Birth order - does it matter?

There are many studies on the importance of birth order in humans. How it can determine personality as well as success. I've never seen a study of birth order in dogs, but from my unscientific observation, the studies work just as well for dogs. A friend has two Irish Wolfhound puppies, both male, full brothers but from different litters, about 8 months apart in age.

They follow the classic formula. The first born is serious, worried about getting things right, and feels driven to be perfect. The younger brother is carefree, not worried about anything.

Look at the photos below. Can you tell which is which?




The older brother is on the left. The whole time I was taking photos, he was focused on me, worried about what he was supposed to be doing, what did I want, wondering if he should be protecting his brother. Meanwhile his brother was enjoying life, and thinking "Yay, a human to pet me!"

I don't think birth order in a litter matters, but in a household of several dogs, it could be very important.