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Estimates of the probability that nearby explosions of supernovae have occurred during the earth's history and the biologic effects of the radiation therefrom are presented. They suggest that cosmic radiation from supernovae could have caused the extinction of many exposed animals without the simultaneous extinction of plant life. This suggests that supernovae should be considered as one possible mechanism by which fauna become extinct.
In a review of existing theories of learning, Seligman (Psychol. Rev. 77, 406-418, 1970) suggested that humans should have an evolutionary derived preparedness to associate fear-relevant (e.g. snakes) events with aversive reinforcers. The preparedness hypothesis has been extensively tested by Ohman and his colleagues. One argument against a non-preparedness explanation for the Ohman findings has been that culturally aversive stimuli, like pictures of guns have not shown the same resistance towards extinction as pictures of snakes. However, the effect of pointing a gun directly towards the S vs pointing it to the side has not been tested. Therefore both slides of guns and snakes, directed both towards and aside from the subject, were used as conditioned stimuli (CSs) in the present study. A second question that has been discussed in the preparedness-literature is the quality of the unconditioned stimulus (UCS), i.e. if only shock can act as UCS for prepared CSs. Thus, both shock and noise UCSs were used in the present study. Skin conductance responses (SCRs) were recorded as dependent measures. The results showed conditioned acquisition, i.e. larger SCRs to CS+ than to CS-, in all groups except for the shock and noise UCS groups with the gun pointing aside as CS+ (where actually larger responses were observed to the CS-, i.e. the gun pointing towards). The extinction data showed significantly larger SCRs to CS+ than to CS- for both snakes and guns directed towards the S. Strongest resistance to extinction was observed for the group with the gun pointed towards as CS+ and with noise as UCS. The gun with noise as UCS pointed towards the S was not different from the snake with shock as UCS. Taken together, the results have shown three things; (a) directing a fear-relevant CS towards the S was a potent manipulation, and especially directing a gun with noise as UCS; (b) shock was overall not superior to noise as UCS, and especially not for snake CSs; (c) a weak form of unique belongingness was demonstrated.
It is widely believed that morphological constraints are responsible for the observed pattern of decreasing major morphological innovation in both the Metazoa and Metaphytes over geological time. This is readily seen as the decreasing trend of origination of higher taxa: phyla, classes, and orders. Currently, there are two competing evolutionary hypotheses that have been proposed to explain this phenomenon: (1) the empty ecospace hypothesis and (2) the developmental constraint hypothesis. To distinguish between hypotheses 1 and 2, the change of morphological innovation before and after several mass extinction events was measured in the Crinoidea and Blastozoa. Mass extinction intervals provided a means in which to remove ecospace limiting constraints and allow the developmental constraint hypothesis to be thoroughly tested. Within the Crinoidea, disparity was measured before and after three mass extinctions. Within the Blastozoa, disparity was measured before and after two mass extinctions. For each taxon, three suites of characters were analyzed: ecological, nonecological, or "developmental" and a combination of the two previous suites plus 50 additional characters. Four different measures of disparity were used to analyze each character suite. In the majority of the cases investigated, disparity rebounds to comparable levels or in some cases higher levels in both the Crinoidea and Blastozoa. The results indicate that developmental constraints are not responsible for the decrease in disparity throughout the geologic range of the taxa. The more likely scenario is that increasingly structured ecological guilds have made it much more difficult to allow large increases in disparity.
Quantitative study of protein-protein and protein-ligand interactions in solution requires accurate determination of protein concentration. Often, for proteins available only in "molecular biological" amounts, it is difficult or impossible to make an accurate experimental measurement of the molar extinction coefficient of the protein. Yet without a reliable value of this parameter, one cannot determine protein concentrations by the usual uv spectroscopic means. Fortunately, knowledge of amino acid residue sequence and promoter molecular weight (and thus also of amino acid composition) is generally available through the DNA sequence, which is usually accurately known for most such proteins. In this paper we present a method for calculating accurate (to +/- 5% in most cases) molar extinction coefficients for proteins at 280 nm, simply from knowledge of the amino acid composition. The method is calibrated against 18 "normal" globular proteins whose molar extinction coefficients are accurately known, and the assumptions underlying the method, as well as its limitations, are discussed.
Evolutionary games have been applied as simple mathematical models of populations where interactions between individuals control the dynamics. Recently, it has been proposed to use this type of model to describe the evolution of tumour cell populations with interactions between cells. We extent the analysis to allow for synergistic effects between cells. A mathematical model of a tumour cell population is presented in which population-level synergy is assumed to originate through the interaction of triplets of cells. A threshold of two cooperating cells is assumed to be required to produce a proliferative advantage. The mathematical behaviour of this model is explored. Even this simple synergism (minor clustering effect) is sufficient to generate qualitatively different cell-population dynamics from the models published previously. The most notable feature of the model is the existence of an unstable internal equilibrium separating two stable equilibria. Thus, cells of a malignant phenotype can exist in a stable polymorphism, but may be driven to extinction by relatively modest perturbations of their relative frequency. The proposed model has some features that may be of interest to biological interpretations of gene therapy. Two prototypical strategies for gene therapy are suggested, both of them leading to extinction of the malignant phenotype: one approach would be to reduce the relative proportion of the cooperating malignant cell type below a certain critical value. Another approach would be to increase the critical threshold value without reducing the relative frequency of cells of the malignant phenotype.
