I am confused.

So I'm in a psychology course in school, and I do not understand heritability at all. We were talking about it today in class, and apparently there are two ways to explain it.
From a psychological standpoint, what is the heritability of having 10 fingers? Because I thought it was 1, and so did my class and my teacher, but apparently it's 0?

I'm so confused, can anyone help me understand this?

For example, the number of fingers on a human hand or toes on a human foot is genetically determined: the genes code for five fingers and toes in almost everyone, and five fingers and toes develop in any normal environment. But the heritability of number of fingers and toes in humans is almost certainly very low. That's because most of the variation in numbers of toes is environmentally caused, often by problems in fetal development. For example, when pregnant women took thalidomide some years ago, many babies had fewer than five fingers and toes. And if we look at numbers of fingers and toes in adults, we find many missing digits as a result of accidents. But genetic coding for six toes is rare in humans (though apparently not in cats). So genetically caused variation appears to be small compared to environmentally caused variation. If someone asks, then, whether numbers of toes is genetic or not, the right answer is: "it depends what you mean by genetic." The number of toes is genetically determined, but heritability is low because genes are not responsible for much of the variation

Ok, I think I understand.
Thanks!

......and I was going to say ,,,,, first you have to beable to count to ten >>>.in order to know what that " is " .

I thought that some Amish populations have marked genetic disposition for six fingers ?