Full Idea
Without something like a hypothesis about the genes of ravens, we simply do not know what would count as a relevantly similar bird for comparison.
Gist of Idea
To pick a suitable contrast to ravens, we need a hypothesis about their genes
Source
Peter Lipton (Inference to the Best Explanation (2nd) [2004], 06 'Unsuitable')
Book Reference
Lipton,Peter: 'Inference to the Best Explanation (2nd ed)' [Routledge 2004], p.99
A Reaction
Lipton is endorsing the view that explanation should be 'contrastive', as well as aiming to discover the inner nature of ravens. He makes a good case for the contrastive approach.