First Online: 23 March 2020
Compliance with Ethical Standards
: No sources of funding were used to conduct this study or prepare this manuscript.
: Ann-Kathrin Heider and Harald Mang have no conflicts of interest that are directly relevant to the content of this review. The present work was performed in fulfillment of the requirements for obtaining the degree “Dr. rer. biol. hum.” by AH from the Friedrich-Alexander-Universität Erlangen-Nürnberg.