What is the theme in Endurance: Shackleton's Incredible Voyage by Alfred Lansing?

Polar Adventure would be the main theme of the story. Shackleton could offer very few tangible reasons for undertaking the ill-fated expedition. Certainly a trans-Antarctic expedition had never been accomplished, but the reward for executing such an expedition was to be found only in the doing of it and not in any real economic or political gain, though certainly national honor and fervor accounted for much of the expedition's funding. Shackleton himself was fairly uninterested in the science—either biological or geological—of the undertaking and seems to have included scientists only in order to secure funding from various sources. Indeed, the entire expedition seems fairly devoid of purpose beyond doing it because it had not been done before. It is evident, therefore, that the entire voyage was nothing more, nor less, than a grand adventure.