The embryo of an animal first looks like a hollow sphere. Invaginations then appear at different stages of development, which will give rise to the body's structures (the brain, digestive tract, etc.). According to a hypothesis that dates back more than a century, buckling could be the dominant mechanism that triggers invagination—buckling being a term that describes the lateral deformation of a material under compression. Although this explanation has long won the support of biologists, it has never been subjected to formal proof, mainly because of the difficulty—if not the impossibility—of measuring the tiny forces involved. This gap has finally been filled thanks to a study carried out by a multidisciplinary team of scientists from the University of Geneva (UNIGE). This tour de force, published in the journal Developmental Cell, owes its success to a long collaboration between specialists in biological experimentation, analytical theoretical physics and computer simulation.