Sex

Sexual reproduction is a method of biological reproduction in which each organism's cells carry two copies of the genetic software, and each of two parents passes the equivalent of one copy to the offspring.

Meiosis
When a cell begins to divide, the two copies in one cell become four. The vast majority of cells in a body are created with mitosis, a cell division that produces two cells, each with one pair of copies. These cells with a pair of copies are called "diploid". But each individual also has a pair of organs called gonads. Gonads, or "nads" for short, contain specialized cells capable of performing meiosis, a different kind of cell division that produces four cells. Once the genetic software has been copied in meiosis, the copies are shuffled to contain parts of the copies from both parents. Finally, the cell divides in four to make "gametes", or "haploid" cells with only one copy.

Animals are oogamous. This means they have two types of gametes, one large and non-motile and the other small and motile. A gonad called an "ovary" produces eggs, or large cells containing most of the machinery for running genetic software. Another kind of gonad called a "testicle" produces sperm, or tiny cells just large enough to carry a copy of the genetic software and propel it to the egg. Vertebrate sperm cells are suspended in a liquid called "semen" or "cum" (from the Latin eiaculatum cum spermatozoa meaning "ejaculate with seed-creatures"), which contains nutrients for the sperm. Individuals with testicles are called "male", and those with ovaries are called "female". These are not fully functional until an individual has metamorphosed into adult stage.

Sex
To create offspring, two adults perform a ritual called "sex", short for software exchange. Sex rituals vary per species, but all successful sex rituals end in fertilization, the entry of a sperm into an egg to complete a pair of copies inside the egg. Fertilization can occur in one of three ways:
 * Spawning
 * The female deposits unfertilized eggs, and the male deposits semen over them. Seen in fish.


 * Intercourse
 * The male squirts semen into a jack on the female. Seen in mammals and birds.


 * Reverse intercourse
 * The female deposits eggs into a jack on the male. Seen in seahorses.

Sperm are similar in ways to both bacteria and viruses. It's like a bacterium in that it can move under its own power and react to stimuli, such as another man's sperm. But it's like a virus in that its reason for existence is to insert its genetic software into a cell before that cell divides.

Organisms have a "sex drive", or an urge to perform sex as a means of continuation of the species. This sex drive may manifest itself in actions using the sex organs that simulate intercourse. Such actions performed alone are "masturbation", and actions with more than one participant (including intercourse itself) are called "sexual contact".

Sometimes unwanted software accompanies the genetic payload. Sexually transmitted viruses can cause blisters on the sex equipment, liver scarring, or even immune failure.

Some species perform pregnancy, or the development of a fertilized egg into a live individual. Most mammals and some reptiles, for example, get pregnant. Others will wrap the fertilized egg in an outer covering, called an eggshell, and "lay" it, or expel it from the body. Insects, fish, amphibians, most reptiles, and birds lay eggs. Some species that lay eggs abandon the eggs; others incubate the egg, or keep it warm, until it hatches, whether by sitting on it or by burying it in a warm place.

Sexes
Some species are hermaphrodites, capable of performing either the male or female role in sex. Other species have two mating types or "sexes", from the Latin sexus meaning division, and each individual is either male or female. A few species have a compromise mechanism called dichogamy or sequential hermaphroditism: they start their adult life as one sex but change to the other sex later in life.

Compared to simultaneous hermaphroditism, sexes avoid needing to spend energy on maintaining both sex organs and help avoid the inbreeding depression associated with self-fertilization. Sexes also represent a division of labor between individuals optimized for pregnancy and raising offspring and individuals optimized for other tasks, such as gathering resources and protecting offspring. Thus, individuals exhibit secondary sex characteristics, or differences between male and female bodies. These vary in their scope from one species to another: some species have almost identical sexes, some have larger males, and some even more bizarre dimorphisms such as parasite-like males with no purpose other than to fertilize a female (as in bees and anglerfish). Some individuals' primary and secondary characteristics develop differently from the majority of the species. Individuals with such sex differentiation disorders are called "intersex".

Among most sapient species, tertiary sex characteristics, also called "genders," arise out of cultural elaboration of the secondary characteristics. These include adornment and behavior patterns. However, at least one African tribe occasionally inverts the usual specialization: men just as often do the breastfeeding and women bring home the bacon, and only a few leadership jobs are reserved for men. Actual male lactation is not unknown. Furthermore, a preschool in Sweden is teaching children to say "friend" instead of using gender-specific pronouns.

Sex bans
Cultures often place prohibitions on sexual contact in various situations in order to avoid the spread of sexually transmitted diseases (STDs), unwanted pregnancies, and inbreeding depression. In various cultures at various times, the following have been among these bans:
 * Pedophilia: Sexual attraction to or contact with a child near the age of puberty by a much older adult. This is often a strong indicator of child abuse.
 * Prostitution: Sexual contact for consideration.
 * Homosexuality: Sexual contact between participants of the same sex.
 * Adultery: Sexual contact outside of a recognized pair bond.
 * Pornography: Fixation of a depiction of external sex organs or sexual contact in a way intended to arouse portions of the brain associated with sex drive, without any serious literary or scientific value. Viewing porn is said to encourage states of mind that lead to adultery (Matthew 5:28).
 * Bestiality: Sexual contact with an "animal" (bioincompatible creature).
 * Miscegenation: Sexual contact with a different breed of the same species.
 * Incest: Sexual contact with someone too closely related.
 * Rape: Sexual contact without informed consent.

Childfree religious movements, such as the Shakers, have shunned sex entirely. Most have died out, unable to win enough converts to replace members who die.

Game world vs. real world
God uses mostly the same rules in each system of His parallel simulation, but due to the free will of the subjects, things may turn out differently. Everything above applies to both the real world and the game world, except that tetrapod hermaphrodites are far less common in the real world. In the period of rapid evolution after the great flood, several species of the game world developed sequentially hermaphrodite sex organs as a response to population pressures.

Interesting results came from a man-made simulation using Lego Mindstorms robots.