Older and Smarter?

For more than a half century, researchers have debated the effects of birth order on intellectual performance. Although numerous studies have noted a negative association between the two, critics have argued the results citing uncontrolled differences in factors such as family size, parental IQ, and socioeconomic status. In a new study in the 22 Jun 2007 Science, Kristensen and Bjerkedal reported results from a study of nearly 250,000 Norwegian 18- and 19-year-olds showing that older siblings had higher intelligence quotient (IQ) scores than younger siblings. To test whether the difference could be due to biological factors, as some have proposed, the researchers looked at the scores of young men who became the eldest in the household after an older sibling(s) had died. Their scores, it turns out, were similar on average to those of biological firstborns. These results suggest that the relation between birth order and IQ is dependent on social rank in the family as opposed to true biological rank. An accompanying Perspective by F. J. Sulloway discussed some of the competing theories about birth order and intelligence and their ability to account for the tendency of younger siblings to score higher IQ scores than older siblings when tests are given under the age of about 12.


How Punishment Emerges

In cooperative human societies, punishment is an effective means of discouraging noncooperative, free-loading behavior. From an evolutionary perspective, however, doling out punishment is personally costly (in terms of time and energy, for example). This leads to the question of how punishing behavior can gain a foothold in a population in the first place. In a Report in the 29 Jun 2007 Science, Hauert et al. presented a simple mathematic model to help explain this dilemma. Traditional models of cooperative behavior dictate that participation is compulsory and include cooperators (those who contribute to a collective action), defectors (those who do not contribute but benefit from the public good), and punishers, who act against the defectors. The new work shows that adding a fourth type of individual -- the abstainer -- who neither contributes to the collective good nor consumes the benefits, leads to a more stable society in which the norm is to contribute and in which punishers flourish in order to make defectors conform to the group’s norms. Paradoxically, therefore, the freedom to withdraw from the common enterprise allows the possibility of enforcement to persist. A related Perspective by R. Boyd and S. Mathew and a podcast interview with Dr. K. Sigmund, senior author of the study, highlighted the findings.


Neuronal Networking

Studies of how individual neurons respond to sensory inputs or motor decisions in discrete regions of the brain have revealed important insights into the physiological basis of cognition and behavior. However, it is now clear that distinct regions of the mammalian brain must synchronize their activity to support certain organized behaviors. Two Reports in the 15 Jun 2007 Science offered new details about the neuronal interactions that influence visual attention and processing. Saalmann et al. simultaneously measured neuronal activity in the medial temporal (MT) area -- a brain region important for the perception of movement early in the visual pathway -- and the posterior parietal cortex, which is involved in more downstream spatial processing, of macaques performing a visual matching task. The team showed that feedback from the latter region amplifies activity in the former, presumably allowing the monkeys to focus their attention on a specific location in space. Womelsdorf et al. analyzed activity in areas of the cat and monkey brain involved in visual processing and found that the interaction of two neuronal groups depended on the phase relation between their rhythmic activities. As noted in an accompanying Perspective by R. T. Knight, "[t]he studies show that network interactions among anatomically discrete brain regions underlie cognitive processes and dispel any phrenological notion that a given innate mental faculty is based solely in just one part of the brain."


Itch Relief from Cannabinoids

Cannabinoids are a class of chemicals that may be best known for the psychoactive properties they impart to marijuana. But the body also produces cannabinoids, which perform various regulatory functions and have been implicated in a growing number of physiological roles in the central and peripheral nervous systems. According to a Report in the 8 Jun 2007 Science, these chemicals also appear to play an important role in regulating allergic response. Karsak et al. found that genetically engineered mice lacking two known cannabinoid receptors developed allergic contact dermatitis -- an itchy skin rash in response to specific allergens -- on the skin around their metal ear tags. Wild-type mice only showed an allergic response when they were treated with drugs that block cannabinoid receptors. Treatment of the afflicted mice with cannabinoids, either topically or by injection, reduced their inflammation. Although the precise molecular mechanism underlying the protective role of endocannabinoids and their receptors against contact skin allergy is not clear, the results point to a new target for potential therapeutic intervention.


