In all fairness, this is likely a structural data anomaly. ie, it is driven by the number of majors at the school, and their level of abstraction. Here are some historical data points.

Notice the arbitary abstraction of, eg

Bio Sciences Human Biology

1955 1. History 2. Economics 3. Psychology 4. Political Science 5. Bio Sciences

1965 1. History 2. Political Science 3. English 4. Psychology 5. Economics

1975 1. Psychology 2. Bio Sciences 3. Economics 4. History 5. English

1985 1. Economics 2. Human Biology 3. Bio Sciences 4. Electrical Engr 5. English

1995 1. Bio Sciences 2. Human Biology 3. Economics 4. Psychology 5. English

and now we look at 2010 (from quora)

Biological Sciences (1.32%) but Human Biology (12.58%) Biology (5.74%)

=~20% of Standford majors in 2010 are "biology majors" in plain language usage.

Based on data on Bachelor's Degrees conferred in the 2009-2010 school year[1], the top majors are:

    Human Biology (12.58%)
    Economics (8.10%)
    International Relations (6.20%)
    Biology (5.74%)
    Computer Science (4.94%)
    Engineering (4.71%)
    Psychology (4.54%)
    Political Science (4.25%)
    English (3.96%)
    History (3.62%)
    Management Science and Engineering (3.39%)
    Mechanical Engineering (3.10%)
    Science, Technology, and Society (2.30%)
    Communication (2.18%)
    Electrical Engineering (2.07%)
    Mathematics (2.01%)
    Earth Systems (1.84%)
    Physics (1.84%)
    Sociology (1.49%)
    Biological Sciences (1.32%)*