Reproductive inequality in humans and other mammals.

To address claims of human exceptionalism, we determine where humans fit within the greater mammalian distribution of reproductive inequality. We show that humans exhibit lower reproductive skew (i.e., inequality in the number of surviving offspring) among males and smaller sex differences in reproductive skew than most other mammals, while nevertheless falling within the mammalian range. Additionally, female reproductive skew is higher in polygynous human populations than in polygynous nonhumans mammals on average. This patterning of skew can be attributed in part to the prevalence of monogamy in humans compared to the predominance of polygyny in nonhuman mammals, to the limited degree of polygyny in the human societies that practice it, and to the importance of unequally held rival resources to women's fitness. The muted reproductive inequality observed in humans appears to be linked to several unusual characteristics of our species-including high levels of cooperation among males, high dependence on unequally held rival resources, complementarities between maternal and paternal investment, as well as social and legal institutions that enforce monogamous norms.

Barriers to chimpanzee gene flow at the south-east edge of their distribution.

Populations on the edge of a species' distribution may represent an important source of adaptive diversity, yet these populations tend to be more fragmented and are more likely to be geographically isolated. Lack of genetic exchanges between such populations, due to barriers to animal movement, can not only compromise adaptive potential but also lead to the fixation of deleterious alleles. The south-eastern edge of chimpanzee distribution is particularly fragmented, and conflicting hypotheses have been proposed about population connectivity and viability. To address this uncertainty, we generated both mitochondrial and MiSeq-based microsatellite genotypes for 290 individuals ranging across western Tanzania. While shared mitochondrial haplotypes confirmed historical gene flow, our microsatellite analyses revealed two distinct clusters, suggesting two populations currently isolated from one another. However, we found evidence of high levels of gene flow maintained within each of these clusters, one of which covers an 18,000 km2 ecosystem. Landscape genetic analyses confirmed the presence of barriers to gene flow with rivers and bare habitats highly restricting chimpanzee movement. Our study demonstrates how advances in sequencing technologies, combined with the development of landscape genetics approaches, can resolve ambiguities in the genetic history of critical populations and better inform conservation efforts of endangered species.

Wild origins and mitochondrial genetic diversity of Angolan Colobus monkeys (Colobus angolensis) in AZA-accredited zoos and its implications for ex situ population management.

Across zoo's accredited by the Association of Zoos and Aquariums (AZA), species are typically managed as a single population to retain 90% of the founding members' gene diversity. Often, little is known about the specific geographic origins of the founders or how representative the ex situ population's genetic diversity is of the wild population. This study uses mitochondrial DNA (mtDNA) sequencing to investigate haplotype diversity and geographic female founder origin of the AZA-managed Angolan colobus (Colobus angolensis) monkey population. We obtained fecal samples from individuals closely related to founder animals at five zoos and found four haplotypes among 23 individuals. Analyzed together with wild C. angolensis haplotypes, we found two haplotypes identical to those found in Tanzanian populations: one haplotype, possessed by 13 individuals (descended from three founders), matched an East Usambara Mountains haplotype, while the other, possessed by seven individuals (from four founders), matched a haplotype found in both the South Pare Mountains and Rufiji River. Two haplotypes were not detected in wild populations but were closely related to haplotypes found in the Rufiji River (one individual descended from one founder) and Shimoni, Kenya (two individuals descended from one founder) populations, suggesting nearby origins. Thus, the AZA-managed population of Angolan colobus likely originated from several localities, but all have mtDNA lineages associated with the subspecies C. a. palliatus, a Vulnerable subspecies. Examining founders' mtDNA haplotypes may be a useful addition to the zoo population management toolkit to help improve breeding recommendations by identifying individuals with rare haplotypes and revealing likely kinship among founders.

Mitochondrial genetic diversity and divergence dating of Angolan colobus monkeys (Colobus angolensis) in the eastern forests of Kenya and Tanzania: Implications for subspeciation and reconstructing historical biogeography.

