Why would a tribe of humans come to be consistently taller?

Question

In my setting, there is an isolationist people known as the Jotnar (sing. Jotunn), who are merely humans, but are consistently taller than other human populations, which I think of as reverse pygmies.

But although there's plenty of room for discussion as to why there are populations that are consistently short, I can't find any for the Jotnar. Should it just be chalked up to "Taller is more attractive in their culture"? Or is there a practical reason why they would have developed to be taller?

Know that I want them to still be Homo Sapiens Sapiens. The only real difference in anatomy is that they remove their vestigial structures from their young to replace those structures with magical biotech they had found in ancient ruins. They are technologically and magically advanced, but I'm thinking they were tall even before that could be said about them, back when they were still a neolithic tribe.

Answer 1

Unnatural selection. They sacrifice everyone who's height falls below 1 standard deviation from the mean. This selects for taller people and appeases the god of dirt because the short people were closest to his domain anyway.

Answer 2

Long distance travel and jumping are easier with longer legs. This will breed them tall and thin like the Maasai in Africa. Their use of the spear builds upon their advantage of a longer reach.

Competition can also breed people taller. When humans fight other humans, body mass is important. It is easier to hang more muscle and other body mass on a taller frame. The extra reach provided doesn't hurt either. The ruling classes of several cultures were bigger than average. As an example, the Ali'i, Hawaii's ruling class, were bigger and stronger than the average Hawaiian because they fought with members of the ruling classes of other islands.

People with poor nutrition in their early years tent to grow up stunted. Therefore, being bigger (taller) could be a sign that a person was raised wealthy. That would promote sexual selection for taller mates.

Answer 3

There are several possibilities that come to mind.

You've already mentioned one: Sexual selection. In short, they find taller people more attractive. It could be cultural, it could be hardwired into their genes somehow.

Others include the other modes of natural selection. If taller Jotnar are better at obtaining food and avoiding getting themselves killed, the Jotnar will gradually get taller over time. Ideally, there should be an evolutionary arms race between the Jotnar and some other species. Perhaps there's some predator that a Jotunn can only effectively defend itself against if the predator is shorter than the Jotunn. That way, there's evolutionary pressure for both species to become taller. Or, perhaps there's a tree whose leaves make up a substantial portion of the Jotnar diet. The tree will evolve more height, smoother bark, and fewer branches to make it more difficult for the Jotnar to climb, while the Jotnar will evolve to become taller and better climbers in order to get to those tasty leaves. This might also happen if the Jotnar are going after the tree's fruit rather than leaves if the seeds cannot survive the Jotnar digestive tract.

Do note that if the Jotnar develop technology that compensates for traits that lack, they will have much less pressure to evolve those traits. If they live in a savanna where height would help them see over the grass, they might instead burn and trample the grass around their settlements. If the tasty tree leaves become too high to reach, they might start building stepladders.

Alternatively, the Jotnar's height might be a result of founder effects. If a small population of unusually tall individuals became isolated from the main human population, their descendants will also, on average, be taller than the average human. If this happens repeatedly — for instance, if taller people regularly strike off on their own to found new settlements — then the effect will be magnified.

Similarly, population bottlenecks can greatly accelerate natural selection. In short, if there's some cataclysm that only the tall people survive (maybe a flood or tsunami where tall people are better able to climb to safety), the population that they rebuild will be taller than the one that came before.

Another possibility is that the Jotunn are simply healthier than anyone else on the planet. Humans have gradually become taller over the past centuries because we've created a better food supply. People used to run low on food over the winter, which stunted their growth. You say the Jotnar are technologically and magically advanced; if the rest of the world has a medieval food supply, they will likely be the tallest people on the planet.

Answer 4

Good ol’ natural selection, Baby

As one of the comments said, it may have been natural selection. Maybe these Jotnar folks live in a Savannah, like the ones in Africa. Being taller is beneficial in that environment, as it allows you to see over tall grass, and how are you gonna hint for food if your to short to see over the grass to hunt your prey. The Jotnar May have lived on a mountain in the past, and in higher elevations, people mostly grow taller than on the ground. This may be the reason. Or maybe Jotnar women prefer tall guys, and overtime nature just sorted itself out.

Answer 5

This actually happens

Full blood Osages are known to have been very tall.

The Osages are so tall and robust as almost to warrant the application of the term gigantic: few of them appear to be under six feet, and many are above it. Their shoulders and visages are broad, which tend to strengthen the idea of their being giants.

One account from an early explorer I read chalked it up to the tribe actively practicing Eugenics. In particular, controlling their own tribe's breeding for size like a rancher might do with livestock. However, Eugenic ideas were a fairly popular new thing with Europeans at the time (that had yet to generate the unfortunate history they since have), so I'm not entirely sure I believe his explanation.

