Sexual Intercourse

Sexual Intercourse Definition

Sexual intercourse, or copulation, is the deposition of sperm into a female via a male intromittent organ. In humans, the intromittent organ is the penis, and sperm are deposited into the vagina, where they make their way to towards the uterus to fertilize an egg. However, sexual intercourse is almost as varied as the animal kingdom itself, and occurs in some form or another in most of the large groups of organisms. From the smallest organisms to the largest, sexual intercourse is simply the process of delivering sperm into the female, although the process varies widely.

As opposed to external fertilization, internal fertilization through sexual intercourse increases the change that fertilization will occur among the gametes. During external fertilization, gametes are broadcast into the environemtn, and must find their way to each other through shear numbers. Organsims that reproduce using this method must time the release of their gametes to maximize the production of new offspring. Sexual intercourse not only localizes the deposit of sperm, but greatly reduces the distance and area a sperm must cover to find an egg. Beyond the penis or other intromittent organ entering the female and depositing sperm, the process of sexual intercourse varies widely by animal. Below are a few examples.

Examples of Sexual Intercourse

Sharks

Male sharks have long intromittent organs that hang near their cloaca, or urogenital opening. During shark sexual intercourse, the male will wrap himself around the female or otherwise arrange his body to insert his clasper into the female’s cloaca. The tip of the clasper has hooks and spines, which anchor the clasper inside of the female while the male ejaculates his sperm into the female’s cloaca. Sharks use a special muscular sac under the skin to flush sperm out of the clasper with seawater it collects near the pelvic fins. The sperm must then make their way up her reproductive tract, to eggs descending from her ovaries. Fertilization will occur, and each zygote will grow into a new shark.

Flukes

One of the smallest organisms in the world is the fluke. Flukes are small worms, although not simple in the least. Fluke are hermaphroditic organisms, containing both male and female reproductive organs. When flukes engage in sexual intercourse, both flukes give and receive sperm. This is known as mutual cross-fertilization and enhances both organism’s chances of passing on their genetics. The male intromittent organ in flukes is called the copulatory apparatus (named after its action in copulation) and rests inside a muscularized sac called the cirrus sac. When two flukes engage in sexual intercourse, each fluke flexes their cirrus sac, exposing their copulatory apparatus. The female reproductive tract of each animal contains a vagina, into which the sperm are deposited. After sexual intercourse, the flukes separate, and each develops an egg around its new young, which it lays in a safe place.

Even Stranger Forms of Sexual Intercourse

Dolphins engage in a sexual intercourse that is very similar to that of humans. Male dolphins have a penis, which they use to deposit their sperm in the female’s vagina. Like many animals, sexual intercourse between dolphins is not distributed equally, and females are often battled over. Unlike most animals, dolphins have been seen to engage in sex as a pleasurable act. While this does seem to make them more intelligent, like humans, it comes with its negatives. Dolphins are also one of the only animals capable of raping members of its own species, which large males sometimes use as a threat against smaller males and females.

Think that is strange? Ducks are worse. With intense competition between males for mates, male ducks typically try to reproduce by ambushing females at the same time. Females, in an evolutionary tactic to fend off unwanted mating, developed a curved vagina. In response, the penis of male ducks is often an aggressive and strange shape. Many duck penises are spiraled and barbed, which helps them stay in if the male is able to mount the female. The variations of sexual intercourse are nearly infinite in the animal kingdom, and some of them are remarkably strange.

Related Biology Terms

  • Intromittent organ – The fleshy appendage used to deliver sperm into the female.
  • Ejaculation – The process of pushing sperm out of the intromittent organ, which has many variations.
  • Copulation – Another word for sexual intercourse, often used in biology.
  • Coitus – A term for sexual intercourse that specifically refers to the position two organisms must take during copulation.

Quiz

1. Some species of fish reproduce in the following manner. Females shoot towards the surface, chased by a group of males. Near the surface she turns, and the males rub her underside, releasing eggs. At the same time, the male ejaculates his sperm into the water column. Which of the following happened?
A. Sexual Intercourse
B. Coitus
C. External Fertilization

Answer to Question #1
C is correct. This is an example of external fertilization. Although the two organisms do touch to stimulate the release of gametes, the male does not have an intromittent organ and simply releases his sperm into the water. The timing of his release will determine whether or not his sperm reach eggs. While this is not sexual intercourse, it is thought that internal fertilization and sexual intercourse probably evolved from behaviors similar to this, which reward the proximity and timing of gamete discharge.

2. Which of the following statements is true?
A. Viviparity requires sexual intercourse.
B. Oviparity requires copulation.
C. Ovoviviparous animals rely on external fertilization.

Answer to Question #2
A is correct. Animals that give birth to live young (viviparous animals) and animals that give birth to live young first developed within an egg (ovoviviparous), both require sexual intercourse to deliver sperm to the reproductive tract. Oviparous animals that lay eggs can undergo sexual intercourse (such as birds) or they can externally fertilize the eggs, as in the case of fish.

3. Why would sexual intercourse become a pleasurable act, evolutionarily?
A. Pleasurable sex means more babies
B. Pleasurable sex leads to monogamy, which increases survival
C. This is a myth, only humans engage in sex for pleasure

Answer to Question #3
A is correct. The plain and simple answer is that organisms which are rewarded for having sexual intercourse will have more of it, lead to more babies. While it was long thought that birds formed monogamous relationships on this basis, it was found that most birds that pair to build nests are not sexually exclusive, and offspring in the nest can have different fathers. However, many animals seem to get pleasure out of sexual intercourse. Even female crocodiles have a clitoris, hinting that even crocodiles get some pleasure from sexual intercourse. This could possibly decrease tensions between large, dangerous individuals long enough for fertilization to take place.
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