Try as they might, scientists have been unable to find compelling evidence to support the 'Napoleon complex', the popular idea that shorter men are more aggressive than their taller counterparts.
Now, it seems, the complex may at least apply to certain types of fish, as well as other members of the animal kingdom, new research reveals.
In the same species, the scientists report, smaller males are sometimes more aggressive and prone to launching attacks against would-be intruders — despite the likelihood of losing in an all-out fight.
The 'Napoleon Complex' in male desert gobies
New research suggests that 'small man syndrome' is exhibited in the desert goby, a small Australian freshwater fish.
Conflict between males of the same species is common among animals, says Monash University evolutionary biologist Bob Wong. "But questions remain as to when, how and by whom aggression should be initiated," he explains.
Working with researchers in Sweden and Finland, Dr Wong conducted detailed studies of aggression in a small, colourful species of Australian freshwater fish, the desert goby, or Chlamydogobius eremius.
Found in waterholes, spring-fed pools and desert streams west of Lake Eyre in South Australia, male gobies perform elaborate courtship displays to attract females. Once the females have laid their eggs, it becomes the male's responsibility to guard the nest.
If an intruder approaches, the male will often launch what might be regarded as a kind of pre-emptive strike. The aggression typically occurs in distinctive "bouts". These involve the resident male darting out from the nest, repeatedly attacking the intruding male and then returning to the nest.
"If males are allowed to interact physically, aggression can escalate to combat situations, with the fish locking jaws and grappling with their opponent," Dr Wong says. "In such fights, the winner will typically be the larger male."
To investigate further, the scientists scrutinised the behaviour of gobies in aquaria. The nest's perceived value was manipulated by exposing half of the residents to sexually receptive females for two days before the trial – and then exposing nest-holding males to a male intruder.
Male aggression was unaffected by perceived mating opportunities, Dr Wong says. It was also unaffected by an intruder's size.
"Instead, aggression was negatively related to the size of resident males," he explains. "In particular, smaller gobies attacked sooner and with greater ferocity than larger ones."
If an intruder is more likely to flee than retaliate, small males may benefit from launching an attack because this helps them avoid revealing their inferiority to the intruder.
"Sizing up an opponent can be quite brief and most aggressive interactions end well before it has the opportunity to escalate into an all-out battle," Dr Wong says.
He and his colleagues found that the aggression of males was not affected by the presence of females – or larger male intruders, for that matter. "Instead the level aggression was related to size," Dr Wong says. "In particular, smaller males attacked sooner and with greater intensity than larger males."
Attempts to explain this phenomenon have been made using complex game-theoretical models. "We have another, simpler, explanation," says research collaborator Dr Andreas Svensson of Linnaeus University in Sweden.
Firstly, full-on fighting is rare in nature, he explains. "It is very easy to get animals to fight in the lab, for example, by tricking two males to believe they own the same resource, or by limiting the possibility for one to escape," Dr Svensson notes.
"Then the conflict will escalate, the larger fish will win and it might appear paradoxical that the small male attacked first."
Animal strategies have been shaped by evolution under natural circumstances. In nature, it is quite common to observe small individuals chasing off much larger ones.
"Our explanation is therefore that a small male, who has a small chance of winning against a motivated oppponent, may be best off attacking immdiately – before the intruder has a chance to assess the territory, and before realising the owner is small," Dr Svensson explains. "A large territory owner, on the other hand, has the luxury to wait and see whether the intruder leaves on his own accord. If not, he can still drive away also a motivated intruder, even one that had time to dig in."
The research, presented at the International Behavioural Ecology Congress in Sweden, is published in the peer-reviewed, open-access journal PLoS ONE.
The study involved collecting gobies from the desert and transporting them back to the laboratory.
Males were separated from females based on their brighter colours and introduced into small aquaria containing gravel and a PVC pipe for a nest. In the wild, males compete with each other and defend nests under rocks.
