The answer to this question can be found in the Prologue of this excellent historical study of the reasons for inequalities between different groups of humans. Considering Yali's question as to why Westerners have gained dominance in the world and not any other group of humans, Diamond considers the intelligence of Papa New Guineans, and argues that they show, on average, greater intelligence than Westerners, especially given their ability to survive in an environment in which most Westerners would perish very quickly. In addition, note how Diamond supports his hypothesis:
Modern European and American children spend much of their time being passively entertained by television, radio, and movies. In the average American household, the television set is on for seven hours per day. In contrast, traditional New Guinea children have virtual no such opportunities for passive entertainment and instead spend almost all of their waking hours actively doing something, such as talking or playing with other children or adults. Almost all studies of child development emphasise the role of childhood stimulation and activity in promoting mental development, and stress teh irreversible mental stunting associated with reduced childhood stimulation.
Thus we can see that the actual technological lilmitations of the Papua New Guineans may result in their greater intellectual development compared to their Western counterparts.