Law of noncontradiction

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https://en.wikipedia.org/wiki/Principle

In logic, the law of non-contradiction (LNC) (also known as the law of contradiction, principle of non-contradiction (PNC), or the principle of contradiction) states that contradictory propositions cannot both be true in the same sense at the same time, e. g. the two propositions "p is the case" and "p is not the case" are mutually exclusive. Formally this is expressed as the tautology ¬(p ∧ ¬p). The law is not to be confused with the law of excluded middle which states that at least one, "p is the case" or "p is not the case" holds.

One reason to have this law is the principle of explosion, which states that anything follows from a contradiction. The law is employed in a reductio ad absurdum proof.

To express the fact that the law is tenseless and to avoid equivocation, sometimes the law is amended to say "contradictory propositions cannot both be true 'at the same time and in the same sense'".

It is one of the so called three laws of thought, along with its complement, the law of excluded middle, and the law of identity. However, no system of logic is built on just these laws, and none of these laws provide inference rules, such as modus ponens or De Morgan's laws.

The law of non-contradiction and the law of excluded middle create a dichotomy in "logical space", wherein the two parts are "mutually exclusive" and "jointly exhaustive". The law of non-contradiction is merely an expression of the mutually exclusive aspect of that dichotomy, and the law of excluded middle, an expression of its jointly exhaustive aspect.

Interpretations

One difficulty in applying the law of non-contradiction is ambiguity in the propositions. For instance, if it is not explicitly specified as part of the propositions A and B, then A may be B at one time, and not at another. A and B may in some cases be made to sound mutually exclusive linguistically even though A may be partly B and partly not B at the same time. However, it is impossible to predicate of the same thing, at the same time, and in the same sense, the absence and the presence of the same fixed quality.

Heraclitus

According to both Plato and Aristotle, Heraclitus was said to have denied the law of non-contradiction. This is quite likely if, as Plato pointed out, the law of non-contradiction does not hold for changing things in the world. If a philosophy of Becoming is not possible without change, then (the potential of) what is to become must already exist in the present object. In "We step and do not step into the same rivers; we are and we are not", both Heraclitus's and Plato's object simultaneously must, in some sense, be both what it now is and have the potential (dynamic) of what it might become.

So little remains of Heraclitus' aphorisms that not much about his philosophy can be said with certainty. He seems to have held that strife of opposites is universal both within and without, therefore both opposite existents or qualities must simultaneously exist, although in some instances in different respects. "The road up and down are one and the same" implies either the road leads both ways, or there can be no road at all. This is the logical complement of the law of non-contradiction. According to Heraclitus, change, and the constant conflict of opposites is the universal logos of nature.

Protagoras

Personal subjective perceptions or judgments can only be said to be true at the same time in the same respect, in which case, the law of non-contradiction must be applicable to personal judgments. The most famous saying of Protagoras is: "Man is the measure of all things: of things which are, that they are, and of things which are not, that they are not". However, Protagoras was referring to things that are used by or in some way related to humans. This makes a great difference in the meaning of his aphorism. Properties, social entities, ideas, feelings, judgments, etc. originate in the human mind. However, Protagoras has never suggested that man must be the measure of stars or the motion of the stars.

Parmenides

Parmenides employed an ontological version of the law of non-contradiction to prove that being is and to deny the void, change, and motion. He also similarly disproved contrary propositions. In his poem On Nature, he said,

the only routes of inquiry there are for thinking:

the one that [it] is and that [it] cannot not be
is the path of Persuasion (for it attends upon truth)
the other, that [it] is not and that it is right that [it] not be,
this I point out to you is a path wholly inscrutable
for you could not know what is not (for it is not to be accomplished)

nor could you point it out... For the same thing is for thinking and for being

The nature of the 'is' or what-is in Parmenides is a highly contentious subject. Some have taken it to be whatever exists, some to be whatever is or can be the object of scientific inquiry.

Socrates

In Plato's early dialogues, Socrates uses the elenctic method to investigate the nature or definition of ethical concepts such as justice or virtue. Elenctic refutation depends on a dichotomous thesis, one that may be divided into exactly two mutually exclusive parts, only one of which may be true. Then Socrates goes on to demonstrate the contrary of the commonly accepted part using the law of non-contradiction. According to Gregory Vlastos, the method has the following steps:

1. Socrates' interlocutor asserts a thesis, for example, "Courage is endurance of the soul", which Socrates considers false and targets for refutation.
2. Socrates secures his interlocutor's agreement to further premises, for example, "Courage is a fine thing" and "Ignorant endurance is not a fine thing".
3. Socrates then argues, and the interlocutor agrees, that these further premises imply the contrary of the original thesis, in this case, it leads to: "courage is not endurance of the soul".
4. Socrates then claims that he has shown that his interlocutor's thesis is false and that its negation is true.

Plato's synthesis

Plato's version of the law of non-contradiction states that "The same thing clearly cannot act or be acted upon in the same part or in relation to the same thing at the same time, in contrary ways" (The Republic (436b)). In this, Plato carefully phrases three axiomatic restrictions on action or reaction: in the same part, in the same relation, at the same time. The effect is to momentarily create a frozen, timeless state, somewhat like figures frozen in action on the frieze of the Parthenon.

This way, he accomplishes two essential goals for his philosophy. First, he logically separates the Platonic world of constant change from the formally knowable world of momentarily fixed physical objects. Second, he provides the conditions for the dialectic method to be used in finding definitions, as for example in the Sophist. So Plato's law of non-contradiction is the empirically derived necessary starting point for all else he has to say.

In contrast, Aristotle reverses Plato's order of derivation. Rather than starting with experience, Aristotle begins a priori with the law of non-contradiction as the fundamental axiom of an analytic philosophical system. This axiom then necessitates the fixed, realist model. Now, he starts with much stronger logical foundations than Plato's non-contrariety of action in reaction to conflicting demands from the three parts of the soul.

Aristotle's contribution

The traditional source of the law of non-contradiction is Aristotle's Metaphysics where he gives three different versions.

