Take de Broglie 

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> De Broglie had intended a career in humanities, and received his first degree in history. Afterwards, though, he turned his attention toward mathematics and physics and received a degree in physics
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And Edward Witten,a very famous theoretical physicist

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> Witten attended the Park School of Baltimore (class of '68), and received his Bachelor of Arts with a major in history and minor in linguistics from Brandeis University in 1971. He published articles in The New Republic and The Nation. In 1968 Witten published an article in The Nation arguing that the New Left had no strategy.[citation needed] He worked briefly for George McGovern's presidential campaign. McGovern lost the 1972 election in a landslide to Richard Nixon.  
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>  Witten attended the University of Wisconsin–Madison for one semester as an economics graduate student before dropping out.[citation needed] He returned to academia, enrolling in applied mathematics at Princeton University[citation needed] then shifting departments and receiving a Ph.D. in physics in 1976 under David Gross, the 2004 Nobel laureate in Physics. 
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In china,student major in history or literature won't study mathematics *at all*,and almost everyone think it's impossible for someone receive BA then turn to science,so how did someone receive BA and then become a scientist?