Shandong province in north China has had a reputation for quite a while of producing the largest people in the country. Their average male and female height today is slightly larger than the average American's. The typical rationale the Chinese come up with for this is that it's down to diet (being so far north, their staple cereal crops are much more similar to the ones Europeans rely on). But I don't know of anyone rigorously studying this. The difference in average height is only about an inch though, not the more than half a foot reported for the Osage.

I will add that I have done multiple angles of investigation into human height, and there does seem to be a universal agreement that nutrition is a factor. I'm not saying everyone could be 6'4 like the old Osages if they just ate the right stuff. But I am saying that being calorie limited or spending a lot of time sick in childhood does seem to retard a person's ultimate growth. This means your tribe of giants are likely wealthy (by tribal standards). They never have to worry about going hungry or proper nutrition, and childhood sickness is rare.

Answer 6

Options...

Founder effects

The founders of the tribe were all unusually tall for some reason. Perhaps they were all descended from an ancient basketball team that crashed in the mountains or perhaps it just happened that the group who made it to the remote location to found their tribe were all. An example is Dupuytren's contracture in norway where 30% of men over 60 years old have the condition, mostly due to founder effects.

Puberty Rituals

Puberty rituals vary a great deal around the world but they tend to follow a few patterns.

Young men of the tribe must pass some kind of test in order to be considered real adults and be allowed to marry and start a family within the tribe.

If the tribe practices a puberty ritual which tall people are dramatically more likely to pass then they may strongly select for height over many generations.

Here we see a boy wearing a pair of Bullet Ant Gloves. To pass he must avoid showing signs of pain during the ritual/test.

Pleiotropy

Sometimes a gene which causes one thing also causes other things. So you could have a set of genes that tend to lead to greater average height that are closely linked to a gene which is heavily selected for. Say a gene which grants resistance to an environmental toxin in the location where the tribe lives. Height doesn't give much advantage itself but people who carry resistance genes also tend to be tall which leads to a gradual change in the population.

Eugenics

Possibly the simplest approach. Have the people of your tribe intentionally select for height. When they encounter unusually tall travelers they attempt to induce them to join the tribe. Unusually short people are shunned from the tribe. The very tallest couples in the tribe are honored and encouraged to have many extra children.

Answer 7

Don't forget Signal Theory

Species can take very weird turns in their evolution. Why do many birds have ungainly, bright colours, huge feathers or very obvious features? Why do useless appendages that risk you being more obvious to predators become commonplace? Reason: Signal Theory.

By sending out a signal to your potential mates that you are so unwieldy - yes, you may be more desirable. Basically you are saying "I'm still alive, yet I prosper and spend inordinate resources on frivolous things, therefore mate with me because I have plenty of resources to spare."

Giraffes are in essence ungainly, unusually high creatures - often height is a hindrance with large resources invested beyond the benefits of simply eating leaves. Patterns on Giraffes, and other features, indicate signal theory is equally at play here, female Giraffes may find taller males as sexually attractive simply due to the fact they can be taller.

Some decisions therefore, for instance finding someone attractive or mates, have a convoluted logic to them, not a direct logic.

Height could be seen in this way on your society very easily. There needn't be a 'need' for height, or any direct justification for it, but being taller just like Giraffes could lead to a signal that you may be dominant, more able, or simply have more authority to spare. Perception is everything.

Answer 8

They're human? They're taller as a race?

They're rich...

It's really that simple. All those reasons people can be stunted? In practice, on continents and at a civilizational level, it comes down to childhood nutrition.

There's plenty of speculation and some research about the importance of red meat and milk (Holland, Scandinavia) versus grains and fish (Japan) but (a) you can literally see this on the Chinese subway lines, as grams—who somehow survived the warlord era & the Japanese invasion & the intentional floods to stall that invasion & the Civil War after that & the collectivization after that—can sometimes top out about the level of an African pygmy, mom—who lived under the better but still modest means of the Maoist state—can seem a bit on the short side, and the teenage kid—who's only ever known life since the opening up and, among well-off families, has grown up on imported milk formula—can get over 6'. College girls can demand boyfriends be over 180 or 185 cm and be spoiled for choice. (b) North and South Korea were divided within living memory. The grandkids of that generation? In the wealthy south, they average 5–8 cm taller than in the sustenance farming north. (c) Just a century or two ago, things could be even more divided between the British upper and lower classes, with some studies finding as much as 9" of difference between them.

The Jotnar can be aristocrats, and that can be the end of it.

They can keep herds, individually or communally, that permit consistent and thorough infant nutrition.

They can be traders whose profits and varied diet keep their children (at least for the overclass) well-fed.

They can have magical mushrooms or other mana-given food sources.

