Homology judgements of pre-evolutionary naturalists explained by general human shape matching abilities

Many biological homologies were discovered before Darwin and without agreed criteria. Paradigmatic examples include the phylogenetic homology of mammalian forelimb bones and the serial homology of floral organs in waterlilies. It is generally assumed that perceiving similarities intuitively was the first step towards establishing morphological homologies. However, this assumption has never been tested. We hypothesize that pre-evolutionary naturalists relied on the well-established ability of humans to find visual correspondences between differently shaped objects. By using images of homologous organs and applying an experimental paradigm from cognitive psychology, we found that (1) naïve participants utilised this ability when identifying "corresponding" locations. In addition, (2) these locations were statistically indistinguishable from the locations that pre-evolutionary naturalists and contemporary experts considered homologous. Furthermore, (3) presenting naïve participants with images of intermediate organs influenced their correspondence judgements. This influence was in line with historical reports according to which intermediate organs facilitated the pre-evolutionary recognition of homologies.