Gastrulation and neurulation are accomplished early in development and they affect the whole shape of the embryo. Invagination and other 'inflating origami' manœuvres achieve these stages of early embryology, and they and similar tricks are involved later in development, when specialized organs like eyes and the heart are made. But, given that there are no hands to do the folding, by what mechanical process are these dynamic movements achieved? Partly, as I have already said, by simple expansion itself. Cells multiply all through a sheet of tissue. Its area therefore increases and, having nowhere else to go, it has little choice but to buckle or invaginate. But the process is more controlled than that, and it has been deciphered by a group of scientists associated with the brilliant mathematical biologist George Oster, of the University of California at Berkeley.
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