Early forms of life are vital for evolution - it can be forgotten (6)
I believe the answer is:
larvae
'early forms' is the definition.
Although both the answer and definition are plural nouns, I cannot see how they can define each other.
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for larvae that I've seen before include "Immature forms of invertebrates" , "Insects in immature state" , "Caterpillars, tadpoles etc" , "Insects just out of the eggs" , "Grubs" .)