Both male ornamentation and male combat result in increased male mortality. Because population sizes are limited by a carrying capacity, increased age-specific adult male mortality will result in decreased age-specific adult female mortality, as well as decreased juvenile mortality. As intersexual competition is one form of intraspecific competition, through choosing to mate with ornamented and/or combative males, females in polygamous systems reduce intraspecific competition. Because average male fitness must exactly equal average female fitness, male fitness will paradoxically rise with increasing (...) male mortality. This theory also offers new perspectives on peripheral problems to sexual theory, such as mate location, resource guarding, leks, harems, and others. (shrink)

Turtles are among the most intriguing amniotes but their communication and signaling have rarely been studied. Traditionally, they have been seen as basically just silent armored ‘walking stones’ with complex physiology but no altruism, maternal care, or aesthetic perception. Recently, however, we have witnessed a radical change in the perception of turtle behavioral and cognitive skills. In our study, we start by reviewing some recent findings pertaining to various highly developed behavioral and cognitive patterns with special emphasis on turtles. Then (...) we focus on freshwater turtles and use data about their sexual behavior and size sexual dimorphism to test whether conspicuous coloration of the head is in these animals related to sexual processes. We found that absence of aggressive mating behavior is statistically associated with the presence of conspicuous coloration on turtles’ heads. It also seems that while species with female-biased SSD are characterised by conspicuously colored head ornaments, in species with male-biased SSD conspicuous coloration is absent. Unlike large females, males thus seem to be under pressure to develop conspicuous coloration and engage in non-aggressive behavior using signaling to succeed in courtship. And finally, we discuss possible roles of head color patterns in turtle communication during mating. (shrink)

The differentiation of male and female characteristics in vertebrates and insects has long been thought to proceed via different mechanisms. Traditionally, vertebrate sexual development was thought to occur in two phases: a primary and a secondary phase, the primary phase involving the differentiation of the gonads, and the secondary phase involving the differentiation of other sexual traits via the influence of sex hormones secreted by the gonads. In contrast, insect sexual development was thought to depend exclusively on (...) cell‐autonomous expression of sex‐specific genes. Recently, however, new evidence indicates that both vertebrates and insects rely on sex hormones as well as cell‐autonomous mechanisms to develop sexual traits. Collectively, these new data challenge the traditional vertebrate definitions of primary and secondary sexual development, call for a redefinition of these terms, and indicate the need for research aimed at explaining the relative dependence on cell‐autonomous versus hormonally guided sexual development in animals. (shrink)

Sex, Gender, Ethics, and the Darwinian Evolution of Humanity examines the impact of Darwin's 'Descent of Man' on contemporary biology and the humanities. Its publication in 1871 was a founding event in anthropology. Its content was primarily concerned with the development of sexual life, social life, and intellectual life, not only as outcomes of evolution, but as components that have actively intermixed over time with the evolutionary mechanism of natural selection. The stamp of Darwinism on modern thought is still (...) very important and brings novelties to academic studies. Several fields influenced by Darwinian anthropology developed in recent decades, including evolutionary ethics, the evolution of sociality and sexual communication in animal and plant species. Sociobiology and evolutionary psychology are topics that draw heavily on Darwin's 'Descent of Man'. The understanding of Darwin's thought has also progressed greatly in recent decades, following the systematic study of Darwin's correspondence and notebooks, leading to a reassessment of the development of his thought on humans, social groups, and heredity, and how they come together in his theory of evolution. The book combines a historical perspective on Darwin's achievement and his legacy. It will be of interest to students and scholars in a variety of fields, from experimental biology to the social and historical sciences. (shrink)

