the gap where the gold was

I keep meaning to put a link to retrieverman at the bottom of my posts, because it is his post that I am commenting on, and I keep hitting "publish" before I think of it, so let me start off with the link:
http://www.retrieverman.wordpress.com/

The historical cases where there is a gap right where the most desired size is, can be found in sighthounds and earth going terriers. If you read terrierman at all, you will recall that one of his pet peeves is that show breeders breed dogs too big to fit into the tunnels they need to work in.
http://terriermandotcom.blogspot.com/

If you look at the sizes, you can also see that the toy terriers are bred to be a bit too small for the tunnels - that there is a gap, right where the desired size is.

In other words, we breed terriers too big and too small, but rarely just the right size for the work we use them for.