The sex organs of a green algae Chara are the male antheridia (red) and female archegonia (brown).
A peacock displays his long, colored tail, an example of secondary sex characteristics.
The female genitalia of Lepidoptera
A red deer stag's antlers are secondary sexual characteristics.
Anatomical characteristics of the human male and female

These characteristics are particularly evident in the sexually dimorphic phenotypic traits that distinguish the sexes of a species, but unlike the sex organs (primary sex characteristics), are not directly part of the reproductive system.

- Secondary sex characteristic

The process of sexual differentiation includes development of secondary sexual characteristics, such as patterns of pubic and facial hair and female breasts that emerge at puberty.

- Sex organ
The sex organs of a green algae Chara are the male antheridia (red) and female archegonia (brown).

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Alpha

Sexual selection creates colourful differences between sexes (sexual dimorphism) in Goldie's bird-of-paradise. Male above; female below. Painting by John Gerrard Keulemans

Sexual selection

Mode of natural selection in which members of one biological sex choose mates of the other sex to mate with , and compete with members of the same sex for access to members of the opposite sex (intrasexual selection).

Mode of natural selection in which members of one biological sex choose mates of the other sex to mate with , and compete with members of the same sex for access to members of the opposite sex (intrasexual selection).

Sexual selection creates colourful differences between sexes (sexual dimorphism) in Goldie's bird-of-paradise. Male above; female below. Painting by John Gerrard Keulemans
Victorian cartoonists mocked Darwin's ideas about display in sexual selection. Here he is fascinated by the apparent steatopygia in the latest fashion.
Sexual selection protected flour beetles from extinction in a ten-year experiment.
Male long-tailed widowbird
The peacock tail in flight, the proposed classic example of a Fisherian runaway
The enormous sexually-selected antlers of the Irish elk might have helped it on its way to extinction.
Male mountain gorilla, a species with very large males
Protarchaeopteryx was flightless, but had feathers, perhaps used in courtship, that pre-adapted it for flight.
Among mammals, the male gorilla is much larger than female.
Males of many spiders, such as this Phidippus putnami, have elaborate courtship displays.
A male Abedus indentatus belostomatid bug carries eggs on its back.
Each firefly species attracts mates with its own flash pattern.
Male Dendropsophus microcephalus calling
upright|Territorial fight in the Indian rat snake, Ptyas mucosa
upright |Male Victoria's riflebird displaying to a female
A male satin bowerbird guards its bower from rival males in the hope of attracting females with its decorations.
right|Male southern elephant seals fighting on Macquarie Island for the right to mate
Citronella flower's symmetry may have been subject to sexual selection by its pollinators.

Sexual selection can lead males to extreme efforts to demonstrate their fitness to be chosen by females, producing sexual dimorphism in secondary sexual characteristics, such as the ornate plumage of birds-of-paradise and peafowl, or the antlers of deer.

Or it may do the opposite, driving species divergence—sometimes through elaborate changes in genitalia —such that new species emerge.

Differentiation of the male and female reproductive systems does not occur until the fetal period of development.

Sexual differentiation

Process of development of the sex differences between males and females from an undifferentiated zygote.

Process of development of the sex differences between males and females from an undifferentiated zygote.

Differentiation of the male and female reproductive systems does not occur until the fetal period of development.
The Human Y Chromosome showing the SRY gene which codes for a protein regulating sexual differentiation.

The differentiation of other parts of the body than the sex organ creates the secondary sex characteristics.

A newborn joey suckles from a teat found within its mother's pouch

Reproductive system

A newborn joey suckles from a teat found within its mother's pouch
Didactic model of a mammal urogenital system.
A male common frog in nuptial colors waiting for more females to come in a mass of spawn

The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction.

In addition to differences in nearly every reproductive organ, numerous differences typically occur in secondary sexual characteristics.

Vulvas of different women (pubic hair removed in some cases)

Vulva

Vulvas of different women (pubic hair removed in some cases)
Labeled image of a vulva, showing external and internal views
Vulva with visible parts of the clitoris and the parts lying under the skin
Muscles underlying the vulva and perineum
The length of the labia minora varies significantly between women: while the labia majora completely enclose the labia minora in some women (top row), in other women they protrude and are clearly visible in upright standing position (bottom row). Colloquially, these variations of the labia are also referred to as "innies" and "outies".
Genital tubercle of female at fourteen weeks
Development of genitals showing homologues from indifferent at A to both sexes - female on right
Development of genitals showing homologues from indifferent to both sexes
Non-aroused vulva on the left and a sexually aroused vulva on the right with enlarged and shiny labia minora from vaginal lubrication and vasocongestion
Water warts of molluscum contagiosum
Pubic hair with crab lice
The Labia pride movement resents the ideals of female cosmetic genital surgeries: The Muff March in London, 2011
Female genital piercings include the Nefertiti piercing central and the Christina piercing pictured on either side
Derived from traditional symbols, Hanabira scarification is intended to decorate the pubic area
A gynaecological examination being carried out in 1822
Japanese artist Megumi Igarashi with vulva portrayal
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Glans clitoris with small distance to the opening
Glans clitoris with medium distance to the opening
Lack of contact of the clitoral glans with the penis
Contact of the clitoral glans with the penis with small CUMD
Classification of the 200 women into CUMD categories
Selection of women studied and interviewed
Vulva handsign used as a yogic mudra
Attic red-figure lid. Three female organs and a winged phallus.
Yoni at Mahadev temple
Glans clitoris with medium distance to the opening

The vulva (plural: vulvas or vulvae; derived from Latin for wrapper or covering) consists of the external female sex organs.

Pubic hair is much coarser than other body hair, and is considered a secondary sex characteristic.