Saturday, July 12, 2008

Take That You Evolution Doubters!

Two fine examples of how evolution works and two sucker punches in the face of creationists and evolution doubters. But were is the missing link is one of the older arguments against evolution and despite thousands of examples of "transitional" forms creationists are never satisfied. I guess they never will be but its fun to poke them in the eye with great examples. The evidence is present in molecules as well as fossils of how great transformations were generated by evolution.

The transition from single celled to multi-celled organisms required that there be a complex system of cell signalling proteins for information to be passed from one cell to another. But how can multi-celled organisms evolve without these proteins and why would single celled organisms posses such molecules? A molecular study of single celled choanoflagellates, whose ancient ancestors most likely gave rise to multi-celluar animals have been found to possess three gene markers for cell to cell signalling proteins that are active in multi-cellular organisms. Researchers suspect that in these single celled organisms the signalling proteins play similar but different roles and were co-opted by evolution for signalling purposes during the evolution of multi-cellularity. Evolution tinkers around, building complex parts from what is lying around, moulding existing parts to serve new functions.

Fossils too occasionally throw up fine examples of transformation from one form to another. Flatfish which lie on sandy sea bottoms have both eyes on one side of the head staring into the water column above. Their ancestors presumable had a symmetrical eye arrangement, but evolution doubters argue what good is a slightly asymmetrical head which retains eyes of either side of the head. Natural selection could never have produced such slight asymmetry which would give the fish no adaptive advantage. Two recently discovered fossils of ancient Eocene flatfish from museum collections show exactly the beginnings of this partial asymmetry. The eye has begun its journey towards the other side of the head but not quite. A snapshot of an intermediate stage of evolution frozen in a 50 million years old limestone. The asymmetry of flatfish evolved gradually over time. No need for any mysterious mechanisms or sudden spontaneous origins.

1 comment:

  1. Not super compelling, either of these. The first one, er, what now? We think part of one tiny fraction of the difference between single and multi celled might also exist in this single celled. Awesome! Flatfish - given how they grow there seem to bve a lot of potential explanations for this discovery that don't involve partial forms: