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Five-legged frogs and other abnormalities

I once lived for four months in a Zoological Museum in a small room just under the roof of the building. The great advantage of that abode was that I did not have to pay any rent for staying there; the disadvantage was that the toilet was in the cellar. Therefore, if I needed to go there it required careful planning in advance. First down a narrow flight of stairs, then through the storage area, past the huge stuffed bison, along the displays of various skeletons, down to the taxidermically prepared monkeys and birds, silent and motionlessly in their glass cages, to finally descend into the dark vault of the cellar’s WC. It was an afternoon when a man entered this museum, wanting to see the Director. Since he wasn’t there, I offered to help. The man had with him a five-legged frog he wanted to donate to the museum.

It was a fully grown male frog with a third front leg between the two regular legs. Interestingly the extra leg also possessed the typical nuptial thumb pad that male frogs develop during the mating season to help them cling to a slippery female. Despite its extra leg the frog seemed normal enough and obviously had been able to grow into a mature individual. Together with Professor Juergen Koebke I carried out an anatomical and ultrastructural study on the extra leg’s muscles, blood supply and nerves. We found that the extra leg’s muscles were normal and could contract, but that joints between the bones showed little wear, because the leg did not actively participate when the frog jumped. The question was: what could have caused the development of the extra leg. That there was “a second individual” somehow involved (as with conjoined twins or a partially absorbed twin) was outrightly dismissed. An injury during the tadpole stage to a leg bud resulting in a growth of an additional leg seemed a possibility and that the extra leg might have been the consequence of an exposure to ionizing radiation or the response to a parasitic  trematode attack (because such cases had been described before) were other possibilities.

Abnormalities such as these have always alarmed as well as fascinated humans and when present in humans were (in the past) usually linked to superstitions blaming either the mother, the devil, weather phenomena, or God. More recently we see connections with various kinds of pollutants and for this reason had started to monitor abnormal growths like skin cancers and reduced or increased numbers of limbs and toes in Japanese newts in one specific region of Japan over a period of 10 years. This kind of research that involves field and laboratory work is labour-intensive and despite its importance was unfortunately discontinued. However, what we did find was that the incidences of abnormalities in the newt population had not changed in the 10 years we monitored them. That this should not lead us to be complacent is self-understood, especially with regard to the rise in plastics and their residues in the environment, but it could also suggest that a certain small percentage of abnormalities is a “normal” feature of a natural population. However, to distinguish an abnormality from a variety (e.g., regarding respective wing or feather colours in insects and birds) is not always clear.

Although humans with cyclopia, or cows with two heads or chickens with four-legs etc. are sometimes referred to as “monstrosities”, for humans at least such terminology is unacceptable and efforts are made to identify (and then eliminate) the causes of malformations. This requires collaborations between geneticists, toxicologists, biochemists and scientists of various other disciplines. What I personally find sad is that goldfish monstrosities and Folded Ear cats (even if the genetic defects are known to have serious consequences for their health) are ‘celebrated’ and given prizes in breeder competitions. Isn’t it a bit abnormal to love such abnormalities when one knows that the animals are suffering? 

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