Johannes Zachhuber argues, against Richard Cross, that Gregory of Nyssa holds to a “collection theory” of universals. That is, universals are collections of individuals, but genuine wholes, not merely a summation of individuals. For Gregory, this is not nominalism; universals are real. And the universal is indivisibly immanent in each individual.
Whatever the merits of this take on Gregory’s theory of universals in general, it has some interesting results when applied to the creation of man.
In Zachhuber’s summary, Gregory teaches that “in creating man, God did not so much create the first human individual (although he did do that, of course), but made something that is both complete and incomplete in its beginning.”
Human nature includes all the specific humans that are generated from the first: “Gregory writes of ‘the whole nature extending from the first to the last’ being one.” And God foresees the completion and perfection of the development of humanity from the beginning.
The individual body provides an analogy to the limits of the universal “humanity.” In Gregory’s words, “as the particular man is limited by the quantity of his body, . . .so I think the totality of mankind is in a way encompassed by a single body through the foreseeing power of the God of the whole.”
More fully, in Zachhuber’s terms: “the creation of ‘man’ reported here is essentially the creation of that immanent form in its seminal aspect of potential perfection. This seminal form is only ‘potentially’ complete in its original state and therefore must develop into its actual pleroma. This development, however, is not seen by Gregory as independent of that first creation. On the contrary, it is its unfolding like that of a seed into a living being. This is why the divine foreknowledge is referred to here. The growth of that germinal nature into a pleroma is, in principle, still part of the same creative act of the divinity.”
Gregory “employs expressions like ‘all humanity’ and ‘the whole human item’ to signify humanity in its concrete sense.”
In creating human nature, God simply created Adam: “the first creation must have had as its object something that functions as a generative principle, producing out of itself the totality of future beings. In the case of human beings, it is difficult to envision such a principle apart from the first actual human individual.” In short, “the ‘potential’ creation of humanity described in Gen. 1:27 is ‘hupostasei’ (as Gregory might have said) nothing other than the creation of Adam.”
(Zachhuber, “Once Again: Gregory of Nyssa on Universals,” Journal of Theological Studies 56:1  75-98.)