Whether the Colobus angolensis that reside in the fragmented forests in eastern Kenya and Tanzania represent one subspecies or two has been debated for 50 years. Morphological and more recent genetic and ecological studies suggest that these populations represent two subspecies, C. a. palliatus and C. a. sharpei. However, their distribution of mitochondrial variation remains unresolved since the genetic study only characterized four populations at the range ends. Therefore, we characterized five populations in the area of the hypothesized subspecies divide. We identified eight new haplotypes which, combined with those previously identified, provided 26 haplotypes from nine populations for analysis. Haplotypes found south of the Rufiji River cluster together but separately from northern haplotypes. The largest sequence differences within cytochrome b occur between population pairs representing opposite sides of the river; their mean difference (1.5%) is more than that of other primate subspecies. Analysis of molecular variance attributes most of the variation to that north versus south of the river. These results support the previous subspecies distinction between C. a. palliatus (northern) and C. a. sharpei (southern), divided by the Rufiji River. The estimated time of the most recent common ancestor of all haplotypes indicates that the subspecies have been isolated from each other for approximately 550,000 years. The common ancestor of northern and southern haplogroups was 370,000 and 290,000 years ago, respectively. Nevertheless, the correlation between genetic and geographic distances suggests that isolation-by-distance contributed to population structuring. Significant variation among populations, with only three haplotypes shared between populations, also indicates that an extended period of isolation drove population distinctiveness. Considering these results, we evaluate hypotheses about the founding and differentiation of these subspecies during Pleistocene climatic fluctuations and propose a novel, more direct migration route from Central Africa to their current range navigating Lake Tanganyika, the central Tanzanian corridor, and the Rufiji River.

Nomenclature report 2019: major histocompatibility complex genes and alleles of Great and Small Ape and Old and New World monkey species.

The major histocompatibility complex (MHC) is central to the innate and adaptive immune responses of jawed vertebrates. Characteristic of the MHC are high gene density, gene copy number variation, and allelic polymorphism. Because apes and monkeys are the closest living relatives of humans, the MHCs of these non-human primates (NHP) are studied in depth in the context of evolution, biomedicine, and conservation biology. The Immuno Polymorphism Database (IPD)-MHC NHP Database (IPD-MHC NHP), which curates MHC data of great and small apes, as well as Old and New World monkeys, has been upgraded. The curators of the database are responsible for providing official designations for newly discovered alleles. This nomenclature report updates the 2012 report, and summarizes important nomenclature issues and relevant novel features of the IPD-MHC NHP Database.

Correction to: Nomenclature report 2019: major histocompatibility complex genes and alleles of great and small ape and old and new world monkey species.

The original version of this article contained a spelling error in the Acknowledgments regarding the name of the funding organisation supporting GM and JAH. UKRI-BBSCR should have been UKRI-BBSRC, as is now indicated correctly below.

Sequences of 95 human MHC haplotypes reveal extreme coding variation in genes other than highly polymorphic HLA class I and II.

The most polymorphic part of the human genome, the MHC, encodes over 160 proteins of diverse function. Half of them, including the HLA class I and II genes, are directly involved in immune responses. Consequently, the MHC region strongly associates with numerous diseases and clinical therapies. Notoriously, the MHC region has been intractable to high-throughput analysis at complete sequence resolution, and current reference haplotypes are inadequate for large-scale studies. To address these challenges, we developed a method that specifically captures and sequences the 4.8-Mbp MHC region from genomic DNA. For 95 MHC homozygous cell lines we assembled, de novo, a set of high-fidelity contigs and a sequence scaffold, representing a mean 98% of the target region. Included are six alternative MHC reference sequences of the human genome that we completed and refined. Characterization of the sequence and structural diversity of the MHC region shows the approach accurately determines the sequences of the highly polymorphic HLA class I and HLA class II genes and the complex structural diversity of complement factor C4A/C4B It has also uncovered extensive and unexpected diversity in other MHC genes; an example is MUC22, which encodes a lung mucin and exhibits more coding sequence alleles than any HLA class I or II gene studied here. More than 60% of the coding sequence alleles analyzed were previously uncharacterized. We have created a substantial database of robust reference MHC haplotype sequences that will enable future population scale studies of this complicated and clinically important region of the human genome.

Sexual dimorphism in chimpanzee (Pan troglodytes schweinfurthii) and human age-specific fertility.

