Birth Order

I was reading a few articles on birth order today. I'm the oldest child, and seem to have pretty much all the oldest child traits. I knew all this already, so this is not what I was interested in. I am more interested in what my sister is like.
As the youngest, she is obviously so if you meet her - well, I think she is anyway, but I could be just biased; she is my little sis after all! However, judging by what I've been reading, there are only a couple of traits that I can identify in her that are younger sibling traits - socially outgoing for example, but then again, there are ones that I really can't see in her. Some sources say that younger siblings are agreeable and less likely to provoke, but I've lived with her long enough to know that's not true. In fact, if anything, on reading up on personality traits, she actually seems to have a lot of older sibling traits too.
Maybe growing up in my shadow caused her to develop a similar-but-different personality, or maybe my parents have been very clever in how they brought us up - which, all things considered, I wouldn't have put past them!
The birth order thing also led me to think about what it must be like for my little sister being born into the family with me always having been around. I find the idea of having three permanent figures in the family to be an odd one - I, being the eldest, only had my parents. Lizzy was a later addition.
Then I think, what about the family cats? They were there before I was born, so maybe if I think about it like that? And that's when it starts to make sense. And I suppose, if lizzy ever tried to fathom the feeling of the new addition, maybe she could use our new cat as an example!
I wonder if cats could be affected by the birth order phenomenon?