To understand his theory, it helps to begin in the strange world of quantum mechanics. The wave aspect carries no energy but strongly influences how the particle aspect can behave. Translated into biologist's terms, the wave can be seen as the morphogenetic field for the particle. Sheldrake takes this step and then goes further to suggest that larger forms, like biological organisms, have morphogenetic fields that are more than just the sum of their parts. Earlier in our culture's history, the idea of all space being filled with unseen information carrying fields would have seemed totally bizarre and unbelievable.
Sheldrake suggests that the process is one of resonance, like tuning in a radio station.
The parts that are coming together resonate with the fields generated by similar groups of parts in the past. The uniqueness of the DNA in each organism provides such a seed. In this process, newer forms can gradually dilute the importance of older forms, and so there is an opportunity for composite fields to evolve over time. Our brains, like any other physical form, are constantly generating morphogenetic fields, not only for the general form of the brain, but also for each moment of our existence. As the memory begins to be tuned in, it influences the brain to fill in more of the pattern which, in a feedback process, improves the resonance until the essential features of the past state are recreated in the present.