[tptacek]

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.

[AgentME]

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.

[lostmsu]

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.

[lostmsu]

> 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".