The birth rules of each type present in the neighbourhood are evaluated, taking into account every live cell in the neighbourhood, not only those of the same type; this yields a set of types that claim access to the cell. Then, the type that has population majority in the neighbourhood, i.e. at least half of the live cells in the neighbourhood are of that type, is chosen. In the edge case in which there are two such types (when there are 2*k live cells in the neighbourhood, k of one type and k of another), the type with the lower internal number is chosen (this is biased, sad). The type thus chosen gains access to the cell and turns it into a live cell of the same type.

In the case of built-in GOL types, the lower the internal number, the closer the type is to the right edge of the GOL menu. This does not apply to custom GOL, but the internal number of a custom type is always larger than that of a built-in type. Internal numbers of custom GOL types are difficult to compare, I recommend reading the source to get a good understanding of those.