As if done in a move to validate every teenage boy's reasons for checking out their girlfriend's mother- other than OBVIOUSLY having a thing for cougars- comes a research study by the genetics company 23andMe. They discovered the genes that dictate how big a woman's breasts will be and yes, they are inheritable – mostly – traits.
I say mostly because we all know diet can play a big factor too. Current evidence appears in Japan where the average bust size rarely spiked above a B cup, but have seen a boom in C and D cups in the last generation or so due to the easy access of dairy and beef proteins that were traditionally very rare on the island nation.
The study did go a little further than just mentioning that a gal may have inherited granny's rack. The markers that dictated breast size also played a role in the development of breast cancer. I'm not sure where the facts came from, but I do remember being taught someplace that breast cancer was actually less common in large boobs with more gland tissue (you know where milk production comes from). The more gland tissue, the rounder and firmer a breast is too.
See you can learn little things here and there from me! Though where size and cancer relate, you have to look for yourself, as I'm not 100 percent sure on that. I just recall being taught someplace; it might have been Discovery health. I am the master of educational TV knowledge- question me not!