There’s nothing like making OCs and writing fanfics that make you want to deep dive into the lore of a fictional species. But here the actual canon lore is rather scant, as is most DB lore, in spite of Saiyans being arguably the most well-tread ground in the series. Some things are awfully surprising that there isn’t a canon for them, or how long it took for there to be one. Going forward without Toriyama around anymore, I’m not sure how any future additions to “canon” will feel or count. RIP ever knowing things like who Vegeta’s mom was or how U7 Saiyans fled Sadala.
On this page I’m highlighting certain canon things and observations and the headcanons they’ve led to for me, personally. I'm going to be formatting this in a way where things are (hopefully) logically grouped together. I'll list the canon (or observed) tidbits which inspired these thoughts and the headcanons that sprung from them.
As is the nature of headcanons, these are my own thoughts, conclusions, and opinions, and a lot of them are colored by feelings, interests, and other leanings that are specific to me. I don't expect anyone to "agree" with any of these conclusions, this is all just for the fun of exploring fiction and worldbuilding (and a non-zero amount of self-discovery).
BIOLOGY
Almost all details about the hows and whys and evolution of Saiyans are left up to the viewer. Most of it wouldn't exactly be pertinent to the story and getting into the nitty gritty of alien biology isn't really in the scope or tone of the whole thing, but I'm a nerd about that kind of stuff so I have plenty of headcanons about it!
OBSERVATION
Saiyans (and half-Saiyans) at toddler ages seem to have no less verbal and motor skills than adults, with the exception of Goku, though he was left in the incubation pod until age 3, whacked his head, and was a feral child for years after his grandpa's death. Also with the exception of Goku, they tend to have very good memory recollection skills.
HEADCANON
Saiyans are more precocial than humans, and have a more detailed visual memory. Perhaps Gohan's Saiyan side actually gave him an edge with his studies in this regard.
OBSERVATION
Characters who we see for long stretches of their lives follow a certain growth pattern (or awkward height changes in their designs, your mileage may vary), and signs of aging don't appear until decades after they would for humans.
HEADCANON
Saiyans grow mostly steadily up into their early 30s with the exception of a growth spurt in the mid-late teens. They remain in this prime until they begin rapidly aging around 70 or so.
OBSERVATION
There seem to be more male than female Saiyans, and apart from appearance, both sexes seem not to have any difference in roles or treatment. Saiyans need to eat a fuckton of food compared to other species. The Saiyan characters who settle on Earth are initially baffled by human social norms.
HEADCANON
Some of this arguably bridges into "culture" territory, but it's going here because of the biological basis of it. The material cost of producing a new Saiyan is high (especially historically), so reproduction rates are low. The Frieza Force introduced incubation pods and a stable flow of resources, so the population was able to grow more than would have normally been possible. Both sexes remain reproductively viable for a longer portion of their lives than humans, to be flexible with the availability of resources. Females also only ovulate at will, when they have intent to conceive, also an adaptation to conserve resources.
Males and females are less biologically distinct from one another than humans. Pairing is more often for bonding than reproduction, and male/male is common. With little exception, Saiyans mate for life. Outside of courtship practices/rituals, there are no gender roles, and even then it's only that in a male/female pairing, the female is usually the initiator. Initiating courtship is done with a duel.
OBSERVATION
Saiyan characters show comparatively far less to no sexual attraction compared to most of the human characters (of any gender).
HEADCANON
Relating to the above naturally low reproductive rates, Saiyans are generally disinterested in mating unless they find someone who sparks that part of them into being. They have a puberty in which all the necessary components develop (this coincides with the aforementioned growth spurt), but there is a separate hormone with no human analogue that drives sexuality which remains dormant unless activated (usually by the courtship duel). Also it's fun to headcanon them aspec because seeing this in them when I was discovering my own aspec-ness was nice. I did not think I'd turn out to be one of those people who discover a queerness in their thirties while noticing it in old comfort characters!
OBSERVATION
Saiyans seem to be willing and able to eat anything even if they do have tastes and opinions on quality, and Goku needed a ridiculous amount of tranquilizer to be knocked out even briefly by Princess Snake.
HEADCANON
Because of their insane caloric needs, Saiyans evolved to be able to digest basically anything that can be molecularly processed into usable nutrients. It is also next to impossible to poison them by way of ingested substances.
