It is well known identical proteins are expressed in different areas of the body. Some expressions are quite innocuous, such as expressions of eye color while others are very impactful ( such as insulin regulation within the body ). I know engineers reuse constructs, known as state-machines, all the time. Biochemist know these as Pathways. Perhaps Nature knows more than we do about the occurrence of a black swan.
Black swan as in the ballet or black swans which are alive and well in numbers in western australian waterways? Similar to eye color although how they the WA swans, manage to regulate solar heat with a black coating in summer is of interest.