This is Not "The Chicken or the Egg?" Question

Let's begin with the definition of a "vital" organ: A group of specialized somatic cells performing a function that is essential to the viability of the organism; if such an organ is destroyed or suffers irreparable major damage the organism dies.

Now here is the question: Which came first, an organism with a vital organ or a gene pool capable of controlling developmental mitosis with the precise efficiency required to construct such an organ?