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"The concept of heritability can be expressed in the form of the following question: "What is the proportion of the variation in a given trait within a population that is not explained by the environment or random chance?"[2]"
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The within a population part is critical. I'd encourage looking up twin studies to understand one way this percentage is estimated. I assume you think you know how they are done - you do not, because it directly leads into an understanding of how things like lipstick wearing would be near 0% heritable, while things like handcount at birth would be near 100% heritable.
For what it's worth, you can mechanistically work out lipstick and hands from first principles; just plug rough numbers into the formula.
"Heritability is a statistic used in the fields of breeding and genetics that estimates the degree of variation in a phenotypic trait in a population that is due to genetic variation between individuals in that population."
You are using the term in a colloquial or folk sense. Do you think accents are highly heritable? After all, a child will almost always share the accent of their parent. So in the colloquial sense this would be a 'heritable' trait, but in the genetic sense the heritability of an accent is zero.
â lipstick: highly dependent on XX vs. XY; hands: set by highly conserved Hox genes, variation virtually entirely due to environmental factors.