In 1859, Charles Darwin proposed a mechanism for biological evolution in his most famous work, On the Origin of Species. However, Origin makes little mention of humans. Despite this, Darwin thought deeply about humans and in 1871 published The Descent of Man, his influential and controversial book in which he applied evolutionary theory to humans and detailed his theory of sexual selection. February 2021 will mark the 150th anniversay of it's publication. In A Most Interesting Problem, twelve leading anthropologists, (...) biologists, and journalists revisit The Descent. Following the same organization as the first edition of Descent - less the large section on sexual selection -- each author reviews what Darwin wrote in Descent, comparing his words to what we now know now. There are chapters on evidence for human evolution, our place in the family tree, the origins of civilization, human races, intelligence, and sex differences. An introduction by Darwin biolographer and historian Janet Browne provides context for Descent and a conclusion by Science magazine journalist Ann Gibbons looks to the future of the study of human evolution. All the chapters are written with a broad audience in mind. Ultimately, readers learn that Darwin was remarkably prophetic in some of his predictions, such as that the earliest human fossils would be discovered in Africa. But he was wrong in other areas, particularly in regards to variations between the sexes and races. Thus, A Most Interesting Problem is not so much a celebration of Darwin as it is a tribute to how science works, how scientific ideas are tested, and the role of evidence in helping structure narratives of human origins. The reader is left with a view of how far we have come in our quest for understanding human origins, biological variation, behavior, and evolution. (shrink)

Divided into three parts, this book's purpose, as given in the introduction, is to consider whether or not man is descended from a pre-existing form, his manner ...

In the history of zoology the English anatomist Morrison Watson (1845-1885) is considered to be the discoverer of the masculinized sexual organs of the spotted hyena. Beginning in 1877, Watson had published a series of anatomical studies on the spotted hyena (Watson, 1877, 1878, 1881, Watson and Young, 1879), in which he, in which he for the first time made public the anatomical peculiarities of the female spotted hyena's genitalia. This scientific achievement is well documented. But now we can (...) also state that a hundred years before Watson the Dutch amateur zoologist Robert Jacob Gordon (1743-1795), while serving in the Scots Brigades at the Cape of Good Hope, had already made the same discovery and merely unfortunate personal circumstances prevented publication. During his stay at the Cape, Gordon had studied spotted hyenas intensively and recorded his observations in accurate drawings and comments. These drawings have been preserved as part of a large collection of animal drawings entitled Gordon Atlas. With his discovery, Gordon actually was the first to provide empirical evidence of a '' curious and inexplicable case of dimorphism" (Darwin on a beetle) in mammalians, long before Etienne Geoffrey Saint-Hilaire (Cours de l'histoire naturelle des mammifères, 1829) started examining masculinized sexual organs in the mole or Darwin recognized the importance of sexual dimorphism (Descent of Man, 1871). In this paper we reproduce for the first time all hyena drawings from the Gordon Atlas, including Gordon's handwritten notes in the margins in the original Dutch and in translation. Additionally, we briefly delineate the knowledge about the South African spotted hyena in Gordon's time and indicate that we doubt Watson's explanation for the age-old confusion about the hyena. (shrink)

The concept of animal personality is based on consistent individual differences in behaviour, yet little is known about the factors responsible for such variation. Theory based on sex-specific selection predicts sexual dimorphism in personality-related traits and, in some cases, differences in trait variances between the sexes. In this study, we examined the sources of individual variation for boldness behaviour in guppies (Poecilia reticulata). We first demonstrated heightened boldness expression in males relative to females across feral wild types, artificially (...) selected domestic ‘designer’ guppies, and putative hybrids of the two. Boldness and body size covaried at the strain level but were not associated among individuals within strains. We also found high and repeatable behavioural differences among individuals (0.40 > intraclass r > 0.60) in all sex/strain groups except hybrid strain females. However, there was no evidence for the heightened inter-individual male variance anticipated for personality traits subject to certain forms of directional sex-specific selection. Domestic fish were boldest overall, and indicated the largest sex difference, which is consistent with genetic linkage between boldness and male ornamental colouration. Consistently high intrinsic variation in boldness behaviour, which extends to inbred domesticated fish, may in part underpin the invasive potential of this species. (shrink)

