ScienceWeek

SCIENCEWEEK

February 16, 2007

Vol. 11 - Number 7

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We are the offspring of history, and must establish our own paths in this most diverse and interesting of conceivable universes --one indifferent to our suffering, and therefore offering us maximal freedom to thrive, or to fail, in our own chosen way.

-- Stephen Jay Gould (1941-2002)

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Contents (full text below):

1. Antennae as Gyroscopes

2. Can Droplets and Bubbles Think?

3. Quantum mechanics: The truth about reality

4. The architecture of human kin detection

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1. Science 9 February 2007: Vol. 315. no. 5813, pp. 771 - 772 DOI: 10.1126/science.1136840

Perspectives BIOPHYSICS: Antennae as Gyroscopes R. McNeill Alexander*

Flying insects need to detect unwanted movements of their own bodies, so that they can make any necessary corrections to restore the status quo. They need to know, for example, when their flight is disturbed by an eddy in turbulent air or by an imperfectly executed wing beat. Dragonflies depend on sight for this information. That works well in bright daylight but would not be satisfactory in near-darkness because eyes cannot provide precise information quickly in dim light. Moths active at night need information about unwanted movements to maintain flight stability, especially when hovering to collect nectar from flowers. On page 863 of this issue, Sane and colleagues (1) explain how a hawk moth senses its own rotations.

These researchers found that the moth's movement-detection system depends largely on the Coriolis effect, which keeps spinning gyroscopes stable. This effect is an apparent deflection of an object viewed in a rotating frame of reference, seemingly attributable to an apparent force. We already knew of the importance of Coriolis forces for dipteran flies (house flies, mosquitoes, etc.). Instead of having four wings like other insects, dipterans have only two. Their hind wings have been reduced to tiny club-shaped halteres (see the figure) that beat at the same frequency as the fore wings. If their halteres are cut off, these flies become unstable in flight and soon crash to the ground. Pringle (2) explained how Coriolis forces on the halteres inform flies of rotations of their bodies, enabling them to fly stably. Sane et al. now find that hawk moths can do this with their antennae, although detection of aerodynamic as well as Coriolis forces may have a role.

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2. Science 9 February 2007: Vol. 315. no. 5813, pp. 775 - 776 DOI: 10.1126/science.1138325

Perspectives CHEMISTRY: Can Droplets and Bubbles Think? Irving R. Epstein*

How many of us, at the close of a well-spent evening, have stared into that last glass of beer or champagne and wondered what eternal truths lie in the rising bubbles before us? In this issue, Fuerstman et al. on page 828 (1) and Prakash and Gershenfeld on page 832 (2) report their use of microfluidic technology to construct streams of droplets (liquid-in-liquid) and bubbles (gasin-liquid) that can encode and decode information or perform logical operations.

Since its emergence in the 1990s, microfluidics has become a powerful technique for a wide variety of applications in biotechnology, engineering, physics, and chemistry. By studying processes in channels with typical dimensions of tens to hundreds of micrometers, researchers can conduct controlled reactions while economizing on the consumption of possibly scarce materials. Flow in such channels can be characterized by two dimensionless numbers, the Reynolds number (Re), and the capillary number (Ca). When Re is low, inertial effects are negligible, and fluid flow is laminar and simple. In the narrow spaces of a typical microfluidic device, this is almost always the case.

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3. Nature 445, 723-724 (15 February 2007) | doi:10.1038/445723a; Published online 14 February 2007 Quantum mechanics: The truth about reality

Gregor Weihs

Hopes of keeping quantum mechanics 'real' have been dashed by new measurements of neutrons' quantum behaviour. Despite what our classical sensibilities require, the world is indeed fundamentally random.

