he remarked, ‘You know, Bob, Darwin really knew a lot of biology.’ ”

Darwin knew a lot of biology: more than any of his contemporaries, more than a surprising number of his successors. From prolonged thought and study, he was able to intuit how evolution worked without having access to all the subsequent scientific knowledge that others required to be convinced of natural selection. He had the objectivity to put aside criteria with powerful emotional resonance, like the conviction that evolution should be purposeful. As a result, he saw deep into the strange workings of the evolutionary mechanism, an insight not really exceeded until a century after his great work of synthesis.

Illustration by Thomas Porostocky; Photographs by University of Cambridge

Perhaps as famous as any of Darwin’s books is “The Voyage of the Beagle,” his account of his nearly five-year voyage of exploration, which took him around Cape Horn to the Galápagos Islands. It was on that trip that he made observations, like those of the many varieties of island finches, that provided raw material for his thinking about the process of evolution.

“We call this nano suturing”

Laser healing: Researchers at Massachusetts General Hospital are developing a method to heal surgical incisions with laser light. Surgeons Ying Wang and Min Yao position a metal frame that directs a green surgical laser over the incision. The frame keeps the instrument steady and at a measured distance from the skin. They shine the light onto the cut to activate the dye, leaving it on for three minutes.
Credit: Porter Gifford

Lasers and a century-old dye could supplant needles and thread

MIT Technology Review, February 11, 2009, by Lauren Gravitz — Despite medicine’s inestimable progress over the past century, surgery can still leave scars that look more appropriate to Frankenstein’s monster than to the beneficiary of a precise, modern operation. But in the Wellman Center for Photomedicine at Massachusetts General Hospital, Irene Kochevar and Robert Redmond have developed a method that has the potential to replace the surgeon’s needle and thread. Using surgical lasers and a light-activated dye, the researchers are prompting tissue to heal itself.

Laser-bonded healing is not a new idea. For years, scientists have been trying to find ways to use the heat generated by lasers to weld skin back together. But they’ve had a difficult time finding the right balance. Too little heat and a wound won’t heal; too much and the tissue dies. Eight years ago, one of Kochevar and Redmond’s colleagues was examining pathology slides of cells killed by this kind of thermal healing when it occurred to him that it might be possible to use just the light of a laser, rather than its heat.

While the idea of skin weaving itself back together may sound more like superhero lore than surgical skill, the science is startlingly simple. The team took advantage of the fact that a number of dyes are activated in the presence of light. In the case of Rose Bengal–a stain used in just about every ophthalmologist’s office to detect corneal lesions–the researchers believe that light helps transfer electrons between the dye molecule and collagen, the major structural component of tissue. This produces highly reactive free radicals that cause the molecular chains of collagen to chemically bond to each other, or “cross-link.” Paint two sides of a wound with Rose Bengal, illuminate it with intense light, and the sides will knit themselves back together. “We call this nano suturing,” Kochevar says, “because what you’re doing is linking together the little collagen fibers. It’s way beyond anything that a thread of any kind can do.”

The benefits of such nano suturing are manifold. In just about every case, it appears to result in faster procedures, less scarring, and possibly fewer infections, since it seals openings completely and leaves no gap through which bacteria can penetrate. This makes it particularly well suited for closing not only superficial skin incisions but also those made in eye and nerve operations. In eye surgeries, such as corneal replacement, stitches that can cause irritation and infection must sometimes be left in place for months, which can aggravate complications. In nerve surgeries, damage from scar tissue can decrease the conduction of neural impulses. “If you put a needle through skin, it’s not a big deal,” says Redmond. “But if you put it through a nerve it’s a big deal, because you’re destroying part of the nerve.”

Light Work
The operations take place in a surgical suite of tile and stainless steel. Min Yao, a surgeon on Kochevar and Redmond’s team, has carted a medical laser up from the lab downstairs. The instrument is already used for eye, ear, nose, and throat procedures, and its green light has just the right wavelength for maximum absorption by the pink Rose Bengal stain. The better the light is absorbed, the more it activates the dye and the more complete the collagen cross-linking. The box that generates the laser light is barely larger than a stereo receiver; a thin fiber-optic cable snakes out of its side, and it gives off an appletini-green glow.

