The risk of sperm competition has been argued to shape the evolution of almost every aspect of human sexuality. With the recognition, afforded by recent evolutionary science, that female infidelity was a recurrent feature of modern humans evolutionary history has come the development of a unique area in the study of human mating. Dixson 1998 is consistent with predominantly singlemale mating. We used a questionnaire to investigate psychological responses to the risk of sperm competition for 194 men in committed, sexual relationships in the united states and in germany. In addition to the ostensible impact of female choice on the evolution of more elaborate male genitalia eberhard, 1996, there is reason to believe that sperm competition played a role in shaping the human penis. I therefore first want to clarify exactly what sperm competition is, and explain why we think it is an important factor for the readership of molecular human reproduction to consider. Sperm from one copulation appeared to hinder the retention of sperm at the next copulation for up to 8 days. Sep 24, 2014 where males can successfully avoid sperm competition from rivals, one might expect a decrease in their expenditure on tactics for the engagement in sperm competition and vice versa.
This process is experimental and the keywords may be updated as the learning algorithm improves. Sperm competition results when multiple males mate with the same female, the winners sperm fertilizing her eggs. Psychological and physiological adaptations to sperm. Adaptations for the avoidance of sperm competition can include the use of mate guarding or anti. Human males appear to have evolved mechanisms for anticipating risk of partner extrapair copulation and associated sperm competition. In humans, female physical attractiveness and personality characteristics that attract rival males may increase the likelihood of female sexual infidelity and, therefore, place.
Sperm competition also likely explains variation in the duration of spermatogenesis. My husband wants to watch me with another man and im. No evidence for killer sperm or other selective interactions. Sperm competition is the competitive process between spermatozoa of two or more different males to fertilize the same egg during sexual reproduction. There are, however, striking differences in penis morphology between different species see birkhead, 2000. Sperm competition theory argues that the number of sperm inseminated into a female by a male is a tradeoff between two opposing pressures. Before the church and modern morals females were free to mate with as many males as they cared to. Goetz florida atlantic university abstractwith the recognition, afforded by recent evolutionary science, that female in. Each of these mechanisms of sexual selection has probably played a role over human evolution, but contest competition the use.
Psychological adaptation to human sperm competition. Greater choice and variety of mates increases a females chance to produce more viable offspring. Sexual selection from sperm competition is expected to favor opposing adaptations in males that function either in the avoidance of sperm competition by guarding females from rival males or in the engagement in sperm competition by increased expenditure on the ejaculate. Masturbation simple english wikipedia, the free encyclopedia.
In 1998, craig venter, founder of the institute for genomic research in maryland, usa, announced that he had formed a new private company later to become celera genomics to take on the task of sequencing the human genome. Masturbation for males is the act of stimulating the penis manually to provide selfpleasure. Sperm competition and the evolution of spermatogenesis. Sperm competition in humans classic and contemporary. There is a very simple primal answer to why your husband enjoys this so. Sperm competition and the evolution of reproductive. Behavioural ecologists and evolutionary biologists have for a number of years been interested in the biological implications of sperm from different males competing for fertilization of the egg in the female tract. We used ejaculates from human donors to compare mixes of semen in vitro from the same or different males. Males have adapted to battle with competing sperm date. Number of sperm in human ejaculates varies in accordance with sperm competition theory 1989. Sperm competition is a form of postcopulatory sexual selection whereby male ejaculates simultaneously physically compete to fertilize a single ovum. Mate retention, semen displacement, and human sperm.
Sperm competition occurs whenever sperm from two or more males compete to fertilize a given set of ova parker, 1970, 1998. In some avian species, the tactics are used concurrently, with the result that mate guarding behaviors and ipc. Dec 07, 1999 this study examines one of the possible mechanisms of sperm competition, i. Psychological adaptation to human sperm competition 2002. We examine some of the implications of the possibility that the human penis may have evolved to compete with sperm from other males by displacing rival semen from the cervical end of the vagina prior to ejaculation. Semen displacement as a sperm competition strategy in humans double mating for semen displacement to be adaptive it presupposes situations in which human females have sex with multiple two or more males in fairly close successiontemporal proximity to one another. Sperm competition and the evolution of reproductive systems. It was good for the species, whether the females mate liked it or not. This, unsurprisingly, sparked off a rivalry with the team running the human genome project and a race to be the first to sequence the human genome. Competition can occur when females have multiple potential mating partners. Information about the openaccess article human sperm competition.
