This chapter introduces, from an ontological point of view, the definition: development is a self-directed epigenetic process consisting of sequential phase changes, consequent on interaction of genome, epigenetic systems, and external environment, which transform a living thing into successive stages of an individual of its kind. A developmental potential is a type of capacity-developing capacity. The chapter undertakes to model an illustrative case, prenatal manifestation of human developmental potentials. It seeks a probabilistic model countenanceable not only within multipredicative monism, but when generalized, within rival ontological views on dispositions. We observe that acquisition of a capacity may occur gradually and involve the sequential acquisition of properties. We have introduced developmental potential as a capacity to develop a capacity, characterized such a capacity as a propensity, and related how a probability distribution may be said to project an organism's bounded set of such propensities.