[tptacek]

No, it very obviously is not. This isn't something we need to argue; you can simply go look it up. The number of fingers on your hands: not very heritable. Whether you wear lipstick: very heritable.

You can set your watch to people on message boards making arguments about the genetic determination of intelligence that rely almost entirely on heritability statistics. It seems pretty clearly to be a cargo culting phenomenon; how else could you have very specific heritability numbers without even knowing what the term means? I'm curious where you got it from.

[l0t0b0r0s]

Polydactyly is a condition in which a baby is born with one or more extra fingers. It is a common condition that often runs in families.

Is this not what heritability means?

[dan-robertson]

Heritability means that parents having a trait explains, in a statistical sense, some amount of how much a randomly chosen person has a trait. So some of heritability is genetics and some is the shared environment.

For example, someone is quite likely to speak the same first language as their parents, and for this reason, the statistics for heritability come up with a high number for how heritable a trait first language is. But this isn’t because of some English-speaking gene, it’s because lots of environmental conditions are common between parents and children.

The intuitive reason that the number of fingers on your hand is not heritable is because lots of the variation comes from injuries which are not explained very much by whether one’s parents lost fingers from injury. Genetic causes for an unusual number of fingers are much less common than accidents and so can’t cause much of the variation that is observed across a population.

Because it is quite reasonable to get a high heritability number for something that is not genetically determined (and a low number for something that is), one cannot really argue anything about genetic determinism from heritability numbers.

[l0t0b0r0s]

>some of heritability is genetics and some is the shared environment.

This is not the definition of heritability you are mincing words.

Heres the definition of heritability:

(HAYR-ih-tuh-BIH-lih-tee) The proportion of variation in a population trait that can be attributed to inherited GENETIC factors.

>For example, someone is quite likely to speak the same first language as their parents, and for this reason, the statistics for heritability come up with a high number for how heritable a trait first language is.

you are conflating inheritability with heritability.

The reason we are able to have crops that yield more is because we genetically modified them to do so; not because we grew wild corn in the perfect environment.

[tptacek]

You're lost here. Heritability is defined technically as h^2 = V_a / V_p, with V_a additive genetic variance and V_p phenotypical variance. Look at your hands. The number of fingers on it are extremely genetically determined; the Hox genes that define your body plan are very conserved. V_a is practically zero. But plenty of people have fewer than 5 fingers, and some are born that way (for instance, children exposed in utero to Thalidomide); V_p is nonzero. Evaluate the expression (0/nonzero).

If you read your own words carefully, you're trying to rebut the parent commenter with their own argument.

[sethev]

You cited this reference up thread: "The Wilson Effect: The Increase in Heritability of IQ With Age". It should give you pause for your definition of heritability that this paper is saying it changes with age. As you point out a couple of comments later, genes don't change with age.

If you're going to cite heritability numbers, you have to use the technical definition of heritability (which is what these papers are using).

> Is this not what heritability means?

No, not at all.

[l0t0b0r0s]

Heres the definition of heritability:

(HAYR-ih-tuh-BIH-lih-tee) The proportion of variation in a population trait that can be attributed to inherited genetic factors.

The study title is saying that heritability INCREASES with age: as you age your IQ is more closely correlated to the IQ of your parents from whom you inherited your genes from.

>As you point out a couple of comments later, genes don't change with age.

Your genes dont change but the correlation between you and your parents IQ does.

[tptacek]

You're not making sense. If heritability means genetic determination, as you say it does, and genes are fixed at birth, then heritability can't change as you age.

None of what you're being told is first-principles axiomatic reasoning. This is all stuff you can just go look up. You got so close with that Wikipedia definition of heritability! All you need to do now is understand what those words mean.