[1][better source needed] He spent his childhood in Africa, Asia and South America, traveling around with his father, who worked as a geologist for International Shell.

When he was 16, he developed Alopecia totalis, a condition in which all the hair falls out, which was caused by a culmination of stress and a reaction to malaria medication.

[4] Following this journey, Nelson embarked on more trips, documenting a variety of war zones, including Afghanistan, Kashmir, Yugoslavia, Somalia and El Salvador, and started to work as a professional photojournalist, until the age of 24.

He travelled across the country for 30 months, together with his then wife, Ashkaine Hora Adema, who participated in the making of the book, and became the subsequent business partner of Nelson.

In a TED talk he described the working process used in this project and stated it occasionally took "months trying to find [these indigenous peoples] and then again weeks to gain their trust and permission to photograph [them].

[4] In the book's foreword, Mundiya Kepanga, Papuan chief from the Tari region in the Highlands of Papua New Guinea, writes, "My culture is who I am.

We're gathering [pictures, video and other information] and creating a digital fireplace, sort of like a library in the sky, of all this heritage for future generations.

The film took 90 days to edit, and includes images of the Huli Wigmen from Papua New Guinea, the Kazakhs of Mongolia, the Sadhus of India, the Wodaabe from Chad and a number of other cultures.

[16] Julia Lagoutte writes in the OpenDemocracy: "It is simply not true that tribal people have been "unchanged for thousands of years"; they have been evolving constantly, as we have.

It is clear that for Nelson, their attraction and purity is rooted in their exclusion from the future, and their containment to the past – so that is the only reality he presents in his photos.

"[16] Nelson's project Before They Pass Away came under attack from Stephen Corry, director of Survival International, the global movement for tribal peoples' rights.

[17] Papuan tribal leader Benny Wenda has also criticized Nelson for describing his tribe as "headhunters", when in fact the Dani have never practised cannibalism.

[13] Nelson defended his book by saying that it was never meant to be reportage, but an "aesthetic, romantic, subjective, iconographic representation of people who are normally represented in a very patronising and demeaning way.