ScienceWeek

SCIENCEWEEK

May 18, 2007

Vol. 11 - Number 19

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A star is simpler than an insect.

-- Martin Rees

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Contents (full text below):

1. Developmental Biology: A Decade of Cloning Mystique

2. The New Synthesis in Moral Psychology

3. Childhood Origins of Adult Resistance to Science

4. Optics: Beyond Diffraction

5. Organic Chemistry: Molecular Cross-Talk

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1.

Science 18 May 2007: Vol. 316. no. 5827, pp. 990 - 992 DOI: 10.1126/science.1143512

Developmental Biology: A Decade of Cloning Mystique

Jose Cibelli

Ten years ago, Ian Wilmut, Keith Campbell, and their colleagues from the Roslin Institute in Scotland announced the first cloned adult mammal--a sheep named Dolly--using a technique called somatic cell nuclear transfer (1). Since then, the experiment has been independently replicated in 16 other mammalian species. Laboratories around the world launched efforts to identify the mechanism responsible for this phenomenon. Hundreds of peer-reviewed manuscripts later, we are left with many unanswered questions about the technique and are still unable to substantially increase its efficiency. For all species cloned by this method, less than 10% of embryos transferred into the uterus will produce a healthy clone. Why?

Wilmut and Campbell's curiosity radically changed our views on the plasticity of the genome. The technique, in which the nucleus of an animal's somatic cell is inserted into an enucleated, unfertilized egg cell (called an oocyte) of the same species, essentially takes a differentiated cell and "turns it back," in a developmental sense, to a zygote, poised to develop into a fetus and mature adult that is genetically identical to the animal that provided the somatic cell nucleus. The old dogma that a differentiated cell can never turn back in development has been replaced by a new one stating that somatic cell nuclear transfer is possible and that our failures are attributable to insufficient understanding of the mechanisms that govern how a somatic cell nucleus is reprogrammed by the cytoplasm of an oocyte.

When performing somatic cell nuclear transfer, we are asking a somatic cell to turn into a gamete in a matter of hours, a process that normally takes months (2). Shortly thereafter, we expect such a pseudo-gamete to "turn into a fertilized egg," or zygote (coaxed by electrical or chemical stimulation in vitro), ready to divide and form an embryo. This is a tremendous undertaking for a genome that the day before was governing the identity and physiology of a completely different cell type. Now we are faced with trying to improve a technique that supports a process that is clearly unnatural. Should we? We cannot afford not to. Beyond the obvious practical benefits we might expect from achieving success--such as agricultural cloning (livestock production) and therapeutic cloning (generating stem cell-derived cell lines for understanding devastating diseases)--it poses a scientific challenge that goes to the heart of developmental biology.

Ten years have not been enough time, though; the long list of unanswered questions about animal cloning reflects how our understanding is stalled at a fundamental level. For instance, is somatic cell dedifferentiation or embryonic differentiation the step at which the process stumbles? Can we render a nucleus more susceptible to the reprogramming action of the egg? How much responsibility for the outcome should either constituent be given? Can we reprogram a primate somatic cell? Why do cells, isolated at the same time from the same tissue of a given individual, have different cloning efficiencies? And the most important question: What is the gene(s) whose expression in the egg is critical for reprogramming a somatic nucleus?

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2.

Science 18 May 2007: Vol. 316. no. 5827, pp. 998 - 1002 DOI: 10.1126/science.1137651

The New Synthesis in Moral Psychology

Jonathan Haidt

People are selfish, yet morally motivated. Morality is universal, yet culturally variable. Such apparent contradictions are dissolving as research from many disciplines converges on a few shared principles, including the importance of moral intuitions, the socially functional (rather than truth-seeking) nature of moral thinking, and the coevolution of moral minds with cultural practices and institutions that create diverse moral communities. I propose a fourth principle to guide future research: Morality is about more than harm and fairness. More research is needed on the collective and religious parts of the moral domain, such as loyalty, authority, and spiritual purity.

If you ever become a contestant on an unusually erudite quiz show, and you are asked to explain human behavior in two seconds or less, you might want to say "self-interest." After all, economic models that assume only a motive for self-interest perform reasonably well. However, if you have time to give a more nuanced answer, you should also discuss the moral motives addressed in Table 1. Try answering those questions now. If your total for column B is higher than your total for column A, then congratulations, you are Homo moralis, not Homo economicus. You have social motivations beyond direct self-interest, and the latest research in moral psychology can help explain why.