For this particular test surgery, on the skin of an anesthetized rabbit, surgeon Ying Wang measures and marks a patch of skin to be removed, an elliptical, leaf-shaped patch 1.5 centimeters wide by 3.5 centimeters long. After removing the tissue, Wang begins closing the wound. Surgical cuts typically require two layers of suturing: buried, or subcutaneous, stitches to bring deep tissue together, and superficial ones to close up the skin itself. Wang moves her needle and thread through the subcutaneous layer, working her way deftly from one end of the incision to the other. Then she moves on to the epidermal layer.

Wang closes up the right half of the cut with three stitches, black thread standing out against the rabbit’s pink skin. Then she takes a vial of Rose Bengal and drips the neon-pink dye onto either side of the unclosed portion of the wound. She threads the laser’s fiber-optic cable into a metal stand, which maintains a set distance between laser and tissue while holding the light steady; a lens focuses the beam into a sharp, straight line that can be aligned with the incision. Wang positions the stand on the rabbit’s flank, dons a pair of orange safety glasses, sets a timer, and steps down on the pedal that activates the laser. A green glow washes over the room.

Three minutes later, the timer beeps and Wang releases the pedal. She removes her safety glasses, moves the laser stand away, and inspects her handiwork. A small line is visible–a remnant of the Rose Bengal stain and of the black marker used to trace the location of the incision prior to surgery. But when she tugs on the wound, using a pair of forceps in each hand to pull the skin apart, the skin holds taut, and there’s little visible evidence of the cut itself.

A Bright Future
“It’s a very interesting technology, which would be useful to anyone who does any kind of skin surgery–plastic surgeons, dermatologists,” says Robert Stern, a professor of dermatology at Harvard Medical School and chief of dermatology at Beth Israel Deaconess Medical Center in Boston. He notes that the technology must still prove itself, and he isn’t yet convinced that the benefits will offset the costs of photochemical dyes and laser equipment, which are far pricier than a needle and thread. But, he says, the potential to minimize scarring and perhaps speed healing “could be nice for patients and improve outcomes [too].”

So far, use of the technique in humans has been limited to skin surgeries: in a clinical trial, 31 patients with skin cancers and suspicious moles had their three-to-five-centimeter excisions closed with sutures on one side and photo chemical tissue bonding on the other. The dermatological procedure will be submitted to the U.S. Food and Drug Administration for approval, which the researchers are awaiting before beginning additional human trials. Animal experiments have already shown the technique to be useful in nerve, eye, and blood vessel surgeries, among others–so useful, in fact, that Kochevar and Redmond have surgeons ready and waiting to start human trials the moment the hospital approves them.

“Talk to just about any physician about this, and they have an idea for how it could be used,” Kochevar says. The technology is limited by tissue depth: it works only where light will penetrate, so it could never replace subcutaneous sutures or be effective on dark or opaque tissue like liver and bone. The scientists have licensed the technology to a brand-new startup, still in stealth mode, which plans to commercialize the technology once it receives FDA approval. The company has just begun seeking its first round of funding.

Research News from the Howard Hughes Medical Institute (HHMI)


Duplication architecture of the human genome…

Recent duplication architecture of the human genome. The organization of segmental duplications that are >90 percent sequence identical and >1 kb in length is shown as red bars overlaid on the human genome. Approximately 5–6 percent of the human genome consists of duplicated segments, the majority of which cluster into ~390 duplication hubs. The complex mosaic architecture of one of these duplication hubs in 2p11 is shown in more detail (blue arrow). The ~750 kb consists of 17 gene-rich segments that were duplicatively transposed from the euchromatin to this pericentromeric region 10–20 million years ago. Euchromatic colonization of the region abruptly ceased 10 million years ago.
Julie Horvath and Jeffrey Bailey.

HHMI, February 12, 2009, by Evan E. Eichler PhD — Roughly 10 million years ago, a major genetic change occurred in a common ancestor of gorillas, chimpanzees, and humans. Segments of DNA in its genome began to form duplicate copies at a greater rate than in the past, creating a genetic instability that persists in modern humans and contributes to diseases like autism and schizophrenia. But that gene duplication also may be responsible for a genetic flexibility that has resulted in some uniquely human characteristics.