• Ontological: "It is impossible that the same thing belong and not belong to the same thing at the same time and in the same respect." (1005b19-20)
• Psychological: "No one can believe that the same thing can (at the same time) be and not be." (1005b23–24)
• Logical (aka the medieval Lex Contradictoriarum): "The most certain of all basic principles is that contradictory propositions are not true simultaneously." (1011b13-14)

Aristotle attempts several proofs of this law. He first argues that every expression has a single meaning (otherwise we could not communicate with one another). This rules out the possibility that by "to be a man", "not to be a man" is meant. But "man" means "two-footed animal" (for example), and so if anything is a man, it is necessary (by virtue of the meaning of "man") that it must be a two-footed animal, and so it is impossible at the same time for it not to be a two-footed animal. Thus "it is not possible to say truly at the same time that the same thing is and is not a man" (Metaphysics 1006b 35). Another argument is that anyone who believes something cannot believe its contradiction (1008b).

Why does he not just get up first thing and walk into a well or, if he finds one, over a cliff? In fact, he seems rather careful about cliffs and wells.

Avicenna

Avicenna's commentary on the Metaphysics illustrates the common view that the law of non-contradiction "and their like are among the things that do not require our elaboration." Avicenna's words for "the obdurate" are quite facetious: "he must be subjected to the conflagration of fire, since 'fire' and 'not fire' are one. Pain must be inflicted on him through beating, since 'pain' and 'no pain' are one. And he must be denied food and drink, since eating and drinking and the abstention from both are one [and the same]."

Indian philosophy

The law of non-contradiction is found in ancient Indian logic as a meta-rule in the Shrauta Sutras, the grammar of Pāṇini, and the Brahma Sutras attributed to Vyasa. It was later elaborated on by medieval commentators such as Madhvacharya.

Leibniz and Kant

Leibniz and Kant both used the law of non contradiction to define the difference between analytic and synthetic propositions. For Leibniz, analytic statements follow from the law of non contradiction, and synthetic ones from the principle of sufficient reason.

Russell

The principle was stated as a theorem of propositional logic by Russell and Whitehead in Principia Mathematica as:

${\displaystyle \mathbf{\ast }\mathbf{3}\cdot \mathbf{24}.⊢.\sim (p.\sim p)}$

Dialetheism

Graham Priest advocates the view that under some conditions, some statements can be both true and false simultaneously, or may be true and false at different times. Dialetheism arises from formal logical paradoxes, such as the Liar's paradox and Russell's paradox.

Alleged impossibility of its proof or denial

The law of non-contradiction is alleged to be neither verifiable nor falsifiable, on the grounds that any proof or disproof must use the law itself prior to reaching the conclusion. In other words, in order to verify or falsify the laws of logic one must resort to logic as a weapon, an act which is argued to be self-defeating. Since the early 20th century, certain logicians have proposed logics that deny the validity of the law.

Logics known as "paraconsistent" are inconsistency-tolerant logics in that there, from P together with ¬P, it does not imply that any proposition follows. Nevertheless, not all paraconsistent logics deny the law of non-contradiction and some such logics even prove it.

Some, such as David Lewis, have objected to paraconsistent logic on the ground that it is simply impossible for a statement and its negation to be jointly true. A related objection is that "negation" in paraconsistent logic is not really negation; it is merely a subcontrary-forming operator.

In popular culture

The Fargo episode "The Law of Non-Contradiction", which takes its name from the law, was noted for its several elements relating to the law of non-contradiction, as the episode's main character faces several paradoxes. For example, she is still the acting chief of police while having been demoted from the position, and tries to investigate a man that both was and was not named Ennis Stussy, and who both was and was not her stepfather. It also features the story of a robot who, after having spent millions of years unable to help humanity, is told that he greatly helped mankind all along by observing history.

Principle

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https://en.wikipedia.org/wiki/Principle 

The concept of blind justice is a moral principle.

A principle is a fundamental truth or proposition that serves as the foundation for a system of beliefs or behavior or a chain of reasoning.That is a guide for behavior or evaluation. In law, it is a rule that has to be or usually is to be followed. It can be desirably followed, or it can be an inevitable consequence of something, such as the laws observed in nature or the way that a system is constructed. The principles of such a system are understood by its users as the essential characteristics of the system, or reflecting the system's designed purpose, and the effective operation or use of which would be impossible if any one of the principles was to be ignored. A system may be explicitly based on and implemented from a document of principles as was done in IBM's 360/370 Principles of Operation.

Examples of principles are, entropy in a number of fields, least action in physics, those in descriptive comprehensive and fundamental law: doctrines or assumptions forming normative rules of conduct, separation of church and state in statecraft, the central dogma of molecular biology, fairness in ethics, etc.

In common English, it is a substantive and collective term referring to rule governance, the absence of which, being "unprincipled", is considered a character defect. It may also be used to declare that a reality has diverged from some ideal or norm as when something is said to be true only "in principle" but not in fact.

As law

As moral law

Socrates preferred to face execution rather than betray his moral principles.

 

Main article: Ethics

A principle represents values that orient and rule the conduct of persons in a particular society. To "act on principle" is to act in accordance with one's moral ideals. Principles are absorbed in childhood through a process of socialization. There is a presumption of liberty of individuals that is restrained. Exemplary principles include First, do no harm, the golden rule and the doctrine of the mean.

As a juridic law

Main article: Principle of legality

It represents a set of values that inspire the written norms that organize the life of a society submitting to the powers of an authority, generally the State. The law establishes a legal obligation, in a coercive way; it therefore acts as principle conditioning of the action that limits the liberty of the individuals. See, for examples, the territorial principle, homestead principle, and precautionary principle.

As scientific law

Archimedes principle, relating buoyancy to the weight of displaced water, is an early example of a law in science. Another early one developed by Malthus is the population principle, now called the Malthusian principle. Freud also wrote on principles, especially the reality principle necessary to keep the id and pleasure principle in check. Biologists use the principle of priority and principle of Binomial nomenclature for precision in naming species. There are many principles observed in physics, notably in cosmology which observes the mediocrity principle, the anthropic principle, the principle of relativity and the cosmological principle. Other well-known principles include the uncertainty principle in quantum mechanics and the pigeonhole principle and superposition principle in mathematics.

As axiom or logical fundament

Principle of sufficient reason

Main article: Principle of sufficient reason

The principle states that every event has a rational explanation. The principle has a variety of expressions, all of which are perhaps best summarized by the following:

For every entity x, if x exists, then there is a sufficient explanation for why x exists.

For every event e, if e occurs, then there is a sufficient explanation for why e occurs.

For every proposition p, if p is true, then there is a sufficient explanation for why p is true.

However, one realizes that in every sentence there is a direct relation between the predicate and the subject. To say that "the Earth is round", corresponds to a direct relation between the subject and the predicate.

