Showing papers on "Population published in 1968"

The Tragedy of the Commons

Abstract: The population problem has no technical solution; it requires a fundamental extension in morality.

Receptive fields and functional architecture of monkey striate cortex

Abstract: 1. The striate cortex was studied in lightly anaesthetized macaque and spider monkeys by recording extracellularly from single units and stimulating the retinas with spots or patterns of light. Most cells can be categorized as simple, complex, or hypercomplex, with response properties very similar to those previously described in the cat. On the average, however, receptive fields are smaller, and there is a greater sensitivity to changes in stimulus orientation. A small proportion of the cells are colour coded. 2. Evidence is presented for at least two independent systems of columns extending vertically from surface to white matter. Columns of the first type contain cells with common receptive-field orientations. They are similar to the orientation columns described in the cat, but are probably smaller in cross-sectional area. In the second system cells are aggregated into columns according to eye preference. The ocular dominance columns are larger than the orientation columns, and the two sets of boundaries seem to be independent. 3. There is a tendency for cells to be grouped according to symmetry of responses to movement; in some regions the cells respond equally well to the two opposite directions of movement of a line, but other regions contain a mixture of cells favouring one direction and cells favouring the other. 4. A horizontal organization corresponding to the cortical layering can also be discerned. The upper layers (II and the upper two-thirds of III) contain complex and hypercomplex cells, but simple cells are virtually absent. The cells are mostly binocularly driven. Simple cells are found deep in layer III, and in IV A and IV B. In layer IV B they form a large proportion of the population, whereas complex cells are rare. In layers IV A and IV B one finds units lacking orientation specificity; it is not clear whether these are cell bodies or axons of geniculate cells. In layer IV most cells are driven by one eye only; this layer consists of a mosaic with cells of some regions responding to one eye only, those of other regions responding to the other eye. Layers V and VI contain mostly complex and hypercomplex cells, binocularly driven. 5. The cortex is seen as a system organized vertically and horizontally in entirely different ways. In the vertical system (in which cells lying along a vertical line in the cortex have common features) stimulus dimensions such as retinal position, line orientation, ocular dominance, and perhaps directionality of movement, are mapped in sets of superimposed but independent mosaics. The horizontal system segregates cells in layers by hierarchical orders, the lowest orders (simple cells monocularly driven) located in and near layer IV, the higher orders in the upper and lower layers.

Walker's mammals of the world

Abstract: From aardwolves and bandicoots to yapoks and zorillas, Ernest P. Walker's Mammals of the World is the most comprehensive-the pre-eminent-reference work on mammals. Now, completely revised and updated, this fascinating guide is better than ever. Providing a complete account of every genus of mammal in all historical time, the sixth edition is 25 percent longer than its predecessor. Of the previous generic accounts, 95 percent have been substantively modified, and there are 80 new ones-among them, three remarkable, large ungulates recently discovered in the forests of Indochina. New also is a full account of the woolly mammoth, now known to have survived until less than 4,000 years ago. Each section of the book describes one genus and includes facts such as scientific and common names, the number and distribution of species, measurements and physical traits, habitat, locomotion, daily and seasonal activity, population dynamics, home range, social life, reproduction, and longevity. Textual summaries present accurate, well-documented descriptions of the physical characteristics and living habits of mammals in every part of the world. As in the last two editions, the names and distributions of every species of every genus are listed in systematic order. These lists have now been cross-checked to ensure coverage of all species in the comprehensive new Smithsonian guide, Mammal Species of the World. Facts on the biology of mammals have been brought together from more than 2,700 newly cited references, nearly all published in the last decade. Also new are the latest data on reproduction, longevity, fur harvests, numbers in the wild and in captivity, and conservation status. The sixth edition also records all official classifications of every mammal species and subspecies in the massive 1996 IUCN Red List of Threatened Animals. The illustrations-more than 1,700-include virtually every genus of mammal. Among them are pictures by such noted wildlife photographers as Leonard Lee Rue III, Bernhard Grzimek, David Pye, and Warren T. Houck. Mammals pictured here for the first time include the just-discovered giant muntjac deer of Viet Nam, a rodent known only from the Solomon Islands, a large fruit bat whose male suckles the young, and an extremely rare web-footed tenrec of Madagascar. Since its publication in 1964, Walker's Mammals of the World has become a favorite guide to the natural world for general readers as well as an invaluable resource for professionals. This sixth edition represents more than half a century of scholarship-Ernest P. Walker himself devoted more than thirty years to the original project-and remains true to Walker's vision, smoothly combining thorough scholarship with a popular, readable style to preserve and enhance what the Washington Post called "a landmark of zoological literature."