Genes and Disease

By scanning the genomes of thousands of people and comparing the sick with the healthy, researchers are uncovering DNA variations that confer increased risk for a number of common ailments (see the related News Focus by J. Couzin and J. Kaiser in the 11 May issue). A slew of these genome-wide association studies were published in Science this month, adding to the growing catalog of genetic markers associated with disease.

--In the 1 Jun issue (published online 26 Apr), the Diabetes Genetics Initiative, Zeggini et al., and Scott et al. conducted comprehensive surveys of the human genome to identify gene variants that affect risk of type 2 diabetes, a disease that afflicts more than 170 million people worldwide. Sharing their data to increase the statistical power of their results, the team confirmed that at least 10 genetic loci (including 3 not previously identified) contribute to type 2 diabetes risk, each with a modest effect.

--In the 8 June issue (published online 3 May), McPherson et al. and Helgadottir et al. screened for genetic factors that contribute to heart disease. They found that about one of every four Caucasians are homozygous for (carry two alleles) a sequence variant on chromosome 9 that confers elevated risk of disease. The relevant genomic region contains no annotated genes, so the mechanism by which it influences heart disease remains unclear.


Alternative Symbiosis

The symbiosis between legumes, such as peas and soybeans, and nitrogen-fixing soil bacterial called rhizobia has been shown to be mediated by nodulation or Nod factors -- signals secreted by the bacteria that enable them to infect the plant and initiate formation of nodules on the host plant’s roots. These nodules provide an optimal environment within which the microbes convert free nitrogen to ammonia, which the plant uses to grow. In a Research Article in the 1 Jun 2007 Science, Giraud et al. report that some legume-nodulating rhizobia can initiate symbiosis by alternative means. The team determined the complete genome sequence of two species of symbiotic, photosynthetic rhizobia that form nodules on the roots and stems of an aquatic legume and found that both species lack the canonical *nodABC* genes that are required for Nod factor synthesis. Analyses of mutants defective in their ability to induce nodulation indicates that a purine derivative may play a key role in triggering nodule formation in this atypical symbiosis. An accompanying Perspective by J. A. Downie highlighted the study.


Biocalcification Clues

Multicellular animals (metazoans), from primitive sponges to mollusks, insects, and vertebrates, use minerals like calcium carbonate and silica to form skeletal structures including bones, shells, and coral reefs. The process of biocalcification arose among diverse animal lineages during the "Cambrian explosion" between 530 and 520 million years ago, a fact that has led researchers to wonder whether these organisms inherited a common genetic toolkit for this purpose, or whether the ability to biocalcify evolved independently in different lineages. In a Report in the 29 Jun 2007 Science, Jackson et al. looked to the sponge *Astrosclera willeyana*, a prolific reef-building organism that has survived from the Mesozoic era (250 million to 65 million years ago), to address this question. Using a paleogenomics approach, including gene- and protein-expression techniques and phylogenetic reconstructions, the team showed that a key component of the carbonate skeleton-building process was the precursor to the alpha-carbonic anhydrases (alpha-CAs) -- a gene family used by extant animals in a variety of fundamental physiological processes including ion transport and biomineralization. The team isolated sequences from *A. willeyana* that are homologous to known alpha-CAs and together with similar sequences from a related sponge form a sister group to alpha-CAs from all other metazoans. These findings suggest that the last common metazoan ancestor may have possessed a single alpha-CA gene that has subsequently duplicated and diversified in sponges and other animals. An accompanying Perspective by Taylor et al. highlighted the findings.


