... and the ability to be trained into learning arbitrary skills
is IQ. Higher IQ means its easier to train yourself into being able to use a new system of thinking.
Like, being a soldier doesn't require any sort of exceptional intelligence either. It doesn't even require average intelligence. What it requires is an IQ of 85 - below that point, and the US army cannot effectively train you to become a soldier. Despite having every incentive in the world, the US army still rejects about 15% of the population.
