Kin groups and trait groups: population structure and epidemic disease selection

A Monte Carlo simulation based on the population structure of a small-scale human population, the Semai Senoi of Malaysia, has been developed to study the combined effects of group, kin, and individual selection. The population structure resembles D.S. Wilson's structured deme model in that local breeding populations (Semai settlements) are subdivided into trait groups (hamlets) that may be kin-structured and are not themselves demes. Additionally, settlement breeding populations are connected by two-dimensional stepping-stone migration approaching 30% per generation. Group and kin-structured group selection occur among hamlets the survivors of which then disperse to breed within the settlement population. Genetic drift is modeled by the process of hamlet formation; individual selection as a deterministic process, and stepping-stone migration as either random or kin-structured migrant groups. The mechanism for group selection is epidemics of infectious disease that can wipe out small hamlets particularly if most adults become sick and social life collapses. Genetic resistance to a disease is an individual attribute; however, hamlet groups with several resistant adults are less likely to disintegrate and experience high social mortality. A specific human gene, hemoglobin E, which confers resistance to malaria, is studied as an example of the process. The results of the simulations show that high genetic variance among hamlet groups may be generated by moderate degrees of kin-structuring. This strong microdifferentiation provides the potential for group selection. The effect of group selection in this case is rapid increase in gene frequencies among the total set of populations. In fact, group selection in concert with individual selection produced a faster rate of gene frequency increase among a set of 25 populations than the rate within a single unstructured population subject to deterministic individual selection. Such rapid evolution with plausible rates of extinction, individual selection, and migration and a population structure realistic in its general form, has implications for specific human polymorphisms such as hemoglobin variants and for the more general problem of the tempo of evolution as well.     

Endogamy in settlement populations of semai senoi: Potential mate pool analysis and simulation

Abstract

Two methods have been used to evaluate potential endogamy in three settlement populations of a swidden farming group, the Semai Senoi of Malaysia. One method involved determining the number of potential mates available to individuals in each population based on demographic structure and cultural rules concerning appropriate mates. A Monte Carlo simulation of Semai settlement populations was also carried out under two different regimes of mate choice. Both procedures suggest that individuals in the largest Semai settlements are potentially able to marry endogamously but that in smaller groups few potential mates are available and many persons must marry exogamously or remain unmarried. The relatively high rate of marital migration required among small settlement populations implies that newly founded small groups would be unlikely to become sufficiently isolated to form distinct breeding populations.     

Genetic microdifferentiation in the Semai Senoi of Malaysia.

Blood samples, demographic and cultural data were collected from seven settlements of Semai Senoi, a swidden farming ethnic group of Malaysia. Three genetic loci (ABO blood group, hereditary ovalcytosis, and hemoglobin) were analyzed in a total sample of 546 individuals. These data indicate a considerable degree of genetic microdifferentiation in this area of the Semai distribution. Parent-offspring birthplace data (analyzed by means of a migration matrix) and settlement histories show that settlements are not strongly isolated. Genetic differences in the study area demonstrate a reasonable correspondence with migration and the history of the settlements. Genetic convergence also occurs through the addition of migrant groups to established populations leading to new patterns of marriage between donor and recipient groups. The genetic structure of the total Semai population through time thus comprises a mosaic of shifiting allele frequencies in a series of semi-isolated local populations.     

Social group fission and the origin of intergroup genetic differentiation among the rhesus monkeys of Cayo Santiago.

The serum transferrin locus is used to investigate the roles of the lineal effect of fission, male migration effect of fission, and genetic drift in causing intergroup genetic differentiation among the rhesus macaques of Cayo Santiago. These three mechanisms prove sufficient to explain the degrees of differentiation between the newly formed social groups A, K, and L as of July 1, 1971. The lineal effect of fission provides a baseline of intergroup differentiation which is altered by forces leading to intragroup genetic change, the male migration effect and genetic drift. The importance of population dynamics for the distribution of alleles among subgroups of a population is recognized.     

