Another point of canon about psionics is that they are present in almost every known living thing at some level -- but completely absent from Hivers. That is a mystery that puzzles Hivers and those acquainted with them, and a point of much frustration to Hivers, as well as an active area of research for them. (Or maybe the idea that Hivers lack psionics is the result of a Manipulation so successful that even most Hivers believe it?)
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What about the genetic question? Not all characteristics are genetic or environmental. Some are developmental. An obvious example is fingerprints. We don't inherit them. We don't get the patterns from any predictable environmental influence. They're something fixed by genetic rules (we get them on our fingertips, they're mostly parallel at an approximately constant spacing, but loops and cusps and whorls appear when space runs out for going parallel, and they start forming in an apparently random way that makes them practically unique), but develop randomly according to those rules.
What about the links to intelligence (which is roughly half environmental), education (which is entirely environmental, except to the extent that there may be a genetic component to the motivation to seek education), and social standing (which is largely inherited, but not genetically inherited)? As far as I'm aware, canon doesn't say there's any link there; it's strictly a game mechanic.