Male

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The symbol of the Roman god Mars (god of war) is often used to represent the male sex. It also stands for the planet Mars and is the alchemical symbol for iron. Mars symbol.svg
The symbol of the Roman god Mars (god of war) is often used to represent the male sex. It also stands for the planet Mars and is the alchemical symbol for iron.

Male (symbol: ) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, [1] [2] [3] or ovum, in the process of fertilisation. A male organism cannot reproduce sexually without access to at least one ovum from a female, but some organisms can reproduce both sexually and asexually. [4] Most male mammals, including male humans, have a Y chromosome, [5] [6] which codes for the production of larger amounts of testosterone to develop male reproductive organs.

Contents

In humans, the word male can also be used to refer to gender, in the social sense of gender role or gender identity. [7] [ better source needed ] The use of "male" in regard to sex and gender has been subject to discussion.

Overview

The existence of separate sexes has evolved independently at different times and in different lineages, an example of convergent evolution. [8] [9] The repeated pattern is sexual reproduction in isogamous species with two or more mating types with gametes of identical form and behavior (but different at the molecular level) to anisogamous species with gametes of male and female types to oogamous species in which the female gamete is very much larger than the male and has no ability to move. There is a good argument that this pattern was driven by the physical constraints on the mechanisms by which two gametes get together as required for sexual reproduction. [10] [ page needed ]

Accordingly, sex is defined across species by the type of gametes produced (i.e.: spermatozoa vs. ova) and differences between males and females in one lineage are not always predictive of differences in another. [9] [11] [12]

Male/female dimorphism between organisms or reproductive organs of different sexes is not limited to animals; male gametes are produced by chytrids, diatoms and land plants, among others. In land plants, female and male designate not only the female and male gamete-producing organisms and structures but also the structures of the sporophytes that give rise to male and female plants.[ citation needed ]

Evolution

The evolution of anisogamy led to the evolution of male and female function. [13] Before the evolution of anisogamy, mating types in a species were isogamous: the same size and both could move, catalogued only as "+" or "-" types. [14] :216 In anisogamy, the mating type is called a gamete. The male gamete is smaller than the female gamete, and usually mobile. [15] Anisogamy remains poorly understood, as there is no fossil record of its emergence. Numerous theories exist as to why anisogamy emerged. Many share a common thread, in that larger female gametes are more likely to survive, and that smaller male gametes are more likely to find other gametes because they can travel faster. Current models often fail to account for why isogamy remains in a few species. [16] Anisogamy appears to have evolved multiple times from isogamy; for example, female Volvocales (a type of green algae) evolved from the plus mating type. [16] [14] :222 Although sexual evolution emerged at least 1.2 billion years ago, the lack of anisogamous fossil records make it hard to pinpoint when males evolved. [17] One theory suggests male evolved from the dominant mating type (called mating type minus). [18]

Symbol, etymology, and usage

Symbol

A common symbol used to represent the male sex is the Mars symbol ♂, a circle with an arrow pointing northeast. The Unicode code-point is:

U+2642MALE SIGN (♂)

The symbol is identical to the planetary symbol of Mars. It was first used to denote sex by Carl Linnaeus in 1751. The symbol is sometimes seen as a stylized representation of the shield and spear of the Roman god Mars. According to William T. Stearn, however, this derivation is "fanciful" and all the historical evidence favours "the conclusion of the French classical scholar Claude de Saumaise (Salmasius, 15881683)" that it is derived from θρ, the contraction of a Greek name for the planet Mars, which is Thouros. [19]

Etymology

Borrowed from Old French masle, from Latin masculus ("masculine, male, worthy of a man"), diminutive of mās ("male person or animal, male"). [20]

Usage

In humans, the word male can be used in the context of gender, such as for gender role or gender identity of a man or boy. [7] For example, according to Merriam-Webster, "male" can refer to "having a gender identity that is the opposite of female". [21] According to the Cambridge Dictionary, "male" can mean "belonging or relating to men". [22]

Male can also refer to a shape of connectors. [23] [24]

Males across species

Species that are divided into females and males are classified as gonochoric in animals, as dioecious in seed plants [2] and as dioicous in cryptogams. [25] :82

Males can coexist with hermaphrodites, a sexual system called androdioecy. They can also coexist with females and hermaphrodites, a sexual system called trioecy. [26]

Sex determination

Photograph of an adult male human, with an adult female for comparison. Both models have partially shaved body hair; e.g. clean-shaven pubic regions. Anterior view of human female and male, with labels 2.png
Photograph of an adult male human, with an adult female for comparison. Both models have partially shaved body hair; e.g. clean-shaven pubic regions.

