After having several hamsters over the years I've noticed that larger hamsters tend to be calmer while the smaller ones seem to be far more energetic and often times more afraid of people. Why are larger hamsters calmer than smaller species of hamsters?
I think it is because the large ones are of variety named Syrian hamsters, and the smaller ones are Dwarf hamsters. I am assuming that because it would match exactly the behavior pattern you are observing. Dwarf is an umbrella term accounting for a few differient but quite similar behavior‑wise varieties. And yes, Syrian ones are more chilled, calm and willing to interact with humans while Dwarf ones are hectic, much harder to tame and trust people.
As I understand reason for that is genetics as they are of two distinct genera (Mesocricetus is the genus of Syrian hamsters and Phodopus is the one for Dwarf hamsters) and in the wild they face different enviromental conditions of their respective habitats. For example Syrian hamsters are living in warmer climates than Dwarf ones, thus more calmness in their physical activity was promoted during their evolution and they evolved to be different it that aspect. Also, some Dwarf spieces face extremely low temperatures in the wild, which besides promoting increased motor activity also promotes living in larger, close groups to conserve heat. In contrast, Syrian hamsters hate to be accompanied by others of the same kind, they have to be kept alone and thus their only social stimulus comes from their owner, enabling more focus into developing bonds with people.
Also, it is not only a phenomenon observed in hamsters: in general smaller animals tend to be proportionally faster and more active to maintain homeostasis and it is because of square–cube law.
As for sources I used:
- and a bit of intuition.