Bipolar Thoughts

I know a few sets of identical twins, and oddly enough a few of my friends from high school and college have recently had twins. And I have always had this question:

Why aren’t they identical?

Usually when they are young it is very difficult to tell them apart, but as they age they generally become very distinct. I suppose the answer is simple: environmental factors. Smoking,weight, diet, exercise all have massive bearing on how you age. Also your stress, your line of work, where you live (if you don’t live near your twin) could all weigh on you as well.

But then you notice strange details that are distinct. The shapes of their nose or eyes are different. Their voices aren’t the same. And of course none of that is to speak of different tastes and interests, lifestyles, work ethic, competitive natures, etc.