Insights into Plant Domestication

The spread of agriculture, made possible by the domestication of crops, transformed humanity from communities of foragers to more complex societies fueled by farming and food surpluses. A collection of articles in the 29 June 2007 Science explored various aspects of plant domestication, from new revelations about its ancient origins to its impacts on today’s ecosystems. As noted in a News Focus by M. Balter growing data suggest that the road from gathering wild plants to cultivating them and finally domesticating them was long and winding, and that plants were domesticated independently in many parts of the globe ( listen to a related podcast interview). In a related Report, Dillehay et al. presented new radiocarbon dates from agricultural sites in northern Peru showing that cultivation of squash began around 10,000 years ago, followed by peanuts about 8500 years ago, and cotton by 6000 years ago. These data suggest that horticulture took hold in the Americas nearly as early as it did in many parts of the Old World.

Meanwhile, Dubcovsky and Dvorak reviewed recent insights from molecular genetics and genomics to understand how gene mutations and genome ploidy (the number of chromosome sets in a cell) paved the way for successful domestication of our modern cultivated wheat varieties. And Kareiva et al. reviewed the influences of plant and animal domestication on the global ecosystem. On average the net benefits of domestication to humankind have been positive, but the authors note that scientists can help to more wisely shape the future path of domestication by quantifying tradeoffs such as reduced biodiversity and ecosystem resilience. Dr. Kareiva discussed these ideas in a related podcast interview.


Walking on Twos

Walking upright on two legs is one of the defining features that make us human. It has generally been assumed that bipedalism arose sometime after the divergence of the human lineage from those of chimpanzees and other great apes. But findings reported by Thorpe et al. in the 1 Jun 2007 Science now suggest that the earliest stages of upright walking evolved even earlier -- in apes living in trees rather than in hominids walking on the ground. The team observed that orangutans, a more distant relative of humans than chimps, walk in a way that resembles human bipedal movement when they navigate thin, flexible tree branches. Whereas chimpanzees and other apes that occasionally stroll upright during foraging do so with bent knees, orangutans -- using their hands for stability -- keep their knees and hip joints extended, like humans running on springy athletic tracks do. These observations suggest that the ancient ability to walk upright was retained from a common great ape ancestor and increasingly used by ancestral humans as they moved out of the trees, whereas chimps and gorillas lost this ability and independently acquired knuckle walking as their predominant mode of locomotion. An accompanying Perspective by P. O’Higgins and S. Elton and a related podcast interview with senior author Dr. Crompton, highlighted the Report.


Earthquakes in Parallel

Many of the world’s most disastrous earthquakes and volcanic eruptions take place at subduction zones -- areas under the ocean where one tectonic plate collides with another, sending sections of Earth’s crust down into the mantle. The deep layers of seismic activity in these areas are called Wadati-Benioff zones and can be found as deep as 700 km. Some areas are known to host parallel planes of seismicity referred to as double Benoiff zones, or DBZ s, but these have been thought to be rare. Not so, according to a Report by Brudzinski et al. in the 8 Jun 2007 Science. Analysis of global seismicity catalogs and characterization of the layer separation at 16 subduction zones revealed two parallel seismic strips, rather than a single broad zone, in most cases. The team also found that older oceanic plates show a greater distance between regions of seismicity than younger ones. As noted in an accompanying Perspective by A. Rietbrock, the widespread occurrence of DBZs -- typically between 50 and 300 km deep -- sets important new constraints on the geophysical and geochemical processes that give rise to earthquakes.