“Because of the architecture of the human genome, genetic material is constantly being added and deleted in certain regions,” says Howard Hughes Medical Institute investigator and University of Washington geneticist Evan Eichler. “These are really like volcanoes in the genome, blowing out pieces of DNA.”

Intrachromosomal expansion of a segmental duplication during the evolution of humans and great apes. The figure shows the results of fluorescent in situ hybridization of a 20-kb segmental duplication (low-copy repeat chromosome 16 a) to both interphase nuclei and extracted metaphase primate chromosomes. HSA (human), PTR (common chimpanzee), PPA (bonobo), GGO (gorilla), PPY (orangutan), MFU (macaque), PAN (baboon), (PCR) silver-leaf monkey, and CMO (marmoset). The segment expanded in the great ape lineage and led to the differential restructuring of human and great ape chromosomes. The segment contains one of the most rapidly evolving genes within the human genome (morpheus or nuclear pore interacting protein).
From Johnson, M.E., Viggiano, L., Bailey, J.A., Abdul-Rauf, M., Goodwin, G., Rocchi, M., and Eichler, E.E. 2001. Nature 413:514–519. © 2001 Nature Publishing Group.

Detection and characterization of structural variation in the human genome. A: Detection of a deletion of the GSTM1 gene by discordant paired-end sequence analysis of fosmid clones (red) against the human reference sequence. B: Sequence comparison between the human genome and the fosmid insert reveals an ~14-kb deletion (green bars indicate intrachromosomal duplications located at the breakpoint). C: A PCR assay designed to the junction of the structural variant shows heterozygotes and homozygotes of both alleles (lane 1, heterozygotes; lanes 2 and 3, homozygotes).

Adapted from Tuzun, E., Sharp, A.J., Bailey, J.A., Kaul, R., Morrison, V.A., Pertz, L.M., Haugen, E., Hayden, H., Albertson, D., Pinkel, D., Olson, M.V., and Eichler, E.E. 2005. Nature Genetics 37:727–732.

Eichler and his colleagues focused on the genomes of four different species: macaques, orangutans, chimpanzees, and humans. All are descended from a single ancestral species that lived about 25 million years ago. The line leading to macaques broke off first, so that macaques are the most distantly related to humans in evolutionary terms. Orangutans, chimpanzees, and humans share a common ancestor that lived 12-16 million years ago. Chimps and humans are descended from a common ancestral species that lived about 6 million years ago.

By comparing the DNA sequences of the four species, Eichler and his
colleagues identified gene duplications in the lineages leading to these
species since they shared a common ancestor. They also were able to estimate
when a duplication occurred from the number of species sharing that
duplication. For example, a duplication observed in orangutan, chimpanzees,
and humans but not in macaques must have occurred sometime after 25
million years ago but before the orangutan lineage branched off.

Eichler’s research team found an especially high rate of duplications in the
ancestral species leading to chimps and humans, even though other
mutational processes, such as changes in single DNA letters, were slowing
down during this period. “There’s a big burst of activity that happens where
genomes are suddenly rearranged and changed,” he says. Surprisingly, the
rate of duplications slowed down again after the lineages leading to humans
and to chimpanzees diverged. “You might like to think that humans are
special because we have more duplications than did earlier species,” he says,
“but that’s not the case.”

These duplications have created regions of our genomes that are especially
prone to large-scale reorganizations. “That architecture predisposes to
recurrent deletions and duplications that are associated with autism and
schizophrenia and with a whole host of other diseases,” says Eichler.

Yet these regions also exhibit signs of being under positive selection,
meaning that some of the rearrangements must have conferred advantages on
the individuals who inherited them. Eichler thinks that uncharacterized genes
or regulatory signals in the duplicated regions must have created some sort of
reproductive edge. “I believe that the negative selection of these duplications
is being outweighed by the selective advantage of having these newly minted
genes, but that’s still unproven,” he said.

