Titktaalik roseae.Image fromhttps://tiktaalik.uchicago.edu/index.html The second post in my series on limb evolution is now up at the BioLogos site. This installment reviews the fossil evidence on fin-to-limb evolution, introducing the famous Tiktaalik . Next up: evidence from developmental biology. The first post at BioLogos outlined limb structure and some historical background.

Last month, I started a series on the topic of limb evolution, here at Quintessence of Dust. That series has been transformed (through a series of intermediates) into a series of posts* at the BioLogos site. The first installment is now up, and it provides an expanded introduction to the topic and a little historical context.

The discovery of deep homology was a milestone in the history of evolutionary thought. Anatomical structures in distantly related organisms, structures with only the barest of functional similarities, were found to be constructed under the influence of remarkably similar genetic pathways. The original and classic example from 1989 involves genes controlling pattern in both insects and mammals – the famous Hox genes.

It is of course a cliche to state that eukaryotic cells (i.e., cells that are not bacteria) are complex. In the case of an animal, tens of thousands of proteins engage in fantastically elaborate interactions that somehow coax a single cell into generating a unique and magnificent organism.