Evolutionary Rate at the Molecular Level

Abstract: Calculating the rate of evolution in terms of nucleotide substitutions seems to give a value so high that many of the mutations involved must be neutral ones.

Housing Segregation, Negro Employment, and Metropolitan Decentralization

Abstract: I. Negro residential segregation, 176. — II. Segregation in Detroit and Chicago, 178. — III. The distribution of negro employment, 179. — IV. Negro employment by occupation and industry, 183. — V. The level of nonwhite employment, 189. — VI. Suburbanization and negro employment, 191. — VII. Postwar dispersal of employment and population in Chicago, 192. — VIII. Conclusions, 196.

Linkage disequilibrium in finite populations

Abstract: A theoretical investigation has been made of the influence of population size (N) and recombination fraction (c) on linkage disequilibrium (D) between a pair of loci. Two situations were studied: (i) where both loci had no effect on fitness and (ii) where they showed heterozygote superiority, but no epistacy. If the populations are initially in linkage equilibrium, then the mean value ofD remains zero with inbreeding, but the mean ofD 2 increases to a maximum value and decreases until fixation is reached at both loci. The tighter the linkage and the greater the selection, then the later is the maximum in the mean ofD 2 reached, and the larger its value. The correlation of gene frequencies,r, in the population of gametes within segregating lines was also studied. It was found that, for a range of selection intensities and initial gene frequencies, the mean value ofr 2 was determined almost entirely byN c and time, measured proportional toN. The implication of these results on observations of linkage disequilibrium in natural populations is discussed.

The Population Bomb

Abstract: Finally with characteristic myopia those breathing a sigh of relief at the prospect of "only" 280 million Americans by 2000 AD neglect to consider what will happen in the early years of the next century as their children struggle to survive For even with luck we are doomed to continued population growth until at least 2045 and the projected population size then will be over three hundred million Hardly a pleasant prospect for a nation now failing to provide properly for 205 million people (excerpt)

Cardiovascular survey methods.

Abstract: Cardiovascular survey methods , Cardiovascular survey methods , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

The Institutionalization of the U.S. House of Representatives

Abstract: Most people who study politics are in general agreement, it seems to me, on at least two propositions. First, we agree that for a political system to be viable, for it to succeed in performing tasks of authoritative resource allocation, problem solving, conflict settlement, and so on, in behalf of a population of any substantial size, it must be institutionalized. That is to say, organizations must be created and sustained that are specialized to political activity.1 Otherwise, the political system is likely to be unstable, weak, and incapable of servicing the demands or protecting the interests of its constituent groups. Secondly, it is generally agreed that for a political system to be in some sense free and democratic, means must be found for institutionalizing representativeness with all the diversity that this implies, and for legitimizing yet at the same time containing political opposition within the system.2 Our growing interest in both of these propositions, and in the problems to which they point, can begin to suggest the importance of studying one of the very few extant examples of a highly specialized political institution which over the long run has succeeded in representing a large number of diverse constituents, and in legitimizing, expressing, and containing political opposition within a complex political system—namely, the U.S. House of Representatives. The focus of my attention here will be first of all descriptive, drawing together disparate strands—some of which already exist in the literature3—in an attempt to show in what sense we may regard the House as an institutionalized organ of government. Not all the necessary work has been done on this rather difficult descriptive problem, as I shall indicate. Secondly, I shall offer a number of speculative observations about causes, consequences, and possible lessons to be draw from the institutionalization of the House.

Cell to cell interaction in the immune response. II. The source of hemolysin-forming cells in irradiated mice given bone marrow and thymus or thoracic duct lymphocytes.

