What is religion for? Should you happen to believe in the real existence of some deity or another that question answers itself, but if you don't, you have to wonder why such an apparently dysfunctional structure — one that consumes vast resources — has persisted in most places throughout human history.

A new exhibition at the British Museum, Power & Taboo, provokes reflections on this big question from the perspective of a society whose complex, polytheistic gods created a very different worldview from the primarily monotheistic stance that shaped the modern European world.

The exhibition covers Polynesia from 1760 to 1860, the period of early contact with an outside world from which the peoples had been largely isolated for many centuries. For the islanders their multiple gods were ever present in the world. They used tapu, from which our word taboo derives, to describe strategies for human control of these gods.

The exhibition begins with a striking, attractive image of a god who seems at first look like a Sesame Street character, wide-eyed, primary-coloured, in a caricature of a frown. But look closer, and those fine feathers that provide the colour make you think of all the small birds that died to provide them, and the sharp teeth (those of dogs') start to look more like the stuff of nightmares.

The impression is magnified further into the exhibition, with one of its greatest treasures - the emphatically swathed and bound wooden statue, some 2 metres long, that may be the Rarotongan creator god Ta'aroa. This was collected by the missionary John Williams in 1827. Such images were often wrapped and bound, their power contained by this ritual. Removing the wrapping would take away both the power and the danger - so this is the only known "god" surviving in its original form.

So what we have here are apparently terrifying, nightmare gods, high-maintenance gods who demanded a lot of work of their adherents. Why might these societies, living in what we might think of as an idyllic world of swaying palm trees and soft sea breezes, have chosen to create such deities? Some thoughts occur.

The feather gods are particularly associated with Hawaii, where the highest-ranking chiefs "owned" the fancy feathers that made up these gods, and wore cloaks and helmets (also exhibited with magnificent examples here) decorated with them. Should you be a chief wanting to maintain your power, the threat of the wrath of a powerful god might certainly come in handy in keeping your people in power, as might the claim that you were descended from their lesser descendants and relations.