1. Darwin’s other big idea

2018 ◽  
pp. 1-15 ◽  
Author(s):  
Leigh W. Simmons
Keyword(s):  
Sexual Selection ◽  
Female Choice ◽  
Egg Production ◽  
Sexual Differences ◽  
The Other ◽  
Sexual Competition ◽  
Sexual Characteristics ◽  
Sexual Selection Theory ◽  
Males And Females ◽  
Selection Of

The idea that males and females often look, sound, smell, and behave differently is uncontroversial. Where those differences came from, however, and what role they play in various species—including humans—is not. ‘Darwin’s other big idea’ outlines Charles Darwin’s sexual selection theory: differential reproduction based on sexual competition, whether between the members of one sex for access to the other, or by selection of particular mating partners. Differences in reproductive parts directly involved in sperm or egg production—primary sexual characteristics—were relatively easy to explain. The other kinds of sexual differences, he proposed, could evolve in one of two ways: male–male competition resulting in weapons, or female choice resulting in ornaments, but this was highly controversial.

Reproductive behavior

2018 ◽  
Author(s):  
Rachel Olzer ◽  
Rebecca L. Ehrlich ◽  
Justa L. Heinen-Kay ◽  
Jessie Tanner ◽  
Marlene Zuk
Keyword(s):  
Sexual Selection ◽  
Sexual Conflict ◽  
Female Choice ◽  
Reproductive Behavior ◽  
Mating Systems ◽  
Insect Behavior ◽  
Sequential Approach ◽  
Evolutionary Mechanisms ◽  
Anatomy And Physiology ◽  
Males And Females

Sex and reproduction lie at the heart of studies of insect behavior. We begin by providing a brief overview of insect anatomy and physiology, followed by an introduction to the overarching themes of parental investment, sexual selection, and mating systems. We then take a sequential approach to illustrate the diversity of phenomena and concepts behind insect reproductive behavior from pre-copulatory mate signalling through copulatory sperm transfer, mating positions, and sexual conflict, to post-copulatory sperm competition, and cryptic female choice. We provide an overview of the evolutionary mechanisms driving reproductive behavior. These events are linked by the economic defendability of mates or resources, and how these are allocated in each sex. Under the framework of economic defendability, the reader can better understand how sexual antagonistic behaviors arise as the result of competing optimal fitness strategies between males and females.

scholarly journals Variation in Chin and Mandibular Symphysis Size and Shape in Males and Females: A CT-Based Study

2020 ◽  
Vol 17 (12) ◽  
pp. 4249
Author(s):  
Tatiana Sella Tunis ◽  
Israel Hershkovitz ◽  
Hila May ◽  
Alexander Dan Vardimon ◽  
Rachel Sarig ◽  
...  
Keyword(s):  
Sexual Selection ◽  
Anatomical Landmark ◽  
Anatomical Structure ◽  
Sexually Dimorphic ◽  
Selection Theory ◽  
Size And Shape ◽  
Size Index ◽  
Sexual Selection Theory ◽  
Males And Females ◽  
Anthropological Literature

The chin is a unique anatomical landmark of modern humans. Its size and shape play an important role from the esthetic perspective. However, disagreement exists in the dental and anthropological literature regarding the sex differences in chin and symphysis morphometrics. The “sexual selection” theory is presented as a possible reason for chin formation in our species; however, many other contradictory theories also exist. This study’s aims were therefore to determine how chin and symphysis size and shape vary with sex, and to discuss “sexual selection” theory as a reason for its formation. Head and neck computed tomography (CT) scans of 419 adults were utilized to measure chin and symphysis sizes and shapes. The chin and symphysis measures were compared between the sexes using an independent-samples t-test, a Mann–Whitney test, and the F-statistic. The chin width was significantly greater in males than in females (p < 0.001), whereas the chin height, area, and size index were significantly greater in females (p < 0.001). Symphysis measures did not differ significantly between the sexes. Size accounted for 2–14% of the chin variance and between 24–33% of the symphysis variance. Overall, the chin was found to be a more heterogeneous anatomical structure than the symphysis, as well as more sexually dimorphic.

scholarly journals Sexual selection and hermaphroditic organisms: Testing theory

2013 ◽  
Vol 59 (4) ◽  
pp. 579-588 ◽  
Author(s):  
Janet L. Leonard
Keyword(s):  
Sexual Selection ◽  
Reproductive Success ◽  
Multiple Mating ◽  
The Other ◽  
Operational Sex Ratio ◽  
Sexual Role ◽  
Sexual Roles ◽  
Sexual Selection Theory ◽  
Variance In Reproductive Success ◽  
Simultaneous Hermaphrodites