OBSERVATION
Saiyans have tails, which are expressive. Outside of those socialized strongly among humans, verbal niceties are not really an inclination among Saiyan characters.
HEADCANON
For simple communication, Saiyans prefer nonverbal methods, and don't have the layers of verbal social song and dance that humans do, and may find it redundant or tiresome. Words are reserved for storytelling, banter, complex instruction, or interacting with other species. Their natural tendencies may have been overwritten somewhat by their annexation into the Cold/Frieza Force, and individuals raised only within this context sit in a strange place in between what is natural and what could be adaptations for surviving and interfacing within the Force.
OBSERVATION
Saiyan hair is overwhelmingly likely to be black, but rarely can present in variants of reddish-brown or blue, and even black hair has different undertones on different characters. Hair shape also appears heritable, and is distinct in its spikiness.
HEADCANON
Saiyan hair shapes, paired with their highly variable heights evolved as a means of recognizing individuals at a distance for group coordination (such as on a battlefield or when hunting/gathering food), along with the use of tail and limb gestures for communication. The encoding of direction and length of hair per follicle is genetic.
Also, the genes for the black pigment are dominant, and the pigment itself is also structurally useful in strengthening the hair. It is similar to but incompatible with human genes for black hair color, and in hybrids only the human colors are expressed. The undertones (red, blue, or neutral/lacking an undertone) are, however, compatible with human colors and may express or modify the offspring's hair color. Saiyan hair is hollow in cross section, like thinner and softer quills, able to hold shape but still flexible.
OBSERVATION
Universe 6 Saiyans lack tails and are smaller and more homogeneous in size than Universe 7 Saiyans. U6 Saiyans still live on Sadala.
HEADCANON
Universe 6 Saiyans adapted to the catastrophe caused on Sadala at first by shrinking and needing less food. As they and the planet recovered, and especially as they became spacefaring, they relied more on verbal communication and lost their tails and variable heights, though they retained their hair.
CULTURE + HISTORY
Saiyan culture and history are both fascinating and frustrating as our knowledge of anything before the last 17 years of their existence is unknown, save for the legendary tale of Yamoshi 1000 years before. While they were known to the galaxy as Frieza's marauding pawns, there are many centuries of time in which they were not doing any of that, minding their own business alongside the Tuffles on Planet Plant. There are many ways to extrapolate backwards, but these are my own interpretations.
CANON
In Yamoshi's story, there is a war between "good" Saiyans and "evil" Saiyans, and in spite of his rebellion, the "evil" ones won, becoming the ancestors of all present day Universe 7 Saiyans.
HEADCANON
Delineating "good" and "evil" like it's some kind of innate thing in an almost subspecies sort of set-up is really reductive in my opinion. It's far more interesting to assume that history and collective memory of a thousand-year-past war has eroded into an oversimplification, and the species' base nature is neutral. The war was a civil war between factions, one of which was, at the time, culturally less benevolent than the other, but neither "good" nor "evil" is innate to Saiyans, they are culturally learned like any other species. This is absolutely true when you look at the living Saiyan characters, all of which have been molded by the events of their lives and the teachings of others as much as their own individual personalities.
CANON
Saiyans only refer to each other by a given name. Out of known royal Saiyans, the line for the throne all share the same name. Only Saiyans in the final generation have known parents. Most of the known Saiyan characters with offspring are not shining examples of parenthood. Most of the Saiyans (and half-Saiyans) with known childhoods have a mentor figure to which they'd bonded in their youth.
HEADCANON
There are no family names in Saiyan culture because outside of the single line of royalty, heredity is not given much value. Before the annexation by King Cold, Saiyan young were raised in a local creche by community caregivers and usually did not know who their own parents were. Rather than familial bonds, Saiyan children form strong friendships as well as bond to a mentor and learn a trade from them, this bond being one of the strongest in the individual's life. After being assimilated into the Cold Force, Saiyans were made to start tracking bloodlines for the logistics of tracking power levels and heredity and the final generation before their demise was raised more in family units, with a parent sometimes taking the mentor bond role.
CANON
The Vegeta we follow in the story is Vegeta IV.