Principle of non-contradiction

Portrait bust of Aristotle; an Imperial Roman copy of a lost bronze sculpture made by Lysippos

 

Main article: Law of noncontradiction

According to Aristotle, “It is impossible for the same thing to belong and not to belong at the same time to the same thing and in the same respect.” For example, it is not possible that in exactly the same moment and place, it rains and does not rain.

Principle of excluded middle

Main article: Law of excluded middle

The principle of the excluding third or "principium tertium exclusum" is a principle of the traditional logic formulated canonically by Leibniz as: either A is B or A isn't B. It is read the following way: either P is true, or its denial ¬P is. It is also known as "tertium non datur" ('A third (thing) is not'). Classically it is considered to be one of the most important fundamental principles or laws of thought (along with the principles of identity, non-contradiction and sufficient reason).

Queer heterosexuality

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https://en.wikipedia.org/wiki/Queer_heterosexuality 

Queer heterosexuality is heterosexual practice or identity that is also controversially called queer. "Queer heterosexuality" is argued to consist of heterosexual, cisgender, and allosexual persons who show nontraditional gender expressions, or who adopt gender roles that differ from the hegemonic masculinity and femininity of their particular culture.

The concept was first discussed in the mid-1990s, critically within radical feminism, and as a positive identification by Clyde Smith in a paper delivered at a conference in Amsterdam in 1997; in 2003, The Village Voice published an article called, "The Queer Heterosexual", which has since been cited by others using the term.

The idea that any heterosexual can be called "queer" is highly contested. Some in the LGBTQ+ community consider the use of the term "queer" by heterosexual people to be an offensive misappropriation, involving people not experiencing oppression for their sexual orientation or gender identity appropriating aspects of queer identities perceived as "fashionable" or attractive, and disregarding the concurrent oppression experienced by those they appropriate from.

Feminist criticism and queer theory

Kitzinger and Wilkinson argued that the rehabilitation of heterosexuality through "'queer' heterosexuality" as "a concept derived from postmodernist and queer theory" is seen as flawed from a radical feminist perspective. Acknowledging that 'queer heterosexuality' is rarely explored in detail, they explain that "the notion of the 'queer heterosexual' had become established in queer theory", gaining currency not because people are convinced it is possible or desirable, but "because queer heterosexuality is a necessary component of 'gender-fucking'" in Butlerian terms. 'Queer heterosexuality' becomes named in the project as destabilising all such categories, and moving towards a world where categories such as 'heterosexual' are rendered redundant. The queer theory was created to understand the concepts of gender, besides the binary, male, and female.

In a 2004 paper, Annette Schlichter describes the discourse on queer heterosexuality as aiming at "the de- and possible reconstruction of heterosexual subjectivity through the straight authors' aspiration to identify as queer". In the paper, a genealogy of queer heterosexuality is outlined, pointing out that "The queer critique of sexual normativity is both bound to the history of specific identities and committed to the destabilization of sexual identities—including those that have become hegemonic", while "Critics concerned about issues of lesbian visibility and difference occasionally raise the specter of the queer heterosexual ... as an indication of the queer project's perversion of social and political identities and their relations to power."

Putting to one side the question of whether the idea of homosexual contagion is necessarily homophobic, Guy Davidson uses the article from the Village Voice as an example of how the idea of queer subversion of heterosexuality can have "politically positive implications", specifically in relation to Tristan Taormino's writing on celebration of the LGBT movement's queering of heterosexual sex practices the production of the "queer heterosexual".

In Straight writ queer, the authors acknowledge that the queer heterosexual is only starting to emerge from the closet, seeking in the book to "identify and out the queer heterosexual" in historic and contemporary literature and to identify "inherently queer heterosexual practices" which critique heteronormativity and open up possibilities for the future. The examples in the book include anchorites, the Marquis de Sade and Algernon Charles Swinburne as examples of queer heterosexuals. "Male masochism disavows a masculinity predicated on phallic mastery, and hence becomes a strategic site for queer heterosexual resistance to heteronormativity".

In a 2018 paper, Heather Brook compares how the term 'same-sex marriage' is similarly oxymoronic to 'queer heterosexuality'. They both challenge and connect to essentialist understandings of heterosexuality. However, where 'same-sex marriage' aims to gain social capital from the normativeness of heterosexual marriage, 'queer heterosexuality' pulls on the fluidity of queerness. Brook describes how both terms incite fear of appropriation and the pejoration of a gendered understanding of societal institutions. Specifically, when straight people use 'queer', a term which was reclaimed by the community it now describes, to describe their heterosexuality, it straightens the word within the social consciousness. Brook posits that queer heterosexuality forces an exploration of how heteronormative institutions like marriage can be defined outside of binary oppositions like "hetero and homo; men and women; queer and straight".

Examination of masculinity

In 2005, Robert Heasley explored queer heterosexuality among a group of men that he identifies as "straight-queer males." According to Heasley, these men are self-identified heterosexuals who do not find social spaces dominated by traditionally masculine personalities to be comfortable. Heasley believes that a lack of understanding of masculinity can be addressed by creating a terminology to describe non-hegemonic masculine behavior. He lists seriously discussing homosexuality, being held or cuddled, hand-holding, dressing femininely, and expressing emotional openness among the behaviors displayed by straight-queer males.

Men who have been surveyed about their "mostly straight" behavior gave various reasons for this self-identification: some felt constrained by traditional models of gender and sexual orientation, others found men attractive. Some had a small amount of sexual interest in men but no desire for romantic same-sex relationships or intercourse, while others felt romantic but not sexual interest in other men.

Controversy

As 'queer' is generally defined either as a synonym for LGBT, or defined as "non-heterosexual", the term 'queer heterosexual' is considered controversial. Some LGBT people disapprove of the appropriation of 'queer' by cisgender heterosexual individuals, as the term has been used as a slur to oppress LGBT people. Straight celebrities self-identifying as queer have also faced backlash, with some arguing that their identities constitute "playing" with the "fashionable" parts of being LGBT, without having to suffer the resulting oppression of being LGBT, thus trivializing the struggles experienced by queer people.

For someone who is homosexual and queer, a straight person identifying as queer can feel like choosing to appropriate the good bits, the cultural and political cache [sic], the clothes and the sound of gay culture, without the laugh riot of gay-bashing, teen shame, adult shame, shame-shame, and the internalized homophobia of lived gay experience.