An important task for future studies is to identify the genes in these regions
and analyze their functions, according to Eichler. “Geneticists have to figure
out the genes in these regions and how variation leads to different aspects of
the human condition such as disease. Then, they can pass that information on
to neuroscientists, physiologists and biochemists who can work out what
these proteins are and what they do,” he says. “There is the possibility that
these genes might be important for language or for aspects of cognition,
though much more work has to be done before we’ll be able to say that for

Science in the 21st Century

This story might bug you

Cyborg beetle: Shown here is a giant flower beetle carrying a microprocessor, radio receiver, and microbattery and implanted with several electrodes. To control the insect’s flight, scientists wirelessly deliver signals to the payload, which sends electrical signals through the electrode to the brain and flight muscles.
Credit: Michel Maharbiz

The insect’s flight path can be wirelessly controlled via a neural implant.

MIT Technology Review, February 2009, by Emily Singer — A giant flower beetle with implanted electrodes and a radio receiver on its back can be wirelessly controlled, according to research presented this week. Scientists at the University of California developed a tiny rig that receives control signals from a nearby computer. Electrical signals delivered via the electrodes command the insect to take off, turn left or right, or hover in midflight. The research, funded by the Defense Advanced Research Projects Agency (DARPA), could one day be used for surveillance purposes or for search-and-rescue missions.

Beetles and other flying insects are masters of flight control, integrating sensory feedback from the visual system and other senses to navigate and maintain stable flight, all the while using little energy. Rather than trying to re-create these systems from scratch, Michel Maharbiz and his colleagues aim to take advantage of the beetle’s natural abilities by melding insect and machine. His group has previously created cyborg beetles, including ones that have been implanted with electronic components as pupae. But the current research, presented at the IEEE MEMS in Italy, is the first demonstration of a wireless beetle system.

The beetle’s payload consists of an off-the-shelf microprocessor, a radio receiver, and a battery attached to a custom-printed circuit board, along with six electrodes implanted into the animals’ optic lobes and flight muscles. Flight commands are wirelessly sent to the beetle via a radio-frequency transmitter that’s controlled by a nearby laptop. Oscillating electrical pulses delivered to the beetle’s optic lobes trigger takeoff, while a single short pulse ceases flight. Signals sent to the left or right basilar flight muscles make the animal turn right or left, respectively.

Most previous research in controlling insect flight has focused on moths. But beetles have certain advantages. The giant flower beetle’s size–it ranges in weight from four to ten grams and is four to eight centimeters long–means that it can carry relatively heavy payloads. To be used for search-and-rescue missions, for example, the insect would need to carry a small camera and heat sensor.

In addition, the beetle’s flight can be controlled relatively simply. A single signal sent to the wing muscles triggers the action, and the beetle takes care of the rest. “That allows the normal function to control the flapping of the wings,” says Jay Keasling, who was not involved in the beetle research but who collaborates with Maharbiz. Minimal signaling conserves the battery, extending the life of the implant. Moths, on the other hand, require a stream of electrical signals in order to keep flying.

The research has been driven in large part by advances in the microelectronics industry, with miniaturization of microprocessors and batteries.

Graphene power: Graphene Energy hopes that graphene electrodes such as this one will increase the energy-storage capacity and power output of ultracapacitors. This image, which shows the edge of a graphene electrode, was made with a scanning-electron microscope.
Credit: Meryl Stoller

Ultracapacitors that store more could help the grid run smoothly.

MIT Technology Review, February 2009, by Katherine Bourzac — Integrating irregular sources of renewable energy, such as wind and solar, with the electrical grid, while keeping power output steady, is going to be a big challenge. Energy-storage devices called ultracapacitors could help by storing sudden surges of power. But much will depend on developing a new generation of ultracapacitors with enough storage capacity to meet the likely demand.

Graphene Energy, a startup based in Austin, TX, hopes that ultracapacitors with electrodes made of graphene–sheets of carbon just an atom thick–will be the solution. The storage capacity of an ultracapacitor is limited only by the surface area of its electrodes, and graphene offers a way to greatly increase the area available.