The sex of a particular organism may be determined by a number of factors. These may be genetic or environmental, or may naturally change during the course of an organism's life. Although most species have only two sexes (either male or female), [8] [9] [2] hermaphroditic animals, such as worms, have both male and female reproductive organs. [27]

Not all species share a common sex-determination system. In most animals, including humans, sex is determined genetically; however, species such as Cymothoa exigua change sex depending on the number of females present in the vicinity. [28] [ better source needed ]

Genetic determination

Most mammals, including humans, are genetically determined as such by the XY sex-determination system where males have XY (as opposed to XX in females) sex chromosomes. It is also possible in a variety of species, including humans, to be XX male or have other karyotypes. During reproduction, a male can give either an X sperm or a Y sperm, while a female can only give an X egg. A Y sperm and an X egg produce a male, while an X sperm and an X egg produce a female. [29]

The part of the Y-chromosome which is responsible for maleness is the sex-determining region of the Y-chromosome, the SRY. [30] The SRY activates Sox9, which forms feedforward loops with FGF9 and PGD2 in the gonads, allowing the levels of these genes to stay high enough in order to cause male development; [31] for example, Fgf9 is responsible for development of the spermatic cords and the multiplication of Sertoli cells, both of which are crucial to male sexual development. [32]

The ZW sex-determination system, where males have ZZ (as opposed to ZW in females) sex chromosomes, may be found in birds and some insects (mostly butterflies and moths) and other organisms. Members of the insect order Hymenoptera, such as ants and bees, are often determined by haplodiploidy, [13] where most males are haploid and females and some sterile males are diploid. However, fertile diploid males may still appear in some species, such as Cataglyphis cursor . [33]

Environmental determination

In some species of reptiles, such as alligators, sex is determined by the temperature at which the egg is incubated. Other species, such as some snails, practice sex change: adults start out male, then become female. [34] In tropical clown fish, the dominant individual in a group becomes female while the other ones are male. [35]

In many arthropods, sex is determined by infection with parasitic, endosymbiotic bacteria of the genus Wolbachia . The bacterium can only be transmitted via infected ova, and the presence of the obligate endoparasite may be required for female sexual viability. [36]

Secondary sex characteristics

Male animals have evolved to use secondary sex characteristics as a way of displaying traits that signify their fitness. Sexual selection is believed to be the driving force behind the development of these characteristics. Differences in physical size and the ability to fulfill the requirements of sexual selection have contributed significantly to the outcome of secondary sex characteristics in each species. [37]

In many species, males differ from females in more ways than just the production of sperm. For example, in some insects and fish, the male is smaller than the female. In seed plants, the sporophyte sex organ of a single organism includes both the male and female parts.

In mammals, including humans, males are typically larger than females. This is often attributed to the need for male mammals to be physically stronger and more competitive in order to win mating opportunities. In humans specifically, males have more body hair and muscle mass than females. [38] [ page needed ] [39] [ page needed ]

Birds often exhibit colorful plumage that attracts females. [40] [ page needed ] This is true for many species of birds where the male displays more vibrant colors than the female, making them more noticeable to potential mates. These characteristics have evolved over time as a result of sexual selection, as males who exhibited these traits were more successful in attracting mates and passing on their genes.

See also

Related Research Articles

<span class="mw-page-title-main">Gamete</span> A haploid sex cell

A gamete is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. The name gamete was introduced by the German cytologist Eduard Strasburger in 1894.

<span class="mw-page-title-main">Reproduction</span> Biological process by which new organisms are generated from one or more parent organisms

Reproduction is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. There are two forms of reproduction: asexual and sexual.

<span class="mw-page-title-main">Sex</span> Trait that determines an organisms sexually reproductive function

Sex is the trait that determines whether a sexually reproducing organism produces male or female gametes. During sexual reproduction, a male and a female gamete fuse to form a zygote, which develops into an offspring that inherits traits from each parent. By convention, organisms that produce smaller, more mobile gametes are called male, while organisms that produce produce larger, non-mobile gametes are called female. An organism that produces both types of gamete is hermaphrodite.

<span class="mw-page-title-main">Sex organ</span> Biological part involved in sexual reproduction

A sex organ, also known as a reproductive organ, is a part of an organism that is involved in sexual reproduction. Sex organs constitute the primary sex characteristics of an organism. Sex organs are responsible for producing and transporting gametes, as well as facilitating fertilization and supporting the development and birth of offspring. Sex organs are found in many species of animals and plants, with their features varying depending on the species.

<span class="mw-page-title-main">Sex-determination system</span> Biological system that determines the development of an organisms sex

A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most organisms that create their offspring using sexual reproduction have two common sexes and a few less common intersex variations.

<span class="mw-page-title-main">Mating</span> Process of pairing in biology

In biology, mating is the pairing of either opposite-sex or hermaphroditic organisms for the purposes of sexual reproduction. Fertilization is the fusion of two gametes. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization. Mating may also lead to external fertilization, as seen in amphibians, fishes and plants. For most species, mating is between two individuals of opposite sexes. However, for some hermaphroditic species, copulation is not required because the parent organism is capable of self-fertilization (autogamy); for example, banana slugs.

