Alien

Because of the many things the term "Alien" can refer to in The Sims 2, this article deals with them all. Although there may be many definitions, all aliens were released with the base game.

Pure Alien
In the most literal sense, "alien" would refer to these beings. These creatures are the outlandish visitors from another planet that abduct your sims during the use of an expensive telescope.

Appearance
Pure aliens always have the following features:
 * Large, dilated, black pupils
 * Pointed ears
 * Long, gaunt faces
 * Small, flat noses
 * Black hair genes
 * Bald heads (except Pollination Technician 9)

Social Caste
From what little information is given from the family history of Pollination Technician 9, a user can see what appears to be a social caste among the lives of aliens on their home planet:
 * Birth Queens are the central reproductive system of the aliens. It appear that whomever impregnates them has no marital attachment to them, and that the sole life purpose of a birth queen is to breed.
 * Colony Drones are the workers of alien society. They appear to serve their overlords similar to worker-bees.
 * Pollination Technicians are the aliens that pilot spacecrafts seen from telescopes and can somehow impregnate male sims, which will in turn give birth to Alien-Sim Hybrids

Reproductive System

 * Natural Reproduction occurs when a colony drone or another male alien impregnates the female of the species, the Birth Queen
 * Pollinational Reproduction occurs when an adult male sim is abducted while stargazing with the expensive telescope, and he returns pregnant with an alien baby. This baby can be very unique, and is known as an Alien-Sim Hybrid

Alien-Sim Hybrids
This is the other term that could define "alien". These sims are playable and are what is defined as one of the many sim "life states".

Appearance
When transitioning to toddler, alien-sim hybrids may express facial features not usually found on normal sims. These attributes can then be passed on when the alien child grows up and reproduces.
 * Almost always has green skin
 * Usually has large, dilated, black pupils.
 * Usually has curved, normal sim ears

Advantages and Uniqueness
This is possibly the simplest of all life states. Unlike pure aliens, alien-sim hybrids are treated equally with other sims and reproduce the same, as well. Advantages of having a hybrid include a unique skintone and facial features. A unique feature to their birth is that when the child is born a different cinematic is used. Another advantage to having a hybrid is that an alien-sim hybrid teenager can apply for an alien scholarship for college.