It is probably a very rough approximation anyway as it doesn't account for what a given body is. A brain the size of a gnat would be insufficient to handle a bo

It is probably a very rough approximation anyway as it doesn't account for what a given body is. A brain the size of a gnat would be insufficient to handle a body the size of an elephant but that doesn't say how relevant the difference is even in the same order of magnitude. A morbid observation of hunters and tanners is that anything the brain of anything they skin is enough to tan its hide. Now that is clearly a chemical process with a very remote relation to actual processing capability given that tanin can subsitute for tanning but not thinking but it does hint at a lower bound size constraint for even the dumbest vertabrate. That aside the point is there would be less nerve input for the brain to process from five grams of fat, five grams of skin, or say an organ like the eye. Let alone any other other details it must acount or provide for. Further complicating things is neural plasticity - if I recall correctly "optical" areas of the born blind tend to be repurposed for other senses as opposed to say mathematical ability. TL;DR: There is evidence but certainly not good enough to tell us anything about sex differences in humans.