Survival of cancer patients in urban and rural areas of Germany—A comparison

BackgroundCancer care services including cancer prevention activities are predominantly localised in central cities, potentially causing a heterogeneous geographic access to cancer care. The question of an association between residence in either urban or rural areas and cancer survival has been analysed in other parts of the world with inconsistent results. This study aims at a comparison of age-standardised 5-year survival of cancer patients resident in German urban and rural regions using data from 11 population-based cancer registries covering a population of 33 million people.Material and methodsPatients diagnosed with cancers of the most frequent and of some rare sites in 1997–2006 were included in the analyses. Places of residence were assigned to rural and urban areas according to administrative district types of settlement structure. Period analysis and district type specific population life tables were used to calculate overall age-standardised 5-year relative survival estimates for the period 2002–2006. Poisson regression models for excess mortality (relative survival) were used to test for statistical significance.ResultsThe 5-year relative survival estimates varied little among district types for most of the common sites with no consistent trend. Significant differences were found for female breast cancer patients and male malignant melanoma patients resident in city core regions with slightly better survival compared to all other district types, particularly for patients aged 65 years and older.ConclusionWith regard to residence in urban or rural areas, the results of our study indicate that there are no severe differences concerning quality and accessibility of oncological care in Germany among different district types of settlement.     

Disentangling herbivore impacts on Populus tremuloides: a comparison of native ungulates and cattle in Canada’s Aspen Parkland

Ungulates impact woody species’ growth and abundance but little is understood about the comparative impacts of different ungulate species on forest expansion in savanna environments. Replacement of native herbivore guilds with livestock [i.e., beef cattle (Bos taurus)] has been hypothesized as a factor facilitating trembling aspen (Populus tremuloides Michx.) encroachment into grasslands of the Northern Great Plains. We used a controlled herbivory study in the Parklands of western Canada to compare the impact of native ungulates and cattle on aspen saplings. Native ungulate treatments included a mixed species guild and sequences of herbivory by different ungulates [bison (Bison bison subsp. bison), elk (Cervus elaphus) then deer (Odocoileus hemionus); or deer, elk, then bison]. Herbivory treatments were replicated in three pastures, within which sets of 40 marked aspen saplings (<1.8 m) were tracked along permanent transects at 2-week intervals, and compared to a non-grazed aspen stand. Stems were assessed for mortality and incremental damage (herbivory, leader breakage, stem abrasion and trampling). Final mortality was greater with exposure to any type of herbivore, but remained similar between ungulate treatments. However, among all treatments, the growth of aspen was highest with exposure only to cattle. Herbivory of aspen was attributed primarily to elk within the native ungulate treatments, with other forms of physical damage, and ultimately sapling mortality, associated with exposure to bison. Overall, these results indicate that native ungulates, specifically elk and bison, have more negative impacts on aspen saplings and provide evidence that native and domestic ungulates can have different functional effects on woody plant dynamics in savanna ecosystems.     

Paleobiogeography of Mesozoic brachiopod faunas from Andean–Patagonian areas in a global context