Different animal groups exhibit a surprisingly diversity of sex determination systems. Moreover, even systems that are superficially similar may utilize different underlying mechanisms. This diversity is illustrated by a comparison of sex determination in three well‐studied model organisms: the fruitfly Drosophila melanogaster, the nematode Caenorhabditis elegans, and the mouse. All three animals exhibit male heterogamety, extensive sexual dimorphism and sex chromosome dosage compensation, yet the molecular and cellular processes involved are now known to be quite unrelated. The (...) similarities must have arisen by convergent evolution. Studies of sex determination demonstrate that evolution can produce a variety of solutions to the same basic problems in development. (shrink)

Different animal groups exhibit a surprisingly diversity of sex determination systems. Moreover, even systems that are superficially similar may utilize different underlying mechanisms. This diversity is illustrated by a comparison of sex determination in three well‐studied model organisms: the fruitfly Drosophila melanogaster, the nematode Caenorhabditis elegans, and the mouse. All three animals exhibit male heterogamety, extensive sexual dimorphism and sex chromosome dosage compensation, yet the molecular and cellular processes involved are now known to be quite unrelated. The (...) similarities must have arisen by convergent evolution. Studies of sex determination demonstrate that evolution can produce a variety of solutions to the same basic problems in development. (shrink)

Animals exist as biodiverse composite organisms that include microbial residents, eukaryotic cells, and organs that collectively form a human being. Through an interdependent relationship and an inherent ability to transmit and reciprocate stimuli in a bidirectional way, a human body or the holobiont secures growth, health, and reproduction. As such, the survival of a holobiont is dependent on the maintenance of biological order including metabolic homeostasis by tight regulation of the communication between its eukaryotic and prokaryotic residents. In this (...) review an overview and perspective are provided on the bidirectional communication between microbes and their host in mutually nurturing biochemical, biological, and social interconnected relationships between the components of the holobiont. An emphasis is placed on exemplifying microbiome‐mediated effects on host functions—aiming to integrate microbiome functionality to host physiology, be it health or disease. Nutrition, immunology, and sexual dimorphism have been traversed extensively to reflect on health and mind states, social interactions, and urbanization defects/effects. Finally, examples of molecular mechanisms potentially orchestrating these complex transkingdom interactions are provided. (shrink)

The view that female mammals are more docile appears to arise in part from imposing human values on animal studies. Many reports of sexual dimorphism in physical aggression favouring the male in laboratory rodents appear to select circumstances where that expectation is supported. Other situations that favour the expression of conflict in females have been (until recently) relatively little studied. Although female rodents generally do not show the “ritualised” forms of conflict that characterise male sexual competition, they (...) can use notably damaging strategies (especially if they are of short duration). Such considerations might weigh in the selection of strategies by our own species. (shrink)

In the history of zoology the English anatomist Morrison Watson (1845–1885) is considered to be the discoverer of the masculinized sexual organs of the spotted hyena. Beginning in 1877, Watson had published a series of anatomical studies on the spotted hyena (Watson, 1877, 1878, 1881, Watson and Young, 1879), in which he, in which he for the first time made public the anatomical peculiarities of the female spotted hyena’s genitalia. This scientific achievement is well documented. But now we can (...) also state that a hundred years before Watson the Dutch amateur zoologist Robert Jacob Gordon (1743–1795), while serving in the Scots Brigades at the Cape of Good Hope, had already made the same discovery and merely unfortunate personal circumstances prevented publication. During his stay at the Cape, Gordon had studied spotted hyenas intensively and recorded his observations in accurate drawings and comments. These drawings have been preserved as part of a large collection of animal drawings entitled Gordon Atlas. With his discovery, Gordon actually was the first to provide empirical evidence of a “curious and inexplicable case of dimorphism” (Darwin on a beetle) in mammalians, long before Étienne Geoffrey Saint-Hilaire (Cours de l’histoire naturelle des mammifères, 1829) started examining masculinized sexual organs in the mole or Darwin recognized the importance of sexual dimorphism (Descent of Man, 1871). In this paper we reproduce for the first time all hyena drawings from the Gordon Atlas, including Gordon’s handwritten notes in the margins in the original Dutch and in translation. Additionally, we briefly delineate the knowledge about the South African spotted hyena in Gordon’s time and indicate that we doubt Watson’s explanation for the age-old confusion about the hyena. (shrink)