Rechenberg was dealing with wall shear stress measurements and Schwefel was responsible for organizing fluid dynamics exercises for other students.

While attending the Hermann Föttinger-Institute for Hydrodynamics (HFI) at TU Berlin, he and Rechenberg began performing experiments upon wings, kinked plates, and other objects related to fluid dynamics.

They realized modifying all the variables at same time via a random manner (e.g., small modifications are more frequent than larger ones).

This was the seminal idea to bring to light the first, two membered, evolution strategy, which was initially used on a discrete problem (optimization of a kinked plate in a wind tunnel) and was handled without computers.

Some time later, Schwefel expanded the idea toward evolution strategies to deal with numerical/parametric optimization and, also, has helped to formalize it as it is known nowadays.