Carbon Sinks Reconsidered

Of all of the carbon dioxide emitted into the atmosphere from human activities, including fossil fuel burning and deforestation, less than half of it actually stays there; the rest is absorbed by the world’s oceans, and by the terrestrial biosphere. Understanding how these sinks will respond to growing carbon dioxide inputs has important implications for our predictions of future climate change. Two Reports in the 22 Jun 2007 Science challenge our current view of the global carbon cycle. Le Quéré et al. (published online 17 May) reported that the rate of uptake by the Southern Ocean -- one of the most important carbon dioxide sinks -- has slowed since 1981 relative to the trend expected for the large increase in atmospheric CO2. The authors attribute the decrease to increased Southern Ocean winds, also the result of human activities, which increase the outgassing of natural carbon dioxide (listen to an interview with Dr. Le Quere in the 18 May podcast). Turning their attention to terrestrial carbon sinks, Stephens et al. measured the vertical atmospheric CO2 distribution at 12 sites around the globe and compared the profiles with corresponding predictions from 12 atmospheric transport models. Their results suggest that the Northern Hemisphere plays a smaller role in carbon dioxide uptake than previously thought and that the tropics may actually be strong carbon sinks as opposed to a net carbon source. An accompanying Perspective by D. F. Baker highlighted the studies.


Solar Core Dynamics

Mechanical waves generated deep within the Sun, reflected in oscillations on the solar surface, can reveal details about the star’s inner structure. Pressure waves or "p modes" trapped in the Sun’s outer layers have long been observed, but they provide limited information about the Sun’s dense inner core, where energy-generating fusion reactions occur. Gravity waves or "g modes" propagate near the center of the Sun and can potentially provide more information about the solar center, but they are very weak at the Sun’s surface making their detection difficult. Now, in a Report in the 15 Jun 2007 Science, published online 3 May, García et al. report the observation -- from 10 years of data captured by the Global Oscillation at Low Frequency (GOLF) instrument aboard the Solar and Heliospheric Observatory -- of a periodic structure in the solar power spectrum that is characteristic of g modes (see the related News story by R. A. Kerr in the 4 May issue). Moreover, comparison of the observed data with predicted g modes from solar models suggests that the core is spinning faster than the surface. An accompanying Perspective by F. Hill noted that although the results are exciting, detection of the g mode signature in the original data set still needs to be confirmed by independent analysis.


Energy in Translation

Researchers have generally assumed that the energy dynamics of reactions involving small molecules with two and three atoms were relatively simple. The vibrational energy of the chemical bonds, as opposed to translational energy (energy produced by the movement of atoms or molecules, by heating for example) was thought to be the primary driver of reactivity. Now results from a new study reported in the 22 Jun 2007 Science challenge that paradigm. Yan et al. explored the role of vibrational and translational energy in a prototypical reaction of a polyatomic molecule using precisely controlled molecular collision experiments. To their surprise, they discovered that when the molecule CHD3 collides with a Cl atom to produce CD3 and HCl, translational energy promotes the reaction as effectively as the vibrational energy involved in stretching of the C-H bond. These findings suggest that even relatively small molecules have highly complex energy distribution dynamics. An accompanying Perspective by F. F. Crim highlighted the study.

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In Science’s STKE

Circadian Calcium Oscillations

Many organisms have a daily internal pacemaker -- a circadian clock -- that regulates the timing of various physiological processes throughout the day and anticipates the daily and seasonal changes of the surrounding environment. In both plants and animals, researchers have discovered slow oscillations in the cytosolic concentration of free calcium ions that span the entire day. This daily oscillation is thought to encode circadian clock signaling information, but the physiological activities that it regulates and the underlying mechanisms that maintain are unclear. In a Perspective in the 12 Jun 2007 issue, Imaizumi et al. highlighted recent work showing that the extracellular calcium-sensing receptor (CAS) plays an important role in generating calcium oscillation in plants. The authors summarized other major findings regarding the daily oscillation of calcium and discussed its hypothetical biological role in plants.

Also in STKE this month:
--Schrum et al. presented a protocol for the analysis of coimmunoprecipitated proteins by flow cytometry (IP-FCM) ( 5 Jun 2007)
--Gadina and Jefferies discussed nuclear and receptor-mediated roles of interleukin-33 in the inflammatory response ( 12 Jun 2007)
--Trivedi et al. described a method useful for investigating the biochemistry and regulation of the early tethering and docking steps of lysosome and phagosome interactions ( 26 Jun 2007)