Human Sperm Competition
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Sperm Competition In Humans
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Author : Todd K. Shackelford
language : en
Publisher: Springer Science & Business Media
Release Date : 2006-11-22
Sperm Competition In Humans written by Todd K. Shackelford and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006-11-22 with Science categories.
In species with internal fertilization, sperm competition occurs when the sperm of two or more males simultaneously occupy the reproductive tract of a female and compete to fertilize an egg (Parker, 1970). A large body of empirical research has demonstrated that, as predicted by sperm competition theory, males and females in many species possess anatomical, behavioral, and physiological adaptations that have evolved to deal with the adaptive challenges associated with sperm competition. Moreover, in recent years, evolutionary biologists and psychologists have begun to examine the extent to which sperm competition may have been an important selective pressure during human evolution. Some research has suggested that male humans, like males of many bird, insect, and rodent species, might be able to adjust the number of sperm they inseminate according to the risk of sperm competition. Other research has examined whether such responses might be accompanied by psychological changes that motivate human males to pursue copulations when the risk of sperm competition is high. Furthermore, there is research suggesting that aspects of human penile anatomy might function to enhance success in sperm competition. Much of this work has been controversial; some of the findings have been disputed and others have been greeted with skepticism. However, the idea that some aspects of human psychology and behavior might best be understood as adaptations to sperm competition remains intriguing and, in certain cases, very persuasive.
Human Sperm Competition
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Author : Robin Baker
language : en
Publisher: eBook Partnership
Release Date : 2014-06-16
Human Sperm Competition written by Robin Baker and has been published by eBook Partnership this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014-06-16 with Science categories.
Since the 1970s, behavioural ecologists and evolutionary biologists have been fascinated by the biological implications of sperm from different males competing for fertilization of the egg in the female reproductive tract. But until Human Sperm Competition there had never been a discussion of the phenomenon for the human species in book form, despite its relevance for a full understanding of human reproduction.The book is a pioneering analysis of the evolutionary biology of human sexuality, proposing that all aspects have been shaped by the phenomenon of sperm competition. Written 20 years ago in 1993-94, the print edition was published in 1995. Despite its age that book's contents are as relevant now as they were two decades ago. Perhaps even more so, because since Baker and Bellis' demonstration that human sperm competition could actually be studied in a variety of ways a number of research groups have taken up the challenge where they left off. Most of these groups have obtained results that build firmly upon Baker and Bellis' original work. A few others created important dialogues. None though have destroyed any crucial part of the foundation first laid down in that 1995 book. But the main way in which Human Sperm Competition remains relevant to this day is that for various reasons - some cultural, some procedural, and yet others due to sheer opportunity - Baker and Bellis were able to do a number of experiments that others since have not had the opportunity to repeat. And the results of those unique experiments were presented in Human Sperm Competition and nowhere else.In the first half of the book the authors explore the role of sperm competition in the evolution of human sexual characteristics, considering for example the architecture of the female reproductive tract, the reasons for male and female infidelity and the possible biological reasons for homosexuality, masturbation and orgasm.In the second half, the mechanism of sperm competition is evaluated in detail, together with the evidence for and the implications of the authors' own Kamikaze Sperm Hypothesis. Human Sperm Competition sets out the thesis that adopting an evolutionary approach to human reproduction exposes the subtle and sophisticated ways in which human sexual anatomy, physiology and behaviour are designed to interact. As a species, understanding this sexual legacy helps explain how we reproduce today and why problems with fertility arise.Over the years, Human Sperm Competition has become a classic in the study of human sexual biology - but although the original hardback is still in print rising costs plus perhaps its classic status have priced it beyond those students who might most wish to read its contents. This digital edition of the original 1995 publication, but at a student-friendly price, now solves this problem.
Special Issue On Human Sperm Competition
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Author : Todd K. Shackelford
language : en
Publisher:
Release Date : 2006
Special Issue On Human Sperm Competition written by Todd K. Shackelford and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with categories.
Sperm Competition And The Evolution Of Animal Mating Systems
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Author : Robert L. Smith
language : en
Publisher: Elsevier
Release Date : 2012-12-02
Sperm Competition And The Evolution Of Animal Mating Systems written by Robert L. Smith and has been published by Elsevier this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012-12-02 with Science categories.
