Primordial black holes are often assumed to form by the collapse of large primordial fluctuations. However, it might not be the only channel. Yukawa forces are attractive, and they can be much stronger than gravity, leading to an instability similar to gravitational collapse in the early universe. I will present recent advancements on the growth of fluctuations in the very early universe from Yukawa forces, from exact analytical solutions to the very first N-body simulations. I will focus on a simple model: heavy fermions interacting via a Yukawa coupling with a scalar field in a quartic potential. I will end with a discussion on how this mechanism may lead to black hole formation.