Wonder braincases

EVOLUTION

Wonder braincases

Some skulls are narrow and delicate while others are squat, fat and powerful. The melding of form and function is displayed perfectly in an animal’s skull so that one can quite easily deduce the manner in which the animal behaves, or the environment in which it lives, by casually glancing at the skull it leaves behind, writes Simon Winchester.

The braincase of a skull may be strongly built and cleverly engineered but how do animals with an instinctive need for brutish behaviour prevent their brains from turning into rice pudding?

Alan Dudley has spent the last four decades collecting skulls. During the day, he selects veneers for gluing to the dashboards of expensive automobiles.

After work, he collects skulls. He has thousands of skulls, ranging from the great hulk of a hippopotamus skull to the tiniest and most delicate tissue-like skull of a wren. Rams and woodpeckers happen to have very dense skulls, especially in that rounded rear area known as the braincase.

Crucially, their braincases are also unusually smooth inside. The brains of most animals that are prone to head banging are relatively small and smooth-surfaced; and they’re bathed in small amounts of cerebrospinal fluid, leaving little room for the brain to move and be shocked by the sudden decelerations and accelerations of their weaponised heads.

Moreover, both rams and woodpeckers are scrupulous in the precise, single-direction fashion in which they smash their heads into hard surfaces. There’s very little side-to-side torsion exerted on the brain. None of the movement induces whiplash injury and other kinds of damage.

Similarly, seabirds like gannets, which have wingspans of six feet, catch fish by spectacular dives into the ocean. They swoop from heights of 100 feet or more and enter the water at 60 mph and hurtle downward, far beneath the surface, pursuing their chosen fish underwater, using their wings to swim.

It’s an awesome performance. They are eagle-eyed and have, unusually for birds, true binocular vision, which helps them lock on target. If lucky, they will consume the fish while still underwater, only eventually bobbing back to the surface to take off, something they do very clumsily, and resume high-altitude patrol. However, their fishing success is one thing. Their survival is quite another. To dive into water from 100 feet may not be lethal for a gannet, but it would, or should, get a fearful migraine. Yet that doesn’t seem to happen.

Gannets manage to bob to the surface with all their mental faculties intact, their brains entirely unhurt, thanks to skull modifications. To mitigate the brain-shattering trauma of a 60-mph collision with a wall of water, air sacs built into the gannet’s face act as cushions.

Its extremely long and narrow beak helps the bird enter the water with a very stealthy kind of impact; and it has no nostrils that would allow water to gush inward and do serious damage to the delicate tissues inside. Its skull is strong, delicate, unpierced and can tilt downward on landing but hold straight ahead when passing at great speed through the water.

Modifications of the skull are many, all produced by evolution to give each animal maximum advantage in adapting to its environment and its lifestyle niche. Some skulls are narrow and delicate while others are squat, fat and powerful. Invariably, the melding of form and function is displayed perfectly in an animal’s skull so that one can quite easily deduce the manner in which the animal behaves, or the environment in which it lives by examining or casually glancing at the skull it leaves behind. If you come across an otherwise modest animal with a large sagittal crest – a coati-mundi, for instance – you’d do well to avoid it, or at least to keep it happy.

When a coati fights, it bites, and the muscles attached to its sagittal crest allow it to come down hard with its canine teeth. It can really hurt and cause damage. In less threatening territory, the eye orbits on certain skulls can be spectacular – the immense orbits of a tarsier, for example, are often as large as the rest of the skull; they provide a classic example of a skull detail that suggests how well or badly an animal can use a certain sense, in this case, its vision.

Similarly, structures called the auditory bullae can show, in bony form, just how well an animal can hear. Springhares and rabbits have very large auditory bullae: It’s said that the chamber enclosed by the bullae resonates perfectly to the whooshing sound of a downward-swooping owl, alerting the rabbit to dive for its burrow and live to enjoy another day.

Until its skull was examined, no one had any idea of how a rabbit was able to do such a thing.As always when at a loss to explain, animal behaviourists have framed an argument that rams carry out their butting for reasons of power, territory or sexual ritual.
Their skulls give nothing away, other than being stronger than usual, they suggest. The rabbit skull, however, is awash with clues as to how this particular animal behaves.

Fascination with skulls

From the shrunken heads of the Amazon to the spun-sugar calavera candies of a Mexican November or the bleached bones of a Georgia O’Keeffe painting, skulls have long exerted a mystical pull on the human imagination.

They have also been eternally attractive to students of pure science; every feature from the shape of sagittal ridges to the functions of cerebral cortexes have been and continue to be studied in laboratories, in the most minutely intimate detail. But in the particular case of the skull, it seems that imagination and science have all too often become conjoined.

The pseudoscience that results from such a combination has over the years had consequences from laughable to downright sinister.

Phrenology, a classic of the pseudosciences (alchemy, palmistry and intelligent design ) is today regarded as little more than a harmlessly amusing conceit. It seems barely credible that Victorians once flocked in droves to private Bloomsbury consulting rooms to have costly quacks with delicate fingers probe the surface of their heads looking for bumps and depressions indicating the relative strength of such qualities as benevolence, veneration and firmness, or to assay how much “amativeness” – sexual desire – might lie untapped within your skull.

Relics from the era – bone (or more commonly plastic) head-models, incised with fine lines showing the demarcation of the zones – continue to sell well, most usually as hat stands.

Much more dangerous, though, was the one-time use of a real science – craniometry, the measurement of the skull – to produce a hierarchy of humankind, based entirely on the size and shape of the head. The Nazis and the South African apartheid apologists employed techniques, based on the so-called cephalic index, to demonstrate which races were advanced and which should be shunned.

The Aryans triumphed in both cases. But the science on which such studies were based, just like that of phrenology, was eventually shown to be the purest bunkum.

 

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