Abstract: The number of discrete hemolytic foci and of hemolysin-forming cells arising in the spleens of heavily irradiated mice given sheep erythrocytes and either syngeneic thymus or bone marrow was not significantly greater than that detected in controls given antigen alone. Thoracic duct cells injected with sheep erythrocytes significantly increased the number of hemolytic foci and 10 million cells gave rise to over 1000 hemolysin-forming cells per spleen. A synergistic effect was observed when syngeneic thoracic duct cells were mixed with syngeneic marrow cells: the number of hemolysin-forming cells produced in this case was far greater than could be accounted for by summating the activities of either cell population given alone. The number of hemolytic foci produced by the mixed population was not however greater than that produced by an equivalent number of thoracic duct cells given without bone marrow. Thymus cells given together with syngeneic bone marrow enabled irradiated mice to produce hemolysin-forming cells but were much less effective than the same number of thoracic duct cells. Likewise syngeneic thymus cells were not as effective as thoracic duct cells in enabling thymectomized irradiated bone marrow-protected hosts to produce hemolysin-forming cells in response to sheep erythrocytes. Irradiated recipients of semiallogeneic thoracic duct cells produced hemolysin-forming cells of donor-type as shown by the use of anti-H2 sera. The identity of the hemolysin-forming cells in the spleens of irradiated mice receiving a mixed inoculum of semiallogeneic thoracic duct cells and syngeneic marrow was not determined because no synergistic effect was obtained in these recipients in contrast to the results in the syngeneic situation. Thymectomized irradiated mice protected with bone marrow for a period of 2 wk and injected with semiallogeneic thoracic duct cells together with sheep erythrocytes did however produce a far greater number of hemolysin-forming cells than irradiated mice receiving the same number of thoracic duct cells without bone marrow. Anti-H2 sera revealed that the antibody-forming cells arising in the spleens of these thymectomized irradiated hosts were derived, not from the injected thoracic duct cells, but from bone marrow. It is concluded that thoracic duct lymph contains a mixture of cell types: some are hemolysin-forming cell precursors and others are antigen-reactive cells which can interact with antigen and initiate the differentiation of hemolysin-forming cell precursors to antibody-forming cells. Bone marrow contains only precursors of hemolysin-forming cells and thymus contains only antigen-reactive cells but in a proportion that is far less than in thoracic duct lymph.

Synthesis of methyl-mercury compounds by extracts of a methanogenic bacterium.

Abstract: THERE have been incidences of extensive alkyl-mercury poisoning in Japan and Sweden. In Japan a large number of people belonging to the fishing population around Minamata Bay were seriously affected by what is now called Minamata disease. This incident was traced back to pollution of the bay with the mercury containing effluent of a large chemical plant. When methyl thiomethyl-mercury was isolated from shellfish in the area of the bay it was suggested that mercury could be alkylated by “plankton and other marine life”2. It was discovered later that the spent catalyst of an acetaldehyde reactor, which caused the pollution, contained approximately 1 per cent methyl mercury; and the biological methylation of mercury was thought to be insignificant.

Nature and extent of penicillin side-reactions, with particular reference to fatalities from anaphylactic shock.

Abstract: An appraisal is made of toxic microbiogenic and allergic side effects occurring in man as a result of large amounts of penicillin increasingly used in medical and veterinary practice The allergic reactions constitute the most common and significant side effects of penicillin The major antigenic determinant in penicillin allergy the penicilloyl group derived from the penicillanic acid nucleus is common to all penicillins and explains at least in part the cross-reactivity of man to any penicillin derivative or preparation Available data do not permit conclusions as to the true frequency of allergic reactions to penicillin which are reported to vary from 07-10% in different studies in different countries Among the side effects the anaphylactic type may occur in about 0015-0004% with a fatality rate from shock of 00015-0002% among treated patients There is no convincing evidence that the frequency of allergic side effects to penicillin has increased in the last 10 years in relation to the increasing worldwide use of penicillin Persons in contact with penicillin may respond by producing antibodies the presence of which can be determined by immunological procedures and these are believed to be partly responsible for sudden penicillin side reactions Routine prospective skin testing prior to penicillin administration cannot however be generally advocated at present but in special instances it can be undertaken in cooperation with specialists and competent laboratories The present investigation includes a study of 151 anaphylactic fatalities reported to have followed penicillin administration Of these persons 14% had evidence of previous allergies of some kind 70% had received penicillin previously and 1/3 of these had already experienced prior sudden allergic reactions In most of these fatal cases the symptoms leading to death occurred within 15 minutes An Expert Committee of the World Health Organization has emphasized that most anaphylactic fatalities can be prevented by measures to reduce penicillin sensitization environmentally in the population on the 1 hand and by the preparedness of doctors on the other (authors modified) (summary in FRE)

Two-tone inhibition in auditory-nerve fibers.

