From http://www.straightdope.com/mailbag/mleonardo.html :

That proves nothing. He painted these pictures because people PAID him to. The Last Supper is on a wall in a Monastery, and many of his other religious paintings were commisioned by churches, monasteries, etc. In addition, religious imagery was still very popular with lay people at that time. I doubt an artist in Europe during the Renaissance who refused to paint religious images would be very successful!

No, it doesn’t prove anything – it was listed as one factor among others to take into consideration. Do you take issue with the conclusion or just this one example?

Incidentally, somebody else also started a thread on this topic:

With regard to the statements DaVinci made about fossils, Stephen J. Gould’s book Leonardo’s Mountain of Clams and the Diet of Worms goes into even greater detail of what Leonardo was trying to prove with his assessments.

According to Gould, Leonardo’s fossil-based arguments had nothing to do with disproving the existence of a world-wide flood (and thereby to disprove the Noachian flood in Genesis, as most modern creationism debaters would do). Leo was trying to support one of the two world-views that were popular in his lifetime, neither of which had any bearing on the veracity of the Old Testament.

Quick-N-Dirty Aviation: Trading altitude for airspeed since 1992.

I do not take issue with the conclusion. I merely feel you gave the subject matter of his paintings too much weight as one of the arguments in favor of his Christianity.