If I saw an angel come down to teach us good, and I was convinced from others seeing him that I was not mad, I should believe in design. If I could be convinced thoroughly that life and mind was in an unknown way a function of other imponderable force, I should be convinced. If man was made of brass or iron and no way connected with any other organism which had ever lived, I should perhaps be convinced. But this is childish writing (citation based on "The Design Matrix" by Mike Gene, emphasis added).
This is a quote from a letter by Charles Darwin to Asa Gray, a professor of botany at Harvard. Darwin wrote it in response to Gray's question, what it would take to convince him that life was designed. I think that Darwin's position here is profoundly unscientific. Yes, science encourages skepticism, but doubt is a double-edged sword. A scientist should always remain, to a reasonable extent, skeptical of his own views. A scientist should take pains to analyse all available data fairly and be prepared to follow evidence wherever it leads.
Now that mathematics has established the existence of empirical limits of reason, such determination against the mysterious and non-formalisable should itself, dialectically, raise scientific doubts. On the other hand, the radicalism of bias is always dangerous as it can make us blind to something essential:
If they hear not Moses and the prophets, neither will they be persuaded, though one rose from the dead (Luke 16:31).
1. M. Gene, The Design Matrix, 2007 (see also the eponymous blog).
2. M. Behe & J. Wells, Then and Only Then.