Answer:
It allows the existing molecules to direct the process of assembly of a new molecule from the smaller and simpler substances.
Explanation:
Complementarity is required for self-replicating molecules as it allows the existing molecules to serve as a template for the formation of a new molecule of its own type. For example, DNA is a self-replicating molecule as it can direct the synthesis of new DNA strands by serving as a template. This is possible as two DNA strands are complementary and the complementary bases of two DNA pairs with each other to make a double helix.
A DNA template with a sequence "AAAA" would direct the synthesis of new DNA with a sequence "TTTT" since Adenine is complementary to the thymine and makes two hydrogen bonds with it.
