Science is Golden

by Karl Kruszelnicki

  Wag the Dog

  It should be pretty easy to read the emotions of a dog. After all, it has been called ‘Man’s Best Friend’. However, if the tail is stiff and doesn’t move, the ears are tucked in close to the head, and the body held in a tight stance, then you should keep away. On the other hand, if the dog’s tail is wagging, and the ears are pricked up and the body is wriggling like a can of worms, then it’s probably safe to pat the dog.

  But what about those occasional cases of a dog still biting, even though its tail is wagging? Well, recent research has given us another clue—the equivalent of fine print in a contract—to help us read the telltale signs of the dog’s wagging tail.

  Left Not Equal to Right

  It all goes back to the nervous system and its lack of perfect symmetry. The left side of the body and the brain are quite similar to the right side, but with some definite differences. Both the nerve pathways that run into the brain, and the brain itself, are wired up in a non-symmetrical way.

  The ancient Greeks noted that some soldiers who suffered damage to the left side of their brain were not able to speak properly. They didn’t know it back then, but the ‘language’ area of nearly all right-handed people is on the left side of the brain.

  By 1861 the French physician Paul Broca had found this specific area in autopsies on some of his patients who had lost their speech. (Mark Dax had made the same discovery in 1836, but Broca got all the credit.) However, around the same time in the mid-1800s, it was also common medical knowledge that the brain was cross-wired to the body. So they knew that the left side of the brain controlled the limbs on the right side of the body (and vice versa).

  And this leads to behaviour that is specific to one side of the body. For example, most people are right-handed. In the case of human beings, we have been this way for a long time—Bronze Age weapons and tools are overwhelmingly designed for the right hand. On the other hand, most male dogs have a strong tendency to be left-pawed, while the females have a weaker tendency to be right-pawed.

  Wag the Dog

  In general terms, the left brain is more linked to approaching something, whereas the right brain is more involved in withdrawing, or moving away. Overall, it appears that the right brain (which controls the left side of the body) is more responsive to stimuli that are negative, and to oddities and emergencies and threats.

  The Golden Rule Is: Tail to the (dog’s) right, it’s all right, Tail to the (dog’s) left, it’s best you left.

  Different Strokes

  Until the 1980s, it was wrongly thought that this ‘lateralisation’ of the body was something that happened only in human beings. In 1988, the eminent animal lateralisation researcher Charles R. Hamilton expressed everyone’s amazement when he wrote: ‘These results lead to the plausible but revolutionary inference that a bird more effectively searches for food with its right eye, while it watches for danger with its left!’

  Since then, we have found evidence for lateralisation in most animals with spines, including reptiles, birds, fish, amphibians and yes, mammals—including dogs.

  Which eye the animal uses to look at something affects how they learn, their spatial memory and their behaviour in avoiding threats. In one study, pigeons were shown 725 abstract patterns. They could remember most of the patterns seen with their right eye (left brain), but did no better than chance with those seen by their left eye. Lateralisation begins at an early age. Bird embryos lie inside the shell, the right eye exposed to the light coming through the shell, while the left eye is blocked from the light by its own body.

  It turns out that this specialisation, i.e. having specific functions located on one side or the other of the brain, has advantages. It makes you better at spotting a predator and quicker in responding.

  Right Comes, Left Goes

  It seems, roughly speaking, that the left brain is linked more to approaching something. The right brain is involved more in withdrawing, or moving away.

  In general, it seems that the right brain (which controls the left side of the body) is more responsive to negative stimuli, and to oddities, emergencies and threats.

  For example, birds tend to watch out for danger with their right brain (or left eye). Chicks leap away far more vigorously if they see danger with their left eye (as compared to their right eye)—and it’s the same with toads. Chameleons will be much more aggressive if they see another chameleon with their left eye (as compared to the right eye). Chimpanzees experiencing negative emotions (e.g. a threat) will scratch the left side of the body more (controlled by the right brain).

  However, the left brain (which controls the right side of the body) is more concerned with considered responses to routine situations.

  And so birds, for example, tend to look for food with the right eye (or left brain). They tend to be better at using this eye to differentiate between various visual stimuli. Honeybees learn more readily if they use their right antenna (left brain). To scan for food, Australian kookaburras use the right eye (left brain) more. In human beings, the left brain seems to be more involved with love, bonding, attachment and safety.

  Dogs Wag Tails

  This brings us to the study undertaken by Dr Giorgio Vallortigara from the University of Trieste in Italy. He chose 30 domestic dogs (15 male and 15 female, aged 1–6 years) from the Obedience School at the Veterinary School of the University of Bari. He exposed these dogs to various situations, and made videos from above of how their tails responded.

  The tail is a structure on the centre-line of the body, pulled on each side by muscles, which are in turn controlled by the left and right brain. Sometimes the different sides cooperate and sometimes they compete. This means that you should be easily able to identify any behaviour that tends to one side or the other.

  When a dog saw its owner, its tail wagged on both sides of the centre line, but far more to the right than to the left. When the dog saw a random human being, the effect was not as pronounced, but still more to the right than to the left. However, when the dog saw a large, dominant unfamiliar dog, its tail wagged far more to the left than to the right.

