The two insides of the body, right and left are not the same and can be found to be flipped backwards (situs inversus). Darwin does not explain the complexity of embryology:-http://www.nytimes.com/2013/06/04/science/growing-left-growing-right-how-a-body-breaks-symmetry.html?pagewanted=1&_r=0&nl=todaysheadlines&emc=edit_th_20130604