Sperm Competition and the Evolution of Animal Mating Systems describes the role of sperm competition in selection on a range of attributes from gamete morphology to species mating systems. This book is organized into 19 chapters and begins with the conceptualization of sperm competition as a subset of sexual selection and its implications for the insects. The following chapter describes the relationship between multiple mating and female fitness, with an emphasis on determining the conditions under which selection on females is likely to counteract selection on males for avoiding sperm competition. Other chapters consider the female perspective on sperm competition; the evolutionary causation at the level of the individual male gamete; and the correlation of high paternal investment and sperm precedence in the insects. The remaining chapters are arranged phylogenetically and explore the sperm competition in diverse animal taxa, such as the Drosophila, Lepidoptera, spiders, amphibians, and reptiles. These chapters also cover the evolution of direct versus indirect sperm transfer among the arachnids or the problem for kinship theory presented by multiple mating and sperm competition in the Hymenoptera. This book further discusses the remarkable potential for sperm competition among certain temperate bat species whose females store sperm through winter hibernation and the mixed strategies and male-caused female genital trauma as possible sperm competition adaptations in poeciliid fishes. The concluding chapter examines the predictions concerning testes size and mating systems in the primates and the possible role of sperm competition in human selection. This book is of great value to reproductive biologists and researchers.
Human Sperm Competition The Influence Of Physical Environmental And Behavioural Variables Upon Ejaculate Composition And An Evaluation Of The Possible Mechanism Of Sperm Competition
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Author : Christopher Bainbridge
language : en
Publisher:
Release Date : 1998
Human Sperm Competition The Influence Of Physical Environmental And Behavioural Variables Upon Ejaculate Composition And An Evaluation Of The Possible Mechanism Of Sperm Competition written by Christopher Bainbridge and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1998 with categories.
Sperm Wars
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Author : Robin Baker
language : en
Publisher: Hachette UK
Release Date : 2020-10-06
Sperm Wars written by Robin Baker and has been published by Hachette UK this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020-10-06 with Psychology categories.
This classic work on the rules of sex -- updated for a new generation -- is still as provocative as the day it was published, providing simple explanations for any and all questions about what happens in the bedroom. Sex isn't as complicated as we make it. In Sperm Wars, evolutionary biologist Robin Baker argues that every question about human sexuality can be explained by one simple thing: sperm warfare. In the interest of promoting competition between sperm to fertilize the same egg, evolution has built men to conquer and monopolize women while women are built to seek the best genetic input on offer from potential sexual partners. Baker reveals, through a series of provocative fictional scene, the far-reaching implications of sperm competition. 10% of children are not fathered by their "fathers;" over 99% of a man's sperm exists simply to fight off all other men's sperm; and a woman is far more likely to conceive through a casual fling than through sex with her regular partner. From infidelity, to homosexuality, to the female orgasm, Sperm Wars turns on every light in the bedroom. Now with new material reflecting the latest research on sperm warfare, this milestone of popular science will still surprise, entertain, and even shock.
Sperm Competition In Humans
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Author : Samantha Jane Leivers
language : en
Publisher:
Release Date : 2014
Sperm Competition In Humans written by Samantha Jane Leivers and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014 with categories.
In species where females mate with multiple males, sperm competition may occur whereby the sperm of two or more males compete on a post copulatory level to fertilise the ova of a single female. Selection via sperm competition has given rise to the evolution of adaptations that affect a male's chances of paternity when a female has mated, or is likely to mate, with another male. These adaptations improve a male's chances of paternity by i) avoiding or preventing sperm competition from occurring (defensive tactics) and ii) by engaging in sperm competition (offensive tactics). Adaptations to sperm competition can be morphological, behavioural or physiological. The aim of this thesis was to investigate the role that sperm competition has played in human evolution, particularly the evolution of defensive psychological adaptations and offensive physiological adaptations. In Chapter 1, I examine the current evidence for morphological, behavioural and physiological adaptations for sperm competition in non-human animals and consider what this tells us about sperm competition in humans. The available evidence suggests that humans have primarily evolved defensive adaptations in response to the risk of sperm competition but that considerable further research investigating offensive adaptations to sperm competition in humans must be conducted before firm conclusions can be drawn. In Chapter 2, I investigate the evolution of psychological adaptations in humans and provide the first known evidence that men can show accuracy in their judgements of faithfulness. This accuracy is dependent on the experimental task and stimuli used. Further investigation showed that priming men to an environment depicting sexual competition from rival males does not improve men's accuracy in judgements of faithfulness. In Chapters 3 and 4, I examine the evolution of physiological adaptations to sperm competition in men by investigating the factors that influence ejaculate quality and how these relate to sperm competition theory. Sperm competition theory predicts that males will increase ejaculate investment when mating with attractive females, although increasing evidence suggests that the quality of the male himself can also influence ejaculate quality (phenotype-linked fertility hypothesis). In Chapter 3, I show that ejaculate quality increases with a composite measure of male mate value, but only when men view images of highly attractivewomen. In Chapter 4, I investigate the extent to which men covary their performance of defensive and offensive sperm competition tactics. If a male's defensive tactics are highly successful at preventing or avoiding sperm competition, one would expect reduced investment in offensive adaptations for the engagement in sperm competition, and vice versa. In this study, I show that men in committed heterosexual relationships who perform more mate guarding behaviours produce ejaculates of poorer quality. These findings suggest that men covary their investment in defensive adaptations that function to avoid or prevent sperm competitions and offensive adaptations that function to engage in sperm competition. Together, these studies examine the role that sperm competition has played through human evolution. I contribute to the literature that suggests that men have evolved psychological adaptations that function to avoid sperm competition by showing that men display some accuracy in their judgements of female faithfulness. Furthermore, I add to a growing literature that variation in men'sejaculate quality can, in part, be attributed to sperm competition risk.
