Don't you see the problem with the above statement? Let me show it to you very simply. Can you tell the IQ of a person by the size of their head? Does a person with an IQ of 150 have a head 3 times the size of one with an IQ of 50? Brain size and intelligence are totally unrelated.
You can tell the intelligence of an individual by the way they behave and from how successful they are at competing. Brain size is not 100 percent correlated with intelligence, but it is correlated.