During the Mesozoic, the Andean region has played a hinging role between high- and low-latitude faunas, which are, respectively, characterized by stocks that display long-term fidelity. This paper is aimed at providing an updated review of Late Triassic to Late Cretaceous South American articulated brachiopods in the light of previous knowledge at worldwide scale. Late Triassic brachiopods from the Argentine–Chilean Andes show unmistakable Maorian (or Notal) faunal elements alongside some more cosmopolitan genera, with certain influence of Eastern Pacific taxa. By Early Jurassic times, differentiation of Tethyan and Boreal Realms became progressively evident in Europe. In South America, Hettangian–Sinemurian brachiopod faunules from the Argentinian Andes are somewhat impoverished, with mostly cosmopolitan genera showing certain affinities to Maorian species, and with the addition of some endemics later. Increasingly, diverse Pliensbachian Andean brachiopods denote close relationships to Celto-Swabian taxa, then by Domerian times, a certain degree of endemism was developed, though somewhat delayed Tethyan influences, and persistent links with New Zealand are subordinately recognizable, too; most Toarcian assemblages reveal basically Celto-Swabian and Iberian affinities as well. East-west austral links across the Pacific may have been favored by migratory routes fringing the Gondwana margin, whereas faunal exchange with the western end of the Tethys appears to reflect an intermittent shallow-marine connection through the Hispanic Corridor. During the Middle Jurassic, distinction of Tethyan and Boreal Realms was maintained in the northern Hemisphere, and the differentiation of an Ethiopian or Southern Tethyan fauna became better characterized. Aalenian and Bajocian brachiopods of the Andes display generic affinities mainly with those from western Europe, with some minor endemic developments; brachiopods recorded from the Bathonian–Callovian of Argentina (and Chile) also occur along the northern Tethyan margin, yet with some genera extending into Indo-Ethiopian areas. During the Late Jurassic, Boreal faunas from high-latitudes became even more strongly differentiated from low-latitude, Tethyan ones. Oxfordian and Tithonian brachiopods from the Andes apparently belong to genera of cosmopolitan or northern Tethyan affiliation, yet there are few elements in common with other eastern Pacific areas, such as Mexico. Early Cretaceous brachiopods, in addition to Andean basins of Chile and western Argentina, are known also from Patagonia and Tierra del Fuego. They belong mostly to widely distributed, mainly Tethyan genera, with some quasi-cosmopolitan and circum-Pacific components (some shared with Antarctica become noticeable). Late Cretaceous brachiopods from northern Patagonia show significant affinities to Maastrichtian ones of northwest Europe and central Asia, which calls for further assessing the potential role that may have played the trans-Saharan passageway in such dispersal. Broad aspects of Mesozoic brachiopod paleobiogeography are fairly well understood, yet details of ranking and naming of certain units are still in need of more agreement.     

The relationship between weather and mortality in ten major metropolitan areas in the united states, 1962–1965

Daily deaths in ten large cities in the United States were correlated with weather elements for the months of January, April, July, and October of the years 1962–1965. In addition to showing the effects of spells of hot, humid weather and pollution episodes (extreme weather), it was determined that large interdiurnal changes of temperature, dewpoint, and pressure were accompanied by fluctuations in daily mortality. This applies to the northcentral and northeastern United States, where increases in mortality were coincident with prefrontal weather, decreases with postfrontal weather. Total mortality was the cause of death which correlated highest with the weather elements. Deaths over age 70, and under 70, follow in that order. There was little essential difference between arteriosclerotic heart disease and stroke in responsiveness to weather events.

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Zusammenfassung Die täglichen Todesfälle in 10 Grosstädten der Vereinigten Staaten wurden mit Wetterelementen der Monate Januar, April, Juli und Oktober der Jahre 1962–1965 korreliert. Es konnte eine Beziehung zwischen Episoden von feuchtwarmemWetter und Luftverschmutzung und Mortalität nachgewiesen werden. Ausserdem ergab sich, dass grosse interdiurnale Schwankungen der Temperatur, des Taupunktes und Luftdruckes von Schwankungen der täglichen Mortalität begleitet sind. In den nordzentralen und nordöstlichen USA fielen Zunahme der Mortalität zusammen mit Vorfronten- und Abnahme mit Nachfronten-Wetter. Die Gesamtmortalität war die Todesursache, die am besten mit den Wetterelementen korrelierte, gefolgt von der Mortalität von Personen über und unter 70 Jahren. Ein wesentlicher Unterschied der Wetteranfälligkeit bei arteriosklerotischen Herzkrankheiten und Schlaganfall bestand nicht.

