According to an article in the International Directory of Company Histories (which I found on findarticles.com) although the native peoples of Australia had been eating the nuts for more than a thousand years, the "discoverers" thought them to be poisonous:
The macadamia tree... originated in Australia, and in 1857 was named after Dr. John Macadam, a chemistry professor at the University of Melbourne and a member of Australia's Parliament who apparently had nothing to do with the plants.
His friends, Baron Ferdinand von Muller... [and] Walter Hill... were the first to classify the tree botanically, having discovered it on an expedition. The honor of providing a name fell upon von Muller, who elected to pay tribute to his friend Macadam.
Hill removed the kernels from the shells in order to plant and cultivate the trees. He believed the nuts were likely poisonous, according to some aborigines at least, and was shocked to discover a young assistant happily snacking on some. When the boy seemed to suffer no ill effects, Hill tried the kernels, found them delicious, and became an enthusiast.
In 1921 a man from Massachusetts, Ernest van Tassel saw the commercial potential of the Mac Nut and planted an orchard of them near Honolulu. A year later the University of Hawaii began an extensive research program that observed 60,000 trees and tested selection and grafting. In 1946 the Mauna Loa was established by Castle & Cooke, the owners of the Dole Pineapple Co. on the Big Island of Hawaii.
Commercial production was reached in 1956 and a state of the art processing plant was built and designed to generate all its own power by burning the shells of the nuts. Since 2004 Hershey's has owned and operated the Muana Loa plantation and production facility, which is in Hilo.
I was given a bag of Homemade Mac Nuts (thank you Dr. Akioka!) that are larger and far sweeter than anything I've found in the stores. He shells and roasts them himself. Recently he told me a story about how a 93 year old man came by his place and taught him how to fertilize the tree; more appropriately, when to fertilize the tree.
The man had been involved with the Mauna Loa plantation since its inception and knew a great deal about Mac Nuts. Dr. Akioka's yields jumped from about 55 pounds one year to over 90 pounds the next! Thank goodness he has enough to share with everyone.