Critics of the term compare the use of 'queer heterosexual' to the appropriation engaged in by celebrities like Madonna, who used vogue dancing – a style and subculture originating amongst gay men, particularly African-American and Latino gay men – in her performances, profiting from the use of it while the style's originators did not. Daniel Harris, author of The Rise and Fall of Gay Culture, said that people who call themselves a 'queer heterosexual' "are under the impression they're doing something brave. [...] I'm a little sick that straight men would use those (terms)". Sky Gilbert referred to Calvin Thomas as "a little heterosexual male desperately wishing to be a card-carrying member of the gay community."

Gay reviewer Jameson Fitzpatrick said of James Franco's Straight James / Gay James: "I can't imagine the difficulty of being a straight, cis person who isn't fooled by the foundational fictions of hetero- and cisnormative power structures and doesn't wish to perpetuate them—except to say that I can't imagine that difficulty could possibly be greater than the various violences that many queer people still face today. This might be key to the problem that persists in Franco's claim to queerness, and what about it that rankles so many gay men: a lack of perspective." Fitzpatrick said he knew many people who might qualify as a queer heterosexual, but none who would use the label for themselves, and none who would "flaunt their privilege" as Fitzpatrick viewed Franco as doing in his book. A discussion of Franco and queer heterosexuality by Anthony Moll rejects the idea that Franco's art is queer: "From the concept of the interview between his straight self and his gay selves, to his ham-handed attempt to discuss queer heterosexuality, Franco comes across as a novice queer theorist who is talking through interesting, yet ultimately incomplete, ideas".

Sociobiological theories of rape

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Sociobiological_theories_of_rape 

 

Criminology and penology

Sociobiological theories of rape explore how evolutionary adaptation influences the psychology of rapists. Such theories are highly controversial, as traditional theories typically do not consider rape a behavioral adaptation. Some object to such theories on ethical, religious, political, or scientific grounds. Others argue correct knowledge of rape causes is necessary for effective preventive measures.

A Natural History of Rape

The idea that rape evolved under some circumstances as a genetically advantageous behavioral adaptation was popularized by biologist Randy Thornhill and anthropologist Craig T. Palmer in their book A Natural History of Rape (2000).

Animal coercive sex

Further information: Sexual coercion among animals, Sexual selection, and Sexual conflict

Behavior resembling rape in humans can be seen in the animal kingdom, including ducks and geese, bottlenose dolphins, and chimpanzees. Indeed, in orangutans, close human relatives, such copulations constitute up to half of observed matings. Such 'forced copulations' involve animals being approached and sexually penetrated while struggling or attempting to escape. Observations of forced sex in animals are uncontroversial; controversial are the interpretation of these observations and the extension of theories based on them to humans. "Thornhill introduces this theory by describing the sexual behavior of scorpionflies. In which the male may gain sex from the female either by presenting a gift of food during courtship or without a nuptial offering, in which case force is necessary to restrain her."

Human rape

Rape is hypothetically homologous to similar behavior in animals. "Human rape appears not as an aberration but as an alternative gene-promotion strategy that is most likely to be adopted by the 'losers' in the competitive, harem-building struggle. If the means of access to legitimate, consenting sex is not available, then a male may be faced with the choice between force or genetic extinction."

Thornhill and Palmer write that "In short, a man can have many children, with little inconvenience to himself; a woman can have only a few, and with great effort." Females thus tend toward selectivity with sexual partners. Rape could be a reproductive strategy for males. They point to several other factors indicating that rape may be a reproductive strategy. Most rapes occur during prime childbearing years. Rapists usually use no more force than necessary to subdue, argued to be since physically injuring victims would harm reproduction. Moreover, "In many cultures rape is treated as a crime against the victim's husband."

Anthropologist Edward H. Hagen states in his Evolutionary Psychology FAQ from 2002 that he believes there is no clear evidence for the hypothesis that rape is adaptive. He believes the adaptivity of rape is possible, but claims there is not enough evidence to be certain one way or the other. However, he encourages such evidence to be obtained: "Whether human males possess psychological adaptations for rape will only be answered by careful studies seeking evidence for such cognitive specializations. To not seek such evidence is like failing to search a suspect for a concealed weapon." He also describes some conditions in the ancestral environment during which the reproductive gains from rape may have outweighed the costs:

• "High status males may have been able to coerce matings with little fear of reprisal."
• "Low status women (e.g., orphans) may have been particularly vulnerable to being raped because males need not have feared reprisals from the woman's family."
• "During war, raping enemy women may have had few negative repercussions."
• "Men who were low status, who were likely to remain low status, and who had few opportunities to invest in kin may have realized reproductive benefits that outweighed the considerable costs (e.g., reprisal by the woman's family)."

McKibbin et al. (2008) argue that there may be several different types of rapists or rape strategies. One is rape by disadvantaged men who cannot get sex otherwise. Another is "specialized rapists" who are more sexually aroused from rape than from consensual sex. A third type is opportunistic rapists who switch between forced and consensual sex depending on circumstances. A fourth type is psychopathic rapists. A fifth type is partner rape due to sperm competition when the male suspects or knows that the female has had sex with another male. There are varying degrees of empirical support for the existence of each of these types. More generally they mention research finding that at least one-third of males "admit they would rape under specific conditions" and that other surveys find that many men state having coercive sexual fantasies. They, as have others, "propose that rape is a conditional strategy that may potentially be deployed by any man."

Women's defenses

Women may have developed several defenses against and strategies to avoid rape. One is a partner preference for men that are effective bodyguards against other men such as physically and socially dominant men (although there may also be other evolutionary reasons for such a preference). Another is great psychological pain which according to some research is greatest during the childbearing years. Other researchers have argued that the emotional pain may cause the women to focus on the social circumstances that enabled the rape with the aim to prevent future rapes.

Other research has found that during the fertile phase of the menstrual cycle women perform fewer behaviors that may increase the risk of an assault. Studies have also found that sensitivity for potential coercive behaviors in males as well as handgrip strength (but only in a simulated coercive situation) increase during the fertile phase of the menstrual cycle. On the other hand, a 2003 study found that the frequency of pregnancy from rape is significantly higher than that of pregnancy in non-coercive intercourse, and advanced the hypothesis that male rapists disproportionately target women exhibiting biological indications of fertility.