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Resume On a mis en parallèle le nombre journalier de décès survenus dans 10 grandes villes des Etats-Unis et des paramètres météorologiques. L'étude se rapporte aux mois de janvier, avril, juillet et octobre des années 1962 à 1965. On a pu en tirer une corrélation entre les périodes chaudes à atmosphère polluée et une mortalité élevée. En outre, des variations interdiurnes prononcées de la température, du point de rosée et de la pression atmosphérique sont accompagnées de fluctuations marquées de la mortalité. Dans le nord-est, le nord et le centre des Etats-Unis, la mortalité augmente par situations préfrontales et diminue par situations postfrontales. La meilleure relation avec les éléments météorologiques est donnée par le nombre total de décès. Suivent ensuite les décès des gens âgés de plus de 70 ans, puis de ceux qui sont plus jeunes. On n'a par contre pas décelé d'effets météorotropiques marqués ni dans le cas de faiblesses cardiaques artériosclérotiques ni dans le cas d'attaques d'apopléxie.

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Condensation of the author's Ph.D. dissertation in meteorology, at the University of Wisconsin, Madison, Wisconsin 1970.     

Distribution patterns of decapod crustaceans in polar areas: a result of magnesium regulation?

Nearly all decapod crustaceans found in Antarctic waters south of the Antarctic Convergence are caridean shrimps (Natantia) while the group of Reptantia is largely absent in this area. Progress in the development of a physiological hypothesis is reported, which explains this distribution pattern based on differences in the regulation of magnesium levels in the haemolymph ([Mg²⁺]_HL) and on the Mg²⁺ dependence of threshold temperatures below which cold-induced failure of cardiac and ventilatory performance occurs. Previous studies had shown that an increase in oxygen consumption and activity levels in the cold can be induced by experimental reduction of [Mg²⁺]_HL in different reptant decapod species. In the present study, we tested the potential of these experimental findings for predicting the effect of low [Mg²⁺]_HL in nature, and investigated temperature-induced changes in oxygen consumption in two species with low but different [Mg²⁺]_HL from southern Chile, Halicarcinus planatus and Acanthocyclus albatrossis ([Mg²⁺]_HL=10.7 and 21.6 mmol l^-1, respectively). In accordance with previous findings, low [Mg²⁺]_HL levels were associated with a reduction of thermal sensitivity and a higher metabolic rate in the cold. A model is developed which describes how [Mg²⁺]_HL reduction caused a threshold temperature (pejus temperature, Tp) to fall, which characterises the onset of cold-induced failure in oxygen supply to tissues. This threshold temperature is interpreted, not only to indicate the limits of cold tolerance, but also of geographical distribution. Tp is shifted towards lower temperatures in Natantia, which are efficient [Mg²⁺]_HL regulators. In contrast, Reptantia, which are poor [Mg²⁺]_HL regulators, appear unable to colonise the permanently cold water of the Antarctic due to insufficient capacity of cardiac performance and, therefore, largely reduced scope for activity at high [Mg²⁺]_HL.     

Facultative primary sex ratio variation: a lack of evidence in birds?

The facultative control of primary sex ratio by breeding birds has become a major focus in evolutionary biology in recent years. A combination of well-developed theoretical literature and rapid publication of empirical results has created considerable confusion, with controversial claims for both extreme control of primary sex ratio versus no control around inherent random variability. We present a robust and quantitative summary of published empirical literature to assess clearly the body of evidence for female birds to control sex assignment in their offspring. Our meta-analytical approach reveals that published studies do not exhibit any variability beyond that which could be expected owing to sampling error. Therefore, we conclude that facultative control of offspring sex is not a characteristic biological phenomenon in breeding birds.     

