The importance of understanding function and evolution.

Ocklenburg et al. (2020, Laterality 2020: Entering the next decade. Laterality) provided the field of laterality research with a stimulating research perspective for the coming decade, based on the current state of the art in both animal and human laterality research. Although this is paper takes many different approaches of laterality into account, we emphasize that the eco-evolutionary approach needs more attention. This concerns the question why organisms are lateralized in the first place, in other words, how does lateralization enhance the Darwinian fitness of the individual. We argue that laterality can be distinguished along four dimensions, and that each of them requires different ultimate explanations. Studying these functional and evolutionary explanations requires the development of ecologically relevant tests, adapted to the species at hand. It also requires experimental manipulation of laterality, testing the effect in (semi)-natural conditions on fitness parameters. Tools for such manipulation of laterality urgently require a better understanding of the developmental plasticity of lateralization, extending the field of evo-devo to that of eco-evo-devo. We also warn against seeing the minority in the distribution of direction or strength of lateralization as being a pathology as such minorities in biology can often be explained as adaptations by natural frequency dependent selection.