A common finding is that if you want to explain data around a trait and you can only know the environment or the gene, the environment is usually the better choice.
The interaction between genes and traits is very counter intuitive for most people. As an example from the lecture, if we asked people how heritabile the number of fingers a person has we would expect the answer would be 100% since it is very rare for a person to be born with 4 fingers. But if we asked if genes or environment is the best method to explain why some people have 4 fingers, genes are a very proof explanation since finger amputation are caused very rarely from genes. The variation of fingers among humans has thus a very low (almost 0%) heritability.
Heritability == the observed variation in the data set that can be explained from genes.