...but it's unlikely everyone is.

There are fairly few true egalitarian societies. They tend to be clan based, in bad lands, and poor. What's more likely is that your grossmen will—somewhere obvious or hidden—have their own 'dwarf' class of untermenschen working for them and being fed their scraps. There's probably an origin story and ideas about them being a different race. Both're probably bupkis. Depending on your narrative, you can go into it and free them from their caloric chains or just use them for color.

Answer 9

Coming from the Netherlands the first thing I had to think of was 'flooding in a flat landscape'. But we quickly started building artificial hills (terps) to live on.
You could make an environment with unhealthy gases which are heavier then air, or some pollutant in the dust. (traces of Beryllium?)

Answer 10

The average Indonesians are 158/147 cm (m/f). The average Dutch person is 183/169. Its commonly believed that this is due to a richer diet, better health care, and drinking a lot of milk.[citation needed].

If the people you wan't to be taller are from an isolationist culture maybe they have a special diet, or a plant/animal that mostly grows there? You can combine this answer with the other answers to create an even bigger effect.

Source: https://en.wikipedia.org/wiki/List_of_average_human_height_worldwide

Answer 11

Scandinavians ("Vikings") are on average quite a lot taller and generally larger than Europeans from further South or West.

Chinese from Siberia are on average quite a lot taller than Chinese from further South.

Wolves that live in the far North of Canada are quite a lot bigger than wolves that live further South. Ditto Siberian tigers versus Indian ones.

Spot a pattern?

It's the square-cube law at work yet again. Loss of heat from a body is proportional to surface area. Amount of heat stored within a body is proportional to volume. Increase height by 10% keeping the same proportions, and area increases approximately 20% (1.1 squared) but volume by 30% (1.1 cubed). All things being equal, larger will be selected for if the climate is cold. (If the problem is keeping cool, not warm, then the converse).

You may spot that spherical is better than tall and slender, but there are other reasons why such a profile isn't the answer. Primitive humans and wolves are both chase predators, and the short and stocky profile is not so good at running down prey. Inuit (Eskimos) traditionally fished and hunted from boats, rather than chasing down their prey. They do tend to have the shorter stockier profile.

If the Jotnar don't live in the frozen North, it's probable that their ancestors did. Alternatively, blame unnatural selection (see the other answers).

Answer 12

I would like to propose a few different theories since any one of them could be the reason:

1. Race for food: Like giraffes, the staple food for the Jotnar grew up at considerable height above ground. So the taller ones had fuller bellies as well as had a better chance of providing for a family.
2. Enhanced appearance: I read a few years back, that the human race on the whole is becoming more beautiful since people who are attractive, get a better shot at siring more offspring. There might have been a case of the taller individuals being preferred for mating.
3. Introduced gigantism: The Jotnar live in an area of enhanced radioactivity or as children are fed a specific fruit/root that causes gigantism.
4. Eugenics: The Jotnar are a warrior race. History tells us that since early times, warriors have tried to look taller and imposing as a psychological tactic to demoralize their enemies. Over a period of time, shorter individuals were killed off/restricted from joining the ranks of their taller brothers/sisters and were thus relegated to menial jobs in the hierarchy. This also limited their capacity of having more children.
5. Fringe population group - The Jotnar descended from an group of outcasts. Their forefathers were exiled since they did not fit in with the general populace. Every time a kid reached beyond a particular height, they were banished to the Jotnar lands to live their life away from the shorter society. Over time, this tribe of tall individuals rose as a powerful group on its own.

I, personally, like the last one.

Answer 13

In our world, many societies have practiced primogeniture. When in doubt as to which son should inherit an estate, primogeniture bequeathes the estate to the oldest son.

In this society, suppose that primogeniture bequeathes the estate to the tallest son. Over time, this would cause a correlation between height and having the resources to support more children. It would also reinforce a standard of beauty, in which (all other things being equal) women would prefer taller men.

Answer 14

Looks like you are looking for a dominant genetic syndrome that causes individuals to be taller than average. Instantly I thought of:

Marfan Syndrome

This genetic disease causes, among other symptoms, above average height.

It is an autosomal dominant disorder, so given an initial population of your tribe with this genetic trait, and unlikely reproduction with foreigners, chances are high that the syndrome will be inherited and tribe members should be taller than average.

Answer 15

Evolution is random. New generations randomly get some different traits, and they pretty much randomly procreate or die. Some causes can significantly affect the likelihoods of individuals with certain traits either procreating or dying, but in a small tribe with small numbers, randomness is a much larger factor than in a larger population.

A small population being cut off from the larger population and getting taller for no specific reason is perfectly plausible in the theory of evolution.

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Another thing is, in terms of story, consider if you add anything of value by trying to explain why they are taller.