It's an interesting thought experiment, but the 1% is an oversimplification - necessary, perhaps, in a general audience. The 1% difference he talks about is not

It's an interesting thought experiment, but the 1% is an oversimplification - necessary, perhaps, in a general audience. The 1% difference he talks about is not phenotype (reasoning ability) but genotype (DNA). It's not hard to imagine a few critical changes such as more cortical folds and improved myelination leading to most of the phenotypic cognitive difference. These could be controlled in some key fractions of a % of the genome. While it works as a metaphor, it's flawed as a general metric. A species in which Hawking-level ability is - if not average - at least commonplace, would require the average IQ to be 2-3 standard deviations higher (relatively) on the human scale. IQ being, itself, a rather flawed metric of course :)