Abstract: Spike discharges from single fibers in the auditory nerve of anesthetized cats were recorded with micro‐electrodes. Rates of discharge were measured as functions of the frequencies and levels of either single tones or two tones presented simultaneously. We found that the presence of a second tone diminishes the responses to the first tone if appropriate stimulus parameters are chosen. All fibers tested showed this two‐tone inhibition. Response areas and inhibitory areas were defined from isorate contours. The general characteristics of the inhibitory areas are found to be similar for a population of over 300 fibers.

The Social group of wild Chimpanzees in the Mahali Mountains

Abstract: There are more than six large groups of wild chimpanzees in the study area, which is in the north-eastern part of the Mahali Mountains of Western Tanzainia. One of these groups was provisionized, that is, customarily fed sugar cane and bananas. The characteristics of the social group of wild chimpanzees are clarified by long-term observation of the baited population. The chimpanzees live in a clear-cut social unit which consists of adult males, adult females, and immature animals. The permanency, stable membership, and integrative nature of the unit-group were confirmed during the course of this study. The size of unit-groups ranges from 30 to 80 head. The unit-group generally splits up into temporary subgroups that repeat joining and parting. The size of the subgroups of the baited population ranges from one to 28 head, the mean being 8.1 head. The centralization of a unitgroup is mainly sustained by the high sociability of adult males. The random nature of the membership of subgroups is emphasized in this paper, although subgroups are usually composed by social bonds on the basis of similar age, sex, blood relationship, and/or sexual attraction. The inter-unit-group interaction is peaceful; the subordinate unit-group avoids the dominant one. The home ranges of unit-groups overlap each other extensively, the overlapping areas being used flexibly by both unit-groups on the basis of dominance-subordination relationship. The member-exchange among unit-groups may sometimes occur, but the extent of openness or closedness of a unit-group has not been well elucidated.

Mathematical Ideas in Biology

Abstract: 1. Some consequences of scale 2. Population regulation: generations separate 3. Population regulation: generations not separate 4. The genetics of families 5. The genetics of populations 6. Target theory 7. Regulation and control 8. Diffusion and similar processes.

Adaptive significance of pigment polymorphisms in colias butterflies. i. variation of melanin pigment in relation to thermoregulation.

Abstract: The identification of the selective forces acting on natural variation in a population of organisms may be a formidable task. Only a few such identifications have been made, as in the studies of Cain and Sheppard (1954 et seq., summarized by Ford, 1964) and others on polymorphism in Cepaea snails, or the studies of Kettlewell (summary: Kettlewell, 1961) on industrial melanism in moths. The wing pigmentation of pierid butterflies presents many opportunities for this sort of analysis. Much natural variation in this system has been noted in the genera Pieris and Colias (Bowden, 1961, 1963; Gerould, 1923; Remington, 1954). These insects deposite two kinds of pigment in their wing scales: melanin, which is black, and pteridines, which may be white, yellow, orange, or red. The wings of different Colias species may possess any of the latter shades as

The Reliability and Validity of the Psychiatric Assessment of the Child: I. Interview with the Child

Abstract: A half-hour diagnostic psychiatric interview was described for use with 7- to 12-year-old children. Four studies of reliability and validity were reported. Inter-rater reliability was examined by having children interviewed by one psychiatrist while a second psychiatrist observed without taking part. At the end of the interview, without any discussion, both psychiatrists independently made separate ratings of the child's psychiatric state. Re-test reliability was examined by having a further series of children interviewed twice, once by each author, with an interval of 1 to 30 days between the interviews. Validity was tested by comparing the interview findings for a randomly selected sample of the general population and a sample of children judged to have psychiatric disorder on the basis of information from teachers and parents. The interviewing psychiatrist knew only the child's name and age and was unaware of the selection group from which the child was drawn. A short psychiatric interview with a child was found to be a reasonably sensitive diagnostic instrument which could give rise to reliable and valid judgments on whether the child exhibited any psychiatric disorder. However, on the whole, individual ratings on specific aspects of behaviour proved to be less reliable than the overall psychiatric diagnosis. There were also marked differences in the reliability and usefulness of the various specific ratings. Depression proved to be a more difficult item than anxiety to rate reliably, but both were found to be reasonably efficient in the differentiation of the child with psychiatric disorder. The child's attention or persistence on cognitive tasks was also rated fairly reliably, and proved to be a surprisingly good indicator of psychiatric disorder. The child's emotional responsiveness at interview and the relationship he formed with the psychiatrist could be rated reliably, and these items also effectively differentiated children with psychiatric disorder from "control" children in the general population. Some of the inferences involved in the diagnostic process were examined in relation to the assessment of anxiety. It was shown, for example, that whereas fidgetiness is commonly taken to be an indicator of anxiety this assumption is frequently misleading. Tension and tremulousness were also less useful indicators of anxiety than tearfulness, an anxious expression and preoccupation with anxiety topics at interview. The main uses and limitations of the interview have been briefly discussed. It is concluded that the interview with the child (aged 7 to 12 years) forms a useful part of the diagnostic procedure in child psychiatry.

