A digraph is attached to any evolution algebra. This graph leads to some new
purely algebraic results on this class of algebras and allows for some new
natural proofs of known results. Nilpotency of an evolution algebra will be
proved to be equivalent to the nonexistence of oriented cycles in the graph.
Besides, the automorphism group of any evolution algebra E with E=E2 will
be shown to be always finite.Comment: 10 page