Looking at the picture i remembered............
Breast appears to an extension .But its not.
‘X’ chromosome decides to have a female type of breast and has its way. Now ‘Y’ chromosome intervenes. Put his foot forward and says ‘no’. A strong ‘no’! And in spite of that ‘X’ chromosome is adamant and produces the female type of breast, to announce its independence. ‘Y’ chromosome suppresses this mutiny with power. I want the flat chest, is the motto. ‘Y’ wins in the end.(ref.MAN IS THE EXTENSION OF WOMAN)