  It’s quite easy to spot the effect if you look at a video of the dog’s wagging tail shot from above, and even easier if it’s slowed down. Unfortunately, in real-time, it’s a subtle effect, and dogs wriggle around so much that the effect is hard to see with the untrained eye. But if you take the time to train your eye, you can spot the difference.

  Now here’s something to remember that may help you out. If the tail wags to the dog’s right, then it’s all right to pat, scratch or play catch with the dog. But if the tail wags to the dog’s left, well it’s best left to itself.

  And here’s the Take Home Message:

  Tail to the right, it’s all right,

  Tail to the left, it’s best you left.

  References

  Blakeslee, Sandra, ‘Dog—happy or scared—appear to talk with their tails’, The New York Times, 25 April 2007.

  Quaranta1, A., Siniscalchi, M. and Vallortigara, G., ‘Asymmetric tail-wagging responses by dogs to different emotive stimuli’, Current Biology, 20 March 2007, pp R199–R201.

  Rogers, Lesley J., ‘Evolution of hemispheric specialization: Advantages and disadvantages’, Brain and Language, 15 June 2000, Vol 73, No 2, pp 236–253.

  Skiba, M., Diekamp, B., Prior, H. and Güntürkün, O., ‘Lateralized interhemispheric transfer of color cues: Evidence for dynamic coding principles of visual lateralization in pigeons’, Brain and Language, 15 June 2000, Vol 73, No 2, pp 254–273.

  Vallortigara, Giorgio, ‘Comparative neuropsychology of the dual brain: A stroll through animals’ left and right perceptual worlds’, Brain and Language, 15 June 2000, Vol 73, No 2, pp 189–219.

  Peacock Plumage

  In early 2008, I was invited to do a Triumphal Tour of India, speaking to the general public, as well as high schools and universities. There were the usual sightseeing opportunities and events—elephants, maidens throwing red rose petals in ou
r path, the Taj Mahal, and peacocks. My primary school–aged daughter, Little Lola, accompanied me. She was so impressed that, on her return, she did a school project on the peacock. She made a magnificent model and wrote an essay that included the widely held belief that the purpose of the splendid plumage of the male (the peacock) is to attract the female (the peahen).

  But this simple ‘fact’ is actually a puzzle, and is almost certainly wrong.

  Cultural Peacock

  The peacock is the National Bird of India—and since 1956, the symbol of the NBC TV network in the USA. It’s also the logo of Sri Lanka Airlines.

  And a peacock feather is always present in the crown of Lord Krishna, a deity in the Hindu faith.

  Peacock 101

  Strictly speaking, this bird is a ‘peafowl’, with a female ‘peahen’ and a male ‘peacock’. But most of us call both genders a peacock.

  There are two major species of peacock—the Blue or Indian Peacock (Pavo cristatus), found in India and Sri Lanka, and the Green or Javanese Peacock (Pavo muticus), which ranges from Burma to Java in Indonesia. In Africa there is also the Congo Peacock (Afropavo congensis), a species discovered as recently as 1936. Although a single feather of this bird was found in 1913, it took a further 23 years to locate the actual species.

  Some 3,000 years ago, the Phoenicians carried the peacock to Egypt. The Romans raised peacocks to add a touch of class to their estates—and to eat.

  Are you lookin’ at me?

  The peacock can raise the long feathers of the train into a glorious semicircle, about two metres across (not bad for a bird only about a metre long).

  Each brilliant metallic green feather carries an iridescent ‘eye’. The feathers keep growing during autumn and winter, and moult once each year in summer.

  Peacock Throne

  The Peacock Throne was one of the most magnificent imperial thrones ever built. It had silver steps and golden legs covered in jewels. Its back was a representation of two peacock trains and again was covered in precious stones.

  It was built for the Mughal emperor Shah Janan in the 17th century. The Persian ruler Nader Shah captured Delhi in 1739 and seized the Peacock Throne. He took it back to Persia, but it was lost in wars with the Kurds, who broke it up for its precious parts.

  Reproductions of the Peacock Throne were later made for subsequent shahs of Persia.

  The peacock is 90–130 cm long and weighs about 5 kg, while the smaller peahen is about 86 cm long and weighs 3–4 kg.

  Now the first thing to realise is that the peacock’s ‘tail’ is not actually a ‘tail’.

  His real tail feathers are quite small and nondescript. The big showy feathers are actually the uppertail coverts on his back, and not part of his tail. To avoid confusion, bird scientists call it a ‘train’. This train is so large that it is cumbersome when folded and can impede the peacock’s pursuit of food or his escape from predators.

  Peacock Evolution

  It’s all a fine balance.

  Animals can evolve characteristics that are so exaggerated, that they can actually pose a danger to their survival. However, if this is offset by increased mating opportunities, then, on average, the animals with exaggerated characteristics might have more babies.

  This is called the ‘Condition-Dependent Theory of Sexual Advertisement’. It states that only males with superior genetic and physical condition can carry such a burdensome characteristic. Hopefully, in the fullness of time, the offspring will inherit this superior constitution, making them better able to find food, evade predators and impress members of the opposite gender.

