Nature exhibits organisms with one-chambered hearts, two-chambered hearts, three-chambered hearts, and four-chambered hearts.

A certain kind of thinker regards this as proof of Darwinism.  See?  First came the one-chambered heart, then the two, then the three, then the four.

But try to imagine a transition.  How could a species make a gradual transition from, say, a two- to a three-chambered heart?  No halfway house could function.

This is not an argument against descent with modification.  But it does count as a strong objection to the gradualist, adaptationist explanation of how the modifications happened.  Other things may evolve; basic forms are conserved.

I first came across the argument years ago in biochemist Michael Denton’s Evolution: A Theory in Crisis.  It was the first work I had read which showed me that there might be purely scientific grounds to reject a theory which up to then I had considered unassailable.

What spurs the recollection is that Denton has just published a new book, Evolution:  Still a Theory in Crisis.  I look forward to reading it.