The heritability of height has increased, because the nutritional environment has become more uniform. To be very specific, “more equal” means both that people have more similar sets of options, and that they exercise similar preferences among these options.
This is interesting, because the increased heritability has coincided exactly with an increased importance of environmental factors from a decision making standpoint. In other words, a contemporary parent picking from {underfeed kids, don’t underfeed kids} can exert more influence over the absolute height of their children than a parent with only the option to underfeed. Of course, modern parents overwhelming opt for the same choice. At the same time, these parent don’t have much influence on the relative height advantage of their child, given a uniformity in options and preferences in the population.
This can happen whenever options and preferences are aligned in a population. For example, no matter how heritable a positive trait is, it will usually be trivial to influence it … in a downward direction. So if you’re looking at a twin study on something like subjective well-being, I’ve found it clarifying to explicitly note the options and preference available to the population. I’m currently reading up on positive psychology, and I keep seeing, even from domain experts, statements like, “X percentage of your happiness is genetically determined”, as if the population they studied were picking actions at random.
I heard something years ago that stuck with me. In an optimum environment, 100% of human variation on everything would be genetic. So if you do everything you can environmentally to improve your kids intelligence, 100% of the variation left must be genetic. Similarly with height, musical ability, etc etc.
So whenever one finds that less than 100% of the variation in some positive trait is genetic, it means at least some of the population is not optimizing the environment to bring out that trait.
Not obviously relevant to the comment above, but on the same topic so I stuck it here.
A thought about heritability and malleability:
The heritability of height has increased, because the nutritional environment has become more uniform. To be very specific, “more equal” means both that people have more similar sets of options, and that they exercise similar preferences among these options.
This is interesting, because the increased heritability has coincided exactly with an increased importance of environmental factors from a decision making standpoint. In other words, a contemporary parent picking from {underfeed kids, don’t underfeed kids} can exert more influence over the absolute height of their children than a parent with only the option to underfeed. Of course, modern parents overwhelming opt for the same choice. At the same time, these parent don’t have much influence on the relative height advantage of their child, given a uniformity in options and preferences in the population.
This can happen whenever options and preferences are aligned in a population. For example, no matter how heritable a positive trait is, it will usually be trivial to influence it … in a downward direction. So if you’re looking at a twin study on something like subjective well-being, I’ve found it clarifying to explicitly note the options and preference available to the population. I’m currently reading up on positive psychology, and I keep seeing, even from domain experts, statements like, “X percentage of your happiness is genetically determined”, as if the population they studied were picking actions at random.
I heard something years ago that stuck with me. In an optimum environment, 100% of human variation on everything would be genetic. So if you do everything you can environmentally to improve your kids intelligence, 100% of the variation left must be genetic. Similarly with height, musical ability, etc etc.
So whenever one finds that less than 100% of the variation in some positive trait is genetic, it means at least some of the population is not optimizing the environment to bring out that trait.
Not obviously relevant to the comment above, but on the same topic so I stuck it here.