Over the past decade, there has been a vast amount of interest in the subject of human sperm competition. Pdf sperm competition occurs when a female copulates with two or more males within a sufficiently brief time period, resulting in the sperm of. Sexual selection from sperm competition is expected to favor opposing adaptations in males that function either in the avoidance of sperm competition by guarding females from rival males or in the engagement in sperm competition by increased expenditure on the. Sperm competition and its evolutionary consequences in humans. Human sperm competition ebook by robin baker 9788461686506. 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. Mate guarding and frequent inpair copulation ipc may have evolved as anticuckoldry tactics in avian species and in humans. Sperm competition occurs between sperm from two or more rival males when they make an attempt to fertilize a female within a sufficiently short period of time. 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. This sperm competition is probably both a lottery and a race, but more than anything it could also be a war, with sperm of different morphologies playing different roles.
This results primarily as a consequence of polyandrous mating systems, or due to extra. Such is the case with human sperm competition no doubt it occurs, but how often and whether it has shaped human evolution still needs clarification. The efficiency of the block declined with time after copulation but was fixed at its current level by an intercopulatory orgasm which. This ejaculation is usually accompanied by a powerful, pleasurable feeling called an orgasm. However, multiple mates for a female means an individual male has. In species where females mate with multiple males, the sperm of two or more males must compete to fertilise available ova. For example, the shape of the human penis may have been selectively shaped by sperm competition. Throughout the book, reference is made to work on the sexual behavioural ecologists and evolutionary biologists have for a number of years been interested in the biological implications of sperm from different males competing for fertilization of. Semen displacement as a sperm competition strategy in humans. Sperm competition occurs when a female copulates with two or more males within a sufficiently brief time period, resulting in the sperm of the different males competing to fertilize ova.
Sperm competition human female human male cervical mucus subordinate male these keywords were added by machine and not by the authors. Evolution and human sexuality wiley online library. Lamunyon d a department of psychology, florida atlantic university, 2912 college avenue, davie, fl 33314, usa. Sperm competition in animals is thought to be an involuntary action, like the beating of a heart or the mobilization of the immune system or, well, that thing that happens upon delivery of said sperm. The reader will not find reliable answers to these questions in baker and bellis book. Mate guarding and frequent inpair copulation in humans. Pdf on jan 1, 2017, robin baker and others published human sperm competition find, read and cite all the research you need on. In this chapter, we present the evidence of sperm competition in humans. The low degree of human sperm competition birkhead 2000. Bellis, journalanimal behaviour, year1993, volume46, pages887909. The penis evolved as an internal fertilization device. When sperm competition occurs, fertilization success may be determined, in part, by the outcome of direct interactions between sperm from rival males.
However, as a guy interested in both the practical application of science and the science itself, i would have liked an inbetween version. On the one hand, the risk that sperm may find themselves in competition with the sperm from another male favours the male inseminating more sperm. Although lloyd doubts this, significant sperm competition has probably occurred over human evolution. This book discusses these implications for human sexual behaviour and human infertility problems. Human sperm competition shackelford major reference. The human penis may have been selected to displace seminal fluids implanted in the female reproductive tract by a rival male. Mate retention, semen displacement, and human sperm competition. Sperm competition favors large testes and rapid evolution of proteins associated with ejaculate. Selection from sperm competition is expected to favor opposing adaptations that function either in the avoidance of or engagement in sperm competition. Pdf adaptation to sperm competition in humans aaron. These values suggest that the risk of sperm competition in humans is. Human sperm competition by robin baker overdrive rakuten. This volume brings together, in one place, a key set of classic and contemporary papers that have examined possible adaptations to sperm competition in humans.
However, multiple mates for a female means each individual male has. Semen displacement as a sperm competition strategy in. 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. Cuckoldry is an adaptive problem faced by parentally investing males of socially monogamous species e. Mechanisms of human sexual selection sexual selection can operate through multiple mechanisms, including contests, mate choice, scrambles, sexual coercion, and sperm competition table 1. A very interesting essay from the journal of evolutionary psychology on sperm competition and its role in shaping the human penis, size, length, width, forceful ejaculation, evolutionary strategies for successful fertilization i. 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 semen displacement hypothesis integrates considerable information about genital morphology and human. Semen displacement as a sperm competition strategy in humans double mating for semen displacement to be adaptive it presupposes situations in which human females have sex with multiple two or more males in fairly close successiontemporal proximity to. One evolutionary response to sperm competition is the variety in penis morphology of many species.
Copulation, masturbation, and infidelity springerlink. The fossil record suggests a human pattern of low bodysize sexual di. Pdf psychological adaptation to human sperm competition. In 1995, dr mark bellis and i published a book called human sperm competition.