October 13, 2012
New Concept Dramatically Alters Theory Of Animal Evolution
April Flowers for redOrbit.com - Your Universe Online
New work by Dr. Stuart A. Newman, professor of cell biology and anatomy at New York Medical College, develops a concept that dramatically alters one of the basic assumptions of the theory of evolution. The assumption is that survival is based on a change's functional advantage if it is to persist.
Newman, whose life's work has supported the theory of evolution, offers an alternative model where he proposes that the origination of the structural motifs of animal form were predictable and relatively sudden, with abrupt morphological transformations favored during the early period of animal evolution.
The study will be published in Science, both online and in print. An interview with Dr. Newman will also be released as a podcast.
The most prevalent thought about evolution is that it takes place opportunistically, by small steps. Each change persists, or doesn't persist, based on its functional advantage. Newman's model, described in the report, is based on recent inferences about the genetics of the single-celled ancestors of the animals and, more surprisingly, the physics of "middle-scale" materials.
More than a half billion years ago, according to the fossil record, an assortment of recurrent "morphological motifs" first appeared in animal bodies and the embryos that generate them. For present—day animals, cells arrange themselves into tissues having non-mixing layers and interior cavities during embryonic development. Embryos have patterned arrangements of cell types. With these, they form segments, exoskeletons and blood vessels. As the embryos develop, they proceed to fold, elongate, and extend appendages. In some species, they generate endoskeletons with repeating elements, such as the human hand.
The motifs, or recurring forms, in animal embryonic development are remarkably similar to the forms assumed by nonliving condensed, chemically active, viscoelastic materials, when they are organized by relevant physical forces and effects. The mechanisms that create these motifs in living embryos are much more complex, however.
Newman's new study suggests the ancestors of present-day animals, as a result of ancient single-celled organisms, came to reside in multicellular clusters. The resulting physical processes relevant to matter at this new spatial scale were immediately mobilized.
The single celled organisms are believed to have contained genes of the "developmental-genetic toolkit" that all present-day animals utilize to direct embryonic development, though they used the genes for single-cell functions. The products of these genes enabled the ancestral clusters to produce the characteristic motifs by harnessing the middle-scale physical effects. Different body forms arose in parallel because not every ancestral cluster contained the same "toolkit" genes. This gave rise to the modern morphologically distinct animal phyla.
Over the hundreds of millions of years since the occurrence of these origination events, natural selection has led to the complex developmental processes which have made embryogenesis much less dependent on potentially inconsistent physical determinants. The physical motifs, however, were retained. Newman asserts that this new perspective provides natural interpretations for aspects of early animal evolution, which have been puzzling in the past. This includes the "explosive" rise of complex body forms that appeared between 540 and 640 million years ago and the failure to add new motifs since that time.
This new model also explains the conserved use of the same set of genes to create development in all of the morphologically diverse phyla, and the "embryonic hourglass" of comparative developmental biology. The hourglass is the observation that the species of a phylum can have drastically different trajectories of early embryonic development, but still wind up with very similar body types.