In 1975, E. O. Wilson (1) predicted that ethics would soon be incorporated into the "new synthesis" of sociobiology. Two psychological theories of his day were ethical behaviorism (values are learned by reinforcement) and the cognitive-developmental theory of Lawrence Kohlberg (social experiences help children construct an increasingly adequate understanding of justice). Wilson believed that these two theories would soon merge with research on the hypothalamic-limbic system, which he thought supported the moral emotions, to provide a comprehensive account of the origins and mechanisms of morality.

As it turned out, Wilson got the ingredients wrong. Ethical behaviorism faded with behaviorism. Kohlberg's approach did grow to dominate moral psychology for the next 15 years, but because Kohlberg focused on conscious verbal reasoning, Kohlbergian psychology forged its interdisciplinary links with philosophy and education, rather than with biology as Wilson had hoped. And finally, the hypothalamus was found to play little role in moral judgment.

Despite these errors in detail, Wilson got the big picture right. The synthesis began in the 1990s with a new set of ingredients, and it has transformed the study of morality today. Wilson was also right that the key link between the social and natural sciences was the study of emotion and the "emotive centers" of the brain. A quantitative analysis of the publication database in psychology shows that research on morality and emotion grew steadily in the 1980s and 1990s (relative to other topics), and then grew very rapidly in the past 5 years.

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3.

Science 18 May 2007: Vol. 316. no. 5827, pp. 996 - 997 DOI: 10.1126/science.1133398

Childhood Origins of Adult Resistance to Science

Paul Bloom and Deena Skolnick Weisberg

Resistance to certain scientific ideas derives in large part from assumptions and biases that can be demonstrated experimentally in young children and that may persist into adulthood. In particular, both adults and children resist acquiring scientific information that clashes with common-sense intuitions about the physical and psychological domains. Additionally, when learning information from other people, both adults and children are sensitive to the trustworthiness of the source of that information. Resistance to science, then, is particularly exaggerated in societies where nonscientific ideologies have the advantages of being both grounded in common sense and transmitted by trustworthy sources.

Scientists, educators, and policy-makers have long been concerned about American adults' resistance to certain scientific ideas (1). In a 2005 Pew Trust poll, 42% of respondents said that they believed that humans and other animals have existed in their present form since the beginning of time, a view that denies the very existence of evolution (2). Even among the minority who claim to accept natural selection, most misunderstand it, seeing evolution as a mysterious process causing animals to have offspring that are better adapted to their environments (3). This is not the only domain where people reject science: Many believe in the efficacy of unproven medical interventions; the mystical nature of out-of-body experiences; the existence of supernatural entities such as ghosts and fairies; and the legitimacy of astrology, ESP, and divination (4). This resistance to science has important social implications, because a scientifically ignorant public is unprepared to evaluate policies about global warming, vaccination, genetically modified organisms, stem cell research, and cloning (1).

Here we review evidence from developmental psychology suggesting that some resistance to scientific ideas is a human universal. This resistance stems from two general facts about children, one having to do with what they know and the other having to do with how they learn.

The main source of resistance concerns what children know before their exposure to science. Recent psychological research makes it clear that babies are not "blank slates"; even 1-year-olds possess a rich understanding of both the physical world (a "naïve physics") and the social world (a "naïve psychology") (5). Babies know that objects are solid, persist over time (even when out of sight), fall to the ground if unsupported, and do not move unless acted upon (6). They also understand that people move autonomously in response to social and physical events, act and react in accord with their goals, and respond with appropriate emotions to different situations (5, 7, 8).

These intuitions give children a head start when it comes to understanding and learning about objects and people. However, they also sometimes clash with scientific discoveries about the nature of the world, making certain scientific facts difficult to learn. The problem with teaching science to children is thus "not what the student lacks, but what the student has, namely alternative conceptual frameworks for understanding the phenomena covered by the theories we are trying to teach" (9).

Children's belief that unsupported objects fall downward, for instance, makes it difficult for them to see the world as a sphere—if it were a sphere, the people and things on the other side should fall off. It is not until about 8 or 9 years of age that children demonstrate a coherent understanding of a spherical Earth (10), and younger children often distort the scientific understanding in systematic ways. Some deny that people can live all over Earth's surface (10), and when asked to draw Earth (11) or model it with clay (12), some children depict it as a sphere with a flattened top or as a hollow sphere that people live inside.

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4.

