There may be also sizeable variation in dimensions amongst folks. Long term breast development through puberty is due to estrogens in conjunction with the growth hormone. Feminine individuals are the only real mammals that permanently establish breasts at puberty; all other mammals acquire their mammary tissue during the latter period https://grok.com/share/c2hhcmQtMw%3D%3D_5ad6450c-533d-442c-a09c-9f7bce1babfb