Science

The ongoing fiscal and political crisis in Brazil has already caused deep cuts to science and education (“Fiscal crisis has Brazilian scientists scrambling,” H. Escobar, In Depth, 28 August, p. [909][1]), and now the environment is in the crosshairs. On 2 October, the Federal Government

The mechanisms of Late Pleistocene megafauna extinctions remain fiercely contested, with human impact or climate change cited as principal drivers. We compared ancient DNA and radiocarbon data from 31 detailed time series of regional megafaunal extinctions and replacements over the past 56,000 years with standard and new combined records of Northern Hemisphere climate in the Late Pleistocene. Unexpectedly, rapid climate changes associated with interstadial warming events are strongly associated with the regional replacement or extinction of major genetic clades or species of megafauna. The presence of many cryptic biotic transitions before the Pleistocene/Holocene boundary revealed by ancient DNA confirms the importance of climate change in megafaunal population extinctions and suggests that metapopulation structures necessary to survive such repeated and rapid climatic shifts were susceptible to human impacts.

Stable isotope analysis of the first fossilized Eremotherium laurillardi remains from Belize offers valuable insights into the conditions within which this individual lived and its ability to adapt to the increasing aridity of the Last Glacial Maximum (LGM). Cathodoluminescence (CL) microscopy was used to identify chemical alteration of the tooth during fossilization. Results demonstrate that the inner orthodentin resists diagenesis, yielding potentially unaltered values. Using an intensive “vacuum milling” technique, the inner orthodentin produced an accelerator mass spectrometry (AMS) date of 26,975 ± 120 calibrated years before the present. The stable carbon and oxygen isotope analysis of this layer shows that the tooth recorded two wet seasons separated by one longer dry season and that this sloth was able to adapt its diet to the marked seasonality of the LGM. This study offers new insights into obtaining reliable isotope data from fossilized remains and suggests that this indi...

As a postdoctoral fellow entering the market for biology faculty positions, I was happy to hear that 25% of NIH Research grants are going to new investigators who have never received an RO1 (Editorial, “Just give them grants,” A. I. Leshner, 16 May, p. [849][1]). My sense of schadenfreude was fulfilled to hear that these funds will come off the backs of senior investigators who, despite clearly being deadwood, are hogging multiple grants. But then I wondered what will happen to me in the phase between being a new investigator and a senior investigator. Surely there must be some intermediate step. The transformation from plucky young innovator to conservative graybeard cannot be instantaneous. After that first RO1, I will have some publications and some data, but not as many as my more senior competitors. And the funding situation for me will be even tighter than before, because a significant fraction of funds will be going to those undeserving, knee-biting, new investigators. Additionally, I will have reached a stage where I have significant responsibilities—graduate students and postdocs will be depending on me for their career advancement and livelihood. So I am left asking, what will happen to new investigators once their honeymoon is over? [1]: /lookup/doi/10.1126/science.1159794

The nature of the intermolecular forces between water molecules is the same in small hydrogen-bonded clusters as in the bulk. The rotational spectra of the clusters therefore give insight into the intermolecular forces present in liquid water and ice. The water hexamer is the smallest water cluster to support low-energy structures with branched three-dimensional hydrogen-bond networks, rather than cyclic two-dimensional topologies. Here we report measurements of splitting patterns in rotational transitions of the water hexamer prism, and we used quantum simulations to show that they result from geared and antigeared rotations of a pair of water molecules. Unlike previously reported tunneling motions in water clusters, the geared motion involves the concerted breaking of two hydrogen bonds. Similar types of motion may be feasible in interfacial and confined water.

Cage, Book, and Prism The array of hydrogen bonds governing the extended structure of liquid water is so intricate that chemists have often sought to understand it by studying simpler clusters. Even so, it has been challenging to get a handle on the preferred arrangement adopted by just six water molecules. Interdependent theoretical and spectroscopic studies have narrowed down the lowest-energy hexamer structures to three isomers—respectively designated the cage, the book, and the prism—but their relative energies remain uncertain. Now, Pérez et al. (p. 897 ; see the Perspective by Saykally and Wales ) have observed all three isomers in a single experiment, using Fourier transform microwave spectroscopy, and were able to establish definitively their energy ordering.

