Mechanics of tissue morphogenesis

How are we made? How does the apparently (and perhaps, deceptively) simple fertilized egg transform from a sphere to the complex geometry of a mature organism? These questions, in one form or another, have fascinated scientists and laypeople for thousands of years. Some of the earliest ideas were that organisms develop from miniature versions of their adult selves, often referred to as homunculi or animalcules, hiding within the heads of sperm. This concept, of preformationism, was largely abandoned in the nineteenth century when the cell theory of life became the predominant viewpoint: all living things are made of cells and so development requires that the single fertilized egg divide successively to give rise to the differentiated cell types of the mature organism.