Meaning in Life: Meeting the Challenges

Responding to comments by Cheshire Calhoun and Arnold Burms, this piece clarifies some of Wolf’s ideas about the relation between meaningfulness in life, on the one hand, and reasons of love, fulfillment, and objective value, on the other. Meaning tends to come from activities whose reasons are grounded in love of a worthy (objectively valuable) object, and not necessarily from reasons having anything to do with an interest in meaningfulness itself. But what counts as a worthy object cannot be determined either from a totally neutral and impersonal point of view or from the points of view of specific other people who matter to the subject.     

Presettlement vegetation of part of northwestern Moffat County, Colorado, described from remnants

A general botanical inventory of a part of northwestern Moffat County, Colorado, resulted in the location of “ remnants ” of the presettlement vegetation spectrum that are largely unaltered by grazing, logging, or other recent human - related land uses. The 69 samples taken from these remnants were classified into 22 plant associations. Composition, structure, environmental location, geographical range, and response to disturbance are discussed for each association, and a photograph of each is presented. Seven of the 22 associations are apparently restricted to the study area. Restricted associations occur in the more extreme environments of the study area, such as on calcareous substrata or very xeric sites. More mesic sites along ephemeral creeks, on north - facing slopes, or on sandstones support plant associations that have much wider ranges, many of them extending across the northern Great Basin.        

大学非英语专业英语口语测试的研究和实践

以语言测试理论为依据,运用定量分析法,对东莞理工学院2006和2007级非英语专业学生进行了大规模英语口语测试及问卷调查,证明了英语口语测试的必要性和可行性,并探讨了中外教师携手合作进行英语口语测试的新模式及其产生的反拨作用,试图为大规模英语口语测试的改革提供一种新思路。     

Increased affiliative response to vasopressin in mice expressing the V1a receptor from a monogamous vole.

Arginine vasopressin influences male reproductive and social behaviours in several vertebrate taxa through its actions at the V1a receptor in the brain. The neuroanatomical distribution of vasopressin V1a receptors varies greatly between species with different forms of social organization. Here we show that centrally administered arginine vasopressin increases affiliative behaviour in the highly social, monogamous prairie vole, but not in the relatively asocial, promiscuous montane vole. Molecular analyses indicate that gene duplication and/or changes in promoter structure of the prairie vole receptor gene may contribute to the species differences in vasopressin-receptor expression. We further show that mice that are transgenic for the prairie vole receptor gene have a neuroanatomical pattern of receptor binding that is similar to that of the prairie vole, and exhibit increased affiliative behaviour after injection with arginine vasopressin. These data indicate that the pattern of V1a-receptor gene expression in the brain may be functionally associated with species-typical social behaviours in male vertebrates.     

Human embryonic stem cell lines derived from single blastomeres

The derivation of human embryonic stem (hES) cells currently requires the destruction of ex utero embryos. A previous study in mice indicates that it might be possible to generate embryonic stem (ES) cells using a single-cell biopsy similar to that used in preimplantation genetic diagnosis (PGD), which does not interfere with the embryo's developmental potential. By growing the single blastomere overnight, the resulting cells could be used for both genetic testing and stem cell derivation without affecting the clinical outcome of the procedure. Here we report a series of ten separate experiments demonstrating that hES cells can be derived from single blastomeres. In this proof-of-principle study, multiple biopsies were taken from each embryo using micromanipulation techniques and none of the biopsied embryos were allowed to develop in culture. Nineteen ES-cell-like outgrowths and two stable hES cell lines were obtained. The latter hES cell lines maintained undifferentiated proliferation for more than eight months, and showed normal karyotype and expression of markers of pluripotency, including Oct-4, SSEA-3, SSEA-4, TRA-1-60, TRA-1-81, nanog and alkaline phosphatase. These cells retained the potential to form derivatives of all three embryonic germ layers both in vitro and in teratomas. The ability to create new stem cell lines and therapies without destroying embryos would address the ethical concerns of many, and allow the generation of matched tissue for children and siblings born from transferred PGD embryos.     

A semiconductor source of triggered entangled photon pairs

Entangled photon pairs are an important resource in quantum optics, and are essential for quantum information applications such as quantum key distribution and controlled quantum logic operations. The radiative decay of biexcitons-that is, states consisting of two bound electron-hole pairs-in a quantum dot has been proposed as a source of triggered polarization-entangled photon pairs. To date, however, experiments have indicated that a splitting of the intermediate exciton energy yields only classically correlated emission. Here we demonstrate triggered photon pair emission from single quantum dots suggestive of polarization entanglement. We achieve this by tuning the splitting to zero, through either application of an in-plane magnetic field or careful control of growth conditions. Entangled photon pairs generated 'on demand' have significant fundamental advantages over other schemes, which can suffer from multiple pair emission, or require post-selection techniques or the use of photon-number discriminating detectors. Furthermore, control over the pair generation time is essential for scaling many quantum information schemes beyond a few gates. Our results suggest that a triggered entangled photon pair source could be implemented by a simple semiconductor light-emitting diode.     

Analysis of one million base pairs of Neanderthal DNA

Neanderthals are the extinct hominid group most closely related to contemporary humans, so their genome offers a unique opportunity to identify genetic changes specific to anatomically fully modern humans. We have identified a 38,000-year-old Neanderthal fossil that is exceptionally free of contamination from modern human DNA. Direct high-throughput sequencing of a DNA extract from this fossil has thus far yielded over one million base pairs of hominoid nuclear DNA sequences. Comparison with the human and chimpanzee genomes reveals that modern human and Neanderthal DNA sequences diverged on average about 500,000 years ago. Existing technology and fossil resources are now sufficient to initiate a Neanderthal genome-sequencing effort.     

Retroviral invasion of the koala genome

Endogenous retroviruses are a common ancestral feature of mammalian genomes with most having been inactivated over time through mutation and deletion. A group of more intact endogenous retroviruses are considered to have entered the genomes of some species more recently, through infection by exogenous viruses, but this event has never been directly proved. We have previously reported koala retrovirus (KoRV) to be a functional virus that is associated with neoplasia. Here we show that KoRV also shows features of a recently inserted endogenous retrovirus that is vertically transmitted. The finding that some isolated koala populations have not yet incorporated KoRV into their genomes, combined with its high level of activity and variability in individual koalas, suggests that KoRV is a virus in transition between an exogenous and endogenous element. This ongoing dynamic interaction with a wild species provides an exciting opportunity to study the process and consequences of retroviral endogenization in action, and is an attractive model for studying the evolutionary event in which a retrovirus invades a mammalian genome.