“Zoology is still a minority subject in universities, and even those who choose to study it often make their decision without appreciating its profound philosophical significance.” - The Selfish Gene, Richard Dawkins.
As we are told by anthropologists human beings are endlessly diverse in their behavior.
Some live in groups, waving or showing some other token of acknowledgment to a familiar face, while others are utterly solitary. If they're also territorial then when met by another member of their race they will puff up their chest, expose their fangs and stretch their tails as a show of intimidation, if not they will simply completely ignore them as if they were an inanimate object. Of the groupish kinds, some form tight communities engaging in communal eating and play, while others form selfish herds who gather together to use each other as meat shields when attacked by predators, as the humans in those herds constantly jockey for favorable positions to avoid predation they contour themselves in marvelous ways as they travel through the air and sea.
Some groups are constructed by families comprising males and females while in others a single birthing female reproduces almost all members of the group, except several males who migrate to the communal hive to provide the sperm for the giant extended family. In such societies, each member of the commune works not for himself but selflessly sacrifices for the betterment of the whole. In some families, males provide extensive parental care, in others less so, while in several groups the female would decapitate the male during the act of copulation his only parental contribution is the feast his corpse would provide to the young produced from the semen preserved in her egg sack.
In some societies, Men regularly engage in competitive and oftentimes violent behavior in an attempt to acquire Women while in many others Men are fearfully guarded at home from roving bands of Women who rape and pillage all that is in their way.
In a few social groups Male violence is a constant factor while in many others it's solely regulated to the mating season (July - August) when Males grow their hair, fangs, and horns as they are transformed externally and internally in preparation for violent combat.
In most societies, Women form strong and lasting bonds with their kids while in a couple of societies when close to giving birth the mother would do so secretly in another person's home in the hope that they would take care of the child (confusing him as their own).
In most times and places, a great deal of effort is invested in raising kids but in one or two tribes almost all effort is invested in reproduction, after exhausting themselves swimming up a river or climbing to a tall tree top, copulation will ensue and then death, the kids will have to raise themselves.
And all of this is but a few examples of the enormous possible diversity of humanity
Postscript
Every time someone talks of “human culture being endlessly variable" I reach for my encyclopedia of animal behavior (it's quite large and may be wielded as a weapon). Human behavior may be infinitely variable but even if it is, it's a small infinity bound within much larger sets, a tiny subset of all that exists in nature boxed into place by the forces of selection and the evolutionary history of man. Most species are rather solitary it's not just their genes that are selfish it's the whole shebang, even if you are a member of their species "They don't think about you at all", This applies even to animals one usually thinks of as social, most species of bees for example are solitary.
For solitary species that do not treat their kind with dispassion, they treat it with disdain, usually due to sexual & territorial competition, often both, this is the case for many of our ape relatives, gorillas form territorial harems, orangutangs meet and mate, the sight of another male is often greeted by hostility by both species, there are no male bonds, no war, no friend to help you move or make a body. So one aspect of human uniqueness is that "man is a wolf to man" in the sense that like wolfs Man is a social animal, but not just any social animal, many groups in nature are based on fake altruism they gather together to avoid predators. Crows will call their "buddies" to feast on carcasses but will only do so when the risk of predation exists, they will not bother to do so if there are enough crows1 (aka meat shields) around them.
Prehaps the social species that most resemble human social behavior are ants, they build large and specialized structures (ventilation tunnels, defensive perimeters) herd animals (aphids), farm (fungus gardens), wage war and keep slaves, have large-scale cooperative societies in which specialized roles are held by “individuals” and mutual aid and medical treatment is provided for one another ( it’s no wonder Sociobiology was written by an entomologist!). But the basis of their whole society is utterly foreign to us, rather than being the result of reciprocal altruism it is based on genuine brotherly (read: sisterly) love between one giant extended family It is not from the benevolence of the butcher, the brewer, or the baker that we expect our dinner, but it so in ants.
Aside from our unique social arrangement, human familial relationships are rather unique as well, largely monogamish, high degree of parental investment (even if the investment is sometimes performed by one parent), no mating season or significant seasonality of behavior, no changing sex like many mollusks, no widespread hermaphroditism like in plants, basically no to allot of things.
So human culture is not endlessly variable because human beings are not endlessly malleable. Since humans dispersed out of Africa over 50k years ago and segmented themselves into thousands of communities across the globe human culture had endless time and many subjects to randomly shift and vary the behavior of Man but it did not do so in every possible direction, there are no roving bands of Women (sorry to disappoint) no tribe in which mothers do not care for their kids and no Man is an island.
Someone had to drag a carcass in his jeep from place to place to figure that one out, See: Animal Behavior: An Evolutionary Approach by John Alcock.