(defclass animal ()
  ((base-element :initform 'carbon :allocation :class :reader animal-base-element)))

(defparameter *a1* (make-instance 'animal))
(animal-base-element *a1*) ; --> carbon

(defgeneric base-element (thing))

(defmethod base-element ((class (eql (find-class 'animal))))
  (animal-base-element (c2mop:class-prototype class)))

(base-element (find-class 'animal)) ; --> carbon