Across vertebrates, species with intense male mating competition and high levels of sexual dimorphism in body size generally exhibit dimorphism in age-specific fertility. Compared with females, males show later ages at first reproduction and earlier reproductive senescence because they take longer to attain adult body size and musculature, and maintain peak condition for a limited time. This normally yields a shorter male duration of effective breeding, but this reduction might be attenuated in species that frequently use coalitionary aggression. Here, we present comparative genetic and demographic data on chimpanzees from three long-term study communities (Kanyawara: Kibale National Park, Uganda; Mitumba and Kasekela: Gombe National Park, Tanzania), comprising 581 male risk years and 112 infants, to characterize male age-specific fertility. For comparison, we update estimates from female chimpanzees in the same sites and append a sample of human foragers (the Tanzanian Hadza). Consistent with the idea that aggressive mating competition favors youth, chimpanzee males attained a higher maximum fertility than females, followed by a steeper decline with age. Males did not show a delay in reproduction compared with females, however, as adolescents in both sites successfully reproduced by targeting young, subfecund females, who were less attractive to adults. Gombe males showed earlier reproductive senescence and a shorter duration of effective breeding than Gombe females. By contrast, older males in Kanyawara generally continued to reproduce, apparently by forming coalitions with the alpha. Hadza foragers showed a distinct pattern of sexual dimorphism in age-specific fertility as, compared with women, men gained conceptions later but continued reproducing longer. In sum, both humans and chimpanzees showed sexual dimorphism in age-specific fertility that deviated from predictions drawn from primates with more extreme body size dimorphism, suggesting altered dynamics of male-male competition in the two lineages. In both species, coalitions appear important for extending male reproductive careers.

Defining KIR and HLA Class I Genotypes at Highest Resolution via High-Throughput Sequencing.

The physiological functions of natural killer (NK) cells in human immunity and reproduction depend upon diverse interactions between killer cell immunoglobulin-like receptors (KIRs) and their HLA class I ligands: HLA-A, HLA-B, and HLA-C. The genomic regions containing the KIR and HLA class I genes are unlinked, structurally complex, and highly polymorphic. They are also strongly associated with a wide spectrum of diseases, including infections, autoimmune disorders, cancers, and pregnancy disorders, as well as the efficacy of transplantation and other immunotherapies. To facilitate study of these extraordinary genes, we developed a method that captures, sequences, and analyzes the 13 KIR genes and HLA-A, HLA-B, and HLA-C from genomic DNA. We also devised a bioinformatics pipeline that attributes sequencing reads to specific KIR genes, determines copy number by read depth, and calls high-resolution genotypes for each KIR gene. We validated this method by using DNA from well-characterized cell lines, comparing it to established methods of HLA and KIR genotyping, and determining KIR genotypes from 1000 Genomes sequence data. This identified 116 previously uncharacterized KIR alleles, which were all demonstrated to be authentic by sequencing from source DNA via standard methods. Analysis of just two KIR genes showed that 22% of the 1000 Genomes individuals have a previously uncharacterized allele or a structural variant. The method we describe is suited to the large-scale analyses that are needed for characterizing human populations and defining the precise HLA and KIR factors associated with disease. The methods are applicable to other highly polymorphic genes.

Bonobos Maintain Immune System Diversity with Three Functional Types of MHC-B.

Fast-evolving MHC class I polymorphism serves to diversify NK cell and CD8 T cell responses in individuals, families, and populations. Because only chimpanzee and bonobo have strict orthologs of all HLA class I, their study gives unique perspectives on the human condition. We defined polymorphism of Papa-B, the bonobo ortholog of HLA-B, for six wild bonobo populations. Sequences for Papa-B exon 2 and 3 were determined from the genomic DNA in 255 fecal samples, minimally representing 110 individuals. Twenty-two Papa-B alleles were defined, each encoding a different Papa-B protein. No Papa-B is identical to any chimpanzee Patr-B, human HLA-B, or gorilla Gogo-B. Phylogenetic analysis identified a clade of MHC-B, defined by residues 45-74 of the α1 domain, which is broadly conserved among bonobo, chimpanzee, and gorilla. Bonobo populations have 3-14 Papa-B allotypes. Three Papa-B are in all populations, and they are each of a different functional type: allotypes having the Bw4 epitope recognized by killer cell Ig-like receptors of NK cells, allotypes having the C1 epitope also recognized by killer cell Ig-like receptors, and allotypes having neither epitope. For population Malebo, these three Papa-B are the only Papa-B allotypes. Although small in number, their sequence divergence is such that the nucleotide diversity (mean proportional distance) of Papa-B in Malebo is greater than in the other populations and is also greater than expected for random combinations of three Papa-B Overall, Papa-B has substantially less diversity than Patr-B in chimpanzee subspecies and HLA-B in indigenous human populations, consistent with bonobo having experienced narrower population bottlenecks.

Signature Patterns of MHC Diversity in Three Gombe Communities of Wild Chimpanzees Reflect Fitness in Reproduction and Immune Defense against SIVcpz.