Ultracapacitors store energy electrostatically, instead of chemically, as in batteries. During charging, electrons come to the surface of one electrode, and electron “holes” form on the surface of the other. This draws positive ions in an electrolyte to the first electrode and negative ions to the second. By contrast, the chemical reactions used to charge batteries limit the speed with which they can be charged and eventually cause the electrode materials to break down. Ultracapacitors can be charged and discharged very rapidly, in seconds rather than minutes, and can be recharged millions of times before wearing out.

However, ultracapacitors currently on the market can’t match batteries for energy density, so they’re mostly used in hybrid systems alongside batteries or for niche applications. Because these devices can handle a rapid influx of large amounts of energy, they’re often used to recover energy–for example, when a city bus breaks or a gantry crane lowers its cargo. Ultracapacitors employed in this way have reduced by 40 percent the energy needed by some cranes used in Japanese ports. A few power tools, including an electric drill, take advantage of the rapid recharging ability of ultracapacitors.

Graphene Energy hopes to open up new ultracapacitor applications by developing devices with far higher power output. These ultracapacitors could perhaps be used to regulate surges in the electrical grid or to power hybrid transportation vehicles. The company has $500,000 in seed funding to commercialize graphene ultracapacitors developed by Rodney Ruoff, a professor of mechanical engineering at the University of Texas at Austin. Ruoff is a cofounder of Graphene Energy and also serves as the company’s technology advisor.

Existing ultracapacitors use electrodes made from activated carbon–a porous, charcoal-like material that has a very high surface area. Activated carbon stores charge in tunnel-like pores, and it takes about one second for it to travel in and out. This is very fast compared with the fastest batteries, but activated carbon has a limited power output.

To make the graphene for its electrodes, Ruoff’s team starts by putting graphite oxide in a water solution. This causes the material to flake into atom-thin sheets of graphene oxide. Next, the oxygen atoms are removed, leaving the graphene behind. So far, Ruoff’s lab has made graphene ultracapacitors that match the performance of those made using activated carbon. With further refinements, he says, they should outperform activated carbon, although the steps that his company is taking to achieve this remain secret.

Based on a description of the graphene ultracapacitors published last September in the journal Nano Letters, John Miller of JME, a research and consulting firm that specializes in electrochemical capacitors, says that it should indeed be possible to improve their performance. The graphene electrode described in this paper is “wadded into a ball like a crumpled piece of paper,” says Miller. “You don’t have full access to the surface.”

If Graphene Energy can grow the electrodes in vertical arrays, like a row of perfectly flat sheets of paper standing on edge, Miller says that the power output could be increased dramatically. In this arrangement, every single carbon atom would be exposed and able to store energy, with virtually no waiting time for the charge to travel down the tunnels found in activated carbon.

However, in addition to improving the performance of its ultracapacitors, Graphene Energy must also develop a method for making them at larger scales–a common challenge across all graphene research.

Dileep Agnihotri, CEO of Graphene Energy, says that the company hopes to test its first prototype product incorporating graphene electrodes by the end of this year.

Another group of researchers hopes to make better ultracapacitor electrodes using carbon nanotubes–rolled-up tubes of graphene that have many of the same properties. “I think both approaches can work in principle,” says Joel Schindall, a professor of electrical engineering and computer science at MIT who is working on the nanotube electrodes. “The key will be getting the growth process right, then working on ways to manufacture it in a cost-effective manner.”

Science in the 21st Century

Air supply: Guzzella’s design replaces a two-liter gasoline engine with a very small 750-milliliter one that’s adequate for cruising speeds.
Credit: Lino Guzzella

Storing energy with compressed air, rather than batteries, could cut the cost of hybrids.

MIT Technology Review, February 11, 2009, by Kevin Bullis — A new kind of hybrid vehicle being developed at the Swiss Federal Institute of Technology in Zurich could save almost as much fuel as today’s gas-electric hybrids, but at a fraction of the cost. Swiss researchers will present the results of experiments with a test version of the new system at the Society for Automotive Engineer’s Congress in April.

Conventional gas-electric hybrids use batteries to store energy recovered during braking, which would otherwise be wasted as heat. They later use that energy to drive an electric motor that assists the car’s gas engine. But the high-cost of batteries, and the added cost of including two forms of propulsion — an electric motor and a gasoline engine — make such hybrids expensive. This has slowed their adoption and limited their impact on overall greenhouse gas emissions from vehicles.