The Oxford Handbook Of Sexual Conflict In Humans
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Author : Todd K. Shackelford
language : en
Publisher: Oxford University Press
Release Date : 2012-01-04
The Oxford Handbook Of Sexual Conflict In Humans written by Todd K. Shackelford and has been published by Oxford University Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012-01-04 with Psychology categories.
Sexual conflict -- what happens when the reproductive interests of males and females diverge -- occurs in all sexually reproducing species, including humans. The Oxford Handbook of Sexual Conflict in Humans is the first volume to assemble the latest theoretical and empirical work on sexual conflict in humans from the leading scholars in the fields of evolutionary psychology and anthropology. Following an introductory section that outlines theory and research on sexual conflict in humans and non-humans, ensuing sections discuss human sexual conflict and its manifestations before and during mating. Chapters in these sections address a range of factors topics and factors, including: - Sexual coercion, jealousy, and partner violence and killing - The ovulatory cycle, female orgasm, and sperm competition - Chemical warfare between ejaculates and female reproductive tracts Chapters in the next section address issues of sexual conflict after the birth of a child. These chapters address sexual conflict as a function of the local sex ratio, men's functional (if unconscious) concern with paternal resemblance to a child, men's reluctance to pay child support, and mate expulsion as a tactic to end a relationship. The handbook's concluding section includes a chapter that considers the impact of sexual conflict on a grander scale, notably on cultural, political, and religious systems. Addressing sexual conflict at its molecular and macroscopic levels, The Oxford Handbook of Sexual Conflict in Humans is a fascinating resource for the study of intersexual behavior.
Promiscuity
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Author : Tim Birkhead
language : en
Publisher: Harvard University Press
Release Date : 2000
Promiscuity written by Tim Birkhead and has been published by Harvard University Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2000 with Science categories.
Birkhead reveals a world in which males and females vie with each other as they strive to maximize their reproductive success. Color illustrations.
Sperm Competition And Its Evolutionary Consequences In The Insects
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Author : Leigh W. Simmons
language : en
Publisher: Princeton University Press
Release Date : 2019-12-31
Sperm Competition And Its Evolutionary Consequences In The Insects written by Leigh W. Simmons and has been published by Princeton University Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2019-12-31 with Science categories.
One hundred years after Darwin considered how sexual selection shapes the behavioral and morphological characteristics of males for acquiring mates, Parker realized that sexual selection continues after mating through sperm competition. Because females often mate with multiple males before producing offspring, selection favors adaptations that allow males to preempt sperm from previous males and to prevent their own sperm from preemption by future males. Since the 1970s, this area of research has seen exponential growth, and biologists now recognize sperm competition as an evolutionary force that drives such adaptations as mate guarding, genital morphology, and ejaculate chemistry across all animal taxa. The insects have been critical to this research, and they still offer the greatest potential to reveal fully the evolutionary consequences of sperm competition. This book analyzes and extends thirty years of theoretical and empirical work on insect sperm competition. It considers both male and female interests in sperm utilization and the sexual conflict that can arise when these differ. It covers the mechanics of sperm transfer and utilization, morphology, physiology, and behavior. Sperm competition is shown to have dramatic effects on adaptation in the context of reproduction as well as far-reaching ramifications on life-history evolution and speciation. Written by a top researcher in the field, this comprehensive, up-to-date review of the evolutionary causes and consequences of sperm competition in the insects will prove an invaluable reference for students and established researchers in behavioral ecology and evolutionary biology.