Habitual fission-fusion and social organization of the Hakone troop T of Japanese macaques in Kanagawa prefecture,Japan

To analyze the socioecological factors of habitual fission-fusion of troop members, which is an underreported phenomenon in Japanese macaques, the seasonal pattern of fission-fusion within the Hakone troop T in Kanagawa Prefecture, Japan, was examined. Although almost all the study troop members were included in a large-sized group in winter, a portion of its members of ten formed small subgroups from spring to autumn. The frequencies and age-sex composition of these subgroups changed seasonally. All troop members participated, more or less, in subgroup formation. Subgroups tended to be composed of animals of the same age-sex class. Troop members did not fission along matrilineal lines. Although the study troop members repeatedly joined with and parted from subgroups, the characteristic social structure of Japanese macaque troops was maintained. Habitual fission-fusion among troop members may be one of a number of foraging strategies that facilitate efficient food gathering when the population density exceeds and /or reaches the carrying capacity of the area. The seasonal variation of pattern and composition type of each subgroup could be attributed to alternation of attractive food plant species, as well as age, rank, and sexual activity of both sexes.     

Blood Drunkenness and the Bloodthirsty Semai: Unmaking Another Anthropological Myth

The Senoi Semai of Malaysia have frequently been cited as examples in the debates over the wellsprings of human violence. Numerous writers have employed selected Semai ethnographic material to support assertions that, their apparent peacefulness notwithstanding, Semai are in reality bloodthirsty killers. This assertion has in turn been used as evidence in support of a variety of approaches whose common thread is a view of aggressiveness and violence as somehow innate in human beings. The authors of this article, whose publications form the basis of most anthropological knowledge of Semai life and culture, draw on their own published and unpublished work as well as on documentation from other sources to refute these interpretations. We hold that Semai life is, as first-hand observers have described it, notably free of interpersonal violence, and we argue that misrepresentations rooted in particular theoretical or philosophical a priori assumptions are scientifically untenable and culturally slanderous.     

Spinner dolphins in a remote Hawaiian atoll: social grouping and population structure

Spinner dolphins (Stenella longirostris) commonly use inshoreisland and atoll habitats for daytime rest and social interactionsand forage over deep waters at night. In Hawaii, they occurthroughout the archipelago. We applied photoidentification mark-recapturetechniques to study the population structure of spinner dolphinsassociated with remote Midway Atoll, far-western Hawaii. AtMidway, spinner dolphins live in stable bisexually bonded societiesof long-term associates, with strong geographic fidelity, noobvious fission-fusion, and limited contacts with other populations.Their large cohesive groups change little over time and arebehaviorally/socially discrete from other spinner dolphin groups.This social pattern differs considerably from the fluid fission-fusionmodel proposed previously for spinner dolphins associated witha large island habitat in the main Hawaiian Archipelago. Thesedifferences correspond to geographic separation and habitatvariation. While in the main islands there are several daytimeresting places available at each island habitat; in far-westernHawaii, areas of suitable habitat are limited and separatedby large stretches of open pelagic waters with potentially highrisk of shark predation. We hypothesize that with deepwaterfood resources in close proximity and other atolls relativelyfar away for easy (day-to-day) access, it is energetically morebeneficial in the remote Hawaiian atolls to remain "at home"than to travel to other atolls, so there is stability insteadof variability; there is no fission-fusion effect. Thus, thegeographic isolation and small size of remote atolls triggera process in which the fluidity of the fission-fusion spinnerdolphin society is replaced with long-term group fidelity andsocial stability.     

Adenosine deaminase polymorphism among the Semai, Temuan, Semelai, and Jakun groups of West Malaysian Orang Asli

812 West Malaysian Orang Asli belonging to four ethnic groups were surveyed for adenosine deaminase (ADA; EC 3.5.4.4) using starch gel electrophoresis. Only the common ADA1 and ADA2 alleles were found, with the frequencies of the latter being 0.025, 0.103, 0.115 and 0.028 in the Semai, Semelai, Temuan, and Jakun groups, respectively. A new 'breeding genetic distance' was applied to these gene frequencies and the Semelai and Temuan were found to be more closely related to each other, and to have considerably more evolutionary flexibility on this scale of 'micro-evolution' than the other two groups. The Semai and Jakun were more similar to each other on the basis of these ADA gene frequencies.     