Structural modulations of plasmalemmal vesicles.

Abstract: Structural modulations affecting a small fraction of the population of plasmalemmal vesicles of vascular endothelia are described. They include forms which are apparently produced by the fusion of the vesicular membrane with the plasmalemma and by the successive elimination of the layers of the two fused membranes. Such modulations are assumed to represent stages in the discharge process of vesicular contents. Other forms, characterized by their flask shape and elongated neck, are assumed to represent stages in the formation and loading of membrane invaginations, followed by their being pinched off to form isolated vesicles. Stages in a membrane-fusion process leading to the formation of apertured fenestrae and channels are also described in fenestrated endothelia. The visualization of these structural details is greatly facilitated by staining tissue specimens with uranyl acetate before dehydration.

The introduction, increase, and crash of reindeer on St. Matthew Island.

Abstract: Reindeer (Rangifer tarandus), introduced to St. Matthew Island in 1944, increased from 29 animals at that time to 6,000 in the summer of 1963 and underwent a crash die-off the following winter to less than 50 animals. In 1957, the body weight of the reindeer was found to exceed that of reindeer in domestic herds by 24 53 percent among females and 46 61 percent among males. The population also responded to the high quality and quantity of the forage on the island by increasing rapidly due to a high birth rate and low mortality. By 1963, the density of the reindeer on the island had reached 46.9 per square mile and ratios of fawns and yearlings to adult cows had dropped from 75 and 45 percent respectively, in 1957 to 60 and 26 percent in 1963. Average body weights had decreased from 1957 by 38 percent for adult females and 43 percent for adult males and were comparable to weights of reindeer in domestic herds. Lichens had been completely eliminated as a significant component of the winter diet. Sedges and grasses were expanding into sites previously occupied by lichens. In the late winter of 196364, in association with extreme snow accumulation, virtually the entire population of 6,000 reindeer died of starvation. With one known exception, all of the surviving reindeer (42 in 1966) were females. The pattern of reindeer population growth and die-off on St. Matthew Island has been observed on other island situations with introduced animals and is believed to be a product of the limited development of ecosystems and the associated deficiency of potential populationregulating factors on islands. Food supply, through its interaction with climatic factors, was the dominant population regulating mechanism for reindeer on St. Matthew Island. St. Matthew Island, 128 square miles in area and located in the Bering Sea Wildlife Refuge in the north central Bering Sea (Fig. 1), supports a poorly developed land fauna. Native land mammals are restricted to a vole (Microtus abbreviatus) and the arctic fox ( Alopex lagopus ), although a resident population of polar bears (Thalarctos maritimus) existed there in Recent times (Elliot 1882). The reindeer on St. Matthew Island were the result of the release of 24 females and 5 males on August 20, 1944, by the U. S. Coast Guard (Klein 1959). Shortly afterwards, the Coast Guard loran station on the island was abandoned and the island has been uninhabited since then. Specimens taken for study purposes and those shot by Coast Guard personnel as a recreational pursuit have been the only harvest from the herd. With the exception of 10 in 1966, these were all taken during 1957-63 and totaled 105 animals. This paper reports on the population dynamics and range interrelationships of this island reindeer herd from the time of introduction through its rapid increase and crash die-off until July, 1966. I appreciate the field cooperation of colleagues Dr. Francis H. Fay, Dr. Vernon L. Harms, Jack Manley, and Gerry Cowan and the assistance of James Whisenhant and Dr. Detlef Eisfeld. Dr. Eisfeld also did the analyses of the reindeer ovarian material and, through discussion, provided useful suggestions for the interpretation of the data. Sam Harbo provided advice in the statistical treatment of data.

