Why does one chick develop so much faster?

[lilchickenz]

Do you know why one chick develops so much faster? I have 3 speckled sussex which I ordered from a hatchery last week. This chick is bigger, has longer wings and is sprouting a tail while the other two still look the same way they did a week ago, maybe slightly larger wings. Does it mean she might be a he or older or just developing faster? Side note: any ideas what breed the yellow one is? Photo:

 

[Fred's Hens]

Different chicks grow differently. Just like humans.

Sometimes a faster growing chick just is tilted that way by its genetics. Sometimes, the faster growing chick just spends more time at the feeder. Actually, the faster sprout of tail is often sign of a female.