Socioeconomic status and incidence of pediatric leukemia in Canada: 1992–2010

BackgroundLeukemia is the most common cancer among Canadian children, representing about a third of pediatric cancers in Canada and is responsible for about one-third of pediatric cancer deaths. Understanding the effect of socioeconomic status (SES) on pediatric leukemia incidence provides valuable information for cancer control and interventions in Canada.MethodsUsing a linked data from the Canadian Cancer Registry (CCR), Canadian Census of Population (CCP) and National Household Survey (NHS) we aimed to quantify socioeconomic inequalities in the incidence of pediatric leukemia from 1992 to 2010. We used the concentration index (C) approach to quantify income- and education-related inequalities in the incidence of pediatric leukemia over time.ResultsThough there were fluctuations in incidence over the study period, our results showed that the total incidence of pediatric leukemia in Canada was generally consistent from 1992 to 2010. Incidence rate of 47 per 1,000,000 as at 1992 rose to 57 per 1,000,000 in 2010. The estimated values of the C over the study period failed to show any significant association between pediatric leukemia incidence and household income or education status.ConclusionsAlthough pediatric leukemia incidence is not rising significantly, it is not reducing significantly either. The incidence of pediatric leukemia showed no significant association with socioeconomic status. Future cancer control interventions should focus more on mitigating risk factors that are independent of socioeconomic status.     

A comparison of the dynamical impact of seasonal mechanisms in a herbivore–plant defence system

Plant defences can reduce herbivore fitness and may promote cycles in some herbivore populations. In this study, we model the interaction between plant defences and herbivores and include seasonal forcing, a ubiquitous environmental influence in natural systems. We compare the impacts of two different seasonal mechanisms on the dynamics of the herbivore–plant defence system. The first mechanism involves a fixed breeding season length and a variable birth rate within the breeding season; the second involves a variable breeding season length and a fixed birth rate within the breeding season. When parameterised for a specific cyclic system, namely field voles and silica, our model predicts that a variable season length gives multi-year cycles for a larger region in parameter space than a variable birth rate. Our results highlight the complexity of the dynamical effects of seasonal forcing and that these effects are strongly dependent on the type of seasonal mechanism.     

Are vegetated areas more attractive for juvenile fish in estuaries? A comparison in a tropical estuary

Seagrass beds are some of the essential nursery areas for fish, due to the great structural complexity found in these environments. Despite their importance, they are among the most threatened coastal ecosystems and their influence on fish assemblages is still poorly studied. Therefore, this study aimed to compare the composition and structure of fish assemblages found in vegetated and unvegetated areas in a tropical estuary. Samples were taken in two areas with seagrass (Halodule wrightii) and two where this vegetation is absent (tidal flats), observing variations in the hydrological regime between the dry and rainy seasons of 2014. A total of 86 species were recorded, of which 11 occurred only in vegetated areas and 31 only in the unvegetated regions. No difference was found in diversity between vegetated and unvegetated areas, but the values of abundance and biomass were higher in unvegetated areas. Thus, the environmental characteristic of unvegetated areas proved to be a major factor in determining the biomass and richness patterns. Analysis of the abiotic data set indicated that temperature and dissolved oxygen are the variables that act as environmental filters in the temporal differentiation of the structure of fish assemblages, while salinity and total dissolved solids are related to variation between seagrass beds and tidal flats. In addition, our results show that these areas are used by the species in different stages of their ontogenetic development, which may be linked to differences related to the availability of food resources and the possibility of refuge from predation.     

Linking dispersal and marriage in humans: Life history data from Oakham,Massachusetts, USA (1750–1850)

Despite the emphasis on inbreeding avoidance and competition for mates in explaining primate dispersal, little is known about how dispersal and mating interconnect in humans. I examine the link between dispersal and marriage using life history data from Oakham, MA (1750–1850). I find that dispersal status, timing, and destination were linked to marital status, timing, and spouse's place of origin. Men, unmarried individuals, and individuals with spouses from Oakham were less likely to disperse than their counterparts. Individuals with spouses from Oakham also married earlier than others. For women, dispersal and marriage often coincided, and women were more likely to disperse to their spouses' town of origin than were men. Although dispersal coincided with marriage in at least two-thirds of dispersal events, the majority of cases were inconsistent with both inbreeding avoidance and mating competition explanations. Where one of these explanations was still plausible, dispersal seemed more likely linked to competition for mates than to inbreeding, with resource availability also likely shaping dispersal, and male control of resources contributing to sex biases in dispersal.     

