The heritability statistic that occurs in the literature is the ratio of genetic variance to phenotypic variance.
Two corrollaries:
* When discussing heritability results from the literature, we are discussing that statistic, not your intuitive understanding of what the word should mean.
* In the scientific literature, your conception of heritability doesn't operate. In the scientific sense, the number of hands you have has low heritability, despite being genetically determined.
I think you're going to find "let's check Wiktionary" is not the decisive move in these kinds of discussions that it is elsewhere.
> In the scientific sense, the number of hands you have has low heritability, despite being genetically determined.
This is only a surprise because unlike layman the author of this joke insists on considering heritability among humans specifically. While "heritability among humans" sounds like a reasonable comment to a layman, the author of this joke is misleading the layman, because layman (before being mislead) correctly thinks of "heritability" as "heritability among all living things with genes".
Another great example of the unintuitiveness of heritability is the fact that earrings are highly heritable. Earrings are highly correlated to a specific genetics (being female), so they're very "heritable", even though that correlation is an arbitrary cultural fashion.
See my sibling comment. This is misleading for the same reason, but in this case the cause of misleading is narrowing the timespan under consideration to approximately now.