Evolution by small steps and rugged landscapes in the RNA virus phi6.
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Fisher's geometric model of adaptive evolution argues that adaptive evolution should generally result from the substitution of many mutations of small effect because advantageous mutations of small effect should be more common than those of large effect. However, evidence for both evolution by small steps and for Fisher's model has been mixed. Here we report supporting results from a new experimental test of the model. We subjected the bacteriophage phi6 to intensified genetic drift in small populations and caused viral fitness to decline through the accumulation of a deleterious mutation. We then propagated the mutated virus at a range of larger population sizes and allowed fitness to recover by natural selection. Although fitness declined in one large step, it was usually recovered in smaller steps. More importantly, step size during recovery was smaller with decreasing size of the recovery population. These results confirm Fisher's main prediction that advantageous mutations of small effect should be more common. We also show that the advantageous mutations of small effect are compensatory mutations whose advantage is conditional (epistatic) on the presence of the deleterious mutation, in which case the adaptive landscape of phi6 is likely to be very rugged. (+info)
Declining survival probability threatens the North Atlantic right whale.
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The North Atlantic northern right whale (Eubalaena glacialis) is considered the most endangered large whale species. Its population has recovered only slowly since the cessation of commercial whaling and numbers about 300 individuals. We applied mark-recapture statistics to a catalog of photographically identified individuals to obtain the first statistically rigorous estimates of survival probability for this population. Crude survival decreased from about 0.99 per year in 1980 to about 0.94 in 1994. We combined this survival trend with a reported decrease in reproductive rate into a branching process model to compute population growth rate and extinction probability. Population growth rate declined from about 1. 053 in 1980 to about 0.976 in 1994. Under current conditions the population is doomed to extinction; an upper bound on the expected time to extinction is 191 years. The most effective way to improve the prospects of the population is to reduce mortality. The right whale is at risk from entanglement in fishing gear and from collisions with ships. Reducing this human-caused mortality is essential to the viability of this population. (+info)
Awareness of and attitude of elderly subjects regarding health care and welfare in rapidly ageing population in Japan.
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OBJECTIVES: We aimed to obtain information on the degree of knowledge and understanding about the current systems of health care and welfare held by the elderly, in order to achieve comprehensiveness in family practice. METHOD: We conducted a study on the awareness of healthy elderly persons by direct interview. The study was carried out in Kuni Village in a remote mountainous region in Japan, where the elderly population accounts for 24.8% of the total population. The subjects were self-dependent in their daily living activities and were aged 65 years and older. RESULTS: The subjects' knowledge of health care and welfare systems was generally good, and the degree of their utilization of these systems was also good. But 83.3% of those who did not want to utilize the welfare system indicated their preference to depend on their family for support. CONCLUSION: Family physicians must endeavour to offer comprehensive care to their patients by including these systems for rapidly ageing communities. (+info)
Light on population health status.
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A new approach to illustrating and analysing health status is presented which allows comparisons of various aspects of health in a population at different times and in different populations during given periods. Both quantitative and qualitative elements can be represented, the impact of interventions can be monitored, and the extent to which objectives are achieved can be assessed. The practical application of the approach is demonstrated with reference to the health profiles to Tunisia in 1966 and 1994. (+info)
Health of the elderly in a community in transition: a survey in Thiruvananthapuram City, Kerala, India.
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Results of a survey to assess the health and functional status of the elderly (defined as those who are 60 years or older) in Thiruvananthapuram city, the capital of Kerala state, India, are discussed. As the process of development results in longevity without concomitant economic success, traditional support systems break down. The differences in status of the elderly dependent on gender and socioeconomic class are highlighted. Women are poorer and generally suffer more morbidity than men in old age, even though their death rates are lower. The better-off among the elderly enjoy a quality of life much superior to their poor brethren. Thus, in transitional societies such as Kerala, socioeconomic status and gender play a significant role in determining the quality of life of the elderly, a finding which may have some policy implications. (+info)
Driving through: postpartum care during World War II.
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In 1996, public outcry over shortened hospital stays for new mothers and their infants led to the passage of a federal law banning "drive-through deliveries." This recent round of brief postpartum stays is not unprecedented. During World War II, a baby boom overwhelmed maternity facilities in American hospitals. Hospital births became more popular and accessible as the Emergency Maternal and Infant Care program subsidized obstetric care for servicemen's wives. Although protocols before the war had called for prolonged bed rest in the puerperium, medical theory was quickly revised as crowded hospitals were forced to discharge mothers after 24 hours. To compensate for short inpatient stays, community-based services such as visiting nursing care, postnatal homes, and prenatal classes evolved to support new mothers. Fueled by rhetoric that identified maternal-child health as a critical factor in military morale, postpartum care during the war years remained comprehensive despite short hospital stays. The wartime experience offers a model of alternatives to legislation for ensuring adequate care of postpartum women. (+info)
The dynamics of mass migration.
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We specify a set of equations defining a dynamic model of international migration and estimate its parameters by using data specially collected in Mexico. We then used it to project the a hypothetical Mexican community population forward in time. Beginning with a stable population of 10,000 people, we project ahead 50 years under three different assumptions: no international migration; constant probabilities of in- and out-migration, and dynamic schedules of out- and in-migration that change as migratory experience accumulates. This exercise represents an attempt to model the self-feeding character of international migration noted by prior observers and theorists. Our model quantifies the mechanisms of cumulative causation predicted by social capital theory and illustrates the shortcomings of standard projection methodologies. The failure to model dynamically changing migration schedules yields a 5% overstatement of the projected size of the Mexican population after 50 years, an 11% understatement of the total number of U.S. migrants, a 15% understatement of the prevalence of U.S. migratory experience in the Mexican population, and an 85% understatement of the size of the Mexican population living in the United States. (+info)
Food safety in the 21st century.
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The global importance of food safety is not fully appreciated by many public health authorities despite a constant increase in the prevalence of foodborne illness. Numerous devastating outbreaks of salmonellosis, cholera, enterohaemorrhagic Escherichia coli infections, hepatitis A and other diseases have occurred in both industrialized and developing countries. In addition, many of the re-emerging or newly recognized pathogens are foodborne or have the potential of being transmitted by food and/or drinking water. More foodborne pathogens can be expected because of changing production methods, processes, practices and habits. During the early 21st century, foodborne diseases can be expected to increase, especially in developing countries, in part because of environmental and demographic changes. These vary from climatic changes, changes in microbial and other ecological systems, to decreasing freshwater supplies. However, an even greater challenge to food safety will come from changes resulting directly in degradation of sanitation and the immediate human environment. These include the increased age of human populations, unplanned urbanization and migration and mass production of food due to population growth and changed food habits. Mass tourism and the huge international trade in food and feed is causing food and feedborne pathogens to spread transnationally. As new toxic agents are identified and new toxic effects recognized, the health and trade consequences of toxic chemicals in food will also have global implications. Meeting the huge challenge of food safety in the 21st century will require the application of new methods to identify, monitor and assess foodborne hazards. Both traditional and new technologies for assuring food safety should be improved and fully exploited. This needs to be done through legislative measures where suitable, but with much greater reliance on voluntary compliance and education of consumers and professional food handlers. This will be an important task for the primary health care system aiming at "health for all". (+info)