Investigation of deaths from pulmonary, coronary, and cerebral thrombosis and embolism in women of child-bearing age.

Abstract: The use of oral contraceptives in the United Kingdom has increased progressively during the past seven years and it is estimated that between 10 and 15% of married women were regularly using this method of contraception in 1967. During these years numerous accounts have been published in the medical and lay press of individual or small groups of patients who developed thromboembolic disorders while taking oral contraceptives. In the three-and-a-half-year period ending 31 December 1967 the Committee on Safety of Drugs received 1,024 reports of thrombosis or embolism occurring after the use of oral contraceptives or similar preparations. Eighty-eight of these reports referred to a fatal episode. The Food and Drug Administration (1963) in the U.S.A. reviewed some 350 reports of thrombosis or embolism in women taking Enovid (a mixture of norethynodrel and mestranol, marketed in the United Kingdom as Enavid). As no informa tion was available about the morbidity from these conditions in women not using oral contraceptives, the Food and Drug Administration confined its attention to reports of death. The mortality from thromboembolic disease among users of oral contraceptives was estimated to be 12.1 per million women per year, compared with 8.4 per million in the general population, and this difference in mortality rates was not statistically significant. In 1966 the Food and Drug Administration showed that among the five million women estimated to have been taking oral contraceptives in the United States in 1965, 85 deaths from " idiopathic " thromboembolism would have been expected on the basis of national mortality statistics, whereas only 13 such deaths were reported. It was suggested that physicians in the United States were becoming increasingly fearful of reporting adverse reactions because of the risk of litigation. In the same year the Committee on Safety of Drugs was informed of 19 thromboembolic deaths among the 400,000 women who were estimated to have been using c-al contra ception in the United Kingdom. Ten of the 19 women had no recognized predisposing conditions. In November 1965 the Committee on Safety of Drugs (Cahal, 1965) published its findings up to the end of August 1965. In the preceding 12-month period 16 deaths from thrombo embolism had been reported among users of oral contraceptives. Thirteen deaths would have been expected on .the basis of the Registrar General's statistics, and the Committee did not regard the difference as clear evidence of a thrombogenic effect. They did point out, however, that, whereas only two cases of pul monary embolism would have been expected, eight had been reported. The Committee therefore decided to enlarge the scope of its investigation to include all deaths from thrombosis or embolism in women of child-bearing age recorded by the Registrars General in England and Wales and Northern Ireland in 1966. Protocols for the investigation were considered by the Committee during the last quarter of 1965, and the study began on 1 January 1966. During 1966 and early 1967 studies were also undertaken by the Royal College of General Practitioners of patients with thromboembolic disease seen in general practice and by the Medical Research Council's Statistical Research Unit of women admitted to hospital. In April 1967 the results of these two studies, together with those of the Committee on Safety of Drugs, were considered by a subcommittee of the Medical Research Council under the chairmanship of Lord Platt, and a preliminary report to the Council was published in May 1967. Though two of the investigations were at that time incomplete it was concluded that there could be no reasonable doubt that some types of thromboembolic disorder were caused by oral contraceptives. From the preliminary results of the investi gation by the Committee on Safety of Drugs it was estimated that the risk of death from thromboembolism among women who used oral contraceptives might amount to an excess of three deaths per 100,000 women per year over the correspond ing mortality in non-users. The Royal College of General Practitioners has published a full report of its investigation elsewhere (Royal College of General Practitioners, 1967), and that of the Medical Research Council's Statistical Research Unit appears elsewhere in this issue (Vessey and Doll, 1968). The present communication describes the final results of the investigation of deaths under taken by the Committee on Safety of Drugs.