"The nests are important because males will later court and try to entice females to the nest where she will lay her eggs," Dr Wong says. "He will then have to look after and defend the developing brood until the eggs hatch."
In the laboratory, he explains, sections of PVC piping work just as well and males will quickly settle into the artificial nest and defend it like any good rocky overhang. Once settled, nest-holding males were presented with another male intruder who acted as a potential nest challenger.
The fight is on
Animals often fight each another for access to limited resources such as food, shelter and mates. Victory in combat, Dr Wong says, is usually determined by differences in the physical strength of opponents: larger animals tend to win more fights.
Exceptions, however, exist, he points out. "This is especially true when it comes to disputes over the acquisition and defence of territories. Territory holders, for example, are often at an advantage when it comes to winning fights against intruders."
In many species, smaller individuals are able to successfully maintain territories against physically stronger intruders. "Such observations suggest that factors other than physical strength can also play an important role in determining the outcome of territorial disputes," Dr Wong says.
The desert goby
Tough and testy, the hardy desert goby lives in brackish water found in some of the deserts of central Australia.
The peculiar fish can tolerate extreme conditions and can be found in water twice as salty as the ocean. They also survive huge fluctuations in temperature – important survival skills for desert-dwelling fish.
Females lay eggs that are cared for by the father, who will aggressively defend his nest against intruders. Once he attracts a female back to his nest to lay her eggs, he fans the eggs with his pectoral fins to keep them oxygenated.
The aggressive male gobies were said to display the "Napoleon complex", named after the French emperor Napoleon Bonaparte, who was believed to have compensated for his allegedly short stature with an aggressive personality. The complex refers to the idea that small males are more aggressive than larger ones.
Previous studies have shown little support for the Napoleon complex in humans. "They have reported no difference in personality-type or aggression between short and tall men," Dr Wong says. "Some results suggest that short men are more prone to jealousy, but as far as short temper, overt aggression, and so on, are concerned, studies have not shown this at all."
The Napoleon complex, in fact, may be a misnomer. "Napoleon Bonaparte was not short, but rather of average height, for people at that time," Dr Svensson notes. "The misunderstanding seems to stem from conversion errors between French and English units and the fact that he liked to surround himself with tall bodyguards."
But studies on other species suggest that the so-called Napoleon complex might be a common phenomenon in the animal world.
"Some lab-based studies have regarded it as a paradox because smaller individuals often lose," Dr Wong says. "This may not be the case in the wild. In fact, there are examples of birds, for instance, which are highly successful at driving away much larger intruders that venture into their territory."
These include the highly territorial northern harriers, Circus cyaneus, which can scare off other species of raptors.
Similarly, in the mangrove killifish, Kryptolebias marmoratus, attacked individuals will often retreat immediately from an aggressor, even when it is smaller than they are.
Might this apply to most animal species? "I cannot be sure I will get the same results even if using some closely related fish species, let alone a most remote relative like a mammal," Dr Svensson says.
Some shore-bird species, he explains, have so-called "conventional sex roles" – males fight over access to females – where closely related species have reversed sex roles, namely where females are bigger and more ornamented and fight over males.
"Animal species are different, depending on their genetics and the environment and the social structure they live in," Dr Svensson says. "Even close relatives can differ greatly."
Humans have the added complexity of being part of relatively quickly changing cultures. "These change much faster than evolution. "For example, in the 1600's fat women were attractive in Western Europe; a mere 400 years later, skinny women were considered to be more attractive."
Aggressive behaviour in humans is shaped by intricate written and unwritten codes of conduct, he adds. These have shifted through over time and may obscure any evolution-selected behaviours.
"Thus, even if our closest relatives, such as gorillas, chimpanzees and bonobos, all expressed the Napoleon complex, this would still not mean that humans do as well," Dr Svensson concludes.
• Read the PlosOne research article at here
• Find out more about desert gobies here
• Watch aggression in action at midday today when IMAX Melbourne will screen Sea Rex 3D: Journey to a Prehistoric World. Details here
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