> That's a poor assertion because even if detivative-free algorithms weren't already a thing, there are a myriad of smoothing techniques that enable nondifferen

> That's a poor assertion because even if detivative-free algorithms weren't already a thing, there are a myriad of smoothing techniques that enable nondifferentiable objective functions to be approximated by differentiable functions. The function you wish to optimise may be non differentiable because the domain is discrete. E.g. to perform feature selection one can binary encode which features are included and which are excluded, with the fitness function being the accuracy of a model using the included features as inputs and trained for X iterations.