Major histocompatibility complex (MHC) class I molecules determine immune responses to viral infections. These polymorphic cell-surface glycoproteins bind peptide antigens, forming ligands for cytotoxic T and natural killer cell receptors. Under pressure from rapidly evolving viruses, hominoid MHC class I molecules also evolve rapidly, becoming diverse and species-specific. Little is known of the impact of infectious disease epidemics on MHC class I variant distributions in human populations, a context in which the chimpanzee is the superior animal model. Population dynamics of the chimpanzees inhabiting Gombe National Park, Tanzania have been studied for over 50 years. This population is infected with SIVcpz, the precursor of human HIV-1. Because HLA-B is the most polymorphic human MHC class I molecule and correlates strongly with HIV-1 progression, we determined sequences for its ortholog, Patr-B, in 125 Gombe chimpanzees. Eleven Patr-B variants were defined, as were their frequencies in Gombe's three communities, changes in frequency with time, and effect of SIVcpz infection. The growing populations of the northern and central communities, where SIVcpz is less prevalent, have stable distributions comprising a majority of low-frequency Patr-B variants and a few high-frequency variants. Driving the latter to high frequency has been the fecundity of immigrants to the northern community, whereas in the central community, it has been the fecundity of socially dominant individuals. In the declining population of the southern community, where greater SIVcpz prevalence is associated with mortality and emigration, Patr-B variant distributions have been changing. Enriched in this community are Patr-B variants that engage with natural killer cell receptors. Elevated among SIVcpz-infected chimpanzees, the Patr-B*06:03 variant has striking structural and functional similarities to HLA-B*57, the human allotype most strongly associated with delayed HIV-1 progression. Like HLA-B*57, Patr-B*06:03 correlates with reduced viral load, as assessed by detection of SIVcpz RNA in feces.

Increased mortality and AIDS-like immunopathology in wild chimpanzees infected with SIVcpz.

African primates are naturally infected with over 40 different simian immunodeficiency viruses (SIVs), two of which have crossed the species barrier and generated human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2). Unlike the human viruses, however, SIVs do not generally cause acquired immunodeficiency syndrome (AIDS) in their natural hosts. Here we show that SIVcpz, the immediate precursor of HIV-1, is pathogenic in free-ranging chimpanzees. By following 94 members of two habituated chimpanzee communities in Gombe National Park, Tanzania, for over 9 years, we found a 10- to 16-fold higher age-corrected death hazard for SIVcpz-infected (n = 17) compared to uninfected (n = 77) chimpanzees. We also found that SIVcpz-infected females were less likely to give birth and had a higher infant mortality rate than uninfected females. Immunohistochemistry and in situ hybridization of post-mortem spleen and lymph node samples from three infected and two uninfected chimpanzees revealed significant CD4(+) T-cell depletion in all infected individuals, with evidence of high viral replication and extensive follicular dendritic cell virus trapping in one of them. One female, who died within 3 years of acquiring SIVcpz, had histopathological findings consistent with end-stage AIDS. These results indicate that SIVcpz, like HIV-1, is associated with progressive CD4(+) T-cell loss, lymphatic tissue destruction and premature death. These findings challenge the prevailing view that all natural SIV infections are non-pathogenic and suggest that SIVcpz has a substantial negative impact on the health, reproduction and lifespan of chimpanzees in the wild.

Factors associated with the diversification of the gut microbial communities within chimpanzees from Gombe National Park.

The gastrointestinal tract harbors large and diverse populations of bacteria that vary among individuals and within individuals over time. Numerous internal and external factors can influence the contents of these microbial communities, including diet, geography, physiology, and the extent of contact among hosts. To investigate the contributions of such factors to the variation and changes in gut microbial communities, we analyzed the distal gut microbiota of individual chimpanzees from two communities in Gombe National Park, Tanzania. These samples, which were derived from 35 chimpanzees, many of whom have been monitored for multiple years, provide an unusually comprehensive longitudinal depth for individuals of known genetic relationships. Although the composition of the great-ape microbiota has been shown to codiversify with host species, indicating that host genetics and phylogeny have played a major role in its differentiation over evolutionary timescales, the geneaological relationships of individual chimpanzees did not coincide with the similarity in their gut microbial communities. However, the inhabitants from adjacent chimpanzee communities could be distinguished based on the contents of their gut microbiota. Despite the broad similarity of community members, as would be expected from shared diet or interactions, long-term immigrants to a community often harbored the most distinctive gut microbiota, suggesting that individuals retain hallmarks of their previous gut microbial communities for extended periods. This pattern was reinforced in several chimpanzees sampled over long temporal scales, in which the major constituents of the gut microbiota were maintained for nearly a decade.