Albert Einstein was convinced that "God does not play dice"; in other words, he could not accept quantum theory, with its inherent randomness, as a fundamental description of the world. Developing the theme in later work with Boris Podolsky and Nathan Rosen1, he hinted that he believed in a more basic layer of truth underlying quantum mechanics. This was to be expressed in 'hidden variables' that reconciled the purely statistical validity of quantum measurements with the classical, deterministic world-view. Writing in Physical Review Letters, Yuji Hasegawa et al.2 deal a further blow to these already beleaguered efforts to inject some realism into quantum physics.

Two theorems developed in the 1960s put severe constraints on attempts to complete quantum physics as Einstein intended. First, John Bell showed that theories of local hidden variables, which don't permit any remote influences, cannot explain certain quantum-physical observations3. Second, Simon Kochen and Ernst Specker independently proved that more general, so-called non-contextual hidden variables (of which more later) are also untenable4. Many experiments have since used Bell's theorem to invalidate local hidden variables. Much less work has been done on the Kochen–Specker theorem, especially for particles other than photons.

Neutrons are convenient guinea-pigs for the kind of delicate experiments needed to investigate these aspects of quantum physics: above all, they have no charge, which often makes it easier to observe the effects involved. Chief among these are the effects of spin, the property of a particle that makes it try to line up in a magnetic field. Quantum physics tells us that spin will be quantized: if you measure it along a chosen direction, it will point either in that direction or in the opposite one, but never in between. In addition, if you have measured spin in the vertical (z) direction and found it to be up, a subsequent measurement in the horizontal direction (x) will randomly yield a right or left value. Similarly, if you measure x first, the z value will be random.

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4. Nature 445, 727-731 (15 February 2007) | doi:10.1038/nature05510; Received 22 July 2006; Accepted 5 December 2006

The architecture of human kin detection

Debra Lieberman1,2, John Tooby1 and Leda Cosmides1

1. Center for Evolutionary Psychology, University of California Santa Barbara, Santa Barbara, California 93106, USA 2. Department of Psychology, University of Hawaii, Honolulu, Hawaii 96822, USA

Evolved mechanisms for assessing genetic relatedness have been found in many species, but their existence in humans has been a matter of controversy. Here we report three converging lines of evidence, drawn from siblings, that support the hypothesis that kin detection mechanisms exist in humans. These operate by computing, for each familiar individual, a unitary regulatory variable (the kinship index) that corresponds to a pairwise estimate of genetic relatedness between self and other. The cues that the system uses were identified by quantitatively matching individual exposure to potential cues of relatedness to variation in three outputs relevant to the system's evolved functions: sibling altruism, aversion to personally engaging in sibling incest, and moral opposition to third party sibling incest. As predicted, the kin detection system uses two distinct, ancestrally valid cues to compute relatedness: the familiar other's perinatal association with the individual's biological mother, and duration of sibling coresidence.

For the past 50 years, evolutionary biologists have argued that genetic relatedness should have played a role in the social evolution of species, such as humans, in which close genetic relatives frequently interact1, 2. According to kin selection theory, computational variants that allocate altruistic effort effectively with respect to kinship outcompete variants that fail to regulate behaviour conditionally in response to relatedness. The effects of relatedness have been documented in a great diversity of taxa, ranging from social amoebas3, social insects4, 5, 6 and shrimp7, to birds8, aphids9, plants10, 11, rodents12 and primates13, 14, 15. To regulate behaviour conditionally in response to different degrees of kinship, organisms require mechanisms to discriminate genetic relatedness. Such mechanisms have been discovered in a variety of nonhuman species16, 17, 18.

Equally, in long-lived, low-fecundity species with an open breeding structure (such as humans), the fitness of offspring is strongly affected by how closely parents are related. In such species, conceptive sexual behaviour between close genetic relatives produces offspring that suffer from inbreeding depression—a decline in fitness caused by rendering more deleterious recessives homozygous19, 20, 21, and aggravated by parasites targeting more genetically homogeneous sets of hosts22, 23. Consequently, heritable variants that cost-effectively reduce inbreeding depression by avoiding mating with close genetic relatives outcompete variants in which mating decisions are unaffected by relatedness.

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