Climate influences a variety of ecological processes. These effects operate through local weather parameters such as temperature, wind, rain, snow, and ocean currents, as well as interactions among these. In the temperate zone, local variations in weather are often coupled over large geographic areas through the transient behavior of atmospheric planetary-scale waves. These variations drive temporally and spatially averaged exchanges of heat, momentum, and water vapor that ultimately determine growth, recruitment, and migration patterns. Recently, there have been several studies of the impact of large-scale climatic forcing on ecological systems. We review how two of the best-known climate phenomena—the North Atlantic Oscillation and the El Niño–Southern Oscillation—affect ecological patterns and processes in both marine and terrestrial systems.

The basis of science is the hypothetico-deductive method and the recording of experiments in sufficient detail to enable reproducibility. We report the development of Robot Scientist “Adam,” which advances the automation of both. Adam has autonomously generated functional genomics hypotheses about the yeast Saccharomyces cerevisiae and experimentally tested these hypotheses by using laboratory automation. We have confirmed Adam's conclusions through manual experiments. To describe Adam's research, we have developed an ontology and logical language. The resulting formalization involves over 10,000 different research units in a nested treelike structure, 10 levels deep, that relates the 6.6 million biomass measurements to their logical description. This formalization describes how a machine contributed to scientific knowledge.

Age-related macular degeneration (AMD), the most common cause of irreversible vision loss in individuals aged older than 50 years, is classified as either wet (neovascular) or dry (nonneovascular). Inherited variation in the complement factor H gene is a major risk factor for drusen in dry AMD. Here we report that a single-nucleotide polymorphism in the promoter region of HTRA1, a serine protease gene on chromosome 10q26, is a major genetic risk factor for wet AMD. A whole-genome association mapping strategy was applied to a Chinese population, yielding a P value of <10(-11). Individuals with the risk-associated genotype were estimated to have a likelihood of developing wet AMD 10 times that of individuals with the wild-type genotype.

Archaeological excavations at Göbekli Tepe, a transitional Neolithic site in southeast Turkey, have revealed the earliest megalithic ritual architecture with characteristic T-shaped pillars. Although human burials are still absent from the site, a number of fragmented human bones have been recovered from fill deposits of buildings and from adjacent areas. We focus on three partially preserved human skulls, all of which carry artificial modifications of a type so far unknown from contemporaneous sites and the ethnographic record. As such, modified skull fragments from Göbekli Tepe could indicate a new, previously undocumented variation of skull cult in the Early Neolithic of Anatolia and the Levant.

Ancient DNA traces the history of hepatitis B Hepatitis B virus (HBV) infections represent a worldwide human health concern. To study the history of this pathogen, Kocher et al . identified 137 human remains with detectable levels of virus dating between 400 and 10,000 years ago. Sequencing and analyses of these ancient viruses suggested a common ancestor between 12,000 and 20,000 years ago. There is no evidence indicating that HBV was present in the earliest humans as they spread out of Africa; however, HBV was likely present in human populations before farming. Furthermore, the virus was present in the Americas by about 9000 years ago, representing a lineage sister to the viral strains found in Eurasia that diverged about 20,000 years ago. —LMZ

To examine a pathway program for middle and high school students from underrepresented backgrounds designed to foster career interest in the biomedical sciences. In 2002, the Institute of Medicine released a report entitled Unequal Treatment, which examined the racial and ethnic disparities in health and health care within the United States and encouraged the development of a diverse health care workforce as a means to reduce health care disparities. Saturday Morning Science (SMS) is a program model presented as a pipeline strategy that addresses this specific recommendation. SMS is a 10-week program that emphasized the importance of science and math. Post-SMS evaluations were conducted to assess biomedical career knowledge, attitudes regarding future career plans, and the effectiveness of the program. A total of 87.5% of middle and high school students who were enrolled in SMS completed the program (113 of 130). Seventy percent of SMS participants were underrepresented minorities. Snapshot program evaluation data exposed new ideas about science (strongly agree/agree, 98%; 64 of 65), exposed new ideas about medicine (strongly agree/agree, 97%; 63 of 65, and increased desire to enter science related field (strongly agree/agree 82% (53 of 65). SMS was designed to motivate students of underrepresented ethnic backgrounds from middle through high school to attend college and prepare for careers in the health sciences. SMS students had the opportunity to interact with scientists, physicians, medical and graduate students, and other academicians. They provided direction and guidance to ensure that students had meaningful experiences specifically designed to expose them to opportunities in the biosciences.

A 20-variable instance of the NP-complete three-satisfiability (3-SAT) problem was solved on a simple DNA computer. The unique answer was found after an exhaustive search of more than 1 million (2 20 ) possibilities. This computational problem may be the largest yet solved by nonelectronic means. Problems of this size appear to be beyond the normal range of unaided human computation.