  This paper describes an Artificial Embryology method (called ``Epigenetic
Tracking'') to generate predefined arbitrarily shaped 2-dimensional arrays of
cells by means of evolutionary techniques. It is based on a model of
development, whose key features are: i) the distinction bewteen ``normal'' and
``driver'' cells, being the latter able to receive guidance from the genome,
ii) the implementation of the proliferation/apoptosis events in such a way that
many cells are created/deleted at once, in order to speed-up the morphogenetic
process. iii) the presence in driver cells of an epigenetic memory, that holds
the position of the cell in the cell lineage tree and represents the source of
differentiation during development. The experiments performed with a number of
100x100 black and white and colour target shapes (the horse, the couple, the
hand, the dolphin, the map of Britain, the foot, the frog, the baby, the
stomach, the french flag, the head) bring to the conclusion that the method
described is able to generate any target shape, outperforming any other known
method in terms of size and variety of the generated shapes. The interpretation
of the proposed method as a model of embryogenesis and its biological
implications are discussed.
