The features that enable them to survive (bigger teeth, stronger legs, brighter feathers) must be inherited in some way, and they are passed on to their offspring.
(The features; enable; them; to survive (bigger teeth, stronger legs, brighter feathers) (them; to survive; bigger teeth, stronger legs, brighter feathers) (The features that enable them to survive (bigger teeth, stronger legs, brighter feathers); must be inherited; ) (they; are passed on; to their offspring)
The features them The features that enable them to survive (bigger teeth, stronger legs, brighter feathers) they
enable to survive must be inherited are passed on
them to survive (bigger teeth, stronger legs, brighter feathers
bigger teeth, stronger legs, brighter feathers
to their offspring