Patterns in the Distribution of Cladocerans (Crustacea: Branchiopoda) in Lakes Across a North–south Transect in Alaska, USA

The remains of cladocerans were examined from the surface sediments of 51 freshwater sites along a north–south transect spanning Alaska. We identified 27 cladoceran taxa from the sediments, consisting primarily of littoral chydorid species. Variations in cladoceran assemblages were related to measured physical and chemical variables using multivariate techniques. Redundancy analysis (RDA) indicated that lake depth, total phosphorus (TP), and altitude all had a significant influence in determining the composition of cladoceran assemblages. Cladoceran communities in tundra and forest-tundra lakes, which were relatively shallow and nutrient-poor, had relatively low abundances of pelagic Cladocera, and were primarily composed of several littoral chydorid species. Among pelagic cladoceran species, there was a distinct shift in dominance from the Bosminidae in lakes in the southern boreal forest region to Daphniidae in lakes in the northern boreal forest. Daphnia dominated lakes had significantly higher total phosphorus, specific conductivity, and calcium concentrations than lakes dominated by Eubosmina. Overall, the relative importance of physical and chemical factors in structuring cladocerans is similar to other previously studied regions, and suggests the Cladocera may be useful as ecological and paleoenvironmental indicators in this region.     

The marriage squeeze in Colombia, 1973–2005: The role of excess male death

Abstract

Colombia has been characterized by extreme levels of civil violence throughout the latter part of the twentieth century, and the burden of excess mortality attributable to this violence has been borne primarily by young men. Populations with a large violent death burden are likely to experience consequences in terms of (1) marriage markets, (2) the dynamics of family formation and dissolution, and (3) patterns of parental investment in offspring. Using data from national censuses and household surveys, we calculate a measure of the marital sex ratio in order to explore the impact of differential male mortality on marriage markets in Colombia. Overall, Colombia is characterized by a female biased sex ratio at all ages. This relative excess of women is particularly pronounced in certain departments of the Central and Pacific regions which have been especially affected by civil violence. We suggest that the low sex ratios which characterized Colombia are partially responsible for the increasingly high frequency of consensual unions and, potentially, female‐biased rural‐urban migration.     

Carbapenem Non-Susceptible Enterobacteriaceae in Quebec,Canada: Results of a Laboratory Surveillance Program (2010–2012)

The emergence and spread of carbapenemase-producing Enterobacteriaceae (CPE) represent a major public health concern because these bacteria are usually extensively resistant to most antibiotics. In order to evaluate their dissemination in Quebec, a surveillance program was introduced in 2010. We report the molecular and epidemiological profiles of CPE isolates collected. Between August 2010 and December 2012, a total of 742 non-duplicate isolates non-susceptible to carbapenems were analysed. AmpC β-lactamase and metallo-β-lactamase production were detected by Etest and carbapenemase production by the modified Hodge test (MHT). Antibiotic susceptibility profiles were determined using broth microdilution or Etest. Clonality of Klebsiella pneumoniae carbapenemase (KPC) strains was analyzed by pulsed-field gel electrophoresis (PFGE). The presence of genes encoding carbapenemases as well as other β-lactamases was detected using PCR. Of the 742 isolates tested, 169 (22.8%) were CPE. Of these 169 isolates, 151 (89.3%) harboured a bla _KPC gene while the remaining isolates carried bla _SME (n = 9), bla _OXA-48 (n = 5), bla _NDM (n = 3), and bla _NMC (n = 1) genes. Among the 93 KPC strains presenting with a unique pattern (unique PFGE pattern and/or unique antibiotics susceptibility profile), 99% were resistant to ertapenem, 95% to imipenem, 87% to meropenem, 97% to aztreonam, 31% to colistin and 2% to tigecycline. In 19 patients, 2 to 5 KPC strains from different species or with a different PFGE pattern were isolated. CPE strains were present in the province of Quebec with the majority of strains harbouring KPC. Alternately, SME, OXA-48 and NMC containing strains were rarely found.     