Dolphin social intelligence: complex alliance relationships in bottlenose dolphins and a consideration of selective environments for extreme brain size evolution in mammals

Bottlenose dolphins in Shark Bay, Australia, live in a large, unbounded society with a fission-fusion grouping pattern. Potential cognitive demands include the need to develop social strategies involving the recognition of a large number of individuals and their relationships with others. Patterns of alliance affiliation among males may be more complex than are currently known for any non-human, with individuals participating in 2-3 levels of shifting alliances. Males mediate alliance relationships with gentle contact behaviours such as petting, but synchrony also plays an important role in affiliative interactions. In general, selection for social intelligence in the context of shifting alliances will depend on the extent to which there are strategic options and risk. Extreme brain size evolution may have occurred more than once in the toothed whales, reaching peaks in the dolphin family and the sperm whale. All three 'peaks' of large brain size evolution in mammals (odontocetes, humans and elephants) shared a common selective environment: extreme mutual dependence based on external threats from predators or conspecific groups. In this context, social competition, and consequently selection for greater cognitive abilities and large brain size, was intense.     

Evolution in metacommunities

A metacommunity can be defined as a set of communities that are linked by migration, and extinction and recolonization. In metacommunities, evolution can occur not only by processes that occur within communities such as drift and individual selection, but also by among-community processes, such as divergent selection owing to random differences among communities in species composition, and group and community-level selection. The effect of these among-community-level processes depends on the pattern of migration among communities. Migrating units may be individuals (migrant pool model), groups of individuals (single-species propagule pool model) or multi-species associations (multi-species propagule pool model). The most interesting case is the multi-species propagule pool model. Although this pattern of migration may a priori seem rare, it becomes more plausible in small well-defined 'communities' such as symbiotic associations between two or a few species. Theoretical models and experimental studies show that community selection is potentially an effective evolutionary force. Such evolution can occur either through genetic changes within species or through changes in the species composition of the communities. Although laboratory studies show that community selection can be important, little is known about how important it is in natural populations.     

DNA Polymorphism in a Subdivided Population: The Expected Number of Segregating Sites in the Two-Subpopulation Model

Using the two subpopulation model, the expected numbers of segregating sites in a number of DNA sequences randomly sampled from a subdivided population were examined for several types of population subdivisions. It is shown that, in the case where the pattern of migration is symmetrical such as the finite island model, the expected number of segregating sites is independent of the migration rate when two or three DNA sequences are randomly sampled from the same subpopulation, but depends on the migration rate when more than three DNA sequences are sampled. It is also shown that the population subdivision can increase the amount of DNA polymorphism even in a subpopulation in some cases.     

Proceedings of the fifty-fourth Annual Meeting of the American Association of physical anthropologists to be held in Knoxville,Tennessee—Holiday Inn World's fair April 10–13, 1985

Empirical analyses and models of the lineal effects of fission indicate that considerable genetic differentiation may occur at the time of group formation, thus confusing the usual positive relationship between historical affiliation and genetic differentiation. We analyze the effects of fission pattern on variation in highly heritable morphological traits among eight social groups on Cayo Santiago. The analysis is performed using general network autocorrelation methods that quantitatively and directly measure the amount of variation in social group mean morphology that can be explained by fission. All of the fission autocorrelation coefficients are strongly negative, indicating that groups most recently formed by fission are most dissimilar. Also, most of the variation between groups can be explained by the fission pattern, indicating that lineal fission is the most important process generating between-group variation on Cayo Santiago.     

Early events in mammalian craniofacial morphogenesis.

