Working with the tables devised by Quetelet, Galton proposed the tabular "classification of men according to their natural gifts" shown [below].
CLASSIFICATION OF MEN ACCORDING TO THEIR NATURAL GIFTS
GRADES OF NATURAL NUMBERS OF MEN COMPRISED IN THE SEVERAL GRADES OF NATURAL ABILITY, WHETHER IN RESPECT ABILITY, SEPARATED TO THEIR GENERAL POWERS OR TO SPECIAL APTITUDES BY EQUAL INTERVALS
Below Above Proportionate; In Each Million In Total Male Population of the United Kingdom, Say Average Average viz., One in of the Same Age 15 Millions, of the Undermentioned Ages 20-30 30-40 40-50 50-60 60-70 70-80 _a_ A 4 256,791 651,000 495,000 391,000 268,000 171,000 77,000 _b_ B 6 161,279 409,000 312,000 246,000 168,000 107,000 48,000 _c_ C 16 63,563 161,000 123,000 97,000 66,000 42,000 19,000 _d_ D 64 15,696 39,800 30,300 23,900 16,400 10,400 4,700 _e_ E 413 2,423 6,100 4,700 3,700 2,520 1,600 729 _f_ F 4,300 233 590 450 355 243 155 70 _g_ G 79,000 14 35 27 21 15 9 4 _x_
All grades All grades below _g_ above G 1,000,000 1 3 2 2 2 0 0
Interpreting this theoretical tabulation, Galton (6) wrote:
It will be seen that more than half of each million is contained in the two mediocre classes _a_ and A; the four mediocre classes _a_, _b_, A, B, contain more than four fifths, and the six mediocre classes more than nineteen twentieths of the entire population. Thus, the rarity of commanding ability and the vast abundance of mediocrity is no accident, but follows of necessity from the very nature of these things.
On decscending the scale, we find by the time we have reached _f_ that we are already among the idiots and imbeciles. We have seen that there are 400 idiots and imbeciles to any million of persons living in this country; but that 30 per cent of their number appear to be light cases, to whom the name of idiot is inappropriate. There will remain 280 true idiots and imbeciles to every million of our population. This ratio coincides very closely with the requirements of class _f_. No doubt a certain proportion of them are idiots owing to some fortuitous cause . . . but the proportion of accidental idiots cannot be very large.
Hence we arrive at the undeniable but unexpected conclusion that eminently gifted men are raised as much above mediocrity as idiots are depressed below it; a fact that is calculated to enlarge considerably our ideas of the enormous difference of intellectual gifts between man and man.