So I've got a species of humanoid giants in the setting. Each individual has their own set of horns, between 1 and 5, that extend from their forehead. The horns determine their adult height, with single-horns generally being 6 feet tall(1.828 meters) and penta-horns generally being 10 feet tall(3.048 meters). Family members tend to have horn counts that are the same among the individuals but sometimes one is born with one less or one more horn nub. The horns are mostly used by the parents to determine and prepare for the sizes of clothes they'll have to make during the growth of their child, but if push comes to shove they are great at impaling things if they can manage it.
Now there is some magic in the setting, but being that I want things to exist as independent from magic as possible, I'd like for it that there be an explainable reason as to why specifically their horn count causes such a large variation in height within this species of giants.
Is there any sort of natural mechanism that would explain why my giants are taller or shorter depending on how many horns they have?
Some extra information, if relevant:
- Most of them live in mountainous or snowy regions with the surrounding forest flora being mostly populated by pine trees. Those who travel or live elsewhere exist, but this is their native biome.
- Bone density and overall muscle size/strength increases proportionately with height, making each individual not look lanky in any sort of sense unless they were of the skinny sort.
- Except for the horns and a slight difference in how their ears and faces look like, they're basically like humans.