The evolution of sexuality in chimpanzees and bonobos

The evolution of nonconceptive sexuality in bonobos and chimpanzees is discussed from a functional perspective. Bonobos and chimpanzees have three functions of sexual activity in common (paternity confusion, practice sex, and exchange for favors), but only bonobos use sex purely for communication about social relationships. Bonobo hypersexuality appears closely linked to the evolution of female-female alliances. I suggest that these alliances were made possible by relaxed feeding competition, that they were favored through their effect on reducing sexual coercion, and that they are ultimately responsible for the relaxed social conditions that allowed the evolution of “communication sex.”     

The evolution of female sexuality and mate selection in humans

Understanding female sexuality and mate choice is central to evolutionary scenarios of human social systems. Studies of female sexuality conducted by sex researchers in the United States since 1938 indicate that human females in general are concerned with their sexual well-being and are capable of sexual response parallel to that of males. Across cultures in general and in western societies in particular, females engage in extramarital affairs regularly, regardless of punishment by males or social disapproval. Families are usually concerned with marriage arrangements only insofar as those arrangements are economically or politically advantageous, but females most often have a voice in arranged marriages. Extended families also concentrate on a couple’s future reproduction rather than on sexual exclusivity. Although marriage for females is often compromised by male or family reproductive interests (which may not in fact differ from female interests), females appear to exercise their sexuality with more freedom than has previously been suggested. Notions of human females as pawns in the male reproductive game, or as traders of sex for male services, should be dispelled.     

The human microbiome in evolution

The trillions of microbes living in the gut—the gut microbiota—play an important role in human biology and disease. While much has been done to explore its diversity, a full understanding of our microbiomes demands an evolutionary perspective. In this review, we compare microbiomes from human populations, placing them in the context of microbes from humanity’s near and distant animal relatives. We discuss potential mechanisms to generate host-specific microbiome configurations and the consequences of disrupting those configurations. Finally, we propose that this broader phylogenetic perspective is useful for understanding the mechanisms underlying human–microbiome interactions.     

The evolution of human biosocial behaviour

The analysis of human behaviour can be approached from three different but complementary perspectives: the first includes the eternal debate about the degree of environmental or genetic determinism of social behaviour; the second, in the context of evolutionary ecology, concerns the evaluation of behavioural responses to morphological and/or environmental changes that have been the key to success in our species; the third, in the context of the analysis of the biology of the health of modern day populations, deals with the biological consequences of social behavioural changes. The secret of the success of a species resides in its capacity to respond behaviourally to the morphological and environmental changes produced during its biological history. What is unique about humans concerns our brains and their derived function: flexible behaviour. The morphological, physiological and behavioural changes that allow thecreation and maintenance of such a large brain are intimately connected to reproduction and therefore to the biosociology of women, the members of the speciesHomo sapiens in whom are combined, with notable success, a prolonged life-cycle, some anatomical and physiological traits and flexible reproductive behaviour, which together confer a decisive demographic advantage on them over other hominids. In summary, as well as contributing to the spread of this information by which women can make informed decisions based on a knowledge of causes, with the aim of optimizing our health it is necessary to consider the possibility of approaching some aspects of our biology and behaviour as patterns fixed by evolution. Three factors would be the most easily adjustable for this purpose: a) to delay the age of sexual maturation, b) to bring forward the age of first maternity, and c) to encourage breastfeeding on demand without substitutes and for a 3–5 month period.     

'Sex and crime' in evolution - why sexuality was so successful

Components of sexuality have fore-runners already in prokaryotes, for instance conjugation, recombination- repair and the molecular constituents needed for nuclear division. For eukaryotes, the basic and predominant mode of propagation is via sexuality, although it is highly complex and costly. Many interactions between individual cells are detrimental for one partner and might be considered as a 'criminal' act performed by the active partner. For instance, the irreversible and non-reciprocal processes of phagocytosis or endocellular parasitism but also the irreversible, asymmetric and sustainable endosymbiosis with a benefit bias in favour of the active partner represent such events. Contrary to this, sexuality in general represents an indirectly reversible, reciprocal, sustainable (by reiteration) and mutually beneficial interaction between equal-ranking cells. After fertilization, a doubled set of genetic information protects against loss of essential genes, while the haplophase allows ridding lethal mutations. Resorting of parental chromosome sets, recombination between homologous chromosomes during meiosis, and new combination of alleles during fertilization, mediate a high genetic variability at a minimum risk of deleterious variants, thus promoting evolutionary adaptability.     

