it’s perfectly possible for one twin to get fat while the other doesn’t. If it doesn’t happen often, it’s because features like willpower are more controlled by genes than we think, not because staying thin doesn’t depend on willpower.
After all, even if we put aside the direct ways in which our genes build our bodies (encoding how our tissues grow) and instead look at our abilities to “make the right choices” and exert “willpower”, we find that those are also greatly determined by genetic factors. Identical twins probably turn out very similar in good part because they have almost identical amounts of those qualities of mind.
I’ve also read that gene expression diverges in twins over time—so if a lot of the difference in body composition is about gene expression, there might be a few pairs of twins where, just by chance, either the willpower or the fat storage changes kick in earlier or more strongly.
“Willpower” is not just one thing—there are people who can’t stick to diets who show a lot of will power in other parts of their lives, and vice versa.
As a young teen I played basketball with a pair of identical twins. One was fairly slight, the other rather stocky and an inch or two taller. Not sure why.
maybe they weren’t identical twins. Unless they did a genetic test they wouldn’t know for sure. I read something once that said that a significant number of same-sex fraternal twins are misidentified as identical.
That is very interesting. I hadn’t thought yet that the way we identify twins right now is just by looking at them (“they look pretty much the same, they must be identical”).
it’s perfectly possible for one twin to get fat while the other doesn’t. If it doesn’t happen often, it’s because features like willpower are more controlled by genes than we think, not because staying thin doesn’t depend on willpower.
Indeed. This is why I wrote:
I don’t think thin people are thin because of willpower.
Willpower was listed as just one factor. It wasn’t mean to be an exhaustive list of all factors.
I’ve also read that gene expression diverges in twins over time—so if a lot of the difference in body composition is about gene expression, there might be a few pairs of twins where, just by chance, either the willpower or the fat storage changes kick in earlier or more strongly.
“Willpower” is not just one thing—there are people who can’t stick to diets who show a lot of will power in other parts of their lives, and vice versa.
As a young teen I played basketball with a pair of identical twins. One was fairly slight, the other rather stocky and an inch or two taller. Not sure why.
maybe they weren’t identical twins. Unless they did a genetic test they wouldn’t know for sure. I read something once that said that a significant number of same-sex fraternal twins are misidentified as identical.
That is very interesting. I hadn’t thought yet that the way we identify twins right now is just by looking at them (“they look pretty much the same, they must be identical”).
in fact, let me draw a picture
what most people think the casual graph is:
genes ----\
willpower ---> fatness
what looking at twins is supposed to convince us:
genes ----> fatness willpower
what’s really going on:
genes ----------------\ willpower ----->