I’m really having trouble wrapping my mind around the concept of heritability.
These numbers are obviously wrong, but let’s just use them for convenience:
Let’s pretend that scientists say that 80% of height is due to my genetics. If I’m 100cm tall, I understand that the scientist is NOT saying that 80 of my cm is due to my genetics.
I also understand that it doesn’t mean that if there are 100 people in my population, it doesn’t mean that 80% of them are only as tall as they are because of their genetics.
Does it mean that 80% of the reason I am as tall as I am is because of my genetics?
I started wondering about this when someone mentioned something to the effect of, “If your dad was a drinker, it runs in the family.” and also things like, “you’ll probably go bald because your mom did”. I understand that heritability is a term used for population studies, but I’m not sure why it doesn’t apply to individuals as well.
And if you read this and think “hoooo boy, OP’s gotta go ALLL the way back to square 1”, I’m more than happy to click a link and read!
Thanks a lot for your help!
In: 2
It depends on how they chose to quantify it exactly, but likely what it means is that 80% of the variability in height across individuals is determined by genetics. The rest then would be determined by environmental factors like diet.
To simplify, suppose that all humans were between 170-180 cm tall, and all heights within this range were equally common. If height were 100% genetics, that would mean that (in theory) you could tell exactly where in that range an individual would fall just by looking at their DNA. “Oh, your DNA in this particular gene goes AACATTTAAGGGTCCAA? Well then that means you must be 177.45 cm tall.”
If 80% of height variability can be explained by genetics, that instead would mean (in this simplified example) that your genes only determine your height to within 2 cm (eliminating the other 80% of the range of possibilities). So e.g. by looking at your DNA, scientists might be able to determine that you are between 172.2-174.2 cm tall. The remaining 2 cm (20%) of variability then is determined by environmental factors.
Real-life variability is more complicated than this, but that’s the basic idea.
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