Abstract Sexual selection is widespread if not ubiquitous in hermaphroditic organisms. Although many phenomena that have been described as sexual selection in gonochores, (e.g. harem polygamy, multiple mating, elaborate courtship, even secondary sexual characters) can be found in some hermaphrodites, what is more interesting is the ways in which sexual selection in hermaphrodites may differ from dioecious taxa. In hermaphrodites, an individual’s mating success includes its success from both sexual roles. Secondly, in many simultaneously hermaphroditic taxa there is strong evidence of sexual selection and yet the operational sex ratio is 1:1, by definition. Many simultaneous hermaphrodites have elaborate courtship and genital anatomy, suggesting sexual selection plays an important role in reproductive success. Sperm competition and cryptic female choice mean that the number of mates acquired is not necessarily a predictor of reproductive success. Even in simultaneous hermaphrodites with reciprocal mating, variance in reproductive success through the male role and through the female role may differ in a population. Moreover hermaphrodites may choose to emphasize one sexual role over the other. Data suggest that the preferred role varies in hermaphrodites, which creates an opportunity to test fundamental predictions and assumptions of sexual selection theory. Hermaphrodites may vary their emphasis on one sexual role over the other either developmentally or behaviorally in response to environmental or social parameters. How they use this capability in acquiring more or higher quality mates still requires study.

Fighting success in relation to body mass and drumming activity in the male wolf spider Hygrolycosa rubrofasciata

1997 ◽  
Vol 75 (9) ◽  
pp. 1532-1535 ◽  
Author(s):  
Janne Kotiaho ◽  
Rauno V. Alatalo ◽  
Johanna Mappes ◽  
Silja Parri
Keyword(s):  
Sexual Selection ◽  
Body Mass ◽  
Wolf Spider ◽  
Male Body ◽  
Male Courtship ◽  
Hygrolycosa Rubrofasciata ◽  
Males And Females ◽  
A Minor ◽  
Selection Of ◽  
Agonistic Encounters

In the wolf spider Hygrolycosa rubrofasciata, males court females by drumming dry leaves with their abdomen. Females prefer to mate with the most actively drumming males, and courtship drumming activity is also positively correlated with male viability. However, body mass of the males seems to have only a minor, if any, effect on female choice or male viability. There is also no correlation between male body mass and courtship drumming activity. We studied the effect of body mass and courtship drumming activity on the outcome of agonistic encounters between male H. rubrofasciata. For this purpose, males and females were randomly placed in a plastic arena, where male courtship drumming activity and agonistic encounters were recorded. Large differences in body mass and drumming activity between two rivals seemed to independently increase the probability of the larger or more active males winning. We conclude that while courtship drumming activity affects the fighting success of the males, and body mass more so, male–male interactions may not be of major importance in sexual selection of H. rubrofasciata.

The Sexual Brain

2021 ◽  
pp. 81-108
Author(s):  
Susan D. Healy
Keyword(s):  
Sex Differences ◽  
Sexual Selection ◽  
Brain Size ◽  
Female Mate Choice ◽  
Brain Regions ◽  
Good Evidence ◽  
The Other ◽  
Female Mate ◽  
Males And Females ◽  
Hippocampal Structure

Morphological and behavioural differences between the sexes are ubiquitous across the animal kingdom. There is also good evidence for differences in some brain regions between males and females, in humans, some rodents, and many songbirds. I look at the data for sex differences in cognition, of which there are some that show differences in spatial cognition and in hippocampal structure, at least some of which may be explained by variation in hormone levels. The thesis of The Mating Mind by Geoffrey Miller considerably increased interest in using sexual selection to explain variation in brain size. From female mate choice, male–male competition, sperm competition, mating strategy, to parental care, there are some data that appear to support selection acting on one species rather than the other in sexually a selected manner but I conclude that the data are not generally supportive of the Sexual Brain Hypothesis.

Reproduction and development

2012 ◽  
Keyword(s):  
Sexual Dimorphism ◽  
Brain Structures ◽  
Sexual Differences ◽  
Tissue Type ◽  
Endocrine Control ◽  
Human Form ◽  
Form And Function ◽  
Sexual Characteristics ◽  
Males And Females ◽  
And Function