Temporal–spatial variation and source analysis of carbon and nitrogen in a tidal wetland of Luoyuan Bay

Carbon and nitrogen are important elements in biogeochemical studies of tidal wetlands. Three wetland zones in Luoyuan Bay in the Fujian province were chosen for this study; the Spartina alterniflora flat zone with Spartina alterniflora growing, the silt zone with no Spartina alterniflora growing and the Spartina alterniflora-silt flat zone – a transition zone between the two. The spatial and seasonal variations of total organic carbon (TOC), total nitrogen (TN), stable isotopes of organic material (δ¹³C, δ¹⁵N), C/N ratio, average particle size and sediment composition in surface and vertical sediments of different ecological zones were analyzed. Carbon and nitrogen accumulation and particle size effects in the different ecological zones were discussed and the indicators of δ¹³C and C/N ratios were also compared. TOC, TN, δ¹³C contents, C/N ratios, and average particle size varied within the ranges of 0.611–1.133%, 0.053–0.090%, ?22.60 to ?18.92‰, 12.3–15.7, and 6.4–8.7 μm, respectively. Sediments were mainly silt-sized. Besides δ¹⁵N values, the other parameters, such as TOC, TN, δ¹³C contents, C/N ratios, and average particle size showed an obvious zonal distribution in surface sediments. The distribution of TOC and TN contents reflected the distribution of Spartina alterniflora within the bay. The profile and seasonal variations of these parameters in different ecological zones indicated that variations in the Spartina alterniflora flat and transition zones were complex because of the effect of Spartina alterniflora. Vertical and seasonal variations were sampled in the silt flat area. The profile and seasonal variations of TOC, TN and δ¹³C were similar in the transition zone and the Spartina alterniflora flat zone. Seasonal concentrations of TOC, TN and δ¹³C decreased from autumn > spring > winter > summer. The seasonal variation of carbon and nitrogen in the sediments may be influenced by temperature, particle size, plankton and benthos. The particle size effect was significant in the surface sediments and profile sediments of the transition zone. However, other factors had a greater effect on the distributions of TOC and TN in the Spartina alterniflora flat and silt flat zones. C/N ratios in sediments of the Spartina alterniflora flat, transition zone and silt flat were close to or > 12, indicating that the organic material source was dominated by terrestrial inputs. However, δ¹³C values decreased from the Spartina alterniflora flat zone > transition zone > silt flat zone indicating that the organic material source was predominantly from marine inputs. Thus the indications from C/N ratios and δ¹³C were different. There was no clear relationship between C/N ratios and δ¹³C values and a better relationship between δ¹³C values and TOC concentrations suggested that δ¹³C values provided a better indication of the organic source. Limited amounts of organic material came from Spartina alterniflora. This study has provided basic data for researching biogeochemical processes of biogenic elements in tidal wetlands and vegetation restoration, and has also provided a reference for assessing and protecting the environment and ecological systems in wetlands.     

Pollen grain size variation in Caryophylloideae: a mixed strategy for pollen deposition along styles with long stigmatic areas?