Naturalistic fallacy

Thornhill and Palmer write that "Rape is viewed as a natural, biological phenomenon that is a product of the human evolutionary heritage". They further state that by categorizing a behavior as "natural" and "biological" they do not in any way mean to imply that the behavior is justified or even inevitable. "Biological" means "of or pertaining to life," so the word applies to every human feature and behavior. But to infer from that, as many critics assert that Thornhill and Palmer do, that what is biological is somehow right or good, would be to fall into the so-called appeal to nature. They make a comparison to "natural disasters as epidemics, floods and tornadoes". This shows that what can be found in nature is not always good and that measures should be and are taken against natural phenomena. They further argue that a good knowledge of the causes of rape, including evolutionary ones, are necessary in order to develop effective preventive measures.

Evolutionary psychologists McKibbin et al. argue that the claim that evolutionary theories are justifying rape is a fallacy in the same way that it would be a fallacy to accuse scientists doing research on the causes of cancer that they are justifying cancer. Instead, they say that understanding the causes of rape may help create preventive measures.

Wilson et al. (2003) argue that evolutionary psychologists like Thornhill and Palmer use the naturalistic fallacy inappropriately to forestall legitimate discussion about the ethical implications of their theory. According to Thornhill and Palmer, a naturalistic fallacy is to infer ethical conclusions (e.g., rape is good) from (true or false) statements of fact (e.g., rape is natural). Wilson et al. point out that combining a factual statement with an ethical statement to derive an ethical conclusion is standard ethical reasoning, not a naturalistic fallacy, because the moral judgment is not deduced exclusively from the factual statement. They further argue that if one combines Thornhill and Palmer's factual premise that rape increases the fitness of a woman's offspring with the ethical premise that it is right to increase fitness of offspring, the resulting deductively valid conclusion is that rape has also positive effects and that its ethical status is ambiguous. Wilson et al. state that Thornhill and Palmer dismiss all ethical objections with the phrase 'naturalistic fallacy' although "it is Thornhill and Palmer who are thinking fallaciously by using the naturalistic fallacy in this way."

Preventing rape

Thornhill and Palmer (2000) suggest a number of possible strategies for preventing rape. One example is explaining to males that they may have predispositions to misread the female invitation of sex. They believe that viewing rape as being due to a desire for domination, and not related to sexual desire, is generally harmful. One example given is the claim that the way women dress will not affect the risk of rape. They argue that the much greater societal freedom of dating without supervision, and removal of many barriers between males and females, have created an environment that has also removed many earlier societal controls against rape. It is recommended that "men and women interact only in public places during the early stages of their relationships".

Victim counseling

Counseling of rape victims may also be improved by evolutionary considerations, according to Thornhill and Palmer, and they argue that the view that rape is due to a domination desire, cannot explain to the victim why the rapist seemed to be sexually motivated.

Evolutionary considerations can also help explain the emotional pain felt, as well as the form it takes. They may also help the rape victim understand why the rape victim's partner may see the rape as a form of infidelity. They also argued that the victim's partner may be helped by such understanding, and be more able to change his or her reaction.

Criticism

See also: Criticism of evolutionary psychology

The 2003 book Evolution, Gender, and Rape, written in response to A Natural History of Rape, compiles the views of twenty-eight scholars in opposition to sociobiological theories of rape. One contributor, Michael Kimmel, criticizes Thornhill and Palmer's argument that female rape victims tend to be sexually attractive young women, rather than children or older women, contrary to what would be expected if rapists selected victims based on inability to resist. Kimmel argues that younger women are the least likely to be married and the most likely to be out on dates with men, and therefore are the most likely to be raped because of opportunity arising from social exposure and marital status. Palmer and Thornhill responded to these critics in an article in the journal Evolutionary Psychology.

Smith et al. (2001) criticized Thornhill and Palmer's hypothesis that a predisposition to rape in certain circumstances is an evolved psychological adaptation. They developed a fitness cost/benefit mathematical model and populated it with estimates of certain parameters (some parameter estimates were based on studies of the Aché in Paraguay). Their model suggested that generally only men with a future reproductive value of one-tenth or less of a typical 25-year-old man would have a net positive cost/benefit fitness ratio from committing rape. On the basis of their model and parameter estimates, they suggested that this would make it unlikely that rape generally would have net fitness benefits for most men.

While defending the evolutionary psychology theory of rape against its more vehement critics, Vandermassen (2010) provides a critique of some aspects of the view. She characterises the view of Thornhill and Palmer as "extreme" (p. 736), as they fail to allow for the influence of any non-sexual motivations in the crime of rape. Vandermassen also notes two problems with the data cited by Thornhill and Palmer regarding the psychological trauma caused by the violence associated with rape: firstly, the data is inaccurately and confusingly presented in the book, often obscuring the fact that they do not support Thornhill and Palmer's "counterintuitive hypothesis" (p. 744) that more physical violence during rape is associated with less psychological pain. Secondly, more recent research has failed to support this hypothesis. A more moderate position, integrating the evolutionary psychology and feminist theories on rape, is presented by Vandermassen, based in part on the work of feminist evolutionary researcher Barbara Smuts.

Hamilton (2008) has criticized Thornhill and Palmer's definition of rape as the coerced vaginal penetration of women of reproductive age. He has suggested that the exclusion of male rape, rape of women outside the reproductive age range, murderous rape, and non-vaginal forms of rape virtually guaranteed the confirmation of their hypothesis that rape is an evolved reproductive strategy and not a crime of violence. Hamilton has argued that evolutionary psychology fails to explain rape because, by evolutionary psychology's own criteria, an adaptation to rape children or men, or non-vaginal rape, would have been eliminated in the course of evolution because it did not confer reproductive advantage on our ancestors.

Evolutionary psychologist David Buss states that clear-cut evidence for or against rape as an adaptation is lacking. He states that rape may instead be a non-adaptive by-product of other evolved mechanisms, such as desire for sexual variety and for sex without investment, sensitivity to sexual opportunities, and a general capacity for physical aggression.

Sperm competition

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Sperm_competition 

 

Stained human sperm

 

Human spermatozoa

Sperm competition is the competitive process between spermatozoa of two or more different males to fertilize the same egg during sexual reproduction. Competition can occur when females have multiple potential mating partners. Greater choice and variety of mates increases a female's chance to produce more viable offspring. However, multiple mates for a female means each individual male has decreased chances of producing offspring. Sperm competition is an evolutionary pressure on males, and has led to the development of adaptations to increase males' chance of reproductive success. Sperm competition results in a sexual conflict of interest between males and females. Males have evolved several defensive tactics including: mate-guarding, mating plugs, and releasing toxic seminal substances to reduce female re-mating tendencies to cope with sperm competition. Offensive tactics of sperm competition involve direct interference by one male on the reproductive success of another male, for instance by physically removing another male's sperm prior to mating with a female. For an example, see Gryllus bimaculatus.