Head-trunk differences are well established in the most primitive vertebrates, and are clear from early developmental stages of all modern forms. The boundary between the two regions is not constant in all vertebrate classes in terms of the number of occipital somites. The occipital region is in some respects a transitional zone, giving rise to trunk-like somitic derivatives in the head. It is also highly specialised, providing a unique population of neural crest cells that are essential for formation of the aorticopulmonary septum (which divides the outflow tract of the heart) in mammals and birds. In the preoccipital hindbrain, rhombomeres represent a segmental structural pattern that is quite distinct from that of the somites, with a segment-specific pattern of gene expression. Expression of some of these genes in mesenchyme close to the primitive streak at earlier stages suggests that this pattern may be established at the time of neural induction. Mammalian embryos have taken cranial specialization further than other classes of vertebrate, particularly in relation to the pattern of development and eventual structural complexity of the forebrain. Mammalian specialisations of craniofacial development are described through references to studies on cranial neurulation, on cranial neural crest cell migration, and on the possible morphogenetic roles of extracellular matrix components.     

Behavioral Flexibility and the Evolution of Primate Social States

Comparative approaches to the evolution of primate social behavior have typically involved two distinct lines of inquiry. One has focused on phylogenetic analyses that treat social traits as static, species-specific characteristics; the other has focused on understanding the behavioral flexibility of particular populations or species in response to local ecological or demographic variables. Here, we combine these approaches by distinguishing between constraining traits such as dispersal regimes (male, female, or bi-sexual), which are relatively invariant, and responding traits such as grouping patterns (stable, fission-fusion, sometimes fission-fusion), which can reflect rapid adjustments to current conditions. Using long-term and cross-sectional data from 29 studies of 22 species of wild primates, we confirm that dispersal regime exhibits a strong phylogenetic signal in our sample. We then show that primate species with high variation in group size and adult sex ratios exhibit variability in grouping pattern (i.e., sometimes fission-fusion) with dispersal regime constraining the grouping response. When assessing demographic variation, we found a strong positive relationship between the variability in group size over time and the number of observation years, which further illustrates the importance of long-term demographic data to interpretations of social behavior. Our approach complements other comparative efforts to understand the role of behavioral flexibility by distinguishing between constraining and responding traits, and incorporating these distinctions into analyses of social states over evolutionary and ecological time.     

Roost switching, roost sharing and social cohesion: forest-dwelling big brown bats, Eptesicus fuscus, conform to the fission-fusion model

We used radiotelemetry to quantify roost switching and assess associations between members of maternity colonies of forest-dwelling big brown bats. Bats remained loyal to small roosting areas of forest within and between years and switched trees often (). For radiotagged bats from the colony in one of these areas, roost-switching frequency was positively correlated with the number of different individuals with which tagged bats shared roosts. We quantified associations between pairs of bats using a pairwise sharing index and found that bats associated more often than predicted when roost and roostmate selection were random but that all tagged bats spent at least some days roosting in different trees, apart from preferred roostmates. Our results suggest that forest-dwelling big brown bats conform to a fission-fusion roosting pattern. Roost switching in forests may reflect the maintenance of long-term social relationships between individuals from a colony that is spread among a number of different trees on a given night. In this fission-fusion scenario, switching between trees, within a local area, could serve to increase the numbers of individuals with which bats maintain associations. We contend that roosting areas in forests are analogous to spatially large roosts in caves, mines and buildings.     

Changing sex ratio of mortality in the Semai Senoi, 1969-1987

An excess of male over female deaths is characteristic of modern national populations, whereas in some high-mortality societies female mortality exceeds that of males. Among the Semai Senoi, a Malaysian Orang Asli ("aboriginal") population, women experienced higher mortality than males in the decades before 1969. This differential occurred in all age classes older than 15 years so that the sex ratio progressively increased with age. A recent (1987) restudy of the Semai population found that sex-specific differential mortality is much reduced. A comparison of the 1969 and 1987 life tables shows a sharp shift in the sex ratios of mortality for the post-15-year-old age classes (the geometric means of age classes 15-44 were 0.768 in 1969 and 0.997 in 1987) so that male and female expectations of further life at age 15 are now nearly identical. In contrast to the best-known cases of high female mortality (mostly in South Asia), Semai sex differential mortality does not include the childhood ages. The Semai have traditionally been relatively sexually egalitarian, and sex bias in care has not occurred. Analysis of sex-specific causes of death for the pre-1969 population suggests that maternal mortality is the major cause of the excess female deaths. The reduced number of maternal deaths seems largely due to better health care, particularly the availability of hospital services. Interestingly, the reduction in female mortality has occurred simultaneously with increased fertility, and overall mortality has continued at relatively high levels (eO less than 36). Thus, rather than forming a component of a unitary demographic transition, declining sex differences in mortality can be accounted for by a specific factor, better maternal care.     

