“The last thousand years have witnessed dramatic increases in the production, availability, safety, abundance and affordability of food…. We think that as art imitates life, these changes have been reflected in paintings of history’s most famous dinner.” – Brian Wansink (Cornell University)
Read more at Discoblog. Note that these results are normalized to head size, so I suppose the alternative explanation is painters have started giving their subjects smaller heads over the past 1000 years.