Darwin’s Mystery was, amongst the many puzzles that great scientist tackled, was the perceived lack of fossils in rocks older than the Cambrian. Why were those earlier rocks bare of life? Did that indicate a vast span of missing time for life to evolve in? Since then we have found somewhat older animal life, but even those ancient forms seemingly appear abruptly and no ready answer has arisen as to why exactly. Two types of explanations have arisen – external and internal. Either the external conditions became “just right” for animals to arise/bloom or something internal in animals made them ready for an abrupt appearance. Several external factors have advocates – a spike in oxygen levels, a decline in certain sulfides (sulfates?), a sudden spate of erosion in the wake of the Cryogenian glaciations. And several internal explanations – new genetic regulatory networks, whole genome duplications, the rise of predators.
But none really address just how animals got together in the first place from single celled organisms and just why those single-celled precursors (of which there are several candidates) began sticking together. What if cells suddenly got stickier? This is what Fernàndez-Busquets, Körnig, Bucior, Burger, & Anselmetti have concluded from a microscopic examination of just how animal cells stick together….
Molecular Biology and Evolution 2009 26(11):2551-2561; doi:10.1093/molbev/msp170 …in an article entitled…
Self-recognition and Ca2+-dependent carbohydrate-carbohydrate cell adhesion provide clues to the Cambrian explosion.
…they argue that the rise in calcium levels in the oceans at the end of the PreCambrian allowed sponge cells to stick together easier thanks to self-recognition proteins in their cell walls.
Perhaps the more interesting report is this blog post… StratigraphyNet post …which summarises the conclusions about the shift in Pre-Cambrian ocean chemistry providing an opportunity for organisms with pre-existing mutations to just stick together.
So an internal and external explanation in one. Question is: what does it tell us about the evolution of animal life on other planets? Does calcium chemistry matter there too? How many more molecular peculiarities are needed for complex life? How many are possible? Inevitable?
As always… need more data.