Why is it necessary men having more red blood cells per cubic millimeter of blood than women?

Agree with Adam. Women go through menstruation therefore lose blood every month and thus will have less RBCs (red blood cells) per cubic millimetre than males. Also fun fact, men tend to have higher levels of iron per cubic millimetre for this same reason (and iron levels ALSO affect RBC production as haemoglobin requires plenty of iron!

Hi, women have reproductive cyclefor every 30days so they loose RBC.Thus less RBC are found in female mammals