If we search under Google Scholar Richard Davdison we cand find papers co-authored by Davidson about this topic. https://scholar.google.com/citations?hl=de&user=vP-2P9wAAAAJ&view_op=list_works&sortby=pubdat https://www.orellfuessli.ch/shop/home/artikeldetails/A1049568889 https://www.pnas.org/doi/10.1073/pnas.0407401101