The ontogeny and evolution of human collaboration

How is the human tendency and ability to collaborate acquired and how did it evolve? This paper explores the ontogeny and evolution of human collaboration using a combination of theoretical and empirical resources. We present a game theoretic model of the evolution of learning in the Stag Hunt game, which predicts the evolution of a built-in cooperative bias. We then survey recent empirical results on the ontogeny of collaboration in humans, which suggest the ability to collaborate is developmentally stable across a range of environments. Lastly, we use an account of innateness developed by Ariew (Philos Sci 63:S19–S27, 1996) and Sober (Routledge encyclopedia of philosophy. Routledge, London, pp 794–797, 1998) to assess the extent that (1) the model predicts the fixation of innate collaboration and (2) the empirical studies show a human’s ability to collaborate to be innate.     

The evolution of human influenza viruses.

The evolution of influenza viruses results in (i) recurrent annual epidemics of disease that are caused by progressive antigenic drift of influenza A and B viruses due to the mutability of the RNA genome and (ii) infrequent but severe pandemics caused by the emergence of novel influenza A subtypes to which the population has little immunity. The latter characteristic is a consequence of the wide antigenic diversity and peculiar host range of influenza A viruses and the ability of their segmented RNA genomes to undergo frequent genetic reassortment (recombination) during mixed infections. Contrasting features of the evolution of recently circulating influenza AH1N1, AH3N2 and B viruses include the rapid drift of AH3N2 viruses as a single lineage, the slow replacement of successive antigenic variants of AH1N1 viruses and the co-circulation over some 25 years of antigenically and genetically distinct lineages of influenza B viruses. Constant monitoring of changes in the circulating viruses is important for maintaining the efficacy of influenza vaccines in combating disease.     

The origin and evolution of human pathogens

What are the genetic origins of human pathogens? An international group of scientists discussed this topic at a workshop that took place in late October 2004 in Baeza (Spain). Focusing primarily on bacterial pathogens, they examined the role that pathogenicity islands and bacteriophages play on determining the virulence properties that distinguish closely related members of a given species, such as host range and tissue specificity. They also discussed an instance in which closely related bacterial species differ in the production of a cell surface modification mediating resistance to an antibiotic as a result of the disparate regulation of homologous genes. In certain pathogens, genes normally carrying out housekeeping functions may adopt new functions, whereas in other organisms, genes that respond to stresses associated with non-host environments are silenced during infection to prevent the expression of products that interfere with the normal colonization process. The adaptive behaviour of certain pathogens relies on gene variation at certain loci that by virtue of containing polymeric repeats in regulatory or coding regions, can generate variants that may or may not express products that modify the cell surface of the organism. The meeting also addressed the properties of ORFan genes, which have no homologues in the sequence databases, as well as the creation of genes de novo by duplication and divergence.     

The femur in early human evolution.

Uni- and multivariate analyses of 5 fossil and 215 extant hominoid femora show that two morphological patterns of hominid femora existed about two million years ago. Femora classified as Homo sp. indet. (KNMER 1472 and 1481) are more like Homo sapiens although not identical.Those classified as Australopithecus robustus (SK 82 and 97) and A. boisei (KNM-ER 1503) are similar to one another but uniquely different from any living hominoid. The strong mophological constrasts imply biomechanical and possible locomotor differences, although these are as yet unknown.     

The major histocompatibility complex and human evolution

Many alleles at the human major histocompatibility complex (HLA) loci diverged before the divergence of humans and great apes from a common ancestor. This fact puts a lower limit on the size of the bottleneck in human evolution: the genus Homo must have been founded by no less than ten and probably by more than 10,000 individuals.     

The ecology of social transitions in human evolution

We know that there are fundamental differences between humans and living apes, and also between living humans and their extinct relatives. It is also probably the case that the most significant and divergent of these differences relate to our social behaviour and its underlying cognition, as much as to fundamental differences in physiology, biochemistry or anatomy. In this paper, we first attempt to demarcate what are the principal differences between human and other societies in terms of social structure, organization and relationships, so that we can identify what derived features require explanation. We then consider the evidence of the archaeological and fossil record, to determine the most probable context in time and taxonomy, of these evolutionary trends. Finally, we attempt to link five major transitional points in hominin evolution to the selective context in which they occurred, and to use the principles of behavioural ecology to understand their ecological basis. Critical changes in human social organization relate to the development of a larger scale of fission and fusion; the development of a greater degree of nested substructures within the human community; and the development of intercommunity networks. The underlying model that we develop is that the evolution of ‘human society’ is underpinned by ecological factors, but these are influenced as much by technological and behavioural innovations as external environmental change.     

The evolution of reciprocity in sizable human groups

The scale and complexity of human cooperation is an important and unresolved evolutionary puzzle. This article uses the finitely repeated n person Prisoners’ Dilemma game to illustrate how sapience can greatly enhance group-selection effects and lead to the evolutionary stability of cooperation in large groups. This affords a simple and direct explanation of the human “exception.”