How come there is such a charcter difference?

[Luke]

Between Bella & Missy? Littermates, brought up exactly the same way..but so different! Bella is very laid back, loves attention yet is independant and is definatley the boss of all cats! Whereas Missy isn't cuddley, strains to get away when picked up, plays wildlys, is really 'scratchy', doesn't like to be far from her owners and is shy around those she doesn't know..
So how come such a charcter difference? I know each cat is an individual but the charcter difference between the sisters is quite amazing...when we popped to see my sis n her family who have Missy (they live across the road from us:roll:) I was kinda taken a back at how different she was from Bella..

[tilly]

I have a brother and sister and they have very diffents characters as well. Tilly is very cuddly whilst buster isn't he prefers to rub around my legs. Also Till;y is very nervous and buster is more adventurous so they are relatively opposite of each other..

Sally