According to Steiner, human beings incarnate by infolding the higher bodies into the physical universe/body, so that, instead of permeating the spiritual worlds, they become enclosed in a little fold into the physical universe. It seems to be a standard procedure within the biological world:
The illustration below shows how Steiner describes it, with each enclosure representing a human being, Animals would not have the group soul in the enclosure: it would be outside.
When we sleep, our astral body and soul leaves the enclosure and when we die the ether body unfolds too.
The more pure our soul, the more it is filled with light and the more connected it is at the top. I believe that it opens fully at initiation, when the crown chakra opens.
These drawings are by Eli Wamberg of his students auras, from his private diary.
Fig 5. a male student, fig. 6. same student, four month later, fig. 7. a female student
and fig. 8. a male student after death.
The following table shows the bodies we had in the four Earth-incarnations we have had until now, how much had been infolded into the physical in each period.
In the old Saturn incarnation we were as today’s minerals, at old Sun as today’s plants and on the old Moon as today’s animals, and today the soul are incarnated too, with the I.
The infolding may be connected to the morphogenesis:
“We all start life as a small ball of cells. These cells proliferate and organize into tissues, which in turn grow and fold into the complex form that defines a human being. The process that leads from a formless ball to a functional organism—known as morphogenesis …”