From The Fold, by Gilles Deleuze:
Folding–unfolding no longer simply means tension–release, contraction–dilation, but enveloping–developing, involution–evolution. The organism is defined by its ability to fold its own parts and to unfold them, not to infinity, but to a degree of development assigned to each species. Thus an organism is enveloped by organisms, one within another (interlocking of germinal matter), like Russian dolls. The first fly contains the seeds of all flies to come, each being called in its turn to unfold its own parts at the right time. And when an organism dies, it does not really vanish, but folds in upon itself, abruptly involuting into the again newly dormant seed by skipping all intermediate stages. The simplest way of stating the point is by saying that to unfold is to increase, to grow; whereas to fold is to diminish, to reduce, ”to withdraw into the recesses of a world.” — Chapter 1, p. 8-9
This makes me think of the basic evolution of leg and arm bones in animals from the original fish fins that they once were. If you look at these bones, you notice a distinct progression from top to bottom in every single one- one bone, connected to two bones, connected to lots of little bones. Even though in every species that progression looks different, sometimes drastically so, having evolved and “unfolded” in different ways, they’ve all unfolded into their new forms from the same original folded configuration, which unifies them all.
Also continuing on this same thought:
For Leibniz, as for the Baroque, the principles of reason are veritable cries: Not everything is fish, but fish are teeming everywhere. . . . Universality does not exist, but living things are ubiquitous. — Chapter 1, p. 9