In legal medicine and also in other fields of medicine a unique characterization of the optical parameters of biological objects is often necessary. In this paper a method for the description of such probes is presented. The range of wavelength considered is the 400 nm... 1100 nm part of the electromagnetic spectrum. The method is based on the determination of reflection-, transmission and extinction-coefficients. The importance of scattering in the case of nonhomogenous, anisotropic biological matter is stressed.
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Benzoporphyrin derivative (BPD) is a potent photosensitizer in biological systems. There are four structural analogues of BPD. The analogues share the same chromophor, which results in their having almost identical optical spectra, extinction coefficients, and yields of singlet oxygen. Small structural differences affect their photosensitizing potency in various biological systems, and thus make them an interesting tool to study the structure-activity relationship. The ranking of the photosensitizing potency of the analogues differed depending on the test system. The more efficient photosensitization of tumor cell lines by the highly lipophilic monoacids as compared to that by less lipophilic diacids correlated positively with the partition coefficient, and was related to the rate of diffusion into the cells. However, in the assay systems where PDT targets were located in the membrane (red blood cells hemolysis, enveloped vesicular stomatitis virus, isolated mitochondria) there was very little difference in photosensitizing potency of BPD analogues. The results indicate that the evaluation of photosensitizers is affected by the test system and thus for photosensitizers screening purposes, the choice of the test system should be made based on the intended ultimate use.
In the life of any species, extinction is the final evolutionary process. It is a common one at present, as the world is entering a major extinction crisis. The pattern of extinction and threat is very non-random, with some taxa being more vulnerable than others. Explaining why some taxa are affected and some escape is a major goal of conservation biology. More ambitiously, a predictive model could, in principle, be built by integrating comparable studies of past and present extinctions. We review progress towards both explanatory and predictive frameworks, comparing correlates of extinction in different groups at different times. Progress towards explanatory models for the current crisis is promising, at least in some well-studied taxa, but the development of a truly predictive model is hampered by the formidable difficulties of integrating studies of present and past extinctions.
The Polish Konik horse (PKH) is one of Europe's best-known native conservation breeds. Traditionally associated with the extinct Eurasian tarpan and conservation grazing, the breed has recently become the subject of multidisciplinary research encompassing genetics, ecology, health, behaviour and reproduction. This narrative review summarises current knowledge on the biological characteristics and contemporary scientific significance of the PKH. Literature published between 2005 and 2026 was identified through searches of PubMed, Scopus, Web of Science and Google Scholar and narratively synthesised. Available evidence suggests that, despite severe historical bottlenecks, the PKH has retained considerable genetic diversity and its characteristic maternal and paternal founder-line structure. Recent molecular studies have revised traditional concepts of the breed's origin, while ecological research supports its important role in conservation grazing and wetland restoration. Behavioural and reproductive studies indicate stable temperament, high reproductive efficiency and adaptation to extensive management systems. However, current knowledge is derived predominantly from observational studies, with relatively few comparative investigations and limited genomic and longitudinal data. The PKH represents a valuable model for research on conservation genetics, environmental adaptation, animal welfare, reproductive biology and ecosystem management. Further interdisciplinary studies are needed to strengthen the evidence base for conservation and breeding strategies.
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The relative positions of branching events in a phylogeny contain information about evolutionary and population dynamic processes. We provide new summary statistics of branching event times and describe how these statistics can be used to infer rates of species diversification from interspecies trees or rates of population growth from intraspecies trees. We also introduce a phylogenetic method for estimating the level of taxon sampling in a clade. Different evolutionary models and different sampling regimes can produce similar patterns of branching events, so it is important to consider explicitly the model assumptions involved when making evolutionary inferences. Results of an analysis of the phylogeny of the mosquito-borne flaviviruses suggest that there could be several thousand currently unidentified viruses in this clade.
Classical fear conditioning investigates how animals learn to associate environmental stimuli with an aversive event. We examined how the mechanisms of fear conditioning apply when humans learn to associate social ingroup and outgroup members with a fearful event, with the goal of advancing our understanding of basic learning theory and social group interaction. Primates more readily associate stimuli from certain fear-relevant natural categories, such as snakes, with a negative outcome relative to stimuli from fear-irrelevant categories, such as birds. We assessed whether this bias in fear conditioning extends to social groups defined by race. Our results indicate that individuals from a racial group other than one's own are more readily associated with an aversive stimulus than individuals of one's own race, among both white and black Americans. This prepared fear response might be reduced by close, positive interracial contact.
Incubation (rest) periods interposed during donor training regimens significantly enhance the "memory transfer" effect reported by some investigators. When extracts from ihe brains of donor rats given interpolated rest during acquisition training were injected into recipient animals, statistically reliable and experimentally reproducible "memory transfer" effects were found.
The dynamics of the spontaneous electrical activity of the rostral, dorsal, ventral and caudal claustrum was studied chronically in 12 dogs with biologically significant distinctions in the physiological state of the animals: extinction of orientative reflexes, replacement of the feeding conditions for the acid and defensive situation and elaboration of internal inhibition. The obtained data correlated with the hypothesis on an intermediate position of the claustrum between the cortex and subcortex and permit expressing a suggestion on availability in this nucleus of special representations for different physiological activities, in particular--orientative, feeding, rejecting and defensive. The ventral claustrum seems to take a maximal part in the orientative behaviour, the rostral and caudal claustrum--in the feeding behaviour, and the dorsal and ventral parts of the nucleus--in the rejecting and the defensive behaviour.