> Heritability is always measured in the context of Environment X. If you change to Environment Y or Z then the heritability will often change greatly. That's

> Heritability is always measured in the context of Environment X. If you change to Environment Y or Z then the heritability will often change greatly. That's not a very meaningful statement. If you took two twins and severely malnourished one of them it would not be useful to say: "See! IQ is mostly environmental!". You have to assume some kind of baseline environment that nearly everyone will share, and that can be full-filled just by the virtue of growing up in a country like America. Otherwise, you are just concerning yourself with insignificant outliers. Here is a twin study that places the heritability at ~80%: https://www.cambridge.org/core/journals/twin-research-and-human-genetics/article/wilson-effect-the-increase-in-heritability-of-iq-with-age/FF406CC4CF286D78AF72C9E7EF9B5E3F https://www.cambridge.org/core/journals/twin-research-and-hu...