Monday, 26 October 2015

God The Amnesiac Creator

Micromelerpeton credneri from the Early Permian of Germany. Regeneration of the forelimb is indicated in the sequence and results in a hand with malformations.

Credit: Kalliopi Monoyios - Science Illustration and Communication
Source: ScienceDaily
Deep-time evolution of regeneration and preaxial polarity in tetrapod limb development | Nature.

"Why doesn't God heal amputees?"

Despite all the claims of faith healers, all the assurances that if you have enough faith and pray hard enough, God will provide for your needs, humans don't regenerate limbs and nor do any other mammals. I suppose a small handful of amputees could be found who wouldn't want their limb(s) restored in full working order but I've never heard of one and I doubt many people have, so it's safe to assume that amongst amputees there are very many who must have tried prayer.

Yet there is no authenticated case of a human limb ever regenerating beyond the tip of a finger occasionally regenerating in children under 5 years old if the amputation is clean and above the nail bed.

There have been one or two obviously fraudulent claims and of course the Catholic Church has an obviously faked 'miracle' that still generates a tidy sum for the local church in Spain, but that's another matter. What I'm talking about in this blog is the fact that amputated limbs never regenerate in humans or other mammals and yet, biologically, there appears to be no mechanical reason for it to be impossible, after all, all limbs generated once in the embryo.

In fact, it is both possible and happens, in a few vertebrates.

Now, it seems the ability to regenerate limbs may well have been present in the early ancestors of tetrapods (which includes all the four-legged vertebrates). What a terrible start to what looks like being another bad week for the creationist industry!

According to a team of paleontologists from the Museum für Naturkunde Berlin, the State University of New York at Oswego and Brown University, the fossil record shows that the capacity for limb regeneration found in modern salamanders was present in two different groups of amphibian from the Carboniferous and Permian periods so was probably present in a common ancestor. The fossils show that tails and limbs could be fully regenerated as they can be in modern salamanders.

Among extant tetrapods, salamanders are unique in showing a reversed preaxial polarity in patterning of the skeletal elements of the limbs, and in displaying the highest capacity for regeneration, including full limb and tail regeneration. These features are particularly striking as tetrapod limb development has otherwise been shown to be a highly conserved process. It remains elusive whether the capacity to regenerate limbs in salamanders is mechanistically and evolutionarily linked to the aberrant pattern of limb development; both are features classically regarded as unique to urodeles. New molecular data suggest that salamander-specific orphan genes play a central role in limb regeneration and may also be involved in the preaxial patterning during limb development. Here we show that preaxial polarity in limb development was present in various groups of temnospondyl amphibians of the Carboniferous and Permian periods, including the dissorophoids Apateon and Micromelerpeton, as well as the stereospondylomorph Sclerocephalus. Limb regeneration has also been reported in Micromelerpeton, demonstrating that both features were already present together in antecedents of modern salamanders 290 million years ago. Furthermore, data from lepospondyl ‘microsaurs’ on the amniote stem indicate that these taxa may have shown some capacity for limb regeneration and were capable of tail regeneration, including re-patterning of the caudal vertebral column that is otherwise only seen in salamander tail regeneration. The data from fossils suggest that salamander-like regeneration is an ancient feature of tetrapods that was subsequently lost at least once in the lineage leading to amniotes. Salamanders are the only modern tetrapods that retained regenerative capacities as well as preaxial polarity in limb development.*

Deep-time evolution of regeneration and preaxial polarity in tetrapod limb development
Nadia B. Fröbisch, Constanze Bickelmann, Jennifer C. Olori & Florian Witzmann
Nature (2015) doi:10.1038/nature15397

*Copyright © 2015, Rights Managed by Nature Publishing Group. Reprinted with permission under licence #3736691135451

The fossil record shows that the form of limb development of modern salamanders and the high regenerative capacities are not something salamander-specific, but instead were much more wide spread and may even represent the primitive condition for all four-legged vertebrates. The high regenerative capacities were lost in the evolutionary history of the different tetrapod lineages, at least once, but likely multiple times independently, among them also the lineage leading to mammals.

Nadia Fröbisch, Museum für Naturkunde,
Leibniz Institute for Evolution and Biodiversity Science, Berlin, Germany
It seems that those who believe in an intelligent, benevolent designer have some explaining to do here, and especially those who pose as the most sophisticated and scientifically literate creationists, the so-called 'intelligent evolution' advocates. What they have to explain is why their supposed designer designed the ability to regenerate limbs millions of years ago in what may well have been our evolutionary ancestors, then forgot how to do it. It surely can't have been the act of an anthropophilic, omnibenevolent designer, to intentionally deprive us of the ability to regenerate limbs, can it?

So, amnesia seems to be the only explanation - if you believe the creationist fairy tale, that is.

Of course, losing the ability during millions of years of evolution by an undirected, mindless process which depends only one one measure for success - leaving the most descendants - there is nothing mysterious in this at all. It's fascinating and interesting and may just point to the discovery of a medical procedure by which humans do what this supposed designer forgot how to do, but it's not hard to explain for science.

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