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For other uses, see Chan.
For other uses, see Shen.

The Andorian and Aenar species are unusual in that there are four distinct Andorian and Aenar sexes, and a union between all four sexes, an act known as the shelthreth, is required for procreation.

Two of the sexes, thaan and chan, are approximately masculine, and the other two sexes, zhen and shen, are approximately feminine. Andorians and Aenar accept the terms "male" and "female", and the pronouns "she/her" and "he/him", while dealing with binary reproductive species. (DS9 novel: Avatar, Book Two)


In the primary Andorian language, known as Andorii, the distinctions are as follows:

  • zhen - This sex roughly corresponds to female, and is the sex of the Andorian who will carry the zygote to term.
  • shen - This sex also roughly corresponds to female and is where all Andorian life originates. Although the zhen carries the infant, the child begins as gametes from the shen.
  • chan - This sex roughly corresponds to male. Physically Chans are smaller than Thaans, Chans are usually a wiry body type.
  • thaan - This sex also roughly corresponds to male. Thaans are bigger than Chans and usually a more muscular body type.

Reproductive process[]

The gametes of each "male" sex contain one third of the number of chromosomes necessary to produce offspring. During the conception of an Andorian child, the thaan fertilizes a shen's egg with his gamete. The chan then also fertilizes the egg. This produces a fertilized egg that develops into a zygote. The shen then transfers the zygote to the zhen's pouch, where it develops into an embryo. The Andorian fetus is incubated and nourished to term in the zhen's pouch. The zhen does not contribute genetically to offspring.

According to DS9 novel: Avatar, Book Two, the zhavey is the child's closest relative biologically.

Name prefixes[]

In some Andorian linguistic traditions, Andorians have name "prefixes" which indicate which of the four sexes they are. The "prefixes" thus encountered are as follows.

Polite form of address[]

Zha, Sha, Cha, Tha


zh'yi, sh'za, ch'te, th'se


zhavey, shreya, charan, thavan


zhei, shei, chei, thei


zhi, shi, chi, thi

Parent by marriage[]

zhadi, shidei, chada, thadu

Child by marriage[]

zhri'za, shri'za, chri'ze, thri'ze


The unique paradigm of the four Andorian and Aenar sexes have long caused reproductive problems on Andor. By the year 2155, the Andorian population was noticeably dropping and the Aenar species numbered fewer than 5000. The Andorian thaan Shran speculated that the Aenar were slowly going extinct. (ENT novel: The Good That Men Do)

By the year 2376, the Andorian species was still dying out. The required union between all four sexes, and a shrinking window of fertility created a reproductive crisis to which there was no known solution.

While in the Gamma Quadrant, an Andorian chan, Starfleet ensign Thirishar ch'Thane, discovered a unique genetic turn key that existed in the non-viable eggs of a species known as the Yrythny. The eggs provided an apparent solution to the Andorian's crisis by making it possible to widen the window of Andorian fertility and making it possible for a zhen to have more than one child at a time. (DS9 - Worlds of Deep Space Nine novel: Andor: Paradigm)

By the 24th century, the Aenar had died out. (TNG - Typhon Pact novel: Paths of Disharmony)

Star Trek Online, set in the early 25th century, contradicts this, with Aenar being a non-playable species.

Chromosomal Problems[]

While the specific date has not been mentioned, the Andorians suffered a "horrific biological holocaust" in their recent history (prior to 2155), in which severe chromosomal damage was inflicted on most zhavey, causing trisomy and hesomy problems for their offspring. As a result, the fertility window for Andorians shrank to a mere 5 years and conception became substantially more difficult.

Andorian scientists attempted to map every family member's genetic lineage in an attempt to identify genetic drift where mutations may have occurred and correct them, but this approach yielded limited success.

As a result of the failure to genetically engineer a solution to the problem faced by the reproductive crisis, Andorian scientists started pairing bond groups to the most genetically compatible mates to ensure an increase success rate for conception. (DS9 novel: This Gray Spirit)


By 2381, it had been discovered that the Yrythny solution was not resolving the problems the Andorians were facing. Many of the potential Andorian children were either miscarried or suffered serious genetic defects. The re-discovery of the Shedai meta-genome provided a potential solution to this issue. (ST - Typhon Pact novel: Paths of Disharmony)

By 2385, it was estimated that the Andorians would be largely extinct by the 25th century if a cure was not found. As a result, a Federation team of doctors led by Julian Bashir discovered the cure for the reproductive issues while illegally utilizing the classified Shedai meta-genome data and disseminated it across Andor with the assistance of the USS Aventine, despite the risk to the careers of all involved. The long term implications of the treatment on the Andorian race would be the elimination of the need for paired quads.

By 2386, the names of those involved in saving the Andorians from this crisis were so well known that Andorian children were being named after them. (ST - The Fall novel: A Ceremony of Losses)


This section is written
from the Real World
point of view
Memory Beta

The writers and editors at Pocket Books extrapolated the four Andorian sexes from Data's line in the TNG episode: "Data's Day" that Andorians marry in groups of four. They freely admit that one does not necessarily equate to the other, but felt that this interpretation afforded the best storytelling opportunities. For an alternate view of Andorian reproduction, see the TNG novel: The Eyes of the Beholders. Also, partially contrary to the novels, the more recent and higher-canon Star Trek: Enterprise TV series portrays the Andorians as having two sexes, and very much the same sexual habits as humans, although no information directly contradicting the possibility of four sexes and the social relationships described in the novels is ever given. Star Trek: Enterprise novels such as The Good That Men Do have brought the television Andorians into line with those in novels.