Early embryology; making a formed body (Introduction)

by David Turell , Thursday, May 21, 2015, 00:20 (3475 days ago) @ David Turell

How to form a body with head and tail and two symmetrical sides:-http://www.evolutionnews.org/2015/05/heads_or_tails096081.html-"These signaling pathways pre-date the animals that use them now. Based on genomic analyses, these signaling molecules have been around well before the first bilaterian animals ever existed. They are expressed in organisms that lack these body axes completely. Even more surprising, many of the molecules used to make complex structures such as muscles, eyes, and brains also predate their use for those purposes.-"What were these signaling molecules used for before there was a left and right, a top and bottom, a head and tail? How did they come to be at all, and why did they persist until they could be co-opted for the establishment of body axes? It has been suggested that they were used to establish body sections in the earliest multicellular animals, but that only pushes the question back a step. Where did that use come from? How did the signaling pathways start?-"With these questions, I conclude the series I began to address the white space in evolutionary thinking -- how to account for the evolution of C. elegans. First there is the problem of getting a cell, then of getting a eukaryotic cell, then of getting a multicellular animal, and now of getting one with a head and a tail and multiple cell types. Saying C. elegans didn't have to solve the problem all at once is merely to suggest that the problems are easier if taken one step at a time. They are not."