Phys. Rev. Lett. 114, 108102 (2015) - Emergence of Upstream Swimming via a Hydrodynamic Transition We demonstrate that upstream swimming of sperm emerges via an orientation disorder-order transition. The order parameter, the average orientation of the sperm head against the flow, follows a 0.5 power law with the deviation from the critical flow shear rate ($$\gamma${}$-${}{$\gamma${}}_{c}$). This ...