Nature 447, 266-267 (17 May 2007) | doi:10.1038/447266a; Published online 16 May 2007

Optics: Beyond Diffraction

Evgenii E. Narimanov & Vladimir M. Shalaev

A material with a cunningly designed optical response overcomes a fundamental limit to image resolution. This 'hyperlens' produces magnified images of objects smaller than the wavelength of the imaging light.

When an object is illuminated, information about features smaller than the wavelength of the incident light is carried in evanescent waves, whose amplitudes decrease exponentially with distance. This rapid decay means that detail is lost when an image of the object is viewed in its far field. Two papers published in Science1, 2 contain experimental details of a 'hyperlens' that circumvents this problem, turning evanescent fields into propagating waves, and so producing magnified far-field images of sub-wavelength structures.

For propagating electromagnetic waves, the wavelength defines the scale over which the accompanying electromagnetic field varies. When an object is moved by a distance much smaller than this wavelength, it will be subjected to essentially the same field as before, and an image formed by the light scattered off the object will also remain unchanged. The light's wavelength therefore gives a measure of the image resolution, generally referred to as the Abbe diffraction limit3, after the nineteenth-century German physicist Ernst Abbe.

At the heart of the hyperlens concept4, 5 lies a nanostructured 'metamaterial' whose dielectric constant — a measure of a material's response to the electric field of the incident light — has opposite signs in two orthogonal directions. The effect of this anisotropy is to do away with the lower limit on the wavelength of a propagating field that is characteristic of a conventional, isotropic medium. With no lower limit on the propagating light's wavelength, there is no diffraction limit — and so, theoretically, unbounded image resolution.

As soon as waves of very small wavelength emerge from this 'optical hyperspace' into air, however, they can no longer propagate, and again become evanescent. To deliver the sub-wavelength information carried by such waves into the far field, one must first increase their wavelength to the point when propagation in air is possible. The cylinder (or half-cylinder) geometry of the hyperlens is specifically designed to achieve this, by slowly increasing the wavelength as the field spreads away from the centre of the device

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5.

Nature 447, 273-274 (17 May 2007) | doi:10.1038/447273a; Published online 16 May 2007

Organic Chemistry: Molecular Cross-Talk

Alexander Greer

There is a long way to go before artificial enzymes can reproduce the functions of the real things. The advent of systems that generate and respond to signals may bring that ideal a step closer.

Molecules are often used as signals in biological systems, triggering reactions to various stimuli. Enzymes in plants, for example, liberate electronically excited oxygen — known as singlet oxygen — in response to stress, eliciting protective responses from other biomolecules1, 2. Such chemical cross-talk has now been demonstrated in a synthetic system, as reported by Natarajan et al.3 in the Journal of the American Chemical Society. They have designed an artificial enzyme that generates singlet oxygen and releases it into the surrounding solution. The oxygen then diffuses to another, remote artificial enzyme, where it is trapped and reacts with acceptor molecules.

Artificial enzymes have been around since the 1980s, when chemists discovered that the hydrophobic interior environment of enzymes could be mimicked by large 'host' molecules that encapsulate small 'guest' molecules4. But despite the great ingenuity applied to the design of the hosts, these systems were primitive compared with natural, highly evolved enzyme pockets. One big problem was devising recognition and capturing strategies for molecules of sufficient quality to accurately direct guests to the artificial-enzyme sites — such exquisite control is essential for reproducing the functions of natural enzymes. An understanding of molecular host–guest binding has slowly developed so that, for example, we now appreciate how non-covalent interactions can immobilize guests in a process known as constrictive binding5. It is also possible to tailor the size and shape of hosts, so that their geometry can direct chemical reactions to selected sites in a guest molecule6, 7.

Natarajan et al have used such ideas in their study3. They trapped two different guest molecules into separate hosts, permanently isolating them from each other (Fig. 1). The first guest was a photosensitizer — a compound that readily transfers light energy to other molecules, so promoting them into excited states. The second isolated guest was an alkene, which acts as an oxygen acceptor. The encapsulated photosensitizer absorbs light and — if the host is open to allow oxygen into its cavity — converts ground-state oxygen into singlet oxygen, which then escapes into the bulk solution. Some of the singlet oxygen reaches the separate alkene-containing hosts, where it reacts with the guest molecule. Because the alkene-containing hosts hold their guests in a particular orientation within the cavity, some parts of the alkene are more accessible to chemical attack than others. The singlet oxygen therefore predominantly attacks the alkene at the most accessible position, yielding mostly one product. In the absence of the host, the singlet oxygen attacks the alkene at several positions, so that a mixture of compounds forms, with no major product8.

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