Lino Guzzella, a professor of mechanical engineering at the Swiss Institute, is developing a hybrid that requires no battery or electric motor. Instead, it stores energy by using the engine’s pistons to compress air. That air can later be released to drive the pistons and propel the vehicle along. Guzzella says that the system will add only about 20 percent to the cost of a conventional engine, whereas the extra components required in hybrid electric vehicles can add 200 percent to the cost. Computer simulations suggest that the design should reduce fuel consumption by 32 percent, which is about 80 percent of the fuel-savings of gas-electric hybrids, he says. Initial experiments have demonstrated that the design can be built.

The overall idea of air (or pneumatic) hybrids isn’t new, but making them efficient has been challenging. “It’s difficult to keep the [energy] losses involved in moving air around small enough that it looks attractive,” says John Heywood, a professor of mechanical engineering at MIT who has also worked on developing air hybrids. What’s more, tanks of compressed air store far less energy than batteries, severely limiting the fuel savings in typical air-hybrid designs, says Doug Nelson, a professor of mechanical engineering at Virginia Tech. This is one of the major drawbacks of cars designed to run solely on compressed air.

Guzzella’s new air-hybrid design makes use of advanced control systems to more precisely control the flow of air, improving overall efficiency. To overcome limited storage capacity, the design relies less on capturing energy from braking than other hybrids, and more on another approach to saving energy: using pneumatic power to boost the performance of smaller, more efficient gasoline engines.

Conventional vehicles use engines that can provide far more power than is needed for cruising–this excess power is used during acceleration and for sustaining very high speeds. But these engines are inefficient, especially since most of the time they operate at far lower loads than they were designed for.

Guzzella’s design replaces a two-liter gasoline engine with a very small 750-milliliter one that’s adequate for cruising speeds. It uses compressed air to provide boosts of power for acceleration. The dense, compressed air provides the oxygen needed to burn larger amounts of fuel than usual, a technique called supercharging.

A similar approach is already used in some production vehicles, where exhaust gases drive a turbocharger. But turbochargers are known for a problem called “turbo lag”–a noticeable delay between when the accelerator is depressed and when the extra power kicks in. The lag is the result of the time it takes for the turbine in a turbocharger to start spinning fast enough. Guzzella says his system suffers no such delay, providing extra power instantly. That’s could make the technology more appealing to consumers, says Zoran Filipi, a professor of mechanical engineering at the University of Michigan, who was not involved with the research.

About 80 percent of the efficiency gain in Guzzella’s system comes from using the small engine. Some of the rest comes from capturing energy from braking and then using it for acceleration–over short distances the car can be propelled by compressed air alone, using no fuel. Fuel is also saved by adjusting the load on the engine to keep it running at optimal efficiency, either by increasing the load by using some of the pistons to compress air, or by decreasing the load by using some compressed air to drive the pistons. Finally, compressed air can be used to restart the engine, making it practical for the system to turn the engine off whenever the car comes to a stop, rather than idling.

Guzzella’s efficiency and performance claims are based on computer models. But he has also demonstrated the basic components of his design in a test engine. The test set-up uses compressed air to drive the pistons, provide supercharging and start the engine. The next steps are to optimize the engine in an attempt to achieve the efficiency levels predicted by the computer models.

Guzzela’s hybrid concept will face stiff competition from other technologies designed to improve fuel efficiency however.

Turbochargers are getting better, and other new technologies have shown promise for addressing the turbo-lag problem, says Michael Duoba, a researcher at the Energy Systems Division of Argonne National Laboratory in Chicago, IL. He also says that what’s most important is not the performance on any one technology, but how well that technology can combine with others now being employed to improve efficiency, such as direct injection and improved transmissions.

But Duoba notes that Guzzella’s system has a distinct advantage. It requires very little extra equipment–just the controls for an extra valve for managing the compressed air and an air tank. The existing engine does the rest. Any time you can make the same equipment do more, he says, “that’s a good thing.”