▲ Naturally High IQ ▼

Evan Hadkins:

Another important implication is that differences between identical twins are not necessarily only attributable to nurture or environmental factors, but may be genetic. As a consequence of this, the heritability of intelligence has probably been systematically under-estimated. Indeed, the fact that males have only one X-chromosome to rely on—the one they got from their mother—almost certainly explains not simply why so many more males than females have IQs below 70 but also why 20% more males than females have IQs above 140. Greater variability is inevitable if only one X chromosome is being expressed as compared with the two on which a woman can normally rely. Furthermore, this in itself could explain why some men outperform women intellectually in some respects: ironically perhaps, these high performing males are expressing a single outstandingly gifted X-chromosome that they got from their mothers.

I enjoy the nature versus nurture debate, and am biased to stories which emphasize the significance of our genetic nature. The above quote makes the point that the variability in IQ generally attributable to environmental factors might relate more to our genetic nature than is commonly thought.