Sperm competition is often compared to having tickets in a raffle; a male has a better chance of winning (i.e. fathering offspring) the more tickets he has (i.e. the more sperm he inseminates a female with). However, sperm are not free to produce, and as such males are predicted to produce sperm of a size and number that will maximize their success in sperm competition. By making many spermatozoa, males can buy more "raffle tickets", and it is thought that selection for numerous sperm has contributed to the evolution of anisogamy with very small sperm (because of the energy trade-off between sperm size and number). Alternatively, a male may evolve faster sperm to enable his sperm to reach and fertilize the female's ovum first. Dozens of adaptations have been documented in males that help them succeed in sperm competition.

Defensive adaptations

Neolamprologus pulcher

Mate-guarding is a defensive behavioral trait that occurs in response to sperm competition; males try to prevent other males from approaching the female (and/or vice versa) thus preventing their mate from engaging in further copulations. Precopulatory and postcopulatory mate-guarding occurs in insects, lizards, birds and primates. Mate-guarding also exists in the fish species Neolamprologus pulcher, as some males try to "sneak" matings with females in the territory of other males. In these instances, the males guard their female by keeping her in close enough proximity so that if an opponent male shows up in his territory he will be able to fight off the rival male which will prevent the female from engaging in extra-pair copulation with the rival male.

Organisms with polygynous mating systems are controlled by one dominant male. In this type of mating system, the male is able to mate with more than one female in a community. The dominant males will reign over the community until another suitor steps up and overthrows him. The current dominant male will defend his title as the dominant male and he will also be defending the females he mates with and the offspring he sires. The elephant seal falls into this category since he can participate in bloody violent matches in order to protect his community and defend his title as the alpha male. If the alpha male is somehow overthrown by the newcomer, his children will most likely be killed and the new alpha male will start over with the females in the group so that his lineage can be passed on.

Strategic mate-guarding occurs when the male only guards the female during her fertile periods. This strategy can be more effective because it may allow the male to engage in both extra-pair paternity and within-pair paternity. This is also because it is energetically efficient for the male to guard his mate at this time. There is a lot of energy that is expended when a male is guarding his mate. For instance, in polygynous mate-guarding systems, the energetic costs of males is defending their title as alpha male of their community. Fighting is very costly in regards to the amount of energy used to guard their mate. These bouts can happen more than once which takes a toll on the physical well-being of the male. Another cost of mate-guarding in this type of mating system is the potential increase of the spread of disease. If one male has an STD, he can pass that on to the females that he's copulating with, potentially resulting in a depletion of the harem. This would be an energetic cost towards both sexes for the reason that instead of using the energy for reproduction, they are redirecting it towards ridding themselves of this illness. Some females also benefit from polygyny because extra pair copulations in females increase the genetic diversity with the community of that species. This occurs because the male is not able to watch over all of the females and some will become promiscuous. Eventually, the male will not have proper nutrition, which makes the male unable to produce sperm. For instance, male amphipods will deplete their reserves of glycogen and triglycerides only to have it replenished after the male is done guarding that mate. Also, if the amount of energy intake does not equal the energy expended, then this could be potentially fatal to the male. Males may even have to travel long distances during the breeding season in order to find a female which absolutely drain their energy supply. Studies were conducted to compare the cost of foraging of fish that migrate and animals that are residential. The studies concluded that fish that were residential had fuller stomachs containing higher quality of prey compared to their migrant counterparts. With all of these energy costs that go along with guarding a mate, timing is crucial so that the male can use the minimal amount of energy. This is why it is more efficient for males to choose a mate during their fertile periods. Also, males will be more likely to guard their mate when there is a high density of males in the proximity. Sometimes, organisms put in all this time and planning into courting a mate in order to copulate and she may not even be interested. There is a risk of cuckoldry of some sort, since a rival male can successfully court the female that the male originally courting her could not do.

However, there are benefits that are associated with mate-guarding. In a mating- guarding system, both parties, male and female, are able to directly and indirectly benefit from this. For instance, females can indirectly benefit from being protected by a mate. The females can appreciate a decrease in predation and harassment from other males while being able to observe her male counterpart. This will allow her to recognize particular traits that she finds ideal so that she'll be able to find another male that emulates those qualities. In polygynous relationships, the dominant male of the community benefits because he has the best fertilization success. Communities can include 30 up to 100 females and, compared to the other males, will greatly increase his chances of mating success.

Males who have successfully courted a potential mate will attempt to keep them out of sight of other males before copulation. One way organisms accomplish this is to move the female to a new location. Certain butterflies, after enticing the female, will pick her up and fly her away from the vicinity of potential males. In other insects, the males will release a pheromone in order to make their mate unattractive to other males or the pheromone masks her scent completely. Certain crickets will participate in a loud courtship until the female accepts his gesture and then it suddenly becomes silent. Some insects, prior to mating, will assume tandem positions to their mate or position themselves in a way to prevent other males from attempting to mate with that female. The male checkerspot butterfly has developed a clever method in order to attract and guard a mate. He will situate himself near an area that possesses valuable resources that the female needs. He will then drive away any males that come near and this will greatly increase his chances of copulation with any female that comes to that area.

In post-copulatory mate-guarding males are trying to prevent other males from mating with the female that they have mated with already. For example, male millipedes in Costa Rica will ride on the back of their mate letting the other males know that she's taken. Japanese beetles will assume a tandem position to the female after copulation. This can last up to several hours allowing him to ward off any rival males giving his sperm a high chance to fertilize that female's egg. These, and other, types of methods have the male playing defense by protecting his mate. Elephant seals are known to engage in bloody battles in order to retain their title as dominant male so that they are able to mate with all the females in their community.

Indian mealmoth

 

Drosophila melanogaster

Copulatory plugs are frequently observed in insects, reptiles, some mammals, and spiders. Copulatory plugs are inserted immediately after a male copulates with a female, which reduce the possibility of fertilization by subsequent copulations from another male, by physically blocking the transfer of sperm. Bumblebee mating plugs, in addition to providing a physical barrier to further copulations, contain linoleic acid, which reduces re-mating tendencies of females. A species of Sonoran desert Drosophila, Drosophila mettleri, uses copulatory plugs to enable males to control the sperm reserve space females have available. This behavior ensures males with higher mating success at the expense of female control of sperm (sperm selection).

