I'm using Yahoo Messenger for Mac and can't get my most recent IMs to show up without having to scroll down.

How do I get the current IMs to appear in the chat box without having to scroll down all the time. It's really annoying. Once my conversation takes up more space than the size of the chat box I have to scroll down to see what my friend wrote. I can't seem to figure out the setting which allows all the current IMs to appear without me having to scroll down each and every time. In other words, my oldest IMs appear in the box and the newer ones are down below.