The following is an article from The Annals of Improbable Research.
(Image credit: Flickr user U.S. Air Force)
by Bethany Morgan, Josie Morgan, Helena Morgan, and Richard Morgan
Colwyn Bay, North Wales, U.K.
The behaviour of surgeons has been described as "domineering," disruptive," and "egregious."1 There have been reports of aggressive behaviour by surgeons, with outbursts of anger, surgeons throwing instruments, and a surgeon being wrestled to the floor by sheriff's deputies (he threw a fit because he had to wait for instruments to be sterilized)2. The origin of such aggressive behaviour is unknown.
We have previously observed cannibal behaviour in tadpoles (aquatic larvae of the common frog, Rana temporaria). An internet search revealed conflicting ideas on the underlying reason for this behaviour; there was no consensus as to whether the cause was hunger3 or overcrowding4. This uncertainty led us to consider other reasons; our theory developed that the behaviour might be a genetically pre-programmed way of bringing nutrition to the few individuals who would ultimately survive to adulthood. Had we witnessed a gruesome example of the principle of survival of the fittest? Furthermore, could such genetically pre-programmed aggressive behaviour have been passed on, during the course of evolution, to more complex organisms such as humankind, and in particular to a sub-group of humans, namely surgeons? The ancestors of frogs and humans are thought to have diverged, evolutionarily, some 340 million years ago5, but could it be possible that human behavioural traits, such as aggression in surgeons, might have appeared prior to that divergence?
(Image credit: Flickr user Benny Mazur)
This year we set about testing our theory. Our aim was to keep tadpoles in conditions which controlled for hunger and population density, and to measure the rates of cannibalism. We postulated that the rates of cannibalism would be the same in groups of tadpoles exposed to different levels of feeding and population density.
Methods
Frogspawn was collected from a garden pond on the day of production. When the tadpoles had fully emerged from the spawn, they were counted out and 50 individuals were placed in each of 4 plastic tanks (B&Q, U.K.). Tanks A and C were large (61 x 34 cm), while tanks B and D were small (30 x 16 cm). Each tank was filled to a standard depth (10 cm) with water from the garden pond. The tanks were kept adjacent to each other in a partly shaded area of the garden. Lids were kept on each tank to keep out birds and other predators and scavengers. It was calculated that the population density in the small tanks was adequate for raising tadpoles, according to advice on a tadpole-rearing website4.
Tanks C and D had extra food (5g of boiled lettuce, modified from advice in our reference websites3,4) added at weekly intervals. Tadpoles in tanks A and B fed on natural food sources found in the pond water. Tadpoles were counted in each tank at weekly intervals, and observed for cannibalism at frequent intervals. Any individuals completing metamorphosis into frogs were removed from the tank and returned to the pond. The water in each tank was replaced with clean pond water if it became cloudy at any time during the experiment.
Efforts were made, within the confines of the study, to ensure the well-being of the tadpoles, and to prevent any unnecessary suffering.
Figure 1 demonstrates one of the individual tadpoles participating in the experiment, and a newly metamorphosed frog awaiting transfer to the pond.
The experiment was concluded when tanks C and D had no tadpoles left (due to mortality in tank D, and metamorphosis---and a lesser rate of mortality---in tank C).
Results
Although the numbers of tadpoles in each tank decreased with time, it was very unusual to see any dead tadpoles, except in tank D (see below). Since predators and scavengers were excluded from the tanks, it can be assumed that the missing tadpoles were eaten by their fellows. One such act of cannibalism was observed in the study period (Figure 2). It was clear that the victim was already dead prior to the act of consumption.
At the end of the study period (18 weeks):
• Tank A (large, no added food) had 31 tadpoles remaining, and 4 frogs had been returned to the pond, a total of 35 survivors.
• Tank B (small, no added food) had 4 surviving tadpoles; no frogs had been returned.
• From tank C (large, added food) 36 frogs were returned, with no remaining tadpoles.
• In tank D (small, added food) all tadpoles disappeared (leaving 24 dead bodies) within 5 weeks, their death coinciding with the water becoming cloudy (it was clearly contaminated by boiled lettuce).
Discussion
Survival rates were very similar in the two large tanks (A and C), regardless of whether extra food was added. The extra food, however, did appear to have a dramatic effect on the tadpoles in tank C, with a much faster rate of metamorphosis into frogs. The lack of an effect on survival rates is clear evidence that hunger is not a motive for acts of cannibalism.
Survival in both the smaller tanks was remarkably less, suggesting that overcrowding may be a factor influencing cannibalistic behaviour. The appearance of cloudy water (in tank D, following addition of extra food) appears to be the most important adverse factor in tadpole survival, and it is our conclusion that acts of cannibalism occur predominantly (or perhaps exclusively) when individuals have died of other causes, such as the effect of cloudy water.
In our study we have found no evidence that tadpoles have a pre-programmed behaviour trait which leads them to attack and devour their fellows. We have therefore rejected our theory that tadpole cannibalism is genetically pre-programmed behaviour. Furthermore we have found no evidence that aggressive behaviour in surgeons has its origins in tadpole cannibalism, and we have rejected this theory.
(Image credit: Flickr user ReSurge International)
In conclusion, the origins of aggressive behaviour in surgeons remain uncertain, and merit further research. Tadpole cannibalism (at least in common frog tadpoles) appears to be a benign behaviour that occurs when individuals have died from other causes.
References
1. "Surgical Behaviour," S. Galandiuk, British Journal of Surgery, vol. 100, no. 8, 2013, pp. 985--6.
2. "Disruptive Clinician Behaviour: a Persistent Threat to Patients," G. Porto and R. Lauve, (accessed March 24, 2013).
3. How To Raise Tadpoles (accessed June 10, 2013).
4. How to Raise Tadpoles (accessed June 10, 2013).
5. The Ancestor's Tale, R. Dawkins, ISBN 9780618619160, 2004, pp. 302--29.
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This article is republished with permission from the January-February 2014 issue of the Annals of Improbable Research.
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