Similarly, Drosophila melanogaster males release toxic seminal fluids, known as ACPs (accessory gland proteins), from their accessory glands to impede the female from participating in future copulations. These substances act as an anti-aphrodisiac causing a dejection of subsequent copulations, and also stimulate ovulation and oogenesis. Seminal proteins can have a strong influence on reproduction, sufficient to manipulate female behavior and physiology.

Another strategy, known as sperm partitioning, occurs when males conserve their limited supply of sperm by reducing the quantity of sperm ejected. In Drosophila, ejaculation amount during sequential copulations is reduced; this results in half filled female sperm reserves following a single copulatory event, but allows the male to mate with a larger number of females without exhausting his supply of sperm. To facilitate sperm partitioning, some males have developed complex ways to store and deliver their sperm. In the blue headed wrasse, Thalassoma bifasciatum, the sperm duct is sectioned into several small chambers that are surrounded by a muscle that allows the male to regulate how much sperm is released in one copulatory event.

A strategy common among insects is for males to participate in prolonged copulations. By engaging in prolonged copulations, a male has an increased opportunity to place more sperm within the female's reproductive tract and prevent the female from copulating with other males.

It has been found that some male mollies (Poecilia) have developed deceptive social cues to combat sperm competition. Focal males will direct sexual attention toward typically non-preferred females when an audience of other males is present. This encourages the males that are watching to attempt to mate with the non-preferred female. This is done in an attempt to decrease mating attempts with the female that the focal male prefers, hence decreasing sperm competition.

Offensive adaptations

Offensive adaptation behavior differs from defensive behavior because it involves an attempt to ruin the chances of another male's opportunity in succeeding in copulation by engaging in an act that tries to terminate the fertilization success of the previous male. This offensive behavior is facilitated by the presence of certain traits, which are called armaments. An example of an armament are antlers. Further, the presence of an offensive trait sometimes serves as a status signal. The mere display of an armament can suffice to drive away the competition without engaging in a fight, hence saving energy. A male on the offensive side of mate-guarding may terminate the guarding male's chances at a successful insemination by brawling with the guarding male to gain access to the female. In Drosophila, males release seminal fluids that contain additional toxins like pheromones and modified enzymes that are secreted by their accessory glands intended to destroy the sperm that have already made their way into the female's reproductive tract from a recent copulation. However, this proved to be wrong because Drosophila melanogaster seminal fluid can actually protect the sperm of other males. Based on the "last male precedence" idea, some males can remove sperm from previous males by ejaculating new sperm into the female; hindering successful insemination opportunities of the previous male.

Mate choice

The "good sperm hypothesis" is very common in polyandrous mating systems. The "good sperm hypothesis" suggests that a male's genetic makeup will determine the level of his competitiveness in sperm competition. When a male has "good sperm" he is able to father more viable offspring than males that do not have the "good sperm" genes. Females may select males that have these superior "good sperm" genes because it means that their offspring will be more viable and will inherit the "good sperm" genes which will increase their fitness levels when their sperm competes.

Studies show that there is more to determining the competitiveness of the sperm in sperm competition in addition to a male's genetic makeup. A male's dietary intake will also affect sperm competition. An adequate diet consisting of increased amounts of diet and sometimes more specific ratio in certain species will optimize sperm number and fertility. Amounts of protein and carbohydrate intake were tested for its effects on sperm production and quality in adult fruit flies (Diptera: Tephritidae). Studies showed these flies need to constantly ingest carbohydrates and water to survive, but protein is also required to attain sexual maturity. In addition, The Mediterranean fruit fly, male diet has been shown to affect male mating success, copula duration, sperm transfer, and male participation in leks. These all require a good diet with nutrients for proper gamete production as well as energy for activities, which includes participation in leks.

In addition, protein and carbohydrate amounts were shown to have an effect on sperm production and fertility in the speckled cockroach. Holidic diets were used which allowed for specific protein and carbohydrate measurements to be taken, giving it credibility. A direct correlation was seen in sperm number and overall of food intake. More specifically, optimal sperm production was measured at a 1:2 protein to carbohydrate ratio. Sperm fertility was best at a similar protein to carbohydrate ratio of 1:2. This close alignment largely factors in determining male fertility in Nauphoeta cinerea. Surprisingly, sperm viability was not affected by any change in diet or diet ratios. It's hypothesized that sperm viability is more affected by the genetic makeup, like in the "good sperm hypothesis". These ratios and results are not consistent with many other species and even conflict with some. It seems there can't be any conclusions on what type of diet is needed to positively influence sperm competition but rather understand that different diets do play a role in determining sperm competition in mate choice.

Evolutionary consequences

One evolutionary response to sperm competition is the variety in penis morphology of many species. For example, the shape of the human penis may have been selectively shaped by sperm competition. The human penis may have been selected to displace seminal fluids implanted in the female reproductive tract by a rival male. Specifically, the shape of the coronal ridge may promote displacement of seminal fluid from a previous matinga thrusting action during sexual intercourse. A 2003 study by Gordon G. Gallup and colleagues concluded that one evolutionary purpose of the thrusting motion characteristic of intense intercourse is for the penis to “upsuck” another man's semen before depositing its own.

Evolution to increase ejaculate volume in the presence of sperm competition has a consequence on testis size. Large testes can produce more sperm required for larger ejaculates, and can be found across the animal kingdom when sperm competition occurs. Males with larger testes have been documented to achieve higher reproductive success rates than males with smaller testes in male yellow pine chipmunks. In chichlid fish, it has been found that increased sperm competition can lead to evolved larger sperm numbers, sperm cell sizes, and sperm swimming speeds.

In some insects and spiders, for instance Nephila fenestrate, the male copulatory organ breaks off or tears off at the end of copulation and remains within the female to serve as a copulatory plug. This broken genitalia is believed to be an evolutionary response to sperm competition. This damage to the male genitalia means that these males can only mate once.

Female choice for males with competitive sperm

Female factors can influence the result of sperm competition through a process known as "sperm choice". Proteins present in the female reproductive tract or on the surface of the ovum may influence which sperm succeeds in fertilizing the egg. During sperm choice, females are able to discriminate and differentially use the sperm from different males. One instance where this is known to occur is inbreeding; females will preferentially use the sperm from a more distantly related male than a close relative.

