Students will manipulate small items like cotton balls, marshmallows, toothpicks, cheerios, croutons, gummi bears, etc. and determine which tools work better for picking things up and "eating" with. The tools imitate a finch beak, insect-eating bird beak, molars, and vertebrate incisors. You can have the students guess the function too. I thank my wife for this idea.
NGSS Third grade 3-LS4-2. Use evidence to construct an explanation for how the variations in characteristics among individuals of the same species may provide advantages in surviving, finding mates, and reproducing.