The Genetics of Inbreeding Populations

Abstract: Publisher Summary This chapter discusses the effects of inbreeding in terms of genetic models of steadily increasing complexity. It correlates theoretical effects with observations and measurements that show that inbreeding populations contain large amounts of genetic variability and that this variability is organized into highly integrated and flexible systems. The observed structure of inbreeding populations results from an appropriate integration of inbreeding into the constellation of genetic and ecological factors that are involved in the regulation of variability and maintenance of flexibility. An understanding of the genetic structure of inbreeding species derives from the combining analyses of theoretical models with studies on experimental and natural populations. Inbreeding can arise in populations either as a result of various mechanisms that affect the mating system, or from restrictions in actual or effective population size. The theoretical effects of inbreeding are introduced in terms of single-locus population models in which population size is assumed sufficiently large to avoid sampling effects and in which it is assumed that selective values, mating system parameters, and other population parameters are constant in all environments. The effects on population structure of linkage and epistatic interactions among different polymorphisms are considered in terms of multilocus genetic models involving deviations from a fixed optimum, heterotic models, and mixed optimum-heterotic models.

The length and variability of the human menstrual cycle.

Abstract: The Center for Population Research collected 30,655 recorded menstrual cycles from 2,316 women. Ninety-five percent of all cycles were between 15 and 45 days long. The mean and standard deviations for the total number of cycles were 29.1 and 7.46, respectively. Cycle lengths between 15 and 45 days averaged 28.1 days with a standard deviation of 3.95 days. Variability of menstrual-cycle lengths is highest for women under 25 years of age and declines steadily to reach a minimum for ages 35 to 39. It is then followed by a slight increase for women aged 40 to 44. The pattern of variability by age is demonstrated equally well by the percent of cycles between 25 and 31 days in length as by the standard deviation.

Genetic variability maintained in a finite population due to mutational production of neutral and nearly neutral isoalleles.

Abstract: 1. The average and the effective numbers of alleles maintained in a finite population due to mutational production of neutral isoalleles were studied by mathematical analysis and computer simulation.2. The exact formula was derived for the effective number (ne) of alleles maintained in a population of effective size Ne, assuming that there are K possible allelic states and mutation occurs with equal frequency in all directions. If the number of allelic states is so large that every mutation is to a new, not pre-existing, allele, we have ne = 4Neu+1 − 2Neu2, where u is the mutation rate. Thus, the approximation formula, ne = 4Neu+1, given by Kimura & Crow (1964) is valid as long as 2Neu2 ≪ 1.3. The formula for the average number of alleles (na) maintained in a population of actual size N and effective size Ne was derived by using the method of diffusion approximation. If every mutation is to a new, not pre-existing, allele, we obtainwhere M = 4Neu. The average number of alleles as a function of M and N is listed in Table 1.4. In order to check the validity of the diffusion approximations, Monte Carlo experiments were carried out using the computer IBM 7090. The experiments showed that the approximations are satisfactory for practical purposes.5. It is estimated that among the mutations produced by DNA base substitutions, synonymous mutations, that is, those which cause no alterations of amino acids, amount roughly to 0·2–0·3 in vertebrates. Incompletely synonymous mutations, that is, those which lead to substitution of chemically similar amino acids at a different position of the polypeptide chain from the active site and therefore produce almost no phenotypic effects, must be very common. Together with synonymous mutations, they might constitute at least some 40% of all mutations. These considerations suggest that neutral and nearly neutral mutations must be more common than previously considered.

Factors Influencing Shell Shape in the Mussel Mytilus Edulis

Abstract: An attempt is made to explain the great variations in gross shell morphology noted in field populations of Mytilus edulis.In any one mussel population, variation in shell form can be attributed to differences in age, old mussels having proportionately heavier shells where width often exceeds shell height. This is invariably accompanied by down-turned, divergent umbones and varying degrees of incurvature of the ventral shell margin.Variations in the age structure of mussel populations from different habitats can also account for local variability in shell morphology. Localities where the life expectancy of mussels is increased due to absence of predators (especially in the upper shore) reveal a high incidence of old ‘ungulate’ individuals, whereas populations in which the mussel turnover is more rapid show a preponderance of relatively young mussels.Shell morphology is greatly influenced by growth rate and density. These probably exert their effect through physical compression which is maximum in localities of fast growth and high density and least in areas of slow growth and low density. High compression leads to an elongate form whereas low compression results in higher, more triangular shaped shells. Growth rates and densities, even within the same habitat, are, however, exceedingly variable.Since all environmental conditions vary in both time and space, wide variation in shell morphology is to be expected, even in animals from the same locality.Transplantation experiments indicate that variation in shell morphology is essentially phenotypic, older animals being more likely to exhibit a form which is characteristic of their particular habitat. Smaller mussels from widely different habitats show remarkable similarity in shell morphology.