While in high school Jared Diamond believed he would become a physician, to follow his father's path. However he chose the Greek classes rather than sciences. And he remained with a great passion for foreign languages since then: while in his sixties he began studying Italian - that being his twelfth tongue.
But let's come back to his young years. He went to Harvard, considering again a scientific career. And again he studied anything rather than sciences: Russian, German, music, oral epic poetry and the like. He thought that anyway he would work in some scientific field for the rest of his life, so why not doing at least in college something really for his soul? And he remained with a great passion for music. Some years later he would propose to his wife by playing the Brahms Intermezzo in A minor.
After Harvard he went to Cambridge University in England, where he finally devoted his time fully to sciences and earned a PhD in physiology. It was the case, you'd say.
After finishing his studies, Jared Diamond returned to US and started working in the field of laboratory research, specializing in the physiology of gall bladder, at Harvard (as a Junior Fellow) and then at UCLA (as a professor at the Medical School). A summer trip to New Guinea brought him the big picture of life and the big meaning. He started a second career that took a more and more precise shape in the years that followed, embracing such fields as ecosystems, evolutionary biology, geographic determinism, anthropology, macrohistory.
He is talking about all this in his books: The Third Chimpanzee (1991: how did humans evolve from being just another specie of big animals to what distinguishes them radically from all other animals?), Guns, Germs and Steel (1997: how did Eurasians - rather than people from the other continents - become the masters of the world?), Why Is Sex Fun (1997: why is human sexuality so radically different from all other animals?), Collapse (2005: why did so many past societies disappear, leaving behind ruined temples, pyramids and palaces?), Natural Experiments of History (2010: can we elaborate a sort of experimental laboratory by comparing different historical events evolving under similar conditions while having different outcomes?), The World Until Yesterday (2012: can we learn from present-day traditional societies for our own good?). The method, as we can see, is to formulate clearly the question and then to advance some possible alternate answers, if any. Each of these books deserves a short discussion. Maybe I should come back to it.
(A Life in Books)