<span class="mw-page-title-main">Sexual differentiation</span> Embryonic development of sex differences

Sexual differentiation is the process of development of the sex differences between males and females from an undifferentiated zygote. Sex determination is often distinct from sex differentiation; sex determination is the designation for the development stage towards either male or female, while sex differentiation is the pathway towards the development of the phenotype.

<span class="mw-page-title-main">Evolution of sexual reproduction</span> How sexually reproducing multicellular organisms could have evolved from a common ancestor species

Sexual reproduction is an adaptive feature which is common to almost all multicellular organisms and various unicellular organisms. Currently, the adaptive advantage of sexual reproduction is widely regarded as a major unsolved problem in biology. As discussed below, one prominent theory is that sex evolved as an efficient mechanism for producing variation, and this had the advantage of enabling organisms to adapt to changing environments. Another prominent theory, also discussed below, is that a primary advantage of outcrossing sex is the masking of the expression of deleterious mutations. Additional theories concerning the adaptive advantage of sex are also discussed below. Sex does, however, come with a cost. In reproducing asexually, no time nor energy needs to be expended in choosing a mate and, if the environment has not changed, then there may be little reason for variation, as the organism may already be well-adapted. However, very few environments have not changed over the millions of years that reproduction has existed. Hence it is easy to imagine that being able to adapt to changing environment imparts a benefit. Sex also halves the amount of offspring a given population is able to produce. Sex, however, has evolved as the most prolific means of species branching into the tree of life. Diversification into the phylogenetic tree happens much more rapidly via sexual reproduction than it does by way of asexual reproduction.

In biology, gonochorism is a sexual system where there are two sexes and each individual organism is either male or female. The term gonochorism is usually applied in animal species, the vast majority of which are gonochoric.

<span class="mw-page-title-main">Anisogamy</span> Sexual reproduction involving a large, female gamete and a small, male gamete

Anisogamy is a form of sexual reproduction that involves the union or fusion of two gametes that differ in size and/or form. The smaller gamete is male, a sperm cell, whereas the larger gamete is female, typically an egg cell. Anisogamy is predominant among multicellular organisms. In both plants and animals gamete size difference is the fundamental difference between females and males.

<span class="mw-page-title-main">Isogamy</span> Sexual reproduction form involving gametes of the same size

Isogamy is a form of sexual reproduction that involves gametes of the same morphology, and is found in most unicellular eukaryotes. Because both gametes look alike, they generally cannot be classified as male or female. Instead, organisms undergoing isogamy are said to have different mating types, most commonly noted as "+" and "−" strains.

<span class="mw-page-title-main">Oogamy</span> Form of sexual reproduction

Oogamy is a form of anisogamy where the gametes differ in both size and form. In oogamy the large female gamete is immotile, while the small male gamete is mobile. Oogamy is a common form of anisogamy, with almost all animals and land plants being oogamous.

Monogamous pairing in animals refers to the natural history of mating systems in which species pair bond to raise offspring. This is associated, usually implicitly, with sexual monogamy.

Mating types are the microorganism equivalent to sexes in multicellular lifeforms and are thought to be the ancestor to distinct sexes. They also occur in macro-organisms such as fungi.

<span class="mw-page-title-main">Hermaphrodite</span> Sexually reproducing organism that produces both male and female gametes

A hermaphrodite is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are of different sexes, either male or female but not both, are gonochoric, which is the opposite of hermaphroditic.

<span class="mw-page-title-main">Female</span> Sex of an organism that produces ova

An organism's sex is female if it produces the ovum, the type of gamete that fuses with the male gamete during sexual reproduction.

<span class="mw-page-title-main">Sexual reproduction</span> Biological process

Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete with a single set of chromosomes combines with another gamete to produce a zygote that develops into an organism composed of cells with two sets of chromosomes (diploid). This is typical in animals, though the number of chromosome sets and how that number changes in sexual reproduction varies, especially among plants, fungi, and other eukaryotes.

<span class="mw-page-title-main">Social selection</span> Term used in biology

Social selection is a term used with varying meanings in biology.

Gametogamy is sexual fusion – copulation or fertlization – of two single-celled gametes of different sex and the union of their gamete nuclei giving the zygote nucleus, as well as whole zygotic content.

Gynogenesis, a form of parthenogenesis, is a system of asexual reproduction that requires the presence of sperm without the actual contribution of its DNA for completion. The paternal DNA dissolves or is destroyed before it can fuse with the egg. The egg cell of the organism is able to develop, unfertilized, into an adult using only maternal genetic material. Gynogenesis is often termed "sperm parasitism" in reference to the somewhat pointless role of male gametes. Gynogenetic species, "gynogens" for short, are unisexual, meaning they must mate with males from a closely related bisexual species that normally reproduces sexually.

References

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Further reading