The trigeminal jaw adductors of primitive snakes and their homologies with the lacertilian jaw adductors

The trigeminal jaw adductor musculature of anilioid snakes is analysed. The group is characterised by primitive characters, viz. the presence of an extensive bodenaponeurosis and of a quadrate aponeurosis. A temporal tendon gives rise to superficial (lb) fibres which are not observed in other snakes: this may be a primitive or a derived feature.
Jaw adductor muscles in snakes are usually subdivided following their relative position in an antero–posterior direction. Lacertilian jaw adductors are subdivided in a transverse plane. A detailed comparison of the anilioid and primitive lacertilian jaw adductors establishes correspondences (homologies) of parts in the transverse plane in both groups. These homologies are corroborated by innervational patterns.
Platynotan lizards are widely accepted as potential snake ancestors. A comparison of homologue jaw adductors shows different evolutionary trends to characterise platynotan lizards and snakes. Theoretically, these findings do not rule out primitive platynotan lizards as snake ancestors. On the basis of the structure of jaw adductors, snakes are to be derived from a primitive lacertilian pattern, be it platynotan or not.     

Cautious climbing and folivory: a model of hominoid differentation

Despite the large and growing number of Miocene fossil catarrhine taxa, suitable common ancestors of great apes and humans have yet to be agreed upon. Considering a) the conservative and primitive nature of the hominoid molar cusp pattern, and b) the variability of secondary dental features, it is difficult to discern whether a hominoid dentition is primitive, secondarily simplified to the primitive condition or too far derived to be ancestral to any of the living forms. Nonetheless, the inability to recognize a common ancestor is primarly due to the absence of a model of hominoid differentiation that provides a basis for its recognition. Vertical climbing as the limiting component of cautious climbing, explains all of the locomotor anatomy shared by living hominoids. Comparison of the shared derived characters of hominoids to those of forms which have converged on hominoidsi.e colobines, atelines, lorisines, paleopropithecines and sloths suggest that early hominoids were probably folivores. In arboreal forms there is a strong link between a large body size, folivory and cautious climbing. Comparison of craniodental characters of committed folivores to committed frugivores from among each of the compared groups with the exception of lorisines, indicates that many of the distinguishing craniodental characters of humans and great apes are adaptations to folivory. Many of these characters, however, are also present in Jolly's seed eating complex. As such folivory may be the heritage factor which Jolly hypothesized to account for differential reduction of canines in fossilTheropithecus and hominids.     

Folding of small RNAs displaying the GNC base-pattern: implications for the self-organization of the genetic system

Theoretical arguments and statistical analyses of present-day coding sequences have long suggested the existence of primitive patterns in RNA sequences, which were thought to have been predominant at the time of the origin of the genetic code. The main propositions were centered around the base-patterns GNC and RNY, where R = A or G , Y = C or U and N = A, G, C or U. A theoretical model of the primitive process of translation explaining the origin of this type of pattern was recently published in the Journal of Theoretical Biology. On the basis of this previous analysis, and on physico-chemical evidence supporting the idea of the GNC base-pattern as the most primitive one, the present paper shows the results of folding simulations of small RNA strands displaying this pattern, which enabled us to specify the characteristics of the suggested primitive form of tRNA. This analysis is notably based on a conjecture of Eigen and Schuster of an early structural (or pattern) similarity between mRNA and tRNA, and, more specifically, of a "joint function of messenger and adaptor". Working with this conjecture, we show that the convergence of the primitive pool of RNAs toward a system containing a high proportion of sequences displaying the GNC base-pattern (according to the evolutionary model) is accompanied by a significant gain in stability of the translation process. In particular, it is demonstrated how the reading frame would be automatically discriminated without the presence of a start codon.