The literature supports a positive correlation between pollen size and style length and that pollen size may be affected by a trade-off with pollen number. A correlation between pollen size and pollinator type has been hypothesized by some authors but not confirmed. To assess these associations, pollen grain number, pollen grain diameter and style length were measured in 53 species of Caryophylloideae that had been classified beforehand as being diurnal, nocturnal or self-pollinated. Surprisingly, many species showed two, and a few even three, distinct pollen grain size classes per individual anther. Therefore, further analyses were based on the different pollen size classes and respective pollen grain numbers. Firstly, we found no indication of a trade-off between pollen size and number. Secondly, a positive linear correlation between style length and pollen grain diameter was found using conventional analysis methods and phylogenetically independent contrasts. Thirdly, when using conventional analysis methods a strong relationship between style length and pollination mode was found, with nocturnal species having significantly longer styles and larger pollen grains than diurnal and selfing species. These results were not supported, however, when calculating comparisons of phylogenetically independent pairs. We discuss our findings in relation to intra-specific pollen polymorphism and pollen degeneration, both of which have been associated with different pollen grain sizes in Caryophylloideae. Furthermore, we discuss the possibility that pollen polymorphism might be a mixed strategy to optimise the success of pollen grains deposited at different pollen–ovule distances on long styles.     

Origin of genetic variation: regulation of genetic recombination in the higher organisms — a theory

Summary Recent studies in the fungi, particularly Neurospora and Schizophyllum, have revealed a number of genetic features which, viewed in conjunction with earlier observations on other organisms, form a pattern, or model, which appears to be basic to the control of recombination in all eukaryotes, including higher organisms. It is assumed that the control is exercised on mechanisms that produce new alleles through recombination, as understood in broad terms and including such a likely phenomenon as gene conversion, which may or may not involve crossing-over, as well as equal and unequal crossing-over. The recombination may thus occur between alleles in either the homozygous or heterozygous condition. In the model, regulatory genes and breeding behaviour are integrated into one self-regulatory system controlling the production of new genetic variation.The model is based on the following five general features, largely substantiated by the results in Neurospora and Schizophyllum: 1) The frequency of recombination in a particular chromosomal region is controlled by specific regulatory genes (rec). 2) There may be a number of such specific, regulatory genes responsible for recombination in a given region. 3) A rec. locus may influence recombination in more than one region. 4) The regulatory genes have no specific physical relationship with the region(s) they control, and are usually located at random in the genome. 5) Of the allelic forms of the regulatory genes it is always the dominant gene which suppresses recombination and the recessive gene which increases recombination. The rec system is epistatic to other genetic elements jointly involved in the overall control of recombination in a specific region. It is suggested that usually the control of recombination in a given region is exercised, cumulatively, by the balance of the dominant and recessive genes of the specific rec loci in the organism. Outbreeding, with the associated high heterozygosity of the regulatory rec loci, virtually switches off recombination, producing few new variations. Inbreeding produces homozygosity of these loci, resulting in certain individuals which will have a considerable number of their regulatory loci in the homozygous recessive condition and in which recombination will be switched on, producing new variation at a high frequency. Inbreeding is thus an integrated, evolutionary system of considerable importance, and is not a degenerate dead end, as many investigators have previously thought.The model has another compensatory function in evolution. In major loci, or in an operon, where there are structural genes and closely linked operator genes, as exemplified by the S locus, there are indications that the present model is concerned with the regulation of both structural and operator genes. The consequences of the model in the two classes of genes, however, are in direct contrast to each other: High heterozygosity which is instrumental in switching off recombination, and which is therefore helpful in maintaining stability in the structural gene, is conducive to functional variation of the operator gene; and high homozygosity, which is instrumental in switching on recombination, and which is therefore helpful in producing variation in the structural gene, is conducive to the stability of the operator gene.This model of the control of genetic variation in a specific chromosomal region is significant in development as well as in evolution, and throws light on a number of hitherto intractable problems peculiar to the higher organisms. For example, the model is helpful in explaining: 1) the origin of new self-incompatibility alleles in the flowering plants; 2) the impressive speciation in the waif flora (and fauna) of the oceanic islands; 3) the presence of high genetic variability in inbreeding species of plants; 4) environmentally-induced heritable variation in certain plants; and 5) the genetic mechanism of antibody diversity in animals.