18 November 2011
This is a child's skull (from a normal human) which clearly shows the "baby teeth" and the not-yet-emerged adult teeth. (Just to clarify - the reason this particular skull looks so odd is that portions of the mandible and maxilla have been cut away in order to show the preemergent dentition in place). It helps one understand how teeth can emerge crowded, and why there are orthodontists.
But I do wonder why this arrangement won via natural selection (or, for some of you, why God chose this method of growing teeth). Why not just have a single set of teeth that gradually get larger? Perhaps someone who went to dental school can tell us...
Photo credit: Stefan Schäfer (with a hat tip to Skipweasel for sending me the link).