Contact with Europeans enabled Māori to access the material culture of Great Britain, then the most advanced industrial country in the world. By 1800 the desire for iron objects such as large ships' nails overcame apprehension about boarding an anchored ship and this drove Māori trading behaviour until 1840. Desirable steel objects and blankets were at first traded for fish. Māori were generally very curious about European culture after initial misunderstandings and apprehension - Māori showed great ability to accept changes and to integrate these into their normal way of life The French expedition of Marion du Fresne, who visited Aotearoa in 1772, gave northern Māori potatoes, wheat, onions, goats, pigs, chickens and other food to raise. Potatoes and pigs rapidly became a key part of Māori agriculture in the north, but the new food was almost exclusively reserved for trading purposes, with Māori themselves still eating fish and fern roots, supplemented by kūmara. Later, as Māori grew large areas of potatoes (Hongi Hika had a 40-acre potato field), whalers would call into the Bay of Islands, in particular, to trade for fresh supplies.