HEADCANON
There was only the one dynasty of royalty, an abrupt and violent upheaval from what was previously scattered clans holding territories and competing naturally. The first king took power by conquering or destroying all the other clans. He established a hitherto unheard of idea of inherited power and destiny with his son, when previously Saiyans lived in the moment and did not believe in such things. The natural order of things was disrupted, and in a few generations the problems with this began to grow...
CANON
There is no known canon between the events of Yamoshi's exploits and the Saiyan-Tuffle War. The surviving Saiyan characters don't know of the Super Saiyan God when Beerus comes to inquire about it.
HEADCANON
Saiyans kept their history by oral tradition. Disruptions such as the conquest of the first king saw this begin to unravel as communities were fractured, assimilated, or destroyed. Keepers of history became fewer in number over the last handful of generations, and much was lost to the average Saiyan aside from major legends such as that about Yamoshi himself, though even that tale was limited.
CANON
The Saiyan-Tuffle War was started by King Vegeta III and took place between Age 720 and Age 730. Though vastly outnumbered, the Saiyans' strength kept them evenly matched for all that time until the 100 year full moon which sealed the Tuffles' fate.
HEADCANON
The war was started to make scapegoats of the Tuffles to distract from the growing restlessness of the Saiyan populus, with the propaganda that they're being mistreated by their diminutive neighbors. Because of the difference in numbers (and the precociousness of Saiyan young), every Saiyan old enough to walk was drafted, and the war left a lasting mark on those who grew up through it.
CANON
The full moon on Planet Plant/Planet Vegeta happens once every hundred years. The frequency of full moons on Sadala is currently unknown. During their time on the Frieza Force, Saiyans were sent to planets timed with the full moon or used the Power Ball technique once it was developed.
HEADCANON
This vast infrequency means that most Saiyans for centuries since coming to Plant would have only experienced the full moon once in their lifetimes, if at all. Whatever their cultural practices surrounding it from evolving on Sadala with its lunar cycle were would have been lost over time. By the time of the Saiyan-Tuffle War, many individuals were likely afraid of the transformation and avoided the moon that night, only to perish with the Tuffles as those that did look at the moon rampaged uncontrollably.
The centuries-long disconnect from the form also meant that most if not all of them had no control during that time and when it was over, awakened naked amongst the carnage with little or no memory of the event. Only one year later, King Cold annexed the Saiyans, now forcing many of them to do this whole thing time and again.
CANON
The final generation of Saiyans was born under the rule of the Frieza Force, and were the only ones to have been so. Nappa, Vegeta, and Raditz worked for the Force about five times longer than any other Saiyans, being the only survivors kept within it.
HEADCANON
These individuals have a warped idea of what Saiyan culture is, but as they are the only survivors of Frieza's genocide, they are the only source of information on Saiyan-ness most other characters have. Tarble and especially Goku simply lack any information or get it through Vegeta. Raditz and especially Vegeta himself were raised to believe the point of Saiyans was to enforce their might on others, when the species had barely done that for a year or two before their births (Raditz's age is unknown), and had only Nappa and the memories of their parents as a cultural conduit after the demise of the rest of the species.
CANON
Goku was initially aggressive upon arriving on Earth, but his demeanor changed when he hit his head. All three Saiyans raised outside of the Frieza Force's influence are kind-hearted, in direct contrast to those who worked in it for decades.
HEADCANON
Though he was sent away as a last resort to save him and not intended as an infiltration baby, the pod Goku was in still was set for such a mission. Hitting his head erased the subliminal programming that accompanied him in the ship en route to Earth, and he became his natural self. Goku is closer to the natural state of Saiyanhood than most of the other Saiyan characters. Independent but gregarious, pride in the group identity (in his case, Earthlings) moreso than the self. Lives in the moment, does not believe anything is set in stone. This is further reinforced by other Saiyans who grew up outside the influence of the Frieza Force - Tarble and Broly, who are also friendly and open.
The introduction of monarchy, the concept of "elites," and eventually the Cold/Frieza Force divided Saiyan culture over time. The lower class remained largely unchanged until the Force took over, but the elite and ruling class broke off its own subculture early on. Pride became individualized, legends became premonitions of destiny rather than mere stories immortalizing warriors of old. Vegeta, while priding himself on being what he believes is a prime example of his species, is actually probably the weirdest guy out of all of them, spending the second half of his life that we follow slowly untwisting and undoing all that generational and direct corruption, while still maintaining his own personal nature and inclinations.