Reproductive inequality among males in the genus Pan.

Reproductive inequality, or reproductive skew, drives natural selection, but has been difficult to assess, particularly for males in species with promiscuous mating and slow life histories, such as bonobos (Pan paniscus) and chimpanzees (Pan troglodytes). Although bonobos are often portrayed as more egalitarian than chimpanzees, genetic studies have found high male reproductive skew in bonobos. Here, we discuss mechanisms likely to affect male reproductive skew in Pan, then re-examine skew patterns using paternity data from published work and new data from the Kokolopori Bonobo Reserve, Democratic Republic of Congo and Gombe National Park, Tanzania. Using the multinomial index (M), we found considerable overlap in skew between the species, but the highest skew occurred among bonobos. Additionally, for two of three bonobo communities, but no chimpanzee communities, the highest ranking male had greater siring success than predicted by priority-of-access. Thus, an expanded dataset covering a broader demographic range confirms that bonobos have high male reproductive skew. Detailed comparison of data from Pan highlights that reproductive skew models should consider male-male dynamics including the effect of between-group competition on incentives for reproductive concessions, but also female grouping patterns and factors related to male-female dynamics including the expression of female choice. This article is part of the theme issue 'Evolutionary ecology of inequality'.

Malaria-driven adaptation of MHC class I in wild bonobo populations.

The malaria parasite Plasmodium falciparum causes substantial human mortality, primarily in equatorial Africa. Enriched in affected African populations, the B*53 variant of HLA-B, a cell surface protein that presents peptide antigens to cytotoxic lymphocytes, confers protection against severe malaria. Gorilla, chimpanzee, and bonobo are humans' closest living relatives. These African apes have HLA-B orthologs and are infected by parasites in the same subgenus (Laverania) as P. falciparum, but the consequences of these infections are unclear. Laverania parasites infect bonobos (Pan paniscus) at only one (TL2) of many sites sampled across their range. TL2 spans the Lomami River and has genetically divergent subpopulations of bonobos on each side. Papa-B, the bonobo ortholog of HLA-B, includes variants having a B*53-like (B07) peptide-binding supertype profile. Here we show that B07 Papa-B occur at high frequency in TL2 bonobos and that malaria appears to have independently selected for different B07 alleles in the two subpopulations.

Impact of simian immunodeficiency virus infection on chimpanzee population dynamics.

Like human immunodeficiency virus type 1 (HIV-1), simian immunodeficiency virus of chimpanzees (SIVcpz) can cause CD4+ T cell loss and premature death. Here, we used molecular surveillance tools and mathematical modeling to estimate the impact of SIVcpz infection on chimpanzee population dynamics. Habituated (Mitumba and Kasekela) and non-habituated (Kalande) chimpanzees were studied in Gombe National Park, Tanzania. Ape population sizes were determined from demographic records (Mitumba and Kasekela) or individual sightings and genotyping (Kalande), while SIVcpz prevalence rates were monitored using non-invasive methods. Between 2002-2009, the Mitumba and Kasekela communities experienced mean annual growth rates of 1.9% and 2.4%, respectively, while Kalande chimpanzees suffered a significant decline, with a mean growth rate of -6.5% to -7.4%, depending on population estimates. A rapid decline in Kalande was first noted in the 1990s and originally attributed to poaching and reduced food sources. However, between 2002-2009, we found a mean SIVcpz prevalence in Kalande of 46.1%, which was almost four times higher than the prevalence in Mitumba (12.7%) and Kasekela (12.1%). To explore whether SIVcpz contributed to the Kalande decline, we used empirically determined SIVcpz transmission probabilities as well as chimpanzee mortality, mating and migration data to model the effect of viral pathogenicity on chimpanzee population growth. Deterministic calculations indicated that a prevalence of greater than 3.4% would result in negative growth and eventual population extinction, even using conservative mortality estimates. However, stochastic models revealed that in representative populations, SIVcpz, and not its host species, frequently went extinct. High SIVcpz transmission probability and excess mortality reduced population persistence, while intercommunity migration often rescued infected communities, even when immigrating females had a chance of being SIVcpz infected. Together, these results suggest that the decline of the Kalande community was caused, at least in part, by high levels of SIVcpz infection. However, population extinction is not an inevitable consequence of SIVcpz infection, but depends on additional variables, such as migration, that promote survival. These findings are consistent with the uneven distribution of SIVcpz throughout central Africa and explain how chimpanzees in Gombe and elsewhere can be at equipoise with this pathogen.