  This is the background to the belief that the peacock’s magnificent feather display has evolved in order to attract the peahen.

  Feather Colour

  The colours in the feathers of the peacock do not come from dyes. Instead, they come from the regular geometric spacing of tiny cylinders of keratin.

  The cylinders are formed into a square array with a spacing of about 150 nm (nanometres, or billionths of a metre). This gives (via some fancy physics, e.g. Bragg Reflection, Fabry-Perot Interference, etc.) a green colour. Blue comes with a spacing of 140 nm, while yellow has a spacing of 165 nm. (The combination of blue and yellow produces the illusion that we see as the colour green.)

  This knowledge is being used in human-made optical devices. It is influencing the design of devices that help carry light down optic fibres, in order to carry massive amounts of information.

  Peacock Display

  The peacock can raise the long feathers of the train into a glorious semicircle, about 2 m in diameter (not bad for a bird that’s only about a metre long). Each brilliant metallic-green feather carries an iridescent ‘eye’. The feathers keep growing during autumn and winter and moult once each year in summer.

  The story goes that when the peacock spies a potential mate, he erects the feathers in his train into a fan. He then draws the fan forward, wraps himself in it and sends ripples through the feathers. He then draws the fan further forward, quivering it so violently that the feathers make a rattling sound and appear to shimmer. This part of the courtship is called the ‘ecstasy’.

  The peacock will then manipulate the muscles at the bottom of each feather to change the loudness of the sound, and does this about twice each second. This is called a ‘shiver’. A peacock keen to impress a peahen can generate up to 20 bouts of shivering, each bout lasting up to six minutes, or more.

  The spectacular display is definitely performed for the benefit of the peahen. But she is not automatically won over. Instead, she will normally perform one of three behaviours—ignore it and pass on by, passively accept the display or actively solicit the display.

  On the surface, this seems like a classic case of ‘sexual advertisement’ by the peacock. But over the years, there have been a few pieces of data that don’t fit this simple picture.

  We Have a Problem…

  First, the peacock often displays his train after the peahen has started the courtship ritual, not before. Surely, if the Big Display is his advertisement as to how good it can get, he should do a display before she starts the courtship.

  Second, over the years, there has been conflicting evidence both for and against the link between the train display and the mating success by the peacock. However, a general consensus for this theory has not been reached.

  Third, as a part of this conflict, there are still continuing arguments about what constitutes the most successful aspect of the train. Is it its length, the diameter of the eyes in the feathers, the number of eyes per square metre, the frequency of the shiver or the symmetry of the train? The question is far from resolved.

  Fourth, the ‘manufacture’ of the train is controlled by oestrogen (female) hormones, which is very unusual for a display ‘ornament’ that supposedly affects mating success. Testosterone (male) hormones are far more common in this arena.

  Fifth, there is actually not that much difference between the trains of peacocks across different populations of their species. So, to a potential mate, one peacock’s plumage is as good as another’s.

  And finally, the ‘quality’ of the train itself does not accurately reflect the genetic and health conditions of the peacock—thus making it a false sexual advertisement.

  So What’s It For?

  This leaves us with the increasingly probable position that the glorious train and display of the peacock is a ‘signal’ or advertisement that might have once had significance, but is now obsolete. In other words, the peahen is really interested in other aspects of the peacock (perhaps his stimulating conversation), but even to qualify in the mating stakes, he needs a pretty train.

  To use mathematical language, perhaps the peacock train display is a necessary, but not sufficient, condition.

  So why does he still have this glorious spread of plumage? Perhaps, like most male creatures, he’s his own biggest fan…

  References

  Blau, Steven K., ‘Light as a feather: Structural elem
ents give peacock plumes their colour’, Physics Today, January 2004, pp 18–20.

  Encyclopædia Britannica, Ultimate Reference Suite DVD, 2006—‘Peacock Throne’.

  ‘Evolution: Vestigial finery’, Nature, 17 April 2008, p 784.

  Kodric-Brown, Astrid and Brown, James H., ‘Why the fittest are the prettiest’, The Sciences, September/October 1985, pp 26–33.

  Takahashi, Mariko, et al., ‘Peahens do not prefer peacocks with more elaborate trains’, Animal Behaviour, 14 April 2008, Vol 75, pp 1209–1219.

  Green Glow of Radiation

  We may not all be nuclear scientists, but there’s one piece of nuclear knowledge that we all agree on—‘radioactivity has a green glow’. But regardless of what you see in The Simpsons, radioactivity does not glow green.

  Cultural References to Glow

  Most of us know the opening sequence of any episode of The Simpsons. Homer Simpson, my Personal Guru in all Matters Scientific, downs tools when the knocking-off bell rings at the nuclear power plant where he works. The radioactive material that he accidentally flips down the back of his shirt quite clearly has a green glow—luckily it’s not reality TV.

  Another fictitious character, Superman, can be brought to his knees only by kryptonite—which, you guessed it, has an unearthly glow. As the Superman character evolved, various shades of kryptonite appeared, but the commonest one has a green glow.