Reproduction and development are large topics, knowledge of which underpins several medical specialities including sexual health, fertility, gynaecology, urology, reproductive endocrinology, obstetrics, and neonatology. Doctors need to know the structure, function, and endocrine control of both male and female systems in order to diagnose and manage conditions specific to either male or female organs, as well as conditions such as impotence and infertility. Not surprisingly, the reproductive system is the only body system that shows major differences in both structure and function between males and females. However, sexual differences go beyond the primary sexual characteristics present at birth and the secondary sexual characteristics that emerge under the influence of sex hormones at puberty. Sexual dimorphism in some brain structures commences at an early age, and differences in the endocrine profiles of males and females produce characteristic changes in morphology, physiology, and behaviour that go beyond simple sexual dimorphism to affect many aspects of life, including sexual differences in susceptibility to disease and the longer life expectancy of women as compared to men that is seen around the world. Whether these differences, mainly beneficial to women, are because females are ‘biologically superior’ or because of a complex mix of genetic, behavioural, and social factors is a matter for discussion and research. Some knowledge of embryology is important to every medical student. As a minimum it provides explanations for the congenital malformations and their consequences that are encountered in many areas of clinical practice. Deeper knowledge will assist those seeking real insights into the structure of the human body. It is the study of embryological development and the knowledge of how each tissue type arises, how one tissue meets another, and how tissues move and change shape during development that explains the relations between tissues and organs in the adult human form. Achieving a full understanding of the dynamics of the formation of the body’s organs and tissues is demanding, but it can replace some of the rote learning of anatomical structures, familiar to many students, with a deeper understanding of form and function.

scholarly journals Migration strategy and divergent sexual selection on bird song

2008 ◽  
Vol 276 (1656) ◽  
pp. 585-590 ◽  
Author(s):  
Sarah A Collins ◽  
Selvino R de Kort ◽  
Javier Pérez-Tris ◽  
José Luis Tellería
Keyword(s):  
Sexual Selection ◽  
Female Choice ◽  
Selection Pressure ◽  
Migratory Birds ◽  
Male Competition ◽  
Migration Strategy ◽  
Migration Patterns ◽  
Complex Song ◽  
Males And Females ◽  
First Time

Migratory birds are assumed to be under stronger sexual selection pressure than sedentary populations, and the fact that their song is more complex has been taken as confirmation of this fact. However, this assumes that sexual selection pressure due to both male competition and female choice increase together. A further issue is that, in many species, songs become less complex during competitive encounters; in contrast, female choice selects for more complex song, so the two selection pressures may drive song evolution in different directions. We analysed song in two sedentary and two migratory populations of blackcaps ( Sylvia atricapilla ), a species in which different song parts are directed to males and females. We found that migratory populations produce longer, female-directed warbles, indicating sexual selection through female choice is the strongest in these populations. However, the part of the song directed towards males is shorter and more repetitive (as observed in individual competitive encounters between males) in non-migratory populations, indicating sedentary populations, are under stronger selection due to male competition. We show for the first time that the intensity of selection pressure from male competition and female choice varies independently between populations with different migratory behaviours. Rapid alterations in the migration patterns of species are thus likely to lead to unexpected consequences for the costs and benefits of sexual signals.

scholarly journals A Phylogenetic Perspective on the Evolution of Chromatic Ultraviolet Plumage Coloration in Grackles and Allies (Icteridae)

The Auk ◽  
2006 ◽  
Vol 123 (1) ◽  
pp. 211-234 ◽  
Author(s):  
Muir D. Eaton
Keyword(s):  
Sexual Selection ◽  
Large Body ◽  
Plumage Coloration ◽  
Behavioral Studies ◽  
Evolutionary Force ◽  
Evolutionary Changes ◽  
Phylogenetic Perspective ◽  
Males And Females ◽  
Museum Study ◽  
Selection Of

Abstract Plumage traits have been studied intensely for more than a century, especially bright and exaggerated plumage. A large body of evidence across a range of avian taxa supports sexual selection as a major evolutionary force acting on plumage colors. The discovery of ultraviolet (UV) coloration in avian plumage resulted in the extension of sexual selection hypotheses to explain the evolution of potential UV plumage traits. However, there have been no comparative evolutionary studies elucidating the origin of UV signals in birds. Here, I used a comparative phylogenetic approach to investigate the evolution of chromatic UV plumage colors in the grackles-and-allies clade of the New World blackbirds (Icteridae). On the basis of reflectance data collected from museum study skins, I have determined that UV plumage signals have evolved multiple times from an ancestral condition that lacked UV plumage signals, with very few unambiguous reversals. Although UV plumage has evolved in both males and females, there have been significantly more evolutionary changes in male UV plumage characters. Concentrated changes tests and correlations of independent contrasts reveal evidence for sexual selection of some male UV plumage characters, as well as an increase in UV plumage coloration for species found in open habitats. These results support the use of objective assessments of avian colors (i.e. spectrophotometry) to properly interpret patterns of plumage evolution generally, and they suggest the need for behavioral studies on the function of chromatic UV signals in several blackbird species. Una Perspectiva Filogenética sobre la Evolución de la Coloración Ultravioleta en los Changos y Chamones (Icteridae)

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