docs: def _initialize_pop(self, pop_size):
          """Generates the initial population and assigns fitnesses."""
          self.initialize_cma_es(pop_size)
          self.toolbox.register("individual", self._make_individual)
          self.toolbox.register("generate", self._generate,
                                self.toolbox.individual)
          self.toolbox.register("population", tools.initRepeat,
                                list, self._initial_individual)
          self.toolbox.register("update", self.update)
          self.population = self.toolbox.population(n=pop_size)
          self.assign_fitnesses(self.population)
          self._model_count += len(self.population)
          return