Post-copulatory inbreeding avoidance

Inbreeding ordinarily has negative fitness consequences (inbreeding depression), and as a result species have evolved mechanisms to avoid inbreeding. Inbreeding depression is considered to be due largely to the expression of homozygous deleterious recessive mutations. Outcrossing between unrelated individuals ordinarily leads to the masking of deleterious recessive mutations in progeny.

Numerous inbreeding avoidance mechanisms operating prior to mating have been described. However, inbreeding avoidance mechanisms that operate subsequent to copulation are less well known. In guppies, a post-copulatory mechanism of inbreeding avoidance occurs based on competition between sperm of rival males for achieving fertilization. In competitions between sperm from an unrelated male and from a full sibling male, a significant bias in paternity towards the unrelated male was observed.

In vitro fertilization experiments in the mouse, provided evidence of sperm selection at the gametic level. When sperm of sibling and non-sibling males were mixed, a fertilization bias towards the sperm of the non-sibling males was observed. The results were interpreted as egg-driven sperm selection against related sperm.

Female fruit flies (Drosophila melanogaster) were mated with males of four different degrees of genetic relatedness in competition experiments. Sperm competitive ability was negatively correlated with relatedness.

Female crickets (Teleogryllus oceanicus) appear to use post-copulatory mechanisms to avoid producing inbred offspring. When mated to both a sibling and an unrelated male, females bias paternity towards the unrelated male.

Empirical support

Scanning electron microscopic image of immature parasperm lancet (infertile sperm morph) of Fusitriton oregonensis showing the tail brush still present, which later develops into part of the body of the parasperm. It is produced when sperm competition occurs.

It has been found that because of female choice (see sexual selection), morphology of sperm in many species occurs in many variations to accommodate or combat (see sexual conflict) the morphology and physiology of the female reproductive tract. However, it is difficult to understand the interplay between female and male reproductive shape and structure that occurs within the female reproductive tract after mating that allows for the competition of sperm. Polyandrous females mate with many male partners. Females of many species of arthropod, mollusk and other phyla have a specialized sperm-storage organ called the spermatheca in which the sperm of different males sometimes compete for increased reproductive success. Species of crickets, specifically Gryllus bimaculatus, are known to exhibit polyandrous sexual selection. Males will invest more in ejaculation when competitors are in the immediate environment of the female.

Evidence exists that illustrates the ability of genetically similar spermatozoa to cooperate so as to ensure the survival of their counterparts thereby ensuring the implementation of their genotypes towards fertilization. Cooperation confers a competitive advantage by several means, some of these include incapacitation of other competing sperm and aggregation of genetically similar spermatozoa into structures that promote effective navigation of the female reproductive tract and hence improve fertilization ability. Such characteristics lead to morphological adaptations that suit the purposes of cooperative methods during competition. For example, spermatozoa possessed by the wood mouse (Apodemus sylvaticus) possess an apical hook which is used to attach to other spermatozoa to form mobile trains that enhance motility through the female reproductive tract. Spermatozoa that fail to incorporate themselves into mobile trains are less likely to engage in fertilization. Other evidence suggests no link between sperm competition and sperm hook morphology.

Selection to produce more sperm can also select for the evolution of larger testes. Relationships across species between the frequency of multiple mating by females and male testis size are well documented across many groups of animals. For example, among primates, female gorillas are relatively monogamous, so gorillas have smaller testes than humans, which in turn have smaller testes than the highly promiscuous bonobos. Male chimpanzees that live in a structured multi-male, multi-female community, have large testicles to produce more sperm, therefore giving him better odds to fertilize the female. Whereas the community of gorillas consist of one alpha male and two or three females, when the female gorillas are ready to mate, normally only the alpha male is their partner.

Regarding sexual dimorphism among primates, humans falls into an intermediate group with moderate sex differences in body size but relatively large testes. This is a typical pattern of primates where several males and females live together in a group and the male faces an intermediate number of challenges from other males compared to exclusive polygyny and monogamy but frequent sperm competition.

Other means of sperm competition could include improving the sperm itself or its packaging materials (spermatophore).

The male black-winged damselfly provides a striking example of an adaptation to sperm competition. Female black-winged damselflies are known to mate with several males over the span of only a few hours and therefore possess a receptacle known as a spermatheca which stores the sperm. During the process of mating the male damselfly will pump his abdomen up and down using his specially adapted penis which acts as a scrub brush to remove the sperm of another male. This method proves quite successful and the male damselfly has been known to remove 90-100 percent of the competing sperm.

Male dunnocks (Prunella modularis) peck at the female's cloaca, removing sperm of previous mates.

A similar strategy has been observed in the dunnock, a small bird. Before mating with the polyandrous female, the male dunnock pecks at the female's cloaca in order to peck out the sperm of the previous male suitor.

In the fly Dryomyza anilis, females mate with multiple males. It benefits the male to attempt to be the last one to mate with a given female. This is because there seems to be a cumulative percentage increase in fertilization for the final male, such that the eggs laid in the last oviposition bout are the most successful.

A notion emerged in 1996 that in some species, including humans, a significant fraction of sperm specialize in a manner such that they cannot fertilize the egg but instead have the primary effect of stopping the sperm from other males from reaching the egg, e.g. by killing them with enzymes or by blocking their access. This type of sperm specialization became known popularly as "kamikaze sperm" or "killer sperm", but most follow-up studies to this popularized notion have failed to confirm the initial papers on the matter. While there is also currently little evidence of killer sperm in any non-human animals certain snails have an infertile sperm morph ("parasperm") that contains lysozymes, leading to speculation that they might be able to degrade a rivals' sperm.

The parasitoid wasp Nasonia vitripennis, mated females can choose whether or not to lay a fertilized egg (which develops into a daughter) or an unfertilized egg (which develops into a son), therefore females suffer a cost from mating, as repeated matings constrain their ability to allocate sex in their offspring. The behaviour of these kamikaze-sperm is referred to in academic literature as "sperm-blocking", using basketball as a metaphor.

Sperm competition has led to other adaptations such as larger ejaculates, prolonged copulation, deposition of a copulatory plug to prevent the female re-mating, or the application of pheromones that reduce the female's attractiveness. The adaptation of sperm traits, such as length, viability and velocity might be constrained by the influence of cytoplasmic DNA (e.g. mitochondrial DNA); mitochondrial DNA is inherited from the mother only and it is thought that this could represent a constraint in the evolution of sperm.