Teddies are a peaceful species that have lived separately from other cookie species for several generations. There are two kinds of Teddies, those that react to stress by holding their arms up, squealing and running for cover and those that react to stress by having what looks like a temper tantrum with arms rigidly at their sides, feet apart and standing still.
A band of monsters have entered the Teddy homeland. These monsters include the

This reduction and replacement continues for several generations but over time the monsters find fewer foolish Teddies to consume as the smart Teddies become the dominant form. So they move on and leave the Teddy World alone.
Well, at least that's one story. You can create your own. This website has a similar story. For the older student to demonstrate the gene shift that takes place this pdf. is better.
Science and cookies, a good combo. PRM