In the 18th and 19th centuries, as Europeans penetrated further and further into some of the most inaccessible parts of the globe, they encountered peoples who seemed to turn everything they thought they knew about human behaviour upside down.
Here were communities who loved and married, fed and fought, lived and died in ways very different to anything that European explorers had ever seen before.
From their attempts to make sense of what they had seen – and to help them understand the nature of what it means to be human – the idea of anthropology was born.
"The science of man", as anthropology was dubbed, had its heyday in the first 50 years of the 20th century.
It was hugely influential, as new information about how other communities organised themselves was translated back into the West, where it provided a blueprint for changing traditional behaviour under the argument of returning to a more "natural" or "free" way of doing things.
But in recent years, many of the assumptions that underpinned the work of key anthropologists have been questioned by new research.
Wider questions have been asked about whether it is possible – or indeed morally desirable – for the observation of one group of humans by another to ever be anything other than subjective; whether indeed a "science of mankind" can ever be possible...
BBC FOUR's season tells the story of some of the great names of anthropology's past, and raises some penetrating questions about its future.