Genetic and 'cultural' similarity in wild chimpanzees.

The question of whether animals possess 'cultures' or 'traditions' continues to generate widespread theoretical and empirical interest. Studies of wild chimpanzees have featured prominently in this discussion, as the dominant approach used to identify culture in wild animals was first applied to them. This procedure, the 'method of exclusion,' begins by documenting behavioural differences between groups and then infers the existence of culture by eliminating ecological explanations for their occurrence. The validity of this approach has been questioned because genetic differences between groups have not explicitly been ruled out as a factor contributing to between-group differences in behaviour. Here we investigate this issue directly by analysing genetic and behavioural data from nine groups of wild chimpanzees. We find that the overall levels of genetic and behavioural dissimilarity between groups are highly and statistically significantly correlated. Additional analyses show that only a very small number of behaviours vary between genetically similar groups, and that there is no obvious pattern as to which classes of behaviours (e.g. tool-use versus communicative) have a distribution that matches patterns of between-group genetic dissimilarity. These results indicate that genetic dissimilarity cannot be eliminated as playing a major role in generating group differences in chimpanzee behaviour.

Two to Tango: Co-evolution of Hominid Natural Killer Cell Receptors and MHC.

Natural killer (NK) cells have diverse roles in hominid immunity and reproduction. Modulating these functions are the interactions between major histocompatibility complex (MHC) class I molecules that are ligands for two NK cell surface receptor types. Diverse killer cell immunoglobulin-like receptors (KIR) bind specific motifs encoded within the polymorphic MHC class I cell surface glycoproteins, while, in more conserved interactions, CD94:NKG2A receptors recognize MHC-E with bound peptides derived from MHC class I leader sequences. The hominid lineage presents a choreographed co-evolution of KIR with their MHC class I ligands. MHC-A, -B, and -C are present in all great apes with species-specific haplotypic variation in gene content. The Bw4 epitope recognized by lineage II KIR is restricted to MHC-B but also present on some gorilla and human MHC-A. Common to great apes, but rare in humans, are MHC-B possessing a C1 epitope recognized by lineage III KIR. MHC-C arose from duplication of MHC-B and is fixed in all great apes except orangutan, where it exists on approximately 50% of haplotypes and all allotypes are C1-bearing. Recent study showed that gorillas possess yet another intermediate MHC organization compared to humans. Like orangutans, but unlike the Pan-Homo species, duplication of MHC-B occurred. However, MHC-C is fixed, and the MHC-C C2 epitope (absent in orangutans) emerges. The evolution of MHC-C drove expansion of its cognate lineage III KIR. Recently, position -21 of the MHC-B leader sequence has been shown to be critical in determining NK cell educational outcome. In humans, methionine (-21M) results in CD94:NKG2A-focused education whereas threonine (-21T) produces KIR-focused education. This is another dynamic position among hominids. Orangutans have exclusively -21M, consistent with their intermediate stage in lineage III KIR-focused evolution. Gorillas have both -21M and -21T, like humans, but they are unequally encoded by their duplicated B genes. Chimpanzees have near-fixed -21T, indicative of KIR-focused NK education. Harmonious with this observation, chimpanzee KIR exhibit strong binding and, compared to humans, smaller differences between binding levels of activating and inhibitory KIR. Consistent between these MHC-NK cell receptor systems over the course of hominid evolution is the evolution of polymorphism favoring the more novel and dynamic KIR system.

Males with a mother living in their group have higher paternity success in bonobos but not chimpanzees.

In many group-living mammals, mothers may increase the reproductive success of their daughters even after they are nutritionally independent and fully grown [1]. However, whether such maternal effects exist for adult sons is largely unknown. Here we show that males have higher paternity success when their mother is living in the group at the time of the offspring's conception in bonobos (N = 39 paternities from 4 groups) but not in chimpanzees (N = 263 paternities from 7 groups). These results are consistent with previous research showing a stronger role of mothers (and females more generally) in bonobo than chimpanzee societies.

An unusual incident of adoption in a wild chimpanzee (Pan troglodytes) population at Gombe National Park.

Allomothering and adoption are well documented across primate species. Multiple hypotheses have been proposed to explain the evolution of such behavior according to the costs and benefits to the caregiver, mother, and infant. Permanent adoptions and allomothering have been observed in chimpanzees, but they typically involve the infants' siblings or nulliparous females. Here, I report a unique incident of adoption where an infant was adopted by its grandmother